Patent Publication Number: US-2021178336-A1

Title: Selectively permeable graphene oxide membrane

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application of PCT/US2017/033654 filed on May 19, 2017, which claims the benefit of U.S. Provisional Application Nos. 62/339,716 filed May 20, 2016; 62/339,721 filed May 20, 2016; 62/340,292 filed May 23, 2016; 62/340,298 filed May 23, 2016, and 62/465,635 filed Mar. 1, 2017; which are all incorporated by references in their entirety. To the extent that the disclosure of the present application is inconsistent with the disclosures of the priority documents, the disclosure of the present application controls. 
    
    
     FIELD 
     The present embodiments are related to multi-layer polymeric membranes, including membranes comprising graphene materials for uses such as water treatment, desalination of saline water, or water removal. 
     BACKGROUND 
     Due to the increase of human population and water consumption coupled with limited fresh water resources on earth, technologies such as sea water desalination and water treatment, such as water recycling to provide safe and fresh water have become more important to our society. Today the desalination process using reverse osmosis (RO) membrane is the leading technology for producing fresh water from saline water. Most of current commercial RO membranes adopt a thin-film composite (TFC) configuration consisting of a thin aromatic polyamide selective layer on top of a microporous substrate which is typically a polysulfone membrane on non-woven polyester. Although these RO membranes can provide excellent salt rejection rate and high water flux, thinner and more hydrophilic membranes are still desired to further improve energy efficiency of the RO process. Therefore, new and better membrane materials and synthetic methods are in high demand to achieve desired properties. 
     SUMMARY 
     This disclosure relates to a Graphene Oxide (GO) based multilayered membranes suitable for high water flux applications. The GO membrane may have been crosslinked by one or more water soluble cross-linkers. Methods of making these GO membrane compositions efficiently and economically are also described. Water can be used as a solvent in preparing these GO membrane compositions, which makes the membrane preparation process more environmentally friendly and more cost effective. 
     Some embodiments include a water permeable membrane comprising a porous support, and a composite, which is in fluid communication with the support, comprising a crosslinked graphene oxide (GO) composite layer; wherein the GO composite layer was crosslinked by a crosslinker comprising a compound of Formula 1, a compound of Formula 2, a compound of Formula 3A, a compound of Formula 3B, a compound of Formula 4, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     or a salt thereof; wherein a dashed line represents the presence or absence of a covalent bond; R 1  and R 2  are independently NH 2 , NHR, or OH; R 5  is H or R; R 6  and R 7  are independently H, CO 2 H, or SO 3 H; R 8 , R 9 , R 10  and R 11  are independently 
     
       
         
         
             
             
         
       
     
     or a salt thereof; R 12  is OH, NH 2 , —NHR, CO 2 H, or SO 3 H; R is optionally substituted C 1-6  alkyl; k is 0 or 1; m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 
     Some embodiments include a water permeable membrane comprising: a porous support; an intermediate layer, which is in physical communication with the porous support, comprising a crosslinked silica nanoparticle and polyvinyl alcohol composite; and a crosslinked graphene oxide composite layer, which is in physical communication with the intermediate layer; wherein the GO composite layer was crosslinked by a crosslinker comprising a polyvinyl alcohol, a compound of Formula 2, a compound of Formula 3A, a compound of Formula 3B, a compound of formula 4, a compound of Formula 5, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     or a salt thereof; wherein R 13  can be H or CO 2 H. 
     Some embodiments include a method of making a water permeable membrane comprising: (1) resting a coating mixture of a single mixed aqueous solution of an optionally substituted graphene oxide and a cross-linker for about 30 min to about 12 hours to create a coating mixture, (2) applying the coating mixture to a substrate; (3) repeating step 2 as necessary to achieve the desired thickness or number of layers; and (4) curing the resulting coated substrate at about 50° C. to about 150° C. for about 1 minute to about 5 hours. 
     Some embodiments include a method of dehydrating an unprocessed fluid, comprising exposing and/or passing the unprocessed fluid to a water permeable membrane described herein. 
     Some embodiments include a method of removing a solute from an unprocessed solution comprising exposing and/or passing the unprocessed solution to a water permeable membrane described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a depiction of a possible embodiment of a membrane without a salt rejection layer, intermediate layer, or a protective coating. 
         FIG. 2  is a depiction a possible embodiment of a membrane with a protective coating but without a salt rejection layer or an intermediate layer. 
         FIG. 3  is a depiction of a possible embodiment of a membrane with an intermediate layer but without a salt rejection layer or a protective coating. 
         FIG. 4  is a depiction of a possible embodiment of a membrane with an intermediate layer and a protective coating but without a salt rejection layer. 
         FIG. 5  is a depiction of a possible embodiment of a membrane with a salt rejection layer but without an intermediate layer or a protective coating. 
         FIG. 6  is a depiction of a possible embodiment of a membrane with a salt rejection layer and a protective coating but without an intermediate layer. 
         FIG. 7  is a depiction of a possible embodiment of a membrane with a salt rejection layer and an intermediate layer but without a protective coating. 
         FIG. 8  is a depiction of a possible embodiment of a membrane with a salt rejection layer, an intermediate layer, and a protective coating. 
         FIG. 9  is a depiction of a possible embodiment for the method of making a membrane. 
         FIG. 10  is a diagram depicting the experimental setup for the mechanical strength testing and water permeability and/or salt rejection testing. 
         FIG. 11  is a diagram depicting the experimental setup for the water vapor permeability and gas leakage testing. 
     
    
    
     DETAILED DESCRIPTION 
     I. General 
     A selectively permeable membrane includes a membrane that is relatively permeable for one material and relatively impermeable for another material. For example, a membrane may be relatively permeable to water or water vapor and relatively impermeable ionic compounds or heavy metals. In some embodiments, the selectively permeable membrane can be permeable to water while being relatively impermeable to salts. In some embodiments, the selectively permeable membrane may comprise multiple layers, wherein at least one layer contains graphene oxide material. 
     Unless otherwise indicated, when a compound or a chemical structure, for example graphene oxide, is referred to as being “optionally substituted,” it includes a compound or a chemical structure that either has no substituents (i.e., unsubstituted), or has one or more substituents (i.e., substituted). The term “substituent” has the broadest meaning known in the art, and includes a moiety that replaces one or more hydrogen atoms attached to a parent compound or structure. In some embodiments, a substituent may be any type of group that may be present on a structure of an organic compound, which may have a molecular weight (e.g., the sum of the atomic masses of the atoms of the substituent) of 15-50 g/mol, 15-100 g/mol, 15-150 g/mol, 15-200 g/mol, 15-300 g/mol, or 15-500 g/mol. In some embodiments, a substituent comprises, or consists of: 0-30, 0-20, 0-10, or 0-5 carbon atoms; and 0-30, 0-20, 0-10, or 0-5 heteroatoms, wherein each heteroatom may independently be: N, O, S, Si, F, Cl, Br, or I; provided that the substituent includes one C, N, O, S, Si, F, Cl, Br, or I atom. Examples of substituents include, but are not limited to, alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl, heteroalkynyl, aryl, heteroaryl, hydroxy, alkoxy, aryloxy, acyl, acyloxy, alkylcarboxylate, thiol, alkylthio, cyano, halo, thiocarbonyl, O-carbamyl, N-carbamyl, O-thiocarbamyl, N-thiocarbamyl, C-amido, N-amido, S-sulfonamido, N-sulfonamido, isocyanato, thiocyanato, isothiocyanato, nitro, silyl, sulfenyl, sulfinyl, sulfonyl, haloalkyl, haloalkoxyl, trihalomethanesulfonyl, trihalomethanesulfonamido, amino, etc. 
     For convenience, the term “molecular weight” is used with respect to a moiety or part of a molecule to indicate the sum of the atomic masses of the atoms in the moiety or part of a molecule, even though it may not be a complete molecule. 
     As used herein, the term “alkyl” has the broadest meaning generally understood in the art and may include a moiety composed of carbon and hydrogen containing no double or triple bonds. Alkyl may be linear alkyl, branched alkyl, cycloalkyl, or a combination thereof and in some embodiments, may contain from one to thirty-five carbon atoms. Fox example, C 1-6  alkyl may include C 1-6  linear alkyl, such as methyl (—CH 3 ), methylene (—CH 2 —), ethyl (—CH 2 CH 3 ), ethylene (—C 2 H 4 —), propyl (—CH 2 CH 2 CH 3 ), propylene (—CH 2 CH 2 CH 2 —), n-butyl (—CH 2 CH 2 CH 2 CH 3 ), n-pentyl (—CH 2 CH 2 CH 2 CH 2 CH 3 ), n-hexyl (—CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 ); C 3-6  branched alkyl, such as C 3 H 7  (e.g. iso-propyl), C 4 H 9  (e.g. branched butyl isomers), C 5 H 11  (e.g. branched pentyl isomers), C 6 H 13  (e.g. branched hexyl isomers); C 3-6  cycloalkyl, such as C 3 H 5  (e.g. cyclopropyl), C 4 H 7  (e.g. cyclobutyl isomers such as cyclobutyl, methylcyclopropyl, etc.), C 5 H 9  (e.g. cyclopentyl isomers such as cyclopentyl, methylcyclobutyl, dimethylcyclopropyl, etc.), C 6 H 11  (e.g. cyclohexyl isomers); and the like. 
     As used herein, the term “fluid” includes any substance that continually deforms, or flows, under an applied shear stress. Such non-limiting examples of fluids include Newtonian and/or non-Newtonian fluids. In some embodiments, examples of Newtonian can be gases, liquids, and/or plasmas. In some embodiments, non-Newtonian fluids can be plastic solids (e.g., corn starch aqueous solution, toothpaste). 
     As used herein, the term “fluid communication” means that a fluid can pass through a first component and travel to and through a second component or more components regardless of whether they are in physical communication or the order of arrangement. 
     II. Membrane 
     The present disclosure relates to water separation membranes made of hydrophilic composite material with low organic compound permeability and high mechanical and chemical stability. This type of membranes may be useful to support a polyamide salt rejection layer as a RO membrane. This type of membrane material may be suitable for solute removal from an unprocessed fluid, such as desalination from saline water, purifying drinking water, or waste water treatment. Some selectively permeable membranes described herein are GO-based membranes having a high water flux, which may improve the energy efficiency of RO membranes and improve water recovery/separation efficiency. In some embodiments, the GO-based membrane can comprise one or more filtering layers, with at least one layer comprising a composite of a crosslinked graphene oxide (GO). It is believed that a crosslinked GO layer, having graphene oxide&#39;s inherent hydrophilicity and selective permeability, can provide a GO-based membrane with broad applications where high water permeability and high selectivity of permeability is desirable. In some embodiments, the GO-based membrane can further comprise a filtering layer of crosslinked silica nanoparticles. It is believed that the additional layer of crosslinked silica nanoparticles can increase material strength. In addition, these selectively permeable membranes can be prepared using water as a solvent, which makes the manufacturing process much more environmentally friendly and cost effective. 
     In some embodiments, the selectively permeable membrane further comprises a porous substrate or support, such as a porous support comprising a polymer or hollow fibers. For some membranes, one or more layers can be disposed on the porous support. In some embodiments where there is a plurality of layers, the layers can comprise a crosslinked graphene oxide (GO) layer and a crosslinked silica nanoparticle layer. The layer(s) can be in fluid communication with the support. The membrane can further comprise a salt rejection layer. In addition, the membrane can also comprise a protective layer. In some embodiments, the protective layer can comprise a hydrophilic polymer. In some embodiments, the fluid passing through the membrane travels through all the components regardless of whether they are in physical communication or their order of arrangement. 
     Some non-limiting examples of a membrane  100  without a salt rejection layer or a silica nanoparticle layer may be configured as shown in  FIGS. 1 and 2 . The membrane  100  can comprise at least a support  120  and one or more filtering layers  110 . The filtering layers can comprise a crosslinked GO layer  113 . In some embodiments, as shown in  FIG. 2 , the membrane may further comprise protective coating  140 . In some embodiments, as shown in  FIG. 1 , the membrane does not have a protective coating. Some non-limiting examples of membranes  300  are similar to membrane  100 , but with the exception of having a plurality of filtering layers  110 , comprising a crosslinked GO layer  113  and a crosslinked silica nanoparticle layer  114  as shown in  FIGS. 3 and 4  with or without a protective coating. The filtering layers may comprise a plurality of crosslinked GO layers or a plurality of silica nanoparticles layers. In some embodiments, the membrane can allow the passage of water and/or water vapor, but resists the passage of solute. The solute restrained can comprise ionic compounds such as salts or heavy metals. 
     In some embodiments, the membrane can be used to remove water from a controlled volume. A membrane may be disposed between a first fluid reservoir and a second fluid reservoir such that the reservoirs are in fluid communication through the membrane. The first reservoir may contain a feed fluid upstream and/or at the membrane. 
     In some embodiments, the membrane selectively allows liquid water or water vapor to pass through while keeping solute, or other liquid material from passing through. The fluid upstream of the membrane can comprise a solution of water and solute, while the fluid downstream of the membrane may contain purified water or processed fluid. In some embodiments, the membrane may provide a durable desalination system that can be selectively permeable to water, and less permeable to salts. In some embodiments, the membrane may provide a durable reverse osmosis system that can effectively filter saline water, polluted water or feed fluids. 
     Some non-limiting examples of a membrane  200  and  400  can additionally comprise a salt rejection layer  115  that may be configured as shown in  FIGS. 5 and 6 . In some embodiments, the membrane  200  can comprise at least a support  120  and a plurality of filtering layers  110 . The plurality of layers can comprise a crosslinked GO layer  113  and a salt rejection layer  115 . The salt rejection layer  115  may be disposed on top of the crosslinked GO layer  113 . As shown in  FIG. 6 , the membrane may further comprise a protective coating,  140 , wherein the protective coating can protect the components of the membrane from harsh environments. In some embodiments, as shown in  FIG. 5 , the membrane does not have a protective coating. In some non-limiting examples of membranes, the plurality of filtering layers can further comprise a crosslinked silica nanoparticle layer  114  as shown in  FIGS. 7 and 8 , with or without a protective coating. In some embodiments, the plurality of layers may comprise a plurality of crosslinked GO layers or a plurality of silica nanoparticles layers. 
     In some embodiments, the membrane exhibits a normalized volumetric water flow rate of about 10-1000 gal·ft 2 ·day −1 ·bar −1 ; about 20-750 gal·ft −2 ·day −1 ·bar −1 ; about 100-500 gal·ft −2 ·day −1 ·bar −1 ; about 500-1000 gal·ft 2 ·day −1 ·bar −1 , about 200-400 gal·ft 2 ·day −1 ·bar −1 , about 10-100 gal·ft 2 ·day −1 ·bar −1 , about 100-200 gal·ft 2 ·day −1 ·bar −1 , at least about 10 gal·ft −2 ·day −1 ·bar −1 , about 20 gal·ft 2 ·day −1 ·bar −1 , about 100 gal·ft 2 ·day −1 ·bar −1 , about 200 gal·ft −2 ·day −1 ·bar −1 , or a normalized volumetric water flow rate in a range bounded by any combination of these values. 
     In some embodiments, a membrane may be a selectively permeable. In some embodiments, the membrane may be an osmosis membrane. In some embodiments, the membrane may be a water separation membrane. In some embodiments, the membrane may be a reverse osmosis (RO) membrane. In some embodiments, the selectively permeable membrane may comprise multiple layers, wherein at least one layer contains a GO-PVA-based composite. 
     III. Crosslinked GO Layer 
     The membranes described herein can comprise a crosslinked GO layer. Some crosslinked GO-layers can comprise a GO-based composite. The GO-based composite comprises a graphene oxide material and a crosslinker. The GO-based composite can also comprise one or more additives. In some embodiments, the GO-based composite is crosslinked wherein the constituents of the composite (e.g., graphene oxide compound, the crosslinker, and/or additives) are chemically bound to any combination of each other to result in a material matrix. 
     In some embodiments, the GO-based composite can have an interlayer distance or d-spacing of about 0.5-3 nm, about 0.6-2 nm, about 0.7-1.8 nm, about 0.8-1.7 nm, about 0.9-1.7 nm, about 1-2 nm, about 1.5-1.7 nm, about 1.61 nm, about 1.67 nm, about 1.55 nm or any distance in a range bounded by any of these values. The d-spacing can be determined by x-ray powder diffraction (XRD). 
     The GO-based composite in layer form can have any suitable thickness. For example, some GO-based composite layers may have a thickness in a range of about 20-1,000 nm, about 50-500 nm, about 500-1000 nm, about 500-700 nm, about 100-400 nm, about 10-30 nm, about 20-50 nm, about 40-70 nm, about 60-90 nm, about 90-110 nm, about 100-140 nm, about 20-100 nm, about 100-200 nm, about 200-500 nm, about 250 nm, about 200 nm, about 100 nm, about 20 nm, or any thickness in a range bounded by any of these values. 
     Graphene Oxide 
     In general, graphene-based materials have many attractive properties, such as a 2-dimensional sheet-like structure with extraordinary high mechanical strength and nanometer scale thickness. The graphene oxide (GO), an exfoliated oxidation of graphite, can be mass produced at low cost. With its high degree of oxidation, graphene oxide has high water permeability and exhibits versatility to be functionalized to have a variety of functional groups, such as amines or alcohols in membrane structures. Unlike traditional membranes, where the water is transported only through the pores of the material, in graphene oxide membranes the transportation of water can be done also between the interlayer spaces. GO&#39;S capillary effect can result in long water slip lengths that offer fast water transportation rate. Additionally, the membrane&#39;s selectivity and water flux can be controlled by adjusting the interlayer distance of graphene sheets, or by the utilization of various crosslinkers, or a combination thereof. 
     In the membranes disclosed herein, a GO material may be optionally substituted. The optionally substituted graphene oxide may contain a graphene which has been chemically modified, or functionalized. A modified graphene may be any graphene material that has been chemically modified, or functionalized. 
     Functionalized graphene includes one or more functional groups not present in graphene oxide, such as functional groups that are not OH, COOH or epoxide group directly attached to a C-atom of the graphene base. Examples of functional groups that may be present in functionalized graphene include halogen, alkene, alkyne, cyano, ester, amide, or amine. 
     In some embodiments, at least about 99%, at least about 95%, at least about 90%, at least about 80%, at least about 70%, at least about 60%, at least about 50%, at least about 40%, at least about 30%, at least about 20%, at least about 10%, or at least about 5% of the graphene molecules may be oxidized or functionalized. In some embodiments, the graphene material is graphene oxide, which may provide selective permeability for gases, fluids, and/or vapors. In some embodiments, graphene oxide can also include reduced graphene oxide. In some embodiments, graphene oxide compound can be graphene oxide, reduced-graphene oxide, functionalized graphene oxide, or functionalized and reduced-graphene oxide. 
     It is believed that there may be a large number (˜30%) of epoxy groups on GO, which may be readily reactive with amino groups at mild conditions, or hydroxyl groups at elevated temperatures. It is also believed that GO sheets have an extraordinary high aspect ratio which provides a large available gas/water diffusion surface as compared to other materials, and it has the ability to decrease the effective pore diameter of any substrate supporting material to minimize contaminant infusion while retaining flux rates. It is also believed that the epoxy or hydroxyl groups increases the hydrophilicity of the materials, and thus contributes to the increase in water vapor permeability and selectivity of the membrane. 
     In some embodiments, the optionally substituted graphene oxide may be in the form of sheets, planes or flakes. In some embodiments, the graphene material may have a surface area of about 100-5000 m 2 /g, about 150-4000 m 2 /g, about 200-1000 m 2 /g, about 500-1000 m 2 /g, about 1000-2500 m 2 /g, about 2000-3000 m 2 /g, about 100-500 m 2 /g, about 400-500 m 2 /g, or any surface area in a range bounded by any of these values. 
     In some embodiments, the graphene oxide may be platelets having 1, 2, or 3 dimensions with size of each dimension independently in the nanometer to micron range. In some embodiments, the graphene may have a platelet size in any one of the dimensions, or may have a square root of the area of the largest surface of the platelet, of about 0.05-100 μm, about 0.05-50 μm, about 0.1-50 μm, about 0.5-10 μm, about 1-5 μm, about 0.1-2 μm, about 1-3 μm, about 2-4 μm, about 3-5 μm, about 4-6 μm, about 5-7 μm, about 6-8 μm, about 7-10 μm, about 10-15 μm, about 15-20 μm, about 50-100 μm, about 60-80 μm, about 50-60 μm, about 25-50 μm, about 20-30 μm, about 30-50 μm, or any platelet size in a range bounded by any of these values. 
     In some embodiments, the GO material can comprise at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, or at least 99% of graphene material having a molecular weight of about 5,000 Daltons to about 200,000 Daltons. 
     Crosslinker 
     In some embodiments, the crosslinked GO layer can comprise a GO-based composite. Some composites can comprise a GO material that was crosslinked with a crosslinker. The GO material and the crosslinker may be covalently linked to form a network of crosslinks or a material matrix. 
     In some embodiments, the crosslinker compound (CLC) containing nucleophilic groups can be polyvinyl alcohol (PVA) (CLC-1), optionally substituted meta-phenylene diamine, optionally substituted biphenyl, optionally substituted triphenylmethane, optionally substituted diphenylamine, optionally substituted 9H-carbazole, or optionally substituted 2,2-bis(hydroxymethyl)propane-1,3-diol. 
     The molecular weight of the polyvinyl alcohol (PVA) in the GO-based composite may be about 100-1,000,000 Daltons (Da), about 10,000-500,000 Da, about 10,000-50,000 Da, about 50,000-100,000 Da, about 70,000-120,000 Da, about 80,000-130,000 Da, about 90,000-140,000 Da, about 90,000-100,000 Da, about 95,000-100,000 Da, about 98,000 Da, or any molecular weight in a range bounded by any of these values. 
     In some embodiments, the crosslinker is an optionally substituted biphenyl represented by Formula 1. 
     
       
         
         
             
             
         
       
     
     wherein R 1  and R 2  are independently NH 2  or OH; and R 3  and R 4  are independently H, OH, NH 2 , CH 3 , —CO 2 H, —CO 2 Li, —CO 2 Na, —CO 2 K, —SO 3 H, —SO 3 Li, —SO 3 Na, or —SO 3 K. 
     In some embodiments, at least two of R 1 , R 2 , R 3  and R 4  can be nucleophilic groups. Some of these nucleophilic groups, such as amino groups can react with the epoxides in the GO to form covalent bonds to generate crosslinked GO composite. In some embodiments, R 1 , R 2 , R 3  and R 4  can be independently NH 2 . In some embodiments, R 1 , R 2 , R 3  and R 4  can be independently OH. In some embodiments, R 1  and R 2  are both NH 2 . In some embodiments, R 1  and R 2  are both OH. In some embodiments, R 3  and R 4  are independently H, CH 3 , or an organic acid group or salt thereof such as —CO 2 H, —CO 2 Li, —CO 2 Na, —CO 2 K, —SO 3 H, —SO 2 Li, —SO 3 Na, or —SO 3 K. In some embodiments, R 3  and R 4  are both OH. In some embodiments, R 3  and R 4  are both —CO 2 Na. 
     In some embodiments, the optionally substituted biphenyl is: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the crosslinker is an optionally substituted triphenylmethane represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     wherein R 1  and R 2  are independently NH 2  or OH; R 5  is H, CH 3 , or C 2 H 5 ; R 6  is H, CH 3 , —CO 2 H, —CO 2 Li, —CO 2 Na, —CO 2 K, —SO 3 H, —SO 3 Li, —SO 3 Na, or —SO 3 K; and n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 
     In some embodiments, at least two of R 1 , R 2 , R 5  and R 6  can be nucleophilic groups. In some embodiments, these nucleophilic groups, such as amino groups can react with the epoxides in the GO to form covalent bonds generating crosslinked GO composite. In some embodiments, R 1  and R 2  can be independently NH 2 . In some embodiments, R 1  and R 2  can be independently OH. In some embodiments, R 1  and R 2  are both OH. In some embodiments, R 5  can be H, CH 3 , or C 2 H 5 . In some embodiments, R 5  is CH 3 . In some embodiments, R 6  can be independently H, CH 3 , or an organic acid group or a salt thereof, such as —CO 2 H, —CO 2 Na, —CO 2 Li, —CO 2 K, —SO 3 H, —SO 3 Na, —SO 3 Li, or —SO 3 K. In some embodiments, R 6  is SO 3 Na. In some embodiments, n is 4. 
     In some embodiments, the optionally substituted triphenylmethane can comprise: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the crosslinker is an optionally substituted diphenylamine or optionally substituted 9H-carbazole represented by formula 3A or 3B: 
     
       
         
         
             
             
         
       
     
     wherein R 1  and R 2  are independently NH 2  or OH; R 6  and R 7  are independently H, CH 3 , CO 2 H, CO 2 Li, CO 2 Na, CO 2 K, SO 3 H, SO 3 Li, SO 3 Na, or SO 3 K; k is 0 or 1; m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 
     With respect to any relevant structural representation, such as Formula 3A or 3B, a dashed line represents the presence or absence of a bond. For example, compounds represented by Formulas 3B-1 and 3B-2 as shown below are included. 
     
       
         
         
             
             
         
       
     
     In some embodiments, at least two of R 1 , R 2 , R 6  and R 7  can be nucleophilic groups. In some embodiments, these nucleophilic groups, such as amino groups, can react with the epoxides in the GO to form covalent bonds generating crosslinked GO composite. In some embodiments, R 1  and R 2  can be independently NH 2  or OH. In some embodiments, R 1  and R 2  can be independently NH 2 . In some embodiments, R 1  and R 2  are both NH 2 . In some embodiments, R 6  and R 7  can be independently H, CH 3 , or an organic acid group or a salt thereof, such as —CO 2 H, —CO 2 Na, —CO 2 Li, —CO 2 K, —SO 3 H, —SO 3 Na, —SO 3 Li, or —SO 3 K. In some embodiments, R 6  and R 7  are independently —SO 3 K. In some embodiments, R 6  and R 7  are both —SO 3 K. In some embodiments, k is 0. In some embodiments, k is 1. In some embodiments, m is 0. In some embodiments, m is 3. In some embodiments, n is 0. In some embodiments, n is 3. In some embodiments, m and n are both 0. In some embodiments, m and n are both 3. 
     In some embodiments, the optionally substituted diphenylamine or optionally substituted 9H-carbazole is: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the crosslinker is an optionally substituted 2,2-bis(hydroxymethyl)propane-1,3-diol represented by Formula 4: 
     
       
         
         
             
             
         
       
     
     wherein R 8 , R 9 , R 10  and Rn can be independently: 
     
       
         
         
             
             
         
       
     
     wherein R 12  is OH, NH 2 , —CO 2 H, —CO 2 Li, —CO 2 Na, —CO 2 K, —SO 3 H, —SO 3 Li, —SO 3 Na, or —SO 3 K; and n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; 
     In some embodiments, R 12  is NH 2  or OH. In some embodiments, R 12  is H. In some embodiments, R 12  is —SO 3 Na. This type of membranes has a high water flux, and is capable of salt rejection. 
     In some embodiments, the optionally substituted bishydroxymethyl propanediol compound can comprise: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the crosslinker is an optionally substituted meta-phenylenediamine represented by Formula 5: 
     
       
         
         
             
             
         
       
     
     wherein R 13  can be H, CO 2 H, CO 2 Li, CO 2 Na, or CO 2 K. In some embodiments, R 13  is H. In some embodiments, R 13  is —COOH. In some embodiments, the optionally substituted meta-phenylenediamine is: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the crosslinked graphene oxide composite layer comprise one or more types of crosslinkers represented by Formula 1, 2, 3A, 3B, 3B-1, 3B-2, 4, or 5, or any combination thereof. 
     In some embodiments, the crosslinker containing nucleophilic groups is polyvinyl alcohol (CLC-1), 
     
       
         
         
             
             
         
       
     
     It is believed that when the cross-linker in the crosslinked GO composite membrane comprises an organic salt, such as sodium salt, potassium salt, or lithium salt, the hydrophilicity of the resulting GO membrane could be increased, thereby increasing the total water flux. 
     It is believed that crosslinking the graphene oxide material can also enhance the GO-based composite&#39;s mechanical strength and water permeable properties by creating strong chemical bonding and wide channels between graphene platelets to allow water to pass through the platelets easily. In some embodiments, the graphene material may comprise crosslinked graphene material at the graphene bases having at least about 1%, about 5%, about 10%, about 20%, about 30%, about 40% about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or all of the graphene material crosslinked to at least one other platelet within the GO-based composite. In some embodiments, the majority of the graphene material may be crosslinked. The amount of crosslinking may be estimated based on the weight of the cross-linker as compared to the total amount of graphene material. 
     In some embodiments, the weight ratio of crosslinker to GO (weight ratio=weight of crosslinker÷weight of graphene oxide) can be about 0.25-15, about 0.2-13, about 0.3-12, about 0.5-10, about 3-9, about 5-8, about 6-8, about 6-7, or about 6.25 (for example 6.25 mg of meta-phenylenediamine cross-linker and 1 mg of optionally substituted graphene oxide), or any ratio in a range bounded by any of these values. 
     In some embodiments, the mass percentage of the graphene base relative to the total composition of the GO-based composite can be about 5-40 wt %, about 5-10 wt %, about 10-15 wt %, about 15-20 wt %, about 20-30 wt %, about 30-40 wt %, about 4-80 wt %, about 4-75 wt %, about 5-70 wt %, about 7-65 wt %, about 7-60 wt %, about 7.5-55 wt %, about 8-50 wt %, about 8.5-50 wt %, about 15-50 wt %, or any mass percentage in a range bounded by any of these values. 
     In some embodiments, the crosslinked GO contains about 66-70 atom %, about 67-69 atom %, about 68-69 atom %, about 20-90 atom %, about 30-80 atom %, about 40-75 atom %, about 60-72 atom %, about 60-70 atom %, about 65-70 atom % carbon, or any percentage of carbon in a range bounded by any of these values based upon the total number of atoms in the crosslinked GO. The percentage of crosslinking can be determined by X-ray photoelectron spectroscopy (XPS). 
     In some embodiments, an optionally substituted graphene oxide crosslinked with cross-linker, can be at least about 5 atom %, about 7 atom %, about 10 atom %, about 12 atom %, about 14 atom %, about 15 atom %, about 16 atom %, about 17 atom %, about 18 atom %, about 19 atom %, or about 20 atom %, about 30-35 atom %, about 25-34 atom %, about 26-31 atom %, about 29-31 atom %, about 30 atom %, about 35 atom %, about 40 atom %, or about 50 atom % oxygen, or any percentage of oxygen in a range bounded by any of these values. The percentage of crosslinking can be determined by XPS. 
     In some embodiments, an optionally substituted graphene oxide crosslinked with cross-linker, can have a carbon to oxygen atom ratio (carbon atoms/oxygen atoms) of about 1-5.5, about 1.5-2.5, about 2-5, about 3-4, about 3-3.5, about 3.2-3.3, or any ratio in a range bounded by any of these values. 
     In some embodiments, the crosslinked GO contains about 0.1-2 atom %, about 0.5-2 atom %, about 0.5-1.5 atom %, or about 0.8-1.2 atom % of nitrogen, about 1 atom %, about 1.1 atom %, less than about 20 atom %, less than about 15 atom %, less than about 13 atom %, less than about 12 atom %, less than about 11 atom % nitrogen, or in any percentage of nitrogen in a range bounded by any of these values based upon the total number of atoms in the crosslinked GO. The percentage of crosslinking can be determined by XPS. 
     In some embodiments, the crosslinked GO contains about 0.1-1.0 atom %, about 0.1-0.5 atom %, about 0.5-1.0 atom %, about 0.2 atom %, about 0.3 atom %, or about 0.8 atom % sulfur, based upon the total number of atoms in the crosslinked GO. The percentage of crosslinking can be determined by XPS. 
     In some embodiments, an optionally substituted graphene oxide crosslinked with a crosslinker, can have an interlayer distance, or d-spacing that can be between about 0.5-3 nm, about 0.6-2 nm, about 0.7-1.7 nm, about 0.8-1.5 nm, about 0.9-1.4 nm, or any distance in a range bounded by any of these values. The d-spacing can be determined by x-ray powder diffraction (XRD). 
     IV. Crosslinked Silica Nanoparticle Layer 
     For some membranes, wherein there is a plurality of filtering layers, at least one layer can be a crosslinked silica nanoparticle layer. In some embodiments, the crosslinked silica nanoparticle layer comprises a silica nanoparticle and a polyvinyl alcohol composite. In some embodiments, the polyvinyl alcohol and the silica nanoparticles are chemically and/or covalently bound to form a material matrix. 
     In some embodiments, the molecular weight of the PVA in the silica nanoparticles layer may be about 100-1,000,000 Daltons (Da), about 10,000-500,000 Da, about 10,000-50,000 Da, about 50,000-100,000 Da, about 70,000-120,000 Da, about 80,000-130,000 Da, about 90,000-140,000 Da, about 90,000-100,000 Da, about 95,000-100,000 Da, about 98,000 Da, or any molecular weight in a range bounded by any of these values. 
     In some embodiments, an average size of the silica nanoparticles in the silica nanoparticles layer may be about 5-1,000 nm, about 6-500 nm, about 7-100 nm, about 7-20 nm, about 500-1000 nm, about 100-500 nm, about 100-200 nm, about 5-10 nm, about 10-20 nm, about 20-50 nm, about 50-100 nm, or any size in a range bounded by any of these values. The average size for a set of nanoparticles can be determined by taking the average volume and then determining the diameter of a sphere with the same volume. In some embodiments, the weight percentage of silica nanoparticles to PVA may be about 0.1% to 90%. 
     The crosslinked silica nanoparticles layer can further comprise an additive mixture. In some embodiments, the additive mixture can comprise a borate salt, a chloride salt, an optionally substituted terephthalic acid, or any combination thereof. 
     In some embodiments, the additive mixture can comprise a borate salt. In some embodiments, the borate salt comprises a tetraborate salt, such as K 2 B 4 O 7 , Li 2 B 4 O 7 , and Na 2 B 4 O 7 . In some embodiments, the borate salt can comprise K 2 B 4 O 7 . In some embodiments, the mass percentage of borate salt to the silicon nanoparticle and PVA composite may be about 0.0-20 wt %, about 0.5-15 wt %, about 1.0-10 wt %, about 1-5 wt %, about 5-10 wt %, about 10-15 wt %, or about 15-20 wt %, or any weight percentage in a range bounded by any of these values. In some embodiments, any combination of polyvinyl alcohol, silica nanoparticles, and borate salt can be covalently bonded to form a material matrix. 
     Some additive mixtures can comprise a chloride salt, such as lithium chloride or calcium chloride. In some embodiments, chloride salt can comprise calcium chloride. In some embodiments, the mass percentage of chloride salt to the silicon nanoparticle and PVA composite may be about 0-1.5 wt %, about 0-1.0 wt %, about 1-1.5 wt %, or about 0.5-1 wt %, or any weight percentage in a range bounded by any of these values. 
     The additive mixture can comprise an optionally substituted terephthalic acid. In some embodiments, the optionally substituted terephthalic acid can comprise 2,5-dihydroxyterephthalic acid (DHTA). In some embodiments, the mass percentage of the optionally substituted terephthalic acid to the silicon nanoparticle and PVA composite can be about 0-5 wt %, about 0-4 wt %, about 0-3 wt %, about 0-1 wt %, about 1-2 wt %, about 2-3 wt %, about 3-4 wt %, about 4-5 wt %, about 1-1.5 wt %, about 1.5-2 wt %, or any weight percentage in a range bounded by any of these values. 
     V. Porous Support 
     A porous support may be any suitable material and in any suitable form upon which a layer, such as a layer of a GO-based composite, may be deposited or disposed. In some embodiments, the porous support can comprise hollow fibers or porous material. In some embodiments, the porous support may comprise a porous material, such as a polymer or a hollow fiber. Some porous supports can comprise a non-woven fabric. In some embodiments, the polymer may be polyamide (Nylon), polyimide (PI), polyvinylidene fluoride (PVDF), polyethylene (PE), polyethylene terephthalate (PET), polysulfone (PSF), polyether sulfone (PES), and/or any mixtures thereof. In some embodiments, the polymer can comprise PET. In some embodiments, the polymer can comprise a polyamide. 
     VI. Salt Rejection Layer 
     Some membranes further comprise a salt rejection layer, e.g. disposed on the GO-based composite. The salt rejection layer can give the membrane low salt permeability. A salt rejection layer may comprise any material that is suitable for preventing the passage of ionic compounds, such as salts. In some embodiments, the salt rejected can comprise KCl, MgCl 2 , CaCl 2 , NaCl, K 2 SO 4 , Mg 2 SO 4 , CaSO 2 , or Na 2 SO 4 . In some embodiments, the salt rejected can comprise NaCl. Some salt rejection layers comprise a polymer, such as a polyamide or a mixture of polyamides. In some embodiments, the polyamide can be a polyamide made from an amine (e.g. meta-phenylenediamine, para-phenylenediamine, ortho-phenylenediamine, piperazine, polyethylenimine, polyvinylamine, or the like) and an acyl chloride (e.g. trimesoyl chloride, isophthaloyl chloride, or the like). In some embodiments, the amine can be meta-phenylenediamine. In some embodiments, the acyl chloride can be trimesoyl chloride. In some embodiments, the polyamide can be made from a meta-phenylenediamine and a trimesoyl chloride (e.g. by a polymerization reaction between meta-phenylenediamine and trimesoyl chloride in the presence of a base and an organic solvent). 
     In some embodiments, the membrane may reject at least about 10%, at least about 30%, at least about 50%, at least about 70%, at least about 80%, at least about 90%, or at least about 97% of sodium chloride, e.g. when exposed to a 1500 ppm NaCl solution under a pressure of 225 psi and a water flux of 5 gallons per square foot per day (GFD). 
     VII. Protective Coating 
     Some membranes may further comprise a protective coating. For example, the protective coating can be disposed on top of the membrane to protect it from the environment. The protective coating may have any composition suitable for protecting a membrane from the environment, Many polymers are suitable for use in a protective coating such as a hydrophilic polymer, e.g. polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), polyethylene oxide (PEO), polyoxyethylene (POE), polyacrylic acid (PAA), polymethacrylic acid (PMMA) and polyacrylamide (PAM), polyethylenimine (PEI), poly(2-oxazoline), polyethersulfone (PES), methyl cellulose (MC), chitosan, poly (allylamine hydrochloride) (PAH), or poly (sodium 4-styrene sulfonate) (PSS), or any combinations thereof. In some embodiments, the protective coating can comprise PVA. 
     VIII. Methods of Fabricating Membranes 
     Some embodiments include methods for making the aforementioned membranes. Some methods include coating the porous support with a crosslinked GO layer. Some methods comprise additional steps of coating a porous support with a crosslinked silica nanoparticle layer. Some methods comprise coating the support with a silica nanoparticles layer before coating the support with a crosslinked GO layer. In some embodiments, the method comprises optionally pre-treating the porous support. In some embodiments, the method can further comprise applying a salt rejection layer. Some methods also include applying a salt rejection layer on the coated membrane, followed by additional curing of resulting assembly. In some methods, a protective layer can also be placed on the assembly. An example of a possible embodiment of making the aforementioned membranes is shown in  FIG. 9 . 
     Optional Pre-Treatment 
     In some embodiments, the porous support can be optionally pre-treated to aid in the adhesion of the composite layer to the porous support. In some embodiments, the pretreatment can be applied to the porous support and then dried. For some pretreatments, dopamine and polyvinyl alcohol can be used. For some pretreatments, the aqueous solution can comprise about 0.01-0.1 wt %, about 0.01 wt %, about 0.02 wt %, about 0.05 wt %, or about 0.1 wt % PVA. In some embodiments, the pretreated support can be dried at about 25-90° C., about 25° C., about 50° C., about 65° C., about 75° C., or about 90° C., for about 2 minutes to about 1 hour, about 2 minutes, about 5 minutes, about 10 minutes, about 30 minutes, about 1 hour, or until the support is dry. 
     Crosslinked Silica Nanoparticle Coating 
     In some embodiments, coating the porous support with a crosslinked silica nanoparticle layer comprises: (a) mixing silica nanoparticles and polyvinyl alcohol to obtain an aqueous coating mixture, (b) applying the coating mixture to the porous support to achieve a coated substrate; (c) repeating step b as necessary to achieve the desired thickness; and (d) curing the coated support. 
     In some embodiments, mixing silica nanoparticles and polyvinyl alcohol to obtain an aqueous coating mixture can be accomplished by dissolving appropriate amounts of silica nanoparticles and polyvinyl alcohol in water. Some methods comprise mixing at least two separate aqueous mixtures, e.g., preparing a silica nanoparticle based aqueous mixture and a polyvinyl alcohol aqueous based mixture separately, then mixing appropriate mass ratios of the two mixtures together to achieve the desired coating mixture. Other methods comprise adding appropriate amounts of silica nanoparticles and polyvinyl alcohol in water to generate a single aqueous mixture. In some embodiments, the mixture can be agitated at temperatures for a period of time sufficient to ensure uniform dissolution of the solute to yield a silica nanoparticle coating mixture. 
     In some embodiments, mixing silica nanoparticles and polyvinyl alcohol can further comprise adding an additive mixture to the dissolved silica nanoparticles and polyvinyl alcohol. In some embodiments, the additive mixture can also be dissolved in an aqueous solution. In some embodiments, the additive mixture can comprise chloride salt, borate salt, or 2,5-dihydroxyterephthalic acid, or any combinations thereof. 
     In some embodiments, applying the silica nanoparticle mixture to the porous support can be done by methods known in the art for creating a layer of desired thickness. In some embodiments, applying the coating mixture to the substrate can be achieved by first immersing the substrate into the coating mixture, and then drawing the solution onto the substrate by applying a negative pressure gradient across the substrate until the desired coating thickness can be achieved. In some embodiments, applying the coating mixture to the substrate can be achieved by blade coating, spray coating, dip coating, die coating, or spin coating. In some embodiments, the method can further comprise gently rinsing the substrate with deionized water after each application of the coating mixture to remove excess loose material. In some embodiments, the coating is done such that a composite layer of a desired thickness is created. The desired thickness of membrane can range from about 5-2000 nm, about 5-1000 nm, about 1000-2000 nm, about 10-500 nm, about 500-1000 nm, about 50-300 nm, about 10-200 nm, about 10-100 nm, about 10-50 nm, about 20-50 nm, or about 50-500 nm, or any thickness in a range bounded by any of these values. In some embodiments, the number of layers can range from 1 to 250, from 1 to 100, from 1 to 50, from 1 to 20, from 1 to 15, from 1 to 10, or from 1 to 5, 5-10, 10-20, 20-50, 50-100, 100-200, 200-300, 100-150, 20, 100, 200, or 150, or any number layers in a range bounded by any of these values. This process results in a fully coated substrate as a silica nanoparticle coated support. 
     For some methods, curing the silica nanoparticle coated support can then be done at a temperature for a period of time sufficient to allow crosslinking between the moieties of the aqueous coating mixture deposited on the porous support. In some embodiments, the coated support can be heated at about 80-200° C., about 90-170° C., about 90-150° C., about 80-90° C., about 100-150° C., or any temperature in a range bounded by any of these values. In some embodiments, the coated substrate can be exposed to heating for about 1 minute to about 5 hours, about 15 minutes to about 3 hours, or about 30 minutes; with the time required decreasing when increasing temperatures. In some embodiments, the substrate can be heated at about 90-150° C. for about 1 minute to about 5 hours. This process results in a cured membrane. 
     Crosslinked GO Layer Coating 
     For some methods, coating the porous support with a crosslinked GO layer can comprise: (a) mixing graphene oxide material, crosslinker, and optional additive mixture in an aqueous solution to create an aqueous coating mixture; (b) applying the coating mixture to a porous support to achieve a coated substrate; (c) repeating step b as necessary to achieve the desired thickness; and (d) curing the coated support. 
     In some embodiments, mixing an aqueous mixture of graphene oxide material, polyvinyl alcohol and optional additives can be accomplished by dissolving appropriate amounts of graphene oxide material, polyvinyl alcohol, and additives (e.g. borate salt, calcium chloride, an optionally substituted terephthalic acid, or silica nanoparticles) in water. Some methods comprise mixing at least two separate aqueous mixtures, e.g., a graphene oxide based aqueous mixture and a polyvinyl alcohol and additives based aqueous mixture, then mixing the two mixtures with an appropriate mass ratio together to achieve the desired coating mixture. Other methods comprise creating one aqueous mixture by dissolving appropriate amounts of graphene oxide material, polyvinyl alcohol, and additives in a single solution. In some embodiments, the mixture can be agitated at temperatures for a period of time sufficient to ensure uniform dissolution of the solute. This process results in a crosslinked GO coating mixture. 
     For some methods, there can be an additional step of resting the GO coating mixture at about room temperature for about 30 minutes to about 12 hours. In some embodiments, resting the coating mixture can be done for about 1 hour to about 6 hours. In some embodiments, resting the coating mixture can be done for about 3 hours. It is believed that resting the coating solution allows the graphene oxide and the cross-linker to begin covalently bonding in order to facilitate a final crosslinked GO layer. This process results in a crosslinked GO coating mixture. 
     In some embodiments, applying the coating mixture to the porous support can be done by methods known in the art for creating a layer of desired thickness. In some embodiments, applying the coating mixture to the substrate can be achieved by vacuum immersing the substrate into the coating mixture first, and then drawing the solution onto the substrate by applying a negative pressure gradient across the substrate until the desired coating thickness can be achieved. In some embodiments, applying the coating mixture to the substrate can be achieved by blade coating, spray coating, dip coating, die coating, or spin coating. In some embodiments, the method can further comprise gently rinsing the substrate with deionized water after each application of the coating mixture to remove excess loose material. In some embodiments, the coating is done such that a composite layer of a desired thickness is created. The desired thickness of membrane can range from about 5-2000 nm, about 5-1000 nm, about 1000-2000 nm, about 10-500 nm, about 500-1000 nm, about 50-300 nm, about 10-200 nm, about 10-100 nm, about 10-50 nm, about 20-50 nm, about 50-500 nm, or any thickness in a range bounded by any of these values. In some embodiments, the number of layers can range from 1 to 250, from 1 to 100, from 1 to 50, from 1 to 20, from 1 to 15, from 1 to 10, or from 1 to 5, 5-10, 10-20, 20-50, 50-100, 100-200, 200-300, 100-150, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40, 20, 100, 200, or 150, or any number layers in a range bounded by any of these values. This process results in a fully coated substrate as a coated support. 
     For some methods, curing the coated support can then be done at a temperature for a period of time sufficient to facilitate crosslinking between the moieties of the aqueous coating mixture deposited on the porous support. In some embodiments, the coated support can be heated at about 50-200° C., about 90-170° C., or about 70-150° C., about 80-90° C., about 100-150° C., about 80° C., about 90° C., or any temperature in a range bounded by any of these values. In some embodiments, the substrate can be exposed to heating for about 1 minute to about 5 hours, about 15 minutes to about 3 hours, or about 30 minutes; with the time required decreasing when increasing temperatures. In some embodiments, the substrate can be heated at about 70-150° C. for about 30 minutes. In some embodiments, the substrate can be heated at about 80° C. for about 30 minutes. This process results in a cured GO composite membrane. 
     Application of Salt Rejection Layer 
     In some embodiments, the method for fabricating membranes further comprises applying a salt rejection layer to the membrane or a cured membrane to yield a membrane with a salt rejection layer. In some embodiments, the salt rejection layer can be applied by dipping the cured membrane into a solution of precursors in mixed solvents. In some embodiments, the precursors can comprise an amine and an acyl chloride. In some embodiments, the precursors can comprise meta-phenylenediamine and trimesoyl chloride. In some embodiments, the concentration of meta-phenylenediamine can be about 0.01-10 wt %, about 0.1-5 wt %, about 5-10 wt %, about 1-5 wt %, about 2-4 wt %, about 4 wt %, about 2 wt %, or about 3 wt %. In some embodiments, the trimesoyl chloride concentration can be about 0.001 vol % to about 1 vol %, about 0.01-1 vol %, about 0.1-0.5 vol %, about 0.1-0.3 vol %, about 0.2-0.3 vol %, about 0.1-0.2 vol %, or about 0.14 vol %. In some embodiments, the coating mixture of meta-phenylenediamine and trimesoyl chloride can be allowed to rest for a sufficient amount of time such that polymerization can take place before the dipping occurs. In some embodiments, the method comprises resting the mixture at room temperature for about 1-6 hours, about 5 hours, about 2 hours, or about 3 hours. In some embodiments, the method comprises dipping the cured membrane in the coating mixture for about 15 seconds to about 15 minutes; about 5 seconds to about 5 minutes, about 10 seconds to about 10 minutes, about 5-15 minutes, about 10-15 minutes, about 5-10 minutes, or about 10-15 seconds. 
     In some embodiments, the salt rejection layer can be applied by coating the cured membrane in separate solutions of an aqueous meta-phenylenediamine and a solution of trimesoyl chloride in an organic solvent. In some embodiments, the meta-phenylenediamine solution can have a concentration in a range of about 0.01-10 wt %, about 0.1-5 wt %, about 5-10 wt %, about 1-5 wt %, about 2-4 wt %, about 4 wt %, about 2 wt %, or about 3 wt %. In some embodiments, the trimesoyl chloride solution can have a concentration in a range of about 0.001-1 vol %, about 0.01-1 vol %, about 0.1-0.5 vol %, about 0.1-0.3 vol %, about 0.2-0.3 vol %, about 0.1-0.2 vol %, or about 0.14 vol %. In some embodiments, the method comprises dipping the cured membrane in the aqueous meta-phenylenediamine for a period of about 1 second to about 30 minutes, about 15 seconds to about 15 minutes; or about 10 seconds to about 10 minutes. In some embodiments, the method further comprises removing excess meta-phenylenediamine from the cured membrane. Then, the method further comprises dipping the cured membrane into the trimesoyl chloride solution for a period of about 30 seconds to about 10 minutes, about 45 seconds to about 2.5 minutes, or about 1 minute. Finally, the method comprises subsequently drying the resultant assembly in an oven to yield a membrane with a salt rejection layer of polyamide made from meta-phenylenediamine and trimesoyl chloride. In some embodiments, the cured membrane can be dried at about 45° C. to about 200° C. for a period of about 5 minutes to about 20 minutes, at about 75° C. to about 120° C. for a period of about 5 minutes to about 15 minutes, or at about 90° C. for about 10 minutes. This process results in a membrane with a salt rejection layer. 
     Application of a Protective Coating 
     In some embodiments, the method for fabricating a membrane can further comprises subsequently applying a protective coating on the GO composite membrane. In some embodiments, applying a protective coating comprises adding a hydrophilic polymer layer. In some embodiments, applying a protective coating comprises coating the membrane with a PVA aqueous solution. Applying a protective layer can be achieved by methods known in the art, such as blade coating, spray coating, dip coating, spin coating, and etc. In some embodiments, applying a protective layer can be achieved by dip coating of the membrane in a protective coating solution for about 1-10 minutes, about 1-5 minutes, about 5 minutes, or about 2 minutes. In some embodiments, the method further comprises drying the membrane at a about 75° C. to about 120° C. for about 5-15 minutes, or at about 90° C. for about 10 minutes. This process results in a membrane with a protective coating. 
     IX. Methods of Dehydrating 
     In some embodiments, a method of dehydrating an unprocessed fluid is described, comprising contacting the unprocessed fluid to one or more of the aforementioned membranes. In some methods, the membranes used can be those without a salt rejection layer. In some embodiments, exposing the unprocessed fluid to the membrane can result in allowing the water to pass through the membrane to a second fluid, or effluent. In some embodiments, exposing the unprocessed fluid to the membrane further comprises allowing sufficient time for the water to pass through the membrane so that the processed fluid achieves the desired water concentration. In some embodiments, the method can allow for processing of unprocessed fluid in a gaseous phase where the water being removed is water vapor. In some embodiments, the method can allow for processing of unprocessed fluid is in the liquid phase where the water being removed is in liquid water. 
     In some embodiments, the method can comprise allowing water vapor to pass through the membrane. In some embodiments, the method can comprise allowing liquid water to pass through the membrane. In some embodiments, the method can comprise allowing a combination of water vapor and liquid water to pass through the membrane. 
     In some embodiments, the method can be used to achieve desired water concentrations of the processed fluid, where the desired water concentrations is such that water vapor content is reduced to the desired levels to avoid condensation, mold growth, and/or spoliation of food in enclosed spaces. 
     X. Methods of Controlling Water or Solute Content 
     In some embodiments, methods of extracting liquid water from an unprocessed aqueous solution containing dissolved solutes, for applications such as pollutant removal or desalination are described. In some embodiments, a method for removing a solute from an unprocessed solution can comprise exposing the unprocessed solution to one or more of the aforementioned membranes. In some embodiments, the method further comprises passing the unprocessed solution through the membrane, whereby the water is allowed to pass through while solutes are retained, thereby reducing the solute content of the resulting water. In some embodiments, passing the unprocessed water containing solute through the membrane can be accomplished by applying a pressure gradient across the membrane. Applying a pressure gradient can be achieved by supplying a means of producing head pressure across the membrane. In some embodiments, the head pressure can be sufficient to overcome osmotic back pressure. 
     In some embodiments, providing a pressure gradient across the membrane can be achieved by producing a positive pressure in the first reservoir and producing a negative pressure in the second reservoir, or producing a positive pressure in the first side of the membrane and producing a negative pressure in the second side of the membrane. In some embodiments, a means of producing a positive pressure in the first reservoir can be accomplished by using a piston, a pump, a gravity drop, and/or a hydraulic ram. In some embodiments, a means of producing a negative pressure in the second reservoir can be achieved by applying a vacuum or withdrawing fluid from the second reservoir. 
     Embodiments 
     The following specific embodiments are contemplated: 
     Embodiment 1. A water permeable membrane comprising: 
     a porous support; and 
     a composite, which is in fluid communication with the support, comprising a crosslinked graphene oxide (GO) composite layer; 
     wherein the GO composite layer was crosslinked by a crosslinker comprising a compound of Formula 2, a compound of Formula 3A, a compound of Formula 3B, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     or a salt thereof; wherein a dashed line represents the presence or absence of a covalent bond; R 1  and R 2  are independently NH 2  or OH; R 5  is H, CH 3 , or C 2 H 5 ; R 6  and R 7  are independently H, CO 2 H, or SO 3 H; k is 0 or 1; m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 
     Embodiment 2. The membrane of embodiment 1, wherein the crosslinker is: 
     
       
         
         
             
             
         
       
     
     Embodiment 3. The membrane of embodiment 1, where the crosslinker is represented by Formula 2.
 
Embodiment 4. The membrane of embodiment 3, wherein the crosslinker is:
 
     
       
         
         
             
             
         
       
     
     Embodiment 5. The membrane of embodiment 1, where the crosslinker is represented by Formula 3A or 3B:
 
Embodiment 6. The membrane of embodiment 5, where the crosslinker is:
 
     
       
         
         
             
             
         
       
     
     Embodiment 7. A water permeable membrane comprising: 
     a porous support; 
     an intermediate layer, which is in physical communication with the porous support, comprising a crosslinked silica nanoparticle and polyvinyl alcohol composite; and 
     a crosslinked graphene oxide composite layer, which is in physical communication with the intermediate layer; 
     wherein the GO composite layer was crosslinked by a crosslinker comprising a polyvinyl alcohol, a compound of Formula 2, a compound of Formula 3A, a compound of Formula 3B, a compound of Formula 5, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     or a salt thereof; wherein R 1  and R 2  are independently NH 2  or OH; R 5  is H, CH 3 , or C 2 H 5 ; R 6  and R 7  are independently H, —CO 2 H, or —SO 3 H; and R 13  is H or CO 2 H; k is 0 or 1; m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10; and n is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. 
     Embodiment 8. The membrane of embodiment 7, wherein the crosslinker is polyvinyl alcohol, 
     
       
         
         
             
             
         
       
     
     Embodiment 9. The membrane of embodiment 7, wherein the crosslinker comprises a polyvinyl alcohol.
 
Embodiment 10. The membrane of embodiment 7, wherein the crosslinker comprises a compound represented by Formula 5.
 
Embodiment 11. The membrane of claim  7 , wherein the crosslinker comprises a compound represented by Formula 2.
 
Embodiment 12. The membrane of claim  7 , where the crosslinker comprises a compound represented by Formula 3A or 3B.
 
Embodiment 13. The membrane of embodiment 7, wherein the silica nanoparticles in the crosslinked silica nanoparticle and polyvinyl alcohol composite are present at about 0.1 wt % to 90 wt % as compared to the weight of the composite in the intermediate layer.
 
Embodiment 14. The membrane of embodiment 7, wherein the average size of the silica nanoparticles is about 5 nm to about 1,000 nm.
 
Embodiment 15. The membrane of embodiment 7, wherein the intermediate layer further comprises an additive, wherein the additive comprises a chloride salt, a borate salt, or a terephthalic-based acid.
 
Embodiment 16. The membrane of embodiment 15, wherein the chloride salt comprises LiCl or CaCl 2 .
 
Embodiment 17. The membrane of embodiment 16, wherein chloride salt is present at 0.0 wt % to about 1.5 wt % as compared to the weight of the composite in the intermediate layer.
 
Embodiment 18. The membrane of embodiment 15, wherein the borate salt comprises K 2 B 4 O 7 , Li 2 B 4 O 7 , or Na 2 B 4 O 7 .
 
Embodiment 19. The membrane of embodiment 18, wherein the borate salt is present at 0.0 wt % to about 20 wt % as compared to the weight of the composite in the intermediate layer.
 
Embodiment 20. The membrane of embodiment 15, wherein the optionally substituted terephthalic acid comprises 2,5-dihydroxyterephthalic acid.
 
Embodiment 21. The membrane of embodiment 20, wherein the 2,5-dihydroxyterephthalic acid is present at 0.0 wt % to about 5.0 wt % as compared to the weight of the composite in the intermediate layer.
 
Embodiment 22. The membrane of embodiment 1 or 7, wherein the support is a non-woven fabric.
 
Embodiment 23. The membrane of embodiment 22, wherein the support comprises polyamide, polyimide, polyvinylidene fluoride, polyethylene, polyethylene terephthalate, polysulfone, or polyether sulfone.
 
Embodiment 24. The membrane of embodiment 1 or 7, wherein the weight ratio of GO crosslinker to the graphene oxide compound is about 0.25 to about 15.
 
Embodiment 25. The membrane of embodiment 1 or 7, wherein the graphene oxide compound comprises graphene oxide, reduced-graphene oxide, functionalized graphene oxide, or functionalized and reduced-graphene oxide.
 
Embodiment 26. The membrane of embodiment 25, wherein the graphene oxide compound is graphene oxide.
 
Embodiment 27. The membrane of embodiment 1 or 7, further comprising a salt rejection layer.
 
Embodiment 28. The membrane of embodiment 27, wherein the salt rejected comprises NaCl.
 
Embodiment 29. The membrane of embodiment 27 or 28, wherein the salt rejection layer is disposed on the top of the composite.
 
Embodiment 30. The membrane of embodiment 27, 28, or 29, wherein the salt rejection layer comprises a polyamide prepared by reacting meta-phenylenediamine and trimesoyl chloride.
 
Embodiment 31. The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, wherein the thickness of the membrane is about 50 nm to about 500 nm.
 
Embodiment 32. The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31, the coating thickness of the membrane on the substrate is about 20 nm to 300 nm.
 
Embodiment 33. The membrane of embodiment 32, the coating thickness is about 100 nm to about 250 nm.
 
Embodiment 34. The membrane of embodiment 32, the coating thickness is about 200 nm.
 
Embodiment 35. The membrane of embodiment 32, the coating thickness is about 20 nm.
 
Embodiment 36. The membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 33, 34, 35, or 36, wherein the relative atomic distribution of N atom is about 1% to about 2% in the GO-crosslinked membrane.
 
Embodiment 37. The membrane of embodiment 36, wherein the relative atomic distribution of N atom is about 1% in the GO-crosslinked membrane.
 
Embodiment 38. A method of making a water permeable membrane comprising: (1) resting a coating mixture of a single mixed aqueous solution of an optionally substituted graphene oxide and a cross-linker for about 30 min to about 12 hours to create a coating mixture, (2) applying the coating mixture to a substrate; (3) repeating step 2 as necessary to achieve the desired thickness or number of layers; and (4) curing the resulting coated substrate at about 50° C. to about 150° C. for about 1 minute to about 5 hours.
 
Embodiment 39. The method of embodiment 38, wherein the coated substrate is cured at about 50° C. to about 120° C. for about 15 minutes to about 2 hours.
 
Embodiment 40. The method of embodiment 38, wherein the coated substrate is cured at about 80° C.
 
Embodiment 41. The method of embodiment 38, wherein the coated substrate is cured for about 30 minutes.
 
Embodiment 42. The method of embodiment 38, wherein the coated substrate is cured at about 80° C. for about 30 minutes.
 
Embodiment 43. The method of embodiment 38, 39, 40, 41, or 42, wherein the coating mixture is applied to the substrate by immersing the substrate into the coating mixture and then drawing the coating mixture into the substrate by applying a negative pressure gradient across the substrate until the desired coating thickness is achieved.
 
Embodiment 44. The method of embodiment 38, 39, 40, 41, 42, or 43, wherein the coating mixture is applied to the substrate by a process comprising blade coating, spray coating, dip coating, or spin coating.
 
Embodiment 45. The method of embodiment 38, 33, 34, or 35, wherein, before applying the coating mixture containing GO composite, the substrate is first coated with a crosslinked SiO 2  nanoparticle composite by a process comprising: (1) applying a coating mixture of a single mixed aqueous solution of polyvinyl alcohol and silica nanoparticles to a substrate, (2) repeating step 1 as necessary to achieve the desired thickness or number of layers, and (3) curing the coated substrate at about 90° C. to about 150° C. for about 1 minute to about 5 hours.
 
Embodiment 46. The method of embodiment 45, wherein the coating mixture further comprises an additive, wherein the additive comprises LiCl, CaCl 2 , borate salt, 2,5-dihydroxyterephthalic acid, or any combination thereof.
 
Embodiment 47. The method of embodiment 38, 39, 40, 41, 42, 43, 44, 45, or 46, further comprising coating the membrane with a salt rejection layer and curing the resulting assembly at about 45° C. to about 200° C. for about 5 minutes to about 20 minutes.
 
Embodiment 48. A method of dehydrating an unprocessed fluid, comprising exposing the unprocessed fluid to the water permeable membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, or 46, or 47.
 
Embodiment 49. A method of removing a solute from an unprocessed solution comprising exposing the unprocessed solution to the water permeable membrane of embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, or 47.
 
Embodiment 50. The method of embodiment 49, further comprising passing the unprocessed solution through the membrane.
 
Embodiment 51. The method of embodiment 41, wherein passing the unprocessed solution through the membrane is achieved by applying a pressure gradient across the membrane.
 
     EXAMPLES 
     It has been discovered that embodiments of the selectively permeable membranes described herein have improved performance as compared to other selectively permeable membranes. These benefits are further demonstrated by the following examples, which are intended to be illustrative of the disclosure only, but are not intended to limit the scope or underlying principles in any way. 
     Example 1.1.1: Preparation of Graphene Oxide Dispersion (GO-1) 
     GO was prepared from graphite using the modified Hummers method. Graphite flakes (2.0 g, Sigma Aldrich, St. Louis, Mo., USA, 100 mesh) were oxidized in a mixture of NaNO 3  (2.0 g, Aldrich), KMnO 4  of (10 g, Aldrich) and concentrated H 2 SO 4  (96 mL, 98%, Aldrich) at 50° C. for 15 hours. The resulting paste like mixture was poured onto 400 g of ice followed by adding 30 mL of hydrogen peroxide (30%, Aldrich). The resulting solution was then stirred at room temperature for 2 hours, filtered through a filter paper and washed with DI water. The solid was collected and then dispersed in DI water with stirring, centrifuged at 6300 rpm for 40 minutes, and the aqueous layer was decanted off. The remaining solid was then dispersed in DI water again, and the washing process was repeated 4 times. The purified GO was then dispersed in DI water under sonication (power of 10 W) for 2.5 hours to get the desired GO dispersion containing 0.4 wt % GO as GO-1. 
     Example 1.1.2: Synthesis of Cross-linker Compound CLC-3.1 
     
       
         
         
             
             
         
       
     
     To a mixture of 3-nitrophenol (6.95 g, 0.05 mol, Aldrich) in ethanol (50 mL, Aldrich), was added NaOH aqueous solution (25 mL, 12 M, Aldrich), and zinc powder (13 g, 0.2 mol, Aldrich) under a nitrogen atmosphere (Airgas, San Marcos, Calif., USA). The resulting mixture was stirred for 10 hours and filtered. The filtrate was acidified by acetic acid (Aldrich) to pH 4, and a precipitate formed. The solid was collected by filtration, washed with water to neutral, and dried under vacuum using a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher Scientific Waltham, Mass. USA) at 60° C./2 torr to afford the desired product (3.8 g, 70% yield) CLC-3.1. The compound was confirmed by LC-MS: 217 [M+1] + .  1 H NMR (DMSO-d 6 , ppm): δ 8.9 (bs, 4H), 6.77 (bs, 2H), 6.15 (bs, 4H). 
     Example 1.1.3: Synthesis of Cross-linker Compound CLC-3.2 
     
       
         
         
             
             
         
       
     
     A mixture of methyl 2-bromo-5-methoxybenzoate (10 g, 46.8 mmol, Aldrich), and freshly activated copper powder (12 g, 189 mmol, Aldrich) in anhydrous dimethylformamide (DMF) (50 mL, Aldrich) was heated at 160° C. for 16 hours under an argon atmosphere (Airgas). The reaction mixture was then cooled to room temperature and poured into ethyl acetate (300 mL, Aldrich). After filtering, the solid was washed with water and brine, dried over Na 2 SO 4  (Aldrich), and then purified by flash column chromatography on silica gel using eluents of hexanes/dichloromethane (100% to 50% hexanes, Aldrich) to give a pale yellow oil (4.7 g, in 70% yield) as the desired intermediate IC-1.  1 H NMR (CDCl 3 ): δ 7.50 (d, J=2.4 Hz, 2H), 7.13 (d, J=8.3 Hz, 2H), 7.07 (dd, J=2.4 and 8.3 Hz, 2H), 3.89 (s, 6H), 3.64 (s, 6H). 
     To a solution of IC-1 in anhydrous dichloromethane (60 mL, Aldrich), BBr 3  in dichloromethane (60 mL, 1M, 60 mmol) (Aldrich) was added at −78° C. The whole solution was then kept stirring at −78° C. and then allowed to warm up slowly to room temperature overnight. The resulting mixture was then poured into an ice water mixture (200 mL) and then extracted three times by ethyl acetate (3×300 mL, Aldrich). The organic phase was washed with brine, dried over Na 2 SO 4  (Aldrich), filtered, concentrated and reprecipitated in ethyl acetate/hexanes (Aldrich) to give a white solid (3.8 g, 98% yield) as a desired intermediate IC-2.  1 H NMR (DMSO-de): δ 12.20 (s, 2H), 9.56 (s, 2H), 7.20 (d, J=2.0 Hz, 2H), 6.90 (d, J=8.3 Hz, 2H), 6.86 (dd, J=2.0 and 8.3 Hz, 2H). LC-MS: 273 [M-H]. 
     To a solution of IC-2 in 30 mL methanol (Aldrich), a NaOH aqueous solution (1.12 g, 28 mmol in 10 mL water, Aldrich) was added. The mixture was stirred for 30 minutes and then the solvents were removed using a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher) at 60° C./2 torr to give a white solid (4.45 g, 100% yield) as the desired product CLC-3.2.  1 H NMR (D 2 O): δ 7.14 (d, J=8.4 Hz, 2H), 6.91 (d, J=2.6 Hz, 2H), 6.82 (dd, J=2.6 Hz and 8.4 Hz, 2H). 
     Example 1.1.4: Synthesis of Cross-linker Compound CLC-4.1 
     
       
         
         
             
             
         
       
     
     To tert-butanol (90 mL, Aldrich) at room temperature, 4,4′,4″-(ethane-1,1,1-triyl)triphenol (5 g, 16 mmol, Aldrich) was added followed by sodium tert-butoxide (1.57 g, 16 mmol, Aldrich) with stirring. The mixture was then stirred at 110° C. for 15 minutes. Subsequently 1,4-butanesultone (1.67 mL, 16 mmol, Aldrich) was added to the mixture, and the reaction was continued overnight. After about 16 hours, the reaction mixture was then cooled. To the reaction mixture hexanes (200 mL, Aldrich) were added and the resulting solution was stirred for 30 minutes. The precipitate was collected, and washed with fresh hexanes (about 500 mL, Aldrich). Then the collected precipitate was added in isopropanol (400 mL, Aldrich) and stirred for 2 hours. Then hexanes (400 mL, Aldrich) were added to the resulting mixture. After stirring for 5 minutes, the precipitate was collected. The product was dried at 60° C./2 torr in a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher Scientific Waltham, Mass. USA) overnight to give a white powder (6.25 g, 82.4% yield) as the desired product CLC-4.1.  1 H-NMR (D 2 O): δ 1.63 (m, 4H), 1.77 (s, 3H), 2.72 (t, 2H), 3.65 (t, 2H), 6.51 (t, 6H), 6.76 (t, 6H). 
     Example 1.1.5: Synthesis of Cross-linker Compound CLC-5.1 
     
       
         
         
             
             
         
       
     
     Benzene-1,4-diamine (5.4 g, 50 mmol) (Aldrich) and 1-fluoro-4-nitrobenzene (5.3 mL, 50 mmol) (Aldrich) were dissolved in dimethylsulfoxide (75 mL, Aldrich), and potassium carbonate (13.8 g, 100 mmol, Aldrich) was added. The reaction mixture was then heated with an oil bath at 90° C. and stirred overnight under nitrogen atmosphere (Airgas). The reaction mixture was cooled to room temperature and added into DI water (250 mL) in a slow stream with stirring and stirred until a solid precipitated out. The reaction mixture was then filtered, and the resulting dark brown solid was washed with plenty of DI water. The crude product was purified by flash column chromatography on silica gel (Aldrich) eluting with 20% to 40% ethyl acetate in hexanes (Aldrich) to provide the desired intermediate compound (6.1 g, 53%) as IC-3. 
     A mixture of IC-3, palladium on carbon (0.5 g, 5%, Aldrich) in ethanol (200 mL, Aldrich) was hydrogenated at 30 psi overnight. After the catalyst being filtered off, the filtrate was concentrated, and re-precipitated in dichloromethane/hexanes to give a solid (1.15 g, 66% yield) as the desired product CLC-5.1. The product was confirmed by LC-MS: 200 [M+1] + . 
     Example 1.1.6: Synthesis of Cross-linker Compound CLC-5.2 
     
       
         
         
             
             
         
       
     
     A suspension of Cu(NO 3 ) 2 .3H 2 O (Aldrich) in acetic acid/acetic anhydride (20 mL/30 mL, Aldrich) was stirred for 1.5 hours at room temperature. To the mixture, 9H-carbazole (4.18 g, 25 mmol, Aldrich) was added in small portion at 15° C. with a cold water bath. While kept stirring, the mixture was warmed up to room temperature over a period of 30 minutes, and subsequently heated at 90° C. for 30 minutes. After cooled to room temperature, the mixture was poured into water (250 mL) and the resulting precipitate was filtered, washed with water, dried in a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher Scientific Waltham, Mass. USA) at 60° C./2 torr. The solid was re-dissolved in acetone (Aldrich) and loaded on silica gel (Aldrich), then purified by flash column chromatography using eluents of hexanes/dichloromethane (3:2 to 1:3, Aldrich). The desired fractions were collected, concentrated and re-precipitated in methanol (Aldrich) to give a yellow solid (1.9 g, 30% yield) as the desired intermediate compound IC-4 which was Confirmed by LCMS: 256 [M-H]. 
     To a suspension of IC-4 in anhydrous DMF (20 mL, Aldrich), was added sodium ted-butoxide (0.285 g, 3 mmol, Aldrich), and the solution turned to red immediately. To the resulting solution, 1,3-propanesultone (0.44 g, 3.6 mmol, Aldrich) was added, and the solution was heated at 80° C. for 2.5 hours. After cooled to room temperature, the mixture was poured into isopropanol (300 mL, Aldrich) to give a yellow precipitate, which was filtered and dried to give the desired intermediate (1.05 g, in 90% yield) as IC-5. IC-5 was confirmed by LC-MS: 401 [M+1] + . 
     A mixture of IC-5, palladium on carbon (5%, 0.5 g, Aldrich) in water/methanol (20 mL/100 mL, Aldrich) was hydrogenated at 30 psi for 5 hours. After the catalyst was filtered off, the filtrate was concentrated to 5 mL and then poured into isopropanol (50 mL, Aldrich). The resulting suspension was poured into diethyl ether (200 mL, Aldrich) to give a white precipitate, which was collected by filtration and dried in air to yield the desired product (0.8 g, 92% yield) as CLC-5.2. CLC-5.2 was confirmed by LCMS: 318 [M-H]. 
     Example 1.1.6: Synthesis of Cross-linker Compound CLC-5.3 
     
       
         
         
             
             
         
       
     
     A mixture of 4-fluoro-1-nitrobenzene (10.6 mL, 100 mmol, Aldrich), meta-phenylenediamine (5.4 g, 50 mmol, Aldrich) and potassium carbonate (16.6 g, 120 mmol, Aldrich) in anhydrous dimethyl sulfoxide (DMSO) (80 mL, Aldrich) was heated to 105° C. for 20 hours. The resulting mixture was poured into water (250 mL) slowly and then extracted with dichloromethane (500 mL, Aldrich). The organic layer was separated, washed with brine, dried over Na 2 SO 4 , filtered, concentrated and then purified by flash column chromatography using eluents of dichloromethane/hexanes (1:10 to 3:2, Aldrich) to give an orange solid (4.8 g, 27% yield) as the desired intermediate IC-6. 
     A suspension of IC-6 (2.0 g), palladium on carbon (0.75 g, 5%, Aldrich) in water/ethanol (40 mL/80 mL, Aldrich) was hydrogenated under 30 psi for 16 hours. After the catalyst was filtered off, the filtrate was concentrated, poured into isopropanol (100 mL, Aldrich). The solid formed was collected by filtration and dried under vacuum using a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher) at 60° C./2 torr to give 1.0 g of the desired product in 60% yield as CLC-5.3. CLC-5.3 was confirmed by LC-MS: 291 [M+1] + . 
     Example 1.1.7: Synthesis of Cross-Linker Compound CLC-5.4 
     
       
         
         
             
             
         
       
     
     To a mixture of IC-6, K 2 CO 3  (0.414 g, 3 mmol) (Aldrich) in anhydrous dimethyl sulfoxide (DSMO) (10 mL) (Aldrich), was added 1,3-propanesultone (0.732 g, 6 mmol) (Aldrich). The mixture was then heated at 80° C. for 2 days. After cooled to room temperature, the mixture was poured into isopropanol (200 mL) (Aldrich). The resulting orange precipitate was filtered and dried in a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher) at 60° C./2 torr for 3 hours to give a solid (1.4 g, 96% yield) as the desired intermediate IC-7. 
     A suspension of IC-7, palladium on carbon (5%, 0.75 g) (Aldrich) in water/ethanol (40 mL/80 mL) (Aldrich) was hydrogenated under 30 psi for 16 hours. After the catalyst was filtered off, the filtrate was concentrated, poured into isopropanol (100 mL) (Aldrich). The solid formed was collected by filtration, and dried under vacuum using a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher) at 60° C./2 torr to give 0.5 g of desired product in 41% yield as CLC-5.4. CLC-5.4 was confirmed by LC-MS: 413 [M+1] + . 
     Example 1.1.8: Synthesis of Cross-Linker Compound CLC-5.5 (Prophetic) 
     
       
         
         
             
             
         
       
     
     To a mixture of or IC-6, K 2 CO 3  (0.414 g, 3 mmol, Aldrich) in anhydrous dimethyl sulfoxide (DSMO) (10 mL, Aldrich), was added 1,3-propanesultone (1.464 g, 12 mmol, Aldrich). The whole mixture was then heated at 80° C. for 2 days. After cooled to room temperature, the mixture was poured into isopropanol (200 mL, Aldrich). The resulting precipitate was filtered and dried in a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher) at 60° C./2 torr for 3 hours to give a solid as the desired intermediate as IC-8. 
     A suspension of IC-8 (1.83 g), palladium on carbon (0.75 g, 5%, Aldrich) in water/ethanol (40 mL/80 mL, Aldrich) can be hydrogenated under 30 psi for 16 hours. After the catalyst is filtered off, the filtrate can be concentrated, poured into isopropanol (100 mL, Aldrich). The solid can be collected by filtration and dried under vacuum using a vacuum oven (Thermo Scientific Precision 6500, Thermo Fisher) at 60° C./2 torr to give the desired product, CLC-5.5. 
     Example 1.1.9: Synthesis of Cross-Linker Compound CLC-6.1 
     
       
         
         
             
             
         
       
     
     With stirring pentaerythritol ethoxylate (7 g, 22.4 mmol, Aldrich 416150, M n =270 avg, ¾ EO/OH, Aldrich) was added followed by sodium tert-butoxide (2.15 g, 22.4 mmol, Aldrich) in tert-butanol (100 mL, Aldrich) at room temperature. The mixture was then heated at 110° C. for 70 minutes with stirring. Subsequently, 1,4-butanesultone (2.29 mL, 22.4 mmol, Aldrich) was added to the reaction mixture and the resulting mixture was stirred overnight. After 17 hours, the excess solution was decanted. The precipitates were washed with hexanes (Aldrich). The precipitates were then dissolved in methanol (125 mL, Aldrich) and dried in vacuo at 50° C. giving a viscous, transparent wax as the desired intermediate CLC-6.1 (8.77 g, yield 73%).  1 H-NMR (D 2 O): δ 1.7-1.8 (m, 4H), 2.90 (t, 2H), 3.3 (s, 8H), and 3.4-3.7 (m, 21H). 
     Example 1.1.10: Synthesis of Cross-Linker Compound CLC-6.2 
     
       
         
         
             
             
         
       
     
     Into N,N′-dimethylformamide (100 mL) (Aldrich) at room temperature, pentaerythritol tetrabromide (6 g, 15.5 mmol, Aldrich) was added with stirring followed by methyl 4-hydroxybenzoate (9.42 g, 61.9 mmol, Aldrich), and then potassium carbonate (27.80 g, 201.5 mmol, Aldrich). The resulting mixture was heated to 150° C. overnight. After about 22 hours, the reaction was cooled down to room temperature and the reaction mixture was poured into DI water (1000 mL) and extracted with ethyl acetate (800 mL, Aldrich). The organic layer was separated and concentrated under vacuum on a rotary evaporator. The resulting residue was purified by column chromatography eluting with a gradient of hexanes and ethyl acetate to give a white powder as the desired product CLC-6.2 (7.19 g, 69% yield).  1 H-NMR (TCE ???): δ 3.8 (s, 12H), 4.4 (s, 8H), 6.9 (d, 8H), and 7.9 (d, 8H). 
     Example 1.1.11: Synthesis of Cross-Linker Compound CLC-6.3 
     
       
         
         
             
             
         
       
     
     Into 50 mL of anhydrous tetrahydrofuran cooled in an ice bath at 0° C., CLC-6.2 (6.5 g, 9.7 mmol) was added. LiAlH 4  (1M in diethyl ether, 58 mL, 58.2 mmol, Aldrich) cooled to 0° C. was added dropwise. Then the reaction solution was allowed to warm to room temperature and stirred for 4 hours. The reaction mixture was poured into chilled water (1000 mL) and neutralized with HCl (1M, Aldrich). Then, the solution was extracted with ethyl acetate (800 mL, Aldrich), layers were separated, and the organic layer was concentrated. The crude product was purified by column chromatography eluting with a gradient of ethyl acetate and methanol to give a white powder as the desired product CLC-6.3 (3.44 g, 63.5% yield).  1 H-NMR (DMSO-de): δ 4.25 (s, 8H), 4.39 (s, 8H), 5.04 (s, 4H), 6.91 (d, 8H), 7.21 (d, 8H). 
     Example 1.1.11: Synthesis of Cross-Linker Compound CLC-6.4 
     
       
         
         
             
             
         
       
     
     To tert-butanol (60 mL, Aldrich) at room temperature, CLC-6.3 was added with stirring followed by sodium tert-butoxide (566 mg, 5.89 mmol, Aldrich). The mixture was heated at 110° C. for 40 minutes. Then 1,4-butane sultone (0.60 mL, 5.89 mmol, Aldrich), additional tert-butanol (75 mL, Aldrich) and N,N′-dimethylformamide (20 mL, Aldrich) were added to the reaction mixture. After stirring for 24 hours, the product was precipitated out by adding hexanes (400 mL, Aldrich). The resulting mixture was stirred for 15 minutes and then filtered. The collected solid was then added into hexanes (100 mL, Aldrich). After stirring for another 15 minutes, the precipitate was collected by filtration again. The solid corrected was then added into a mixture of hexanes (100 mL, Aldrich) and isopropanol (30 mL, Aldrich). After stirring for 15 minutes, the precipitate was filtered and dried at 60° C. in a vacuum oven at 2 torr (Thermo Scientific Precision 6500, Thermo Fisher Scientific Waltham, Mass. USA) for 4 hours to give a white powder as the desired product CLC-6.4 (3.25 g, 76.8% yield).  1 H-NMR (DMSO-d 6 ): δ 1.56 (m, 4H), 2.50 (m, 2H), 4.25-4.38 (m, 16H), 5.06 (s, 2H), 6.93 (d, 8H), and 7.20 (d, 8H). 
     Example 2.1.1: Membrane Preparation—Support Pretreatment 
     Preparing a Support: Porous substrates were purchased to be used as porous supports from various sources and materials, such as PET (Hydranautics, San Diego, Calif. USA), PET2 (Hydranautics), and polyamide (Nylon) (0.1 μm pore, Aldrich). Selected substrates, corresponding to embodiments shown in Table 1 and Table 2, were trimmed to a 7.6 cm diameter. In the embodiments where the substrates were in physical communication with a PVA containing layer, the substrates were pretreated with PVA. Unless otherwise specified, for all other embodiments the substrates were pretreated with dopamine. 
     PVA Substrate Pre-treatment: A 7.6 cm diameter substrate was dipped into a 0.05 wt % PVA (Aldrich) in DI water solution. The substrate was then dried in an oven (DX400, Yamato Scientific Co., Ltd. Tokyo, Japan) at 65° C. to yield a pretreated substrate. 
     Dopamine Substrate Pre-treatment: A 7.6 cm diameter substrate was dip-coated in a dopamine solution (2 g/L dopamine (Aldrich) and 1.3 g/L Trizma base buffer (Aldrich) at pH 8.5). The dopamine was polymerized to form polydopamine on the substrate. Then, the polydopamine-coated substrate was dried in an oven (DX400, Yamato Scientific Co., Ltd. Tokyo, Japan) at 65° C. to yield a pre-treated substrate. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Membrane Embodiments without a SiO 2  Nanoparticle Layer or a Salt Rejection Layer. 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Mass of 
                   
                 Application 
                 Coating 
                 Curing 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Cross- 
                 Crosslinker 
                 Substrate 
                 Method/Pre- 
                 Thickness 
                 Temp 
                 Time 
               
               
                 Embodiment 
                 linker 
                 to GO 
                 Material 
                 Treatment 
                 (nm or lyr) 
                 (° C.) 
                 (min) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 MD-1.2.11.1.1 
                 CLC-1 
                 83:16 
                 PET 
                 Filtration/ 
                 200 
                 90 
                 30 
               
               
                   
                   
                   
                   
                 PT: PVA 
               
               
                 MD-1.1.21.1.1 
                 CLC-2.1 
                 1:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.21.1.2 
                 CLC-2.1 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.21.1.3 
                 CLC-2.1 
                 7:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.22.1.1 
                 CLC-2.2 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.22.1.2 
                 CLC-2.2 
                 7:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.31.1.1 
                 CLC-3.1 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.31.1.2 
                 CLC-3.1 
                 7:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.31.1.3 
                 CLC-3.1 
                 15:1  
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.2.31.1.1 
                 CLC-3.1 
                 3:1 
                 Nylon 0.1 μm 
                 Dip Coating/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.32.1.1 
                 CLC-3.2 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.32.1.2 
                 CLC-3.2 
                 7:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.32.1.3 
                 CLC-3.2 
                 15:1  
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.2.32.1.4 
                 CLC-3.2 
                 3:1 
                 Nylon 0.1 μm 
                 Dip Coating/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.41.1.1 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.41.1.2 
                 CLC-4.1 
                 7:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.41.1.3 
                 CLC-4.1 
                 15:1  
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.2.41.1.1 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 Dip Coating/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.51.1.1 
                 CLC-5.1 
                 1:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.51.1.2 
                 CLC-5.1 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.51.1.3 
                 CLC-5.1 
                 5:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.2.51.1.1 
                 CLC-5.1 
                 3:1 
                 Nylon 0.1 μm 
                 Dip Coating/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.52.1.1 
                 CLC-5.2 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.53.1.1 
                 CLC-5.3 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.54.1.1 
                 CLC-5.4 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.61.1.1 
                 CLC-6.1 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.63.1.1 
                 CLC-6.3 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                 MD-1.1.64.1.1 
                 CLC-6.4 
                 3:1 
                 Nylon 0.1 μm 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                 PT: Dopamine 
               
               
                   
               
               
                 Notes: 
               
               
                 [1] Numbering Scheme is the following: MD-J.K.LL.M.N 
               
               
                 J = 1 - no salt rejection layer/no SiO 2  nanoparticle layer, 2 - no salt rejection layer/with SiO 2  nanoparticle layer, 3 - salt rejection layer/no SiO 2  nanoparticle layer, 4 - salt rejection Layer/with SiO 2  nanoparticle layer; 
               
               
                 K = 1 - mixture filtration method, 2 - mixture film/dip coating method, 3 - layer by layer method; 
               
               
                 LL = 11 - CLC-1 (PVA), 21 - CLC-2.1, 22 - CLC-2.2, 31 - CLC-3.1, 32 - CLC-3.2, 41 - CLC-4.1, 51 - CLC-5.1, 52 - CLC-5.2, 53 - CLC-5.3, 54 - CLC-5.4, 55 - CLC-5.5, 61 - CLC-6.1, 62 - CLC-6.2, 63 - CLC-6.3, 64 - CLC-6.4; 
               
               
                 M = 1 - no protective coating, 2 - with protective coating; 
               
               
                 N = device # within category. 
               
               
                 [2] All PP and PVA/PP substrates are approximately 30 μm thick; whereas the nylon substrates can be between 65-125 μm thick. 
               
               
                 [3] (Prop.) - Indicates a prophetic example. 
               
               
                 [4] No additives. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Membrane Embodiments with a SiO 2  Nanoparticle Layer but without a Salt Rejection Layer. 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Mass of 
                   
                 Mass Ratio of 
                 Application 
                 Coating 
                 Curing 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Cross- 
                 Crosslinker 
                 Substrate 
                 PVA to Si- 
                 Method/Pre- 
                 Thickness 
                 Temp 
                 Time 
               
               
                 Embodiment 
                 linker 
                 to GO 
                 Material 
                 Nanoparticles 
                 treatment 
                 (nm or lyr) 
                 (° C.) 
                 (min) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 MD-2.2.11.1.1 
                 CLC-1 
                 83:16 
                 PET 
                 3:1 
                 Film Coating/ 
                 200 
                 90 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: PVA 
               
               
                 MD-2.1.21.1.1 
                 CLC-2.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.22.1.1 
                 CLC-2.2 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.31.1.1 
                 CLC-3.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.32.1.1 
                 CLC-3.2 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.41.1.1 
                 CLC-4.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 150 
                 80 
                 30 
               
               
                   
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.41.1.2 
                 CLC-4.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                   
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.41.1.3 
                 CLC-4.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 250 
                 80 
                 30 
               
               
                   
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.51.1.1 
                 CLC-5.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.52.1.1 
                 CLC-5.2 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.53.1.1 
                 CLC-5.3 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.54.1.1 
                 CLC-5.4 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.61.1.1 
                 CLC-6.1 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.63.1.1 
                 CLC-6.3 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.64.1.1 
                 CLC-6.4 
                 3:1 
                 PET 
                 3:1 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                 PT: Dopamine 
               
               
                   
               
               
                 Notes: 
               
               
                 [1] Numbering Scheme is the following: MD-J.K.LL.M.N 
               
               
                 J = 1 - no salt rejection layer/no Si-nanoparticle layer, 2 - no salt rejection layer/with Si-nanoparticle layer, 3 - salt rejection layer/no Si-nanoparticle layer, 4 - salt rejection Layer/with Si-nanoparticle layer 
               
               
                 K = 1 -mixture filtration method, 2 -mixture film coating method, 3 -layer by layer method 
               
               
                 LL = 11 - CLC-1 (PVA), 21 - CLC-2.1, 22 - CLC-2.2, 31 - CLC-3.1, 32 - CLC-3.2, 41 - CLC-4.1, 51 - CLC-5.1, 52 - CLC-5.2, 53 - CLC-5.3, 54 - CLC-5.4, 55 - CLC-5.5, 61 - CLC-6.1, 62 - CLC-6.2, 63 - CLC-6.3, 64 - CLC-6.4 
               
               
                 M = 1 - no protective coating, 2 - with protective coating; 
               
               
                 N = device # within category. 
               
               
                 [2] All PP and PVA/PP substrates are approximately 30 μm thick; whereas the nylon substrates can be between 65-125 μm thick. 
               
               
                 [3] (Prop.) - Indicates a prophetic example. 
               
            
           
         
       
     
     Example 2.1.2: Membrane Preparation—Crosslinked GO Coating Mixture Preparation 
     The procedure for creating a crosslinked GO coating mixture is dependent on the type of crosslinker used. All crosslinkers with the exception of PVA have a resting step before curing. 
     Preparation of GO-PVA Coating Mixture: A 10 mL of PVA solution (2.5 wt %) (CLC-1) was prepared by dissolving an appropriate amount of PVA (Aldrich) in DI water. Then, the solutions of GO-1 (1 mL) and PVA-1 in an appropriate amount to achieve the mass ratios of Table 1 were combined with 10 mL of DI water and sonicated for 6 minutes to ensure uniform mixing to create a crosslinked GO coating solution. 
     Preparation of Non-PVA Crosslinker GO Coating Mixture: First, the GO dispersion, GC-1, was diluted with DI water to create a 0.1 wt % GO aqueous solution. Second, a 0.1 wt % aqueous solution of crosslinker was created by dissolving an appropriate amount of crosslinker (e.g., CLC-2.1, CLC-2.2, and etc.) in DI water. For CLC-2.1 and CLC-2.2, both metaphenylenediamine (MPD) (Aldrich) and 3,5-diaminobenzoic acid (DABA) (Aldrich) were purchased. A coating mixture for the embodiment was then created by mixing an aqueous solution of 0.1 wt % CLC-2.1 and 0.1 wt % GO at an appropriate weight ratio to achieve the mass ratio of 1:1 as shown in Table 1. The resulting solution was then rested for about 3 hours, or normally until the GO and amine pre-reacted. This process provides a crosslinked GO coating solution. Other non-PVA crosslinker GO coating mixtures shown in Table 1 were prepared in a similar way. 
     Example 2.1.3: Membrane Preparation—Crosslinked Silicon-Nanoparticle Coating Mixture Preparation 
     A 10 mL of PVA solution (2.5 wt %) as PVA-1 was prepared by dissolving an appropriate amount of PVA (CLC-1) (Aldrich) in DI water. Similarly, a 10 mL of Silicon-nanoparticle solution (2.5 wt %) was prepared by dissolving an appropriate amount of SiO 2  (5-15 nm, Aldrich) in DI water. Then, the solutions of GO-1 (1 mL) and PVA-1 were combined in appropriate amounts to achieve the mass ratio of 16:83 as shown in Table 2, and was further combined with 10 mL of DI water, and sonicated for 6 minutes to ensure uniform mixing to create a crosslinked SiO 2  nanoparticle coating solution. Other crosslinked silicon nanoparticle coating mixtures shown in Table 2 are prepared similarly. 
     Example 2.1.1: Membrane Preparation Procedure 1—Membranes without a Crosslinked SiO 2  Nanoparticle Layer or a Salt Rejection Layer 
     Crosslinked GO Mixture Application by Filtration: For the embodiments identified in Table 1 where the application method was by filtration, the crosslinked GO coating solution was filtered through the pretreated substrate under gravity to draw the solution through the substrate such that a coating layer of the desired thickness was deposited on the support. The resulting membrane was then placed in an oven (DX400, Yamato Scientific) at the temperature specified in Table 1 for the specified time in Table 1 to facilitate crosslinking. This process generated a membrane without either a crosslinked SiO 2  nanoparticle layer or a salt rejection layer. 
     Crosslinked GO Mixture Application by Dip Coating: For the embodiments identified in Table 1 where the application method was by dip coating, the pretreated substrate can be coated in the crosslinked GO coating mixture by dip coating the substrate in the coating mixture. Next, the substrate can be then rinsed completely in DI water to remove any excess particles. This process of dipping the substrate into the coating mixture and then rinsing with DI water for the prescribed number of cycles can be repeated to prepare the desired number of layers or thickness of the coating layer. The resulting membrane can be then kept in an oven (DX400, Yamato Scientific) at the temperature for the period of time specified in Table 2 to facilitate further crosslinking. This process can result in a membrane without either a crosslinked SiO 2  nanoparticle layer or a salt rejection layer. 
     Example 2.1.2: Membrane Preparation Procedure 2—Membranes with a Crosslinked SiO 2  Nanoparticle Layer but without a Salt Rejection Layer 
     Crosslinked SiO 2  Nanoparticle Mixture Application by Filtration: For the embodiments identified in Table 2, the crosslinked SiO 2  nanoparticle coating solution was filtered through the pretreated substrate under gravity to draw the solution through the substrate such that a coating layer of the desired thickness was deposited on the support. The resulting membrane was then placed in an oven (DX400, Yamato Scientific) at 90° C. for 30 minutes to facilitate crosslinking. This process generated a crosslinked SiO 2  nanoparticle coated substrate. 
     Crosslinked GO Mixture Application by Filtration: For the embodiments identified in Table 2, the crosslinked GO coating solution was filtered through the above coated substrate under gravity to draw the solution through the substrate such that a coating layer of the desired thickness was deposited on the support. The resulting membrane was then placed in an oven (DX400, Yamato Scientific) at the temperature for the period of time specified in Table 2 to facilitate crosslinking. This process generated a membrane with a GO coated crosslinked SiO 2  nanoparticle layer but without a salt rejection layer. 
     Example 2.2.1: Addition of a Salt Rejection Layer to a Membrane 
     To enhance the salt rejection capability of the membranes, selected embodiments, such as those without a SiO 2  nanoparticle layer in Table 3 or those with a SiO 2  nanoparticle layer in Table 4, were additionally coated with a polyamide salt rejection layer. A 3.0 wt % MPD aqueous solution was prepared by diluting an appropriate amount of MPD (Aldrich) in DI water. A 0.14 vol % trimesoyl chloride solution was made by diluting an appropriate amount of trimesoyl chloride (Aldrich) in isoparrifin solvent (Isopar E &amp; G, Exxon Mobil Chemical, Houston Tex., USA). The GO-MPD coated membrane was then dipped in the aqueous solution of 3.0 wt % of MPD (Aldrich) for a period of about 10 seconds to about 10 minutes depending on the type of substrate and then removed. Excess solution remaining on the membrane was removed by air dry. Then, the membrane was dipped into the 0.14 vol % trimesoyl chloride solution for about 10 seconds and removed. The resulting assembly was then dried in an oven (DX400, Yamato Scientific) at 120° C. for 3 minutes. This process resulted in a membrane with a salt rejection layer. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Membrane Embodiments without a SiO 2  Nanoparticle Layer with a Salt Rejection Layer. 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Mass of 
                   
                 Application 
                 Coating 
                 Curing 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Cross- 
                 Cross-linker 
                 Substrate 
                   
                 Method/Pre- 
                 Thickness 
                 Temp 
                 Time 
               
               
                 Embodiment 
                 linker 
                 to GO 
                 Material 
                 Additives 
                 treatment 
                 (nm or lyr) 
                 (° C.) 
                 (min) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 MD-3.1.31.1.1 
                 CLC-3.1 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.31.1.2 
                 CLC-3.1 
                 7:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.32.1.1 
                 CLC-3.2 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.32.1.2 
                 CLC-3.2 
                 7:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.41.1.1 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.41.1.2 
                 CLC-4.1 
                 7:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.51.1.1 
                 CLC-5.1 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.52.1.1 
                 CLC-5.2 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.53.1.1 
                 CLC-5.3 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.54.1.1 
                 CLC-5.4 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.61.1.1 
                 CLC-6.1 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.63.1.1 
                 CLC-6.3 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                 MD-3.1.64.1.1 
                 CLC-6.4 
                 3:1 
                 Nylon 0.1 μm 
                 N/A 
                 Filtration/ 
                 20 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                 PT: Dopamine 
               
               
                   
               
               
                 Notes: 
               
               
                 [1] Numbering Scheme is the following: MD-J.K.LL.M.N 
               
               
                 J = 1 - no salt rejection layer/no SiO 2 -nanoparticle layer, 2 - no salt rejection layer/with SiO 2 -nanoparticle layer, 3 - salt rejection layer/no SiO 2 -nanoparticle layer, 4 - salt rejection Layer/SiO 2 -nanoparticle layer; 
               
               
                 K = 1 - mixture filtration method, 2 - mixture film/dip coating method, 3 - layer by layer method; 
               
               
                 LL = 31 - CLC-3.1, 32 - CLC-3.2, 41 - CLC-4.1, 51 - CLC-5.1, 52 - CLC-5.2, 53 - CLC-5.3, 54 - CLC-5.4, 55 - CLC-5.5, 61 - CLC-6.1, 62 - CLC-6.2, 63 - CLC-6.3, 64 - CLC-6.4; 
               
               
                 M = 1 - no protective coating, 2 - protective coating; 
               
               
                 N = device # within category. 
               
               
                 [2] All PP and PVA/PP substrates are approximately 30 μm thick; whereas the nylon substrates can be between 65-125 μm thick. 
               
               
                 [3] (Prop.) - Indicates a prophetic example. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Membrane Embodiments with a SiO 2  Nanoparticle Layer and a Salt Rejection Layer. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Mass of 
                   
                 Mass Ratio of 
                 Mass % of 
                 Application 
                 Coating 
                 Curing 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 Cross- 
                 Crosslinker 
                 Substrate 
                 PVA to SiO 2   
                 Aq. Sol. in 
                 Method/Pre- 
                 Thickness 
                 Temp 
                 Time 
               
               
                 Embodiment 
                 linker 
                 to GO 
                 Material 
                 Nanoparticles 
                 Prot. Layer 
                 treatment 
                 (nm or lyr) 
                 (° C.) 
                 (min) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 MD-2.2.11.1.1 
                 CLC-1 
                 83:16 
                 PET 
                 3:1 
                 — 
                 Film Coating/ 
                 200 
                 90 
                 30 
               
               
                 (Prop.) 
                   
                   
                   
                   
                   
                 PT: PVA 
               
               
                 MD-2.1.21.1.1 
                 CLC-2.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.22.1.1 
                 CLC-2.2 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-2.1.31.1.1 
                 CLC-3.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.32.1.1 
                 CLC-3.2 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.41.1.1 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.41.2.1 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 1.5 wt % PVA   
                 Filtration/ 
                 150 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.41.2.2 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 2.5 wt % PVA   
                 Filtration/ 
                 250 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.41.2.3 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 5 wt % PVA 
                 Filtration/ 
                 150 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.41.2.4 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 5 wt % PVA 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.41.2.5 
                 CLC-4.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 5 wt % PVA 
                 Filtration/ 
                 250 
                 80 
                 30 
               
               
                   
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.51.1.1 
                 CLC-5.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.52.1.1 
                 CLC-5.2 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.53.1.1 
                 CLC-5.3 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.54.1.1 
                 CLC-5.4 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.61.1.1 
                 CLC-6.1 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.63.1.1 
                 CLC-6.3 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                 MD-4.1.64.1.1 
                 CLC-6.4 
                 3:1 
                 Nylon 0.1 μm 
                 3:1 
                 — 
                 Filtration/ 
                 200 
                 80 
                 30 
               
               
                 (Prop.) 
                   
                   
                 Pore 
                   
                   
                 PT: Dopamine 
               
               
                   
               
               
                 Notes: 
               
               
                 [1] Numbering Scheme is the following: MD-J.K.LL.M.N 
               
               
                 J = 1 - no salt rejection layer/no SiO 2 -nanoparticle layer, 2 - no salt rejection layer/with SiO 2 -nanoparticle layer, 3 - salt rejection layer/no SiO 2 -nanoparticle layer, 4-salt rejection Layer/SiO 2 -nanoparticle layer; 
               
               
                 K = 1 - mixture filtration method, 2 - mixture film/dip coating method, 3 - layer by layer method; 
               
               
                 LL = 11 - CLC-1 (PVA), 21 - CLC-2.1, 22 - CLC-2.2, 31 - CLC-3.1, 32 - CLC-3.2, 41 - CLC-4.1, 51 - CLC-5.1, 52 - CLC-5.2, 53 - CLC-5.3, 54 - CLC-5.4, 55 - CLC-5.5, 61 - CLC-6.1, 62 - CLC-6.2, 63 - CLC-6.3, 64 - CLC-6.4; 
               
               
                 M = 1 - no protective coating, 2 - protective coating; 
               
               
                 N = device # within category; 
               
               
                 [2] All PP and PVA/PP substrates are approximately 30 μm thick; whereas the nylon substrates can be between 65-125 μm thick. 
               
               
                 [3] (Prop.) - Indicates a prophetic example. 
               
            
           
         
       
     
     Example 2.2.2: Preparation of a Membrane with a Protective Coating 
     Selected membranes were coated with a protective layer as shown in Table 4. For MD-4.1.41.2.1, a PVA solution of 1.5 wt % was prepared by stirring 15 g of PVA (Aldrich) in 1 L of DI water at 90° C. for 20 minutes until all granules dissolved. The solution was then cooled to room temperature. The substrate was immersed in the solution for 10 minutes and then removed. Excess solution remaining on the membrane was removed by paper wipes. The resulting assembly was dried in an oven (DX400, Yamato Scientific) at 90° C. for 30 minutes. Thus, a membrane with a protective coating can be obtained. Other selected membranes in Table 4 were coated similarly by using different concentrations of PVA. 
     Comparative Example 2.1.1: Preparation of Comparative Membranes (CMDs) 
     Comparative membranes (CMDs), such as CMD-1.1 and CMD-1.2 as shown in Table 5 were prepared using stock substrate components of polysulfone membrane (PSF) (Sterlitech Corporation, Kent, Wash., USA) and polypropolyene (PP) filtration membrane (Celgard LLC, Charlotte, N.C., USA) respectively. For CMD-1.3, a PVA/PP membrane was prepared by immersing a PP filtration membrane in a PVA/water solution (Aldrich) for 10 minutes and then drying the membrane in an oven (DX400, Yamato Scientific) at 90° C. for about 30 minutes. 
     Comparative membranes CMD-2.1.1 through CMD-2.2.2 as shown in Table 5 were also made using methods similar to Examples 2.1.1 through Example 2.2.1 for membranes described above without a SiO 2  nanoparticle layer with the differences outlined in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Comparative Membranes.  
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Mass of  
                   
                 Coating  
               
               
                   
                   
                 Cross-  
                 Crosslinker  
                 Substrate  
                 Thickness  
               
               
                 Membrane  
                 Method  
                 linker  
                 to GO  
                 Material  
                 (nm or lyr) 
               
               
                   
               
               
                 CMD-1.1   
                 n/a  
                 — 
                 — 
                 PSF  
                 — 
               
               
                 CMD-1.2   
                 n/a  
                 — 
                 — 
                 Stretched  
                 — 
               
               
                   
                   
                   
                   
                 PP  
                   
               
               
                 CMD-1.3   
                 n/a  
                 — 
                 — 
                 Stretched  
                 n/a  
               
               
                   
                   
                   
                   
                 PP/PVA  
                   
               
               
                 CMD-2.1.1  
                 Filtration  
                 EDA  
                 1:1  
                 Nylon 0.1 μm  
                 20  
               
               
                   
                   
                   
                   
                 Pore  
                   
               
               
                 CMD-2.1.2  
                 Filtration  
                 EDA  
                 3:1  
                 Nylon 0.1 μm  
                 20  
               
               
                   
                   
                   
                   
                 Pore  
                   
               
               
                 CMD-2.1.3  
                 Filtration  
                 EDA  
                 7:1  
                 Nylon 0.1 μm  
                 20  
               
               
                   
                   
                   
                   
                 Pore  
                   
               
               
                 CMD-2.2.1  
                 Filtration  
                 PPD  
                 3:1  
                 Nylon 0.1 μm  
                 20  
               
               
                   
                   
                   
                   
                 Pore  
                   
               
               
                 CMD-2.2.2  
                 Filtration  
                 PPD  
                 7:1  
                 Nylon 0.1 μm  
                 20  
               
               
                   
                   
                   
                   
                 Pore 
               
               
                   
               
               
                 Notes: 
               
               
                 [1] All PP and PVA/PP substrates are approximately 30 μm thick; whereas the nylon substrates are 65-125 μm thick. 
               
               
                 [2] All comparative examples have GO and a comparative crosslinker (e.g. ethylenediamine [EDA] or para-phenylenediamine [PPD]), wherein the composites were cured in an oven (DX400, Yamato Scientific) at 80° C. for 30 minutes to facilitate further crosslinking. 
               
            
           
         
       
     
     Example 3.1: Membrane Characterization 
     XPS Analysis: Membranes MD-1.1.31.1.1 and MD-1.1.41.1.1 were analyzed by X-ray photoelectron spectroscopy (XPS) to determine the relative distribution of the atomic contents (%). The procedures for XPS are similar to those known in the art. The XPS analysis, shown in Table 6, indicates an increase of nitrogen atom in the GO-MPD membrane as compared to GO (a reference sample), due to the cross-linking of amino groups in the cross-linker of MPD in the GO-MPD membrane. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Analysis Result of GO and GO-Crosslinked Membranes. 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 Samples 
                 Na 
                 C 
                 N 
                 O 
                 S 
                 Cl 
               
               
                   
                   
               
               
                   
                 GO (Ref.) 
                 — 
                 65.2 
                 — 
                 34.0 
                 0.8 
                 — 
               
               
                   
                 GO-CLC-3.1 
                 — 
                 68.8 
                 1.1 
                 29.9 
                 0.2 
                 — 
               
               
                   
                 GO-CLC 4.1 
                 0.5 
                 68.4 
                 1.0 
                 29.8 
                 0.3 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     Example 4.1: Performance Testing of Selected Membranes 
     Mechanical Strength Testing: The water flux of GO-based membrane coated on various porous substrates is expected to be very high, or at least comparable with porous polysulfone substrate widely used in current reverse osmosis membranes. 
     To test the mechanical strength, the membranes can be tested by placing them into a laboratory apparatus similar to the one shown in  FIG. 10 . Once secured in the test apparatus, the membrane can be exposed to the unprocessed fluid at a gauge pressure of 50 psi. The water flux through the membrane can be recorded at different time intervals. For example, the water flux can be recorded at 15 minutes, 60 minutes, 120 minutes, and 180 minutes, and etc. when possible. 
     From the data collected, it was found that the GO-PVA-based membrane can withstand reverse osmosis pressures while providing sufficient flux. 
     Dehydration Characteristics—Water Vapor Permeability Testing: The water vapor permeability of the membranes was tested. For the gas leakage, Nitrogen was chosen to mimic air. 
     A sample cross-sectional diagram of the test setup is shown in  FIG. 11 . The test setup comprises a cross-flow test cell (CF016A, Sterlitech) which forms two plenums on either side of the membrane when a membrane is added, each with its own inlet and an outlet. The membrane was placed in the 45 mm by 45 mm test chamber by sandwiching it between the two halves of the test cell to create two sealed plenums when the shells were mated, with each plenum in fluid communication only through the membrane. Then the inlets and outlets were chosen such that the fluid flow in each plenum was in a counter-flow configuration. Into the first side of the membrane, the wet side, wet N 2  gas was sent into the setup and then exited with some water vapor permeating the membrane sample. Into the second side, the dry side, sweep or dry N 2  gas was sent into the setup and then vented, with the wet gas being entrained from the membrane. Humidity and Temperature were measured at three positions: input and output on the wet N 2  gas side, and output on the dry N 2  gas side using a Humidity/Temperature Transmitters (RHXL3SD, Omega Engineering, Inc., Stamford, Conn., USA). The flow rates were also measured for both wet and dry sides by two Air Flow Sensors (FLR1204-D, Omega). In addition, the gas pressures were measured on both the wet and dry sides by two Digital Pressure Gauges (Media Gauge MGA-30-A-9V-R, SSI Technologies, Inc., Janesville, Wis., USA). 
     For the measurements, selected membranes were placed in the setup and the wet side inlet was set to a relative humidity of between about 80% to about 90%. The dry side inlet had a relative humidity of 0% initially. The upstream pressure for the wet gas stream was set to 0.13 psi. The upstream pressure for the dry gas stream was set to 0.03 psi. From the instruments, the water vapor pressure and absolute humidity at the three measurement stations (input and output on the wet N 2  gas side, and output on the dry N 2  gas side) was calculated based on the measured temperature and humidity. Then the water vapor transmission rate was calculated from the absolute humidity difference, flow rate, and exposed area of the membrane. Lastly, the water vapor permeability was calculated from the water vapor transmission rate and the water vapor pressure difference between the two plenums. The nitrogen flow rate was derived from the dry N 2  output and the wet N 2  inputs as well as the water vapor transmission rate. 
     Dehydration Characteristics—Nitrogen Leakage Testing: The gas leakage of the membranes was tested. For the gas leakage, Nitrogen was chosen to mimic air. For these tests, the same test setup was used as that in the Water Vapor Permeability testing described above with the exception that the dry N 2  gas inlet was closed and the dry N 2  outlet was vented to, instead of atmosphere, a flow measurement instrument (D800286 Gilibrator-2 Standard Air Flow Calibrator; Sensidyne, St. Petersburg, Fla., USA) with a normal test cell (20 cc to 6 LPM, Sensidyne) or a low-flow test cell (1 cc/min to 250 cc/min, Sensidyne) to measure the flow leakage through the membrane. For N 2  flow rates at about 1 cc/min or below, a 0.5 mL manual bubble flow meter was used (#23771, Aldrich), which has a range of about 0.03 cc/min to about 5 cc/min, to determine the leakage rate. 
     For the measurements, the selected membranes were placed in the setup and the wet side inlet was set to a relative humidity of between about 80% to about 90%. The dry side inlet was closed so that only gas leaked through the membrane would go to the flow measurement instrument. The upstream pressure for the wet gas stream was set to 0.13 psi and the leakage of the N 2  through the membrane was measured. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Water Vapor Permeability Measurements of Various Membranes.  
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 N 2  Gas  
               
               
                   
                 Coating  
                 H 2 O vapor  
                 Flow  
               
               
                   
                 Thickness  
                 permeability  
                 Rate  
               
               
                 Membrane  
                 (nm)  
                 (μg/m 2  · s · Pa)  
                 (cc/min) 
               
               
                   
               
               
                 20 nm GO-CLC-3.1 @ 1:3  
                 20 nm  
                 46.2  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.31.1.1)  
                   
                   
                   
               
               
                 20 nm GO-CLC-3.1 (a) 1:7  
                 20 nm  
                 45.4  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.31.1.2)  
                   
                   
                   
               
               
                 20 nm GO-CLC-3.1 @ 1:15  
                 20 nm  
                 43.3  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.31.1.3)  
                   
                   
                   
               
               
                 20 nm GO-CLC-4.1 @ 1:3  
                 20 nm  
                 43.0  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.41.1.1)  
                   
                   
                   
               
               
                 20 nm GO-CLC-4.1 @ 1:7  
                 20 nm  
                 42.3  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.41.1.2)  
                   
                   
                   
               
               
                 20 nm GO-CLC-4.1 @ 1:15  
                 20 nm  
                 45.5  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.41.1.3)  
                   
                   
                   
               
               
                 20 nm GO-CLC-5.1 @ 1:1  
                 20 nm  
                 37.5  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.1.1.1)  
                   
                   
                   
               
               
                 20 nm GO-CLC-5.1 @ 1:3  
                 20 nm  
                 35.6  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.1.1.2)  
                   
                   
                   
               
               
                 20 nm GO-CLC-5.1 @ 1:5  
                 20 nm  
                 38.3  
                 — 
               
               
                 on Nylon 0.1 μm Pore  
                   
                   
                   
               
               
                 (MD-1.1.1.1.3)  
                   
                   
                   
               
               
                 Stretched PP (CMD-1.2)  
                 n/a  
                 55.1  
                 75.29  
               
               
                 Stretched PP/PVA  
                 n/a  
                 51.8  
                 90.00  
               
               
                 (CMD-1.3) 
               
               
                   
               
            
           
         
       
     
     Water Flux and Salt Rejection Testing: The water flux of GO-based membrane coated on a porous substrate was observed to be very high, which is comparable with porous polysulfone substrate widely use in current reverse osmosis membranes. 
     To test the salt rejection capability, the reverse osmosis membranes were tested in a test cell similar to that shown in  FIG. 10 . To test the membranes&#39; ability to reject salt and retain adequate water flux, the membranes were exposed to a 1500 ppm NaCl solution at 225 psi. After approximately 120 minutes when the membrane reached steady state, the salt rejection and the water flux was recorded. As shown in Table 8, the membranes with 20 nm coating thickness demonstrated high NaCl salt rejection and good water flux as compared to their comparative membranes (CMD-2.2.1, CMD-2.1.3 and CMD-2.2.2) respectively. However, the membranes with coating thickness of 150 nm or above have low salt rejection although most of them maintain good water flux with some having higher water flux such as MD-4.1.41.1.1 and MD-4.1.41.2.1. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Performance of Selected Polyamide Coated Membranes.  
               
            
           
           
               
               
               
               
            
               
                   
                   
                 1500 ppm  
                   
               
               
                   
                   
                 NaCl  
                 Water  
               
               
                   
                   
                 Rejection  
                 Flux  
               
               
                   
                 Membrane  
                 (%)  
                 (GFD) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 PA + 20 nm Filtered 3:1 GO-CLC-3.1  
                 96  
                 9.0  
               
               
                   
                 (MD-2.1.31.1.1)  
                   
                   
               
               
                   
                 PA + 20 nm Filtered 7:1 GO-CLC-3.1  
                 93  
                 8.9  
               
               
                   
                 (MD-2.1.31.1.2)  
                   
                   
               
               
                   
                 PA + 20 nm Filtered 3:1 GO-CLC-4.1  
                 97  
                 8.0  
               
               
                   
                 (MD-2.1.41.1.1)  
                   
                   
               
               
                   
                 PA + 20 nm Filtered 7:1 GO-CLC-4.1  
                 95  
                 6.6  
               
               
                   
                 (MD-2.1.41.1.2)  
                   
                   
               
               
                   
                 PA + 200 nm Filtered 3:1 GO-CLC-4.1  
                 11.2  
                 63.0  
               
               
                   
                 (MD-4.1.41.1.1)  
                   
                   
               
               
                   
                 PA + 150 nm Filtered 3:1 GO-CLC-4.1  
                 9.5  
                 129.0  
               
               
                   
                 w/ PVA/SiO 2  Interlayer w/1.5 wt % PVA  
                   
                   
               
               
                   
                 (MD-4.1.41.2.1)  
                   
                   
               
               
                   
                 PA + 250 nm Filtered 3:1 GO-CLC-4.1  
                 13.9  
                 3.4  
               
               
                   
                 w/ PVA/SiO 2  Interlayer w/2.5 wt % PVA  
                   
                   
               
               
                   
                 (MD-4.1.41.2.2)  
                   
                   
               
               
                   
                 PA + 150 nm Filtered 3:1 GO-CLC-4.1  
                 11.5  
                 13.0  
               
               
                   
                 w/ PVA/SiO 2  Interlayer w/ 5 wt % PVA  
                   
                   
               
               
                   
                 (MD-4.1.41.2.3)  
                   
                   
               
               
                   
                 PA + 200 nm Filtered 3:1 GO-CLC-4.1  
                 14.9  
                 9.6  
               
               
                   
                 w/ PVA/SiO 2  Interlayer w/ 5 wt % PVA  
                   
                   
               
               
                   
                 (MD-4.1.41.2.4)  
                   
                   
               
               
                   
                 PA + 250 nm Filtered 3:1 GO-CLC-4.1  
                 40.2  
                 0.6  
               
               
                   
                 w/ PVA/SiO 2  Interlayer w/ 5 wt % PVA  
                   
                   
               
               
                   
                 (MD-4.1.41.2.5)  
                   
                   
               
               
                   
                 PA + 20 nm Filtered 3:1 GO-PPD  
                 59  
                 5.7  
               
               
                   
                 (CMD-2.2.1)  
                   
                   
               
               
                   
                 PA + 20 nm Filtered 7:1 GO-EDA  
                 81  
                 2.5  
               
               
                   
                 (CMD-2.1.3)  
                   
                   
               
               
                   
                 PA + 20 nm Filtered 7:1 GO-PPD  
                 35  
                 10.7 
               
               
                   
                 (CMD-2.2.2) 
               
               
                   
                   
               
               
                   
                 Notes: 
               
               
                   
                 [1] PA: polyamide coating (salt rejection layer). 
               
               
                   
                 [2] Cell Testing Conditions: pressure: 225 psi, temperature: 25° C., pH: 6.5-7.0, run flow: 1.5 L/min 
               
            
           
         
       
     
     Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and etc. used in herein are to be understood as being modified in all instances by the term “about.” Each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Accordingly, unless indicated to the contrary, the numerical parameters may be modified according to the desired properties sought to be achieved, and should, therefore, be considered as part of the disclosure. At the very least, the examples shown herein are for illustration only, not as an attempt to limit the scope of the disclosure. 
     The terms “a,” “an,” “the” and similar referents used in the context of describing embodiments of the present disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illustrate embodiments of the present disclosure and does not pose a limitation on the scope of any claim. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the embodiments of the present disclosure. 
     Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. 
     Certain embodiments are described herein, including the best mode known to the inventors for carrying out the embodiments. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the embodiments of the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the claims include all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. 
     In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the claims. Other modifications that may be employed are within the scope of the claims. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the claims are not limited to embodiments precisely as shown and described.