Patent Publication Number: US-8979978-B2

Title: Graphene membrane with regular angstrom-scale pores

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is the National Stage filing under 35 U.S.C §371 of PCT Application Ser. No. PCT/US12/22798 filed on Jan. 26, 2012. The PCT Application is herein incorporated by reference in its entirety. 
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Porous graphene is considered to be a desirable membrane for gas separation. Theoretical and experimental studies indicate that atom-scale holes in the graphene lattice may provide significant selectivity for separating gases based on molecular size. Further, monolayer graphene, at one atom thick, is a desirable candidate because the gas permeation rate through a membrane increases with decreasing membrane thickness. 
     Consequently, porous graphene membranes are being pursued for their potential to significantly outperform conventional polymeric membranes, e.g., in separating gases that are synthesized at high temperatures. For example, the “shift reaction” used to create hydrogen gas from water and carbon dioxide may run at temperatures over 400° C. Since there is currently no membrane that effectively purifies hydrogen in a single operation, much less at such high temperatures, current hydrogen purification may include capital and energy intensive operations such as cooling, as well as removal of water, carbon dioxide, and other impurities. 
     A graphene membrane with uniformly sized pores may effectively purify hydrogen from the “shift reaction” in a single operation. However, although porous graphene has shown interesting performance in small-scale academic studies, current preparation methods are not capable of preparing a graphene membrane with uniformly sized pores. Known porous graphene examples have been created using a physical process such as electron or ion beams to damage the graphene surface, followed by oxidative expansion of the defects to create pores. Such methods have created porous graphene membranes with pores that vary significantly in size and in areal density over the membrane. 
     The present disclosure appreciates that preparing porous graphene, e.g., for use in separation membranes, may be a complex undertaking. 
     SUMMARY 
     The following summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
     The present disclosure generally describes perforated graphene monolayers, and membranes that include perforated graphene monolayers. An example membrane may include a graphene monolayer with a plurality of discrete pores that are chemically perforated therein. Each of the plurality of discrete pores may have a substantially uniform pore size characterized by one or more carbon vacancy defects in the graphene monolayer such that the graphene monolayer may have substantially uniform pore sizes throughout. 
     The present disclosure also generally describes example methods of forming a plurality of discrete pores in a graphene monolayer. An example method may include contacting a compound represented by R-Het* to a plurality of locations at the graphene monolayer. Het* may be nitrene or activated oxy. R may be one of —R a , —SO2R a , —(CO)OR a , or —SiR a R b R c . R a , R b , and R c  may be independently aryl or heteroaryl. Some example methods may also include providing a separation distance of at least r R  between adjacent locations in the plurality of locations, wherein r R  may be a minimum steric radius of R. Various example methods may also include reacting the compound represented by R-Het* with at least one graphene carbon atom C g  at each of the plurality of locations to form a plurality p of heteroatom-carbon moieties at the graphene monolayer represented by [R-Het-C g ] p graphene. The method may also include forming a plurality of discrete pores in the graphene monolayer by removing a plurality of the heteroatom-carbon moieties represented by R-Het-C g , The plurality of discrete pores may be characterized by a plurality of carbon vacancy defects in the graphene monolayer defined by removing the graphene carbon atoms C g  from the plurality of locations. The graphene monolayer may have substantially uniform pore sizes throughout. 
     The present disclosure also generally describes methods of separating a compound from a fluid mixture. An example method may include providing a fluid mixture that contains a first compound and a second compound. Some example methods may also include providing a membrane that includes a graphene monolayer that may be chemically perforated by a plurality of discrete pores. Each of the plurality of discrete pores may be characterized by one or more carbon vacancy defects such that the graphene monolayer has substantially uniform pore sizes throughout. Each of the plurality of discrete pores may be characterized by a diameter that may be selective for passage of the first compound compared to the second compound. Various example methods may also include contacting the fluid mixture to a first surface of the graphene monolayer. Example methods may further include directing the first compound through the plurality of discrete pores to separate the first compound from the second compound. 
     The present disclosure also generally describes an example membrane. The example membrane may be prepared by a process that includes contacting a compound represented by R-Het* to a plurality of locations at a graphene monolayer. Het* may be nitrene or activated oxy. R may be one of —R a , —SO2R a , —(CO)OR a , or —SiR a R b R c . R a , R b , and R c  may be independently aryl or heteroaryl. Some example membranes may be prepared by a process that also includes providing a separation distance of at least r R  between adjacent locations in the plurality of locations, wherein r R  may be a minimum steric radius of R. The example membrane may be prepared by a process that further includes reacting the compound represented by R-Het* with at least one graphene carbon atom C g  at each of the plurality of locations to form a plurality p of heteroatom-carbon moieties at the graphene monolayer represented by [R-Het-C g ] p graphene. The example membrane may be prepared by a process that also includes forming a plurality of discrete pores in the graphene monolayer by removing a plurality of the heteroatom-carbon moieties represented by R-Het-C g . The plurality of discrete pores may be characterized by a plurality of carbon vacancy defects in the graphene monolayer defined by removing the graphene carbon atoms C g  from the plurality of locations. The graphene monolayer may have substantially uniform pore sizes throughout. 
     The present disclosure also generally describes system for preparing a graphene membrane with substantially uniform pores. The system may include: a reagent activator for preparing an activated reagent from a precursor reagent; a reagent applicator configured to contact the activated reagent to a plurality of locations at a graphene monolayer; a reaction chamber configured to hold the graphene monolayer; a heater configured to thermally cleave a plurality of heteroatom-carbon moieties at the graphene monolayer to form a perforated graphene monolayer; and a support substrate applicator configured to contact the perforated graphene monolayer to a support substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of this disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG. 1A  is a conceptual drawing of an example graphene monolayer, illustrating the hexagonal lattice of carbon atoms and aromatic bonds characteristic of graphene; 
         FIG. 1B  is a conceptual drawing of example graphene monolayer, showing one graphene carbon atom to be removed from a plurality of locations; 
         FIG. 1C  is a conceptual drawing of an example perforated graphene monolayer, including a plurality of discrete pores which may have a substantially uniform pore size characterized by one carbon vacancy defect per pore; 
         FIG. 1D  is a conceptual drawing of an example graphene monolayer, showing graphene carbon atoms to be removed from each of a plurality of locations; 
         FIG. 1E  is a conceptual drawing of an example perforated graphene monolayer, including a plurality of discrete pores which may have a substantially uniform pore size characterized by two carbon vacancy defects per pore; 
         FIG. 2A  is a conceptual drawing of a side view of an example membrane that includes an example perforated graphene monolayer in contact with a permeable substrate; 
         FIG. 2B  is a conceptual drawing of a side view of an example membrane illustrating a method of separating a fluid mixture of two compounds; 
         FIG. 3A  is a conceptual drawing showing a method of forming a plurality of discrete pores in a graphene monolayer, including steric interactions between adjacent reagents; 
         FIG. 3B  is a conceptual drawing showing additional operations which may be included in a method of forming a plurality of discrete pores in a graphene monolayer; 
         FIG. 4  depicts an example reaction scheme corresponding to the general scheme shown in  FIG. 3A  and  FIG. 3B ; 
         FIG. 5A  depicts an example reaction scheme where an example graphene monolayer may be contacted with a plurality of substituted nitrene radicals; 
         FIG. 5B  depicts an example reaction scheme which may be employed for forming pores containing single carbon vacancy defects from nitrene reagents; 
         FIG. 5C  depicts an example reaction scheme which may be employed for forming pores containing double carbon vacancy defects from nitrene reagents; 
         FIG. 5D  depicts an example reaction scheme which employs a 1,2 diether to form a 1,2 diol intermediate compound in the course of forming pores containing double carbon vacancy defects from activated oxy reagents; 
         FIG. 5E  depicts an example reaction scheme which employs a 1,2 diester moiety to form a 1,2 diol intermediate compound in the course of forming pores containing double carbon vacancy defects from activated oxy reagents; 
         FIG. 6  is a flow diagram showing operations that may be used in making an example perforated graphene monolayer or a membrane thereof; 
         FIG. 7  is a block diagram of an automated machine  700  that may be used for making an example perforated graphene monolayer; 
         FIG. 8  illustrates a general purpose computing device that may be used to control the automated machine of  FIG. 7  in making an example perforated graphene monolayer or membrane thereof; 
         FIG. 9  illustrates a block diagram of an example computer program product that may be used to control the automated machine of  FIG. 7  or similar manufacturing equipment in making an example perforated graphene monolayer or example membrane thereof; 
     
    
    
     all arranged in accordance with at least some embodiments as described herein. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     This disclosure is generally drawn, inter alia, to compositions, methods, apparatus, systems, devices, and/or computer program products related to manufacturing or using perforated graphene, for example as part of membrane which may be used in gas separation. 
     Briefly stated, technologies are generally described for a membrane that may include a graphene monolayer having a plurality of discrete pores that may be chemically perforated into the graphene monolayer. The discrete pores may be of substantially uniform pore size. The pore size may be characterized by one or more carbon vacancy defects in the graphene monolayer. The graphene monolayer may have substantially uniform pore sizes throughout. In some examples, the membrane may include a permeable substrate that contacts the graphene monolayer and which may support the graphene monolayer. Such perforated graphene monolayers, and membranes comprising such perforated graphene monolayers may exhibit improved properties compared to conventional polymeric membranes for gas separations, e.g., greater selectivity, greater gas permeation rates, or the like. 
       FIG. 1A  is a conceptual drawing of an example graphene monolayer  100 .  FIG. 1A  illustrates the hexagonal lattice of carbon atoms and aromatic bonds characteristic of graphene. The placement of the carbon-carbon double bonds in example graphene monolayers described herein, for example, in monolayer  100 , is intended to be illustrative of graphene and is not intended to be limiting. 
       FIG. 1B  is a conceptual drawing of example graphene monolayer  100 , showing one graphene carbon atom  102  to be removed from a plurality of locations in example graphene monolayer  100 . Removal of graphene carbon atoms  102  forms example graphene monolayer  106  in  FIG. 1C .  FIG. 1B  also shows a minimum steric separation  104  between adjacent locations in example graphene monolayer  100 . Minimum steric separation  104  may also correspond to the diameter of a circle  105  around graphene carbon atom  102 . Circle  105  may correspond to a minimum steric radius r R  of an R group in a bulky chemical perforation reagent R-Het*. Methods of chemical perforation using bulky reagents R-Het* are described further in the discussion of  FIGS. 4A-5E . 
       FIG. 1C  is a conceptual drawing of an example perforated graphene monolayer  106 . A plurality of discrete pores  108  are chemically perforated in example graphene monolayer  106 . Discrete pores  108  may have a substantially uniform pore size characterized by one or more carbon vacancy defects in graphene monolayer  106 . In various examples, each discrete pore  108  may include hydrogen-passivated carbon atoms  110 .  FIG. 1C  also shows a minimum steric separation  104  between adjacent discrete pores  108 . Minimum steric separation  104  may also correspond to the diameter of circle  105  around discrete pores  108 . 
       FIG. 1D  is a conceptual drawing of an example graphene monolayer  112 , showing graphene carbon atoms  114  and  116  to be removed from each of a plurality of locations in example graphene monolayer  112 , leading to example graphene monolayer  120  in  FIG. 1E .  FIG. 1D  also shows a minimum steric separation  118  between adjacent locations in example graphene monolayer  112 . Minimum steric separation  118  may also correspond to the diameter of a circle  119  around graphene carbon atoms  114  and  116 . Circle  119  may correspond to a minimum steric radius r R  of an R group in a bulky chemical perforation reagent R-Het*. Methods of chemical perforation using bulky reagents R-Het* are described further in the discussion of  FIGS. 4A-5E . 
       FIG. 1E  is a conceptual drawing of an example perforated graphene monolayer  120 . A plurality of discrete pores  122  are chemically perforated in example graphene monolayer  120 . Each of the plurality of discrete pores  122  may have a substantially uniform pore size characterized by two or more carbon vacancy defects in graphene monolayer  120 . In various examples, each discrete pore  120  may include hydrogen-passivated carbon atoms  124 .  FIG. 1E  also shows minimum steric separation  118  between adjacent discrete pores  122 . Minimum steric separation  118  may also correspond to the diameter of circle  119  around discrete pores  122 . 
     As used herein, “graphene” generally means a planar allotrope of carbon characterized by a hexagonal lattice of carbon atoms that may be connected by aromatic carbon-carbon bonds, e.g., as illustrated by graphene  100  in  FIG. 1A . As used herein, a graphene “monolayer” generally may be a one-carbon atom thick layer of graphene. In some examples, the graphene monolayer may include some nonaromatic carbons, e.g., some carbons may be passivated with hydrogen and may be bonded to other carbons by nonaromatic single carbon-carbon bonds. As used herein, a “perforated graphene monolayer” generally may refer to a graphene monolayer that may include a plurality of discrete pores through the graphene monolayer. The discrete pores may pass entirely through the graphene monolayer. The discrete pores may permit selective passage of atomic or molecular species from one side of the graphene monolayer to the other side of the graphene monolayer. As used herein, a “chemically perforated” pore in the graphene may be characteristic of preparation by selective removal of one or more carbon atoms from the graphene lattice, for example, the perforation shown between  FIGS. 1B and 1C , or the perforation shown between  FIGS. 1D and 1E . For example, atomic or molecular species may be reacted with the graphene in a process which results in selective removal of one or more carbon atoms from the graphene lattice. Example procedures for preparing the pores are described further in the discussion of  FIGS. 3A-5E . 
     As used herein, “discrete” pores in a graphene monolayer are distinct from each other by at least one intervening carbon-carbon bond, or in some examples, at least one intervening six-membered graphene ring. For example, in  FIG. 1C , discrete pores  108 A and  108 B are separated by at least four six membered rings or at least five carbon-carbon bonds. Also, for example, in  FIG. 1C , discrete pore  108 C may be separated from each of discrete pores  108 A and  108 B by at least three six-membered rings or at least four carbon-carbon bonds. In another example, in  FIG. 1E , discrete pores  122 A and  122 B are separated by at least four six membered rings or at least five carbon-carbon bonds. Also, for example, in  FIG. 1E , discrete pore  122 C may be separated from each of discrete pores  122 A and  122 B by at least three six-membered rings or at least four carbon-carbon bonds. 
     As used herein, “minimum steric separation” generally may refer to the distance between the centers of adjacent discrete pores, such as distance  104  in  FIG. 1C  or distance  118  in  FIG. 1E . For example, a minimum steric separation corresponding to at least one intervening carbon-carbon bond may be at least about 1 angstrom. In some examples, a minimum steric separation corresponding to at least one intervening six-membered graphene ring may be at least about 4 angstroms. In various examples, a minimum steric separation may range from between about 1 angstrom to about 100 angstroms, for example, at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 20, 25, 35, or 50 angstroms. As used herein, “minimum steric separation” may generally refer to twice a minimum steric radius r R  of an R group in a bulky chemical perforation reagent R-Het* employed to make the discrete pores. Methods of chemical perforation using bulky reagents R-Het* and details of R groups and minimum steric radii r R  are generally described further with respect to  FIGS. 3A-5E . 
     In various examples, the pores may be characterized by one or more carbon vacancy defects in the graphene monolayer such that the graphene layer has substantially uniform pore sizes throughout. In some examples, each of the pores may be characterized by one or more carbon vacancy defects in the graphene monolayer such that the pores have substantially the same number of carbon vacancy defects throughout. 
     As used herein, a “carbon vacancy defect” may be a pore in a graphene monolayer which may be defined by the absence of one or more carbon atoms compared to a graphene monolayer without a carbon vacancy defect. 
     As used herein, a “substantially uniform pore size” means that the discrete pores may be characterized by substantially the same number of one or more carbon vacancy defects per discrete pore. For example, in  FIG. 1C , discrete pores  108  may be characterized as single-carbon vacancy defects corresponding to the absence of carbon atoms  102  from graphene monolayer  100  in  FIG. 1B . In another example, in  FIG. 1E , discrete pores  122  may be characterized as double-carbon vacancy defects corresponding to the absence of carbon atoms  114  and  116  from graphene monolayer  100  in  FIG. 1D . In various examples, discrete pores of substantially uniform pore size may have their carbon vacancy defects arranged in substantially the same relative lattice positions within each discrete pore. For example, a plurality of substantially uniform pores that include six carbon vacancy defects each may correspond to removal of a six membered ring of carbon atoms in the hexagonal graphene lattice. In another example, a plurality of substantially uniform pores that include six carbon vacancy defects each may correspond to removal of a six membered staggered linear chain of carbon atoms in the hexagonal graphene lattice. 
     As used herein, “substantially uniform pore sizes throughout” means that at least about 80% of the discrete pores in a perforated graphene monolayer may have a substantially uniform pore size. In various examples, the percentage of discrete pores in a perforated graphene monolayer that may have a substantially uniform pore size may be: about 85%, about 90%, about 95%, about 96%, about 97%, about 98%, about 99%, about 99.5%, or about 99.9%. In some examples, all of the discrete pores in a perforated graphene monolayer may have a substantially uniform pore size. 
     As used herein, “substantially the same number of one or more carbon vacancy defects” in relation to the plurality of discrete pores means that such discrete pores differ from each other by at most about three carbon vacancy defects. For example, a plurality of pores having substantially the same number of one or more carbon vacancy defects may range between one and three carbon vacancy defects per pore. In various examples, discrete pores may vary in number of carbon vacancy defects by about three, about two, or about one. In some examples, each of the plurality of discrete pores has the same number of carbon vacancy defects. For example, in  FIG. 1C , discrete pores  108  may be characterized as having a single carbon vacancy defect per pore. In another example, in  FIG. 1E , discrete pores  122  may be characterized as having a two-carbon vacancy defect per pore. In other examples, at least about 80% of the discrete pores in a perforated graphene monolayer may the same number of carbon vacancy defects. In various examples, the percentage of discrete pores in a perforated graphene monolayer that may have the same number of carbon vacancy defects may be: about 85%, about 90%, about 95%, about 96%, about 97%, about 98%, about 99%, about 99.5%, or about 99.9%. In some examples, all of the discrete pores in a perforated graphene monolayer may have the same number of carbon vacancy defects. 
     As used herein, the “number” of carbon vacancy defects in reference to “substantially the same number of one or more carbon vacancy defects” means about one or more carbon defects, or in some examples at least about two carbon defects. 
       FIG. 2A  is a conceptual drawing of a side view of an example membrane  200  that includes a perforated graphene monolayer  106  configured in contact with a permeable substrate  202 . Perforated graphene monolayer  106  may include discrete pores  108 . A substrate such as permeable substrate  202  may be configured to contact one or both sides of an example perforated graphene monolayer such as  106 . 
     As used herein, a “permeable substrate”, for example permeable substrate  302 , may be any material that may be employed to provide support to a perforated graphene monolayer such as  106 . As used herein, a “permeable substrate” may also be permeable to at least one atomic or molecular species that traverses the discrete pores in the perforated graphene monolayer. Suitable permeable substrates may include “solution-diffusion” solid membranes that permit atomic or molecular species to diffuse through the solid material of the permeable substrate. Suitable permeable substrates may also be configured as porous membranes, non-woven materials, or filters having pores, voids, channels, or the like, through which atomic or molecular species may travel. Suitable materials for the permeable substrate may include, for example, one or more of polyethylene including ultra high molecular weight polyethylene, polypropylene, polyester, polyurethane, polystyrene, polyolefin, aramide, aromatic polyester, carbon fiber, polysulfone and/or polyethersulfone. Suitable permeable substrates may also include metal meshes and porous ceramics. In various examples, suitable polymeric materials for the permeable substrate may be characterized by a minimum molecular weight cutoff at: about 1,000,000 daltons; about 500,000 daltons; about 250,000 daltons; or about 100,000 daltons. In some examples, a suitable permeable substrate may include a polyether sulfone membrane characterized by a maximum molecular weight cutoff of about 100,000 daltons. 
       FIG. 2B  is a conceptual drawing of a side view of an example membrane  200  that may include a perforated graphene monolayer  106  arranged in contact with a permeable substrate  202 . Perforated graphene monolayer  106  may include discrete pores  108 . In  FIG. 2B , membrane  200  separates a chamber  204  and a chamber  206 . Chamber  204  may be configured to contain a fluid mixture of two compounds  208  and  210 . Chamber  206  may be configured for receiving a purified selection of one of compounds  208  and  210 .  FIG. 2B  depicts the fluid mixture, including first compound  208 , symbolized by dark-filled circles, and second compound  210 , symbolized by white-filled circles. The first and second compounds may also include one or more differences in atomic or chemical character such as differences in elemental composition, isotopic composition, molecular structure, size, mass, hydrophobicity, polarity, polarizability, charge distribution, or the like. For example, the first compound  208  may be smaller than the second compound  210  as symbolized by the relative sizes of the filled circles in  FIG. 2B . In some examples, discrete pores such as  108  may be characterized by a diameter that may be selective for passage of the first compound compared to the second compound. The diameter may select for passage of first compound  208  compared to second molecule  210  based on the one or more differences in atomic or chemical character, e.g., size, ionic nature, chemical affinity for the example membrane, or the like. 
     The fluid mixture of compounds  208  and  210  may be contacted to membrane  200 . First compound  208  may be directed from chamber  204  through pores  108  to chamber  206  to separate first compound  208  from second compound  210 . The first compound  208  may be directed through discrete pores  108  by employing a gradient across the graphene monolayer. The gradient may include differences in one or more properties such as temperature, pressure, concentration, electric field, or electrochemical potential. 
     As used herein, a “fluid mixture” may be any fluid phase, e.g., gas phase, liquid phase, or supercritical phase, which may include at least a first molecular species and a second molecular species, e.g., compounds  208  and  210 . In various examples, the fluid mixture may include: a mixture of gases; a mixture of a vapor in a gas; a mixture of liquids; a solution of a gas dissolved in a liquid; a solution of a solid dissolved in a liquid; a solution of a gas, liquid or solid in a supercritical fluid; or the like. In some examples, the fluid mixture may be in contact with other phases of the two or more different compounds. For example, a fluid mixture that includes fluid phase carbon dioxide as one of the compounds may be in contact with solid phase carbon dioxide. 
     The first and second compounds may include compounds consisting of a single atom, for example, helium, neon, argon, krypton, xenon, and radon. The compounds may also include compounds of two or more atoms connected by one or more covalent bonds, ionic bonds, coordination bonds, or the like. For example, suitable molecules may include water, hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, sulfur dioxide, hydrogen sulfide, a nitrogen oxide, a C1-C4 alkane, a silane, an organic solvent, or a haloacid. An “organic solvent”, as used herein, is a carbon based compound that typically is in liquid form when at an approximate temperature of 25° C. with an approximate atmospheric pressure of 1 atm. Organic solvents may include, for example, acetonitrile; alcohols such as methanol, ethanol, propanol, 2-propanol, 1-butanol, tertiary butanol, ethylene glycol, propylene glycol, or the like; alkanes such as pentane, hexane, heptanes, cyclopentane, cyclohexane, cycloheptane, or the like; ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, glyme, diglyme, or the like; halogenated solvents such as dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, or the like; aromatics such as benzene, toluene, xylenes, or the like; or polar aprotic solvents such as dimethyl sulfoxides, dimethyl formamide, or the like. 
     In some examples, the second molecule may be a liquid, e.g., water or an organic solvent, and the first molecule may be a covalent or ionic molecular compound dissolved in the liquid. 
     In some examples, one molecule may be a polar liquid such as water, and the other molecule may be a salt that includes a cation and an anion. Examples of cations for salts may include metal cations, e.g. alkali metal cations such as lithium, sodium, potassium, or the like; alkali earth metal cations such as calcium or magnesium, or the like; cations of transition metals such as copper, iron, nickel, zinc, manganese, or the like; cations of metals in other groups, such as cations of aluminum; and so on. Examples of anions for salts may include, but are not limited to, fluoride, chloride, bromide, iodide, chlorate, bromate, iodate, perchlorate, perbromate, periodate, hydroxide, carbonate, bicarbonate, sulfate, phosphate, and so on. In some examples, the fluid mixture may be a natural water source such as seawater or groundwater, where the perforated graphene membrane may be employed to separate water from natural solutes, such as sodium chloride, and/or unnatural solutes, such as molecules that are manmade pollutants. 
     As used herein, “separation selectivity” means a ratio of perforated graphene monolayer permeability rates between specific pairs of atomic or molecular species, for example, molecules  208  and  210  in  FIG. 2B . For example, theoretical calculations have been described for a one-atom thick monolayer characterized by pores about 2.5 angstroms in diameter; the ratio of a calculated hydrogen permeability rate divided by a calculated methane permeability rate was 10^ 23 :1. In comparison, currently known “solution diffusion” polymer membranes have a hydrogen to methane separation selectivity of about 150:1. Perforated graphene monolayers described herein may be characterized by a separation selectivity, for example, perforated graphene monolayers  106  in  FIG. 1C ,  120  in  FIG. 1E , and  106  in membrane  200  in  FIG. 2A  and  FIG. 2B . For example, an example perforated graphene monolayer such as  106  may include about one carbon vacancy defect per pore. A hydrogen:methane separation selectivity for perforated graphene monolayer  106  may be characterized as the ratio of permeation rates of molecular hydrogen (H 2 ) compared to methane (CH 4 ). In some examples, the hydrogen:methane separation selectivity may be at least about 200:1; or in various examples, between about 200:1 and about 10 23 :1, for example, at least about: 10 3 :1; 10 4 :1; 10 5 :1; 10 6 :1; 10 9 :1; 10 12 :1; 10 15 :1; 10 18 :1; or 10 21 :1. 
       FIG. 3A  is a conceptual drawing showing a method of forming a plurality of discrete pores  108  in a graphene monolayer  100  to form perforated graphene monolayer  106 .  FIG. 3A  shows a side view of graphene monolayer  100 . A reagent R-Het* may be contacted to a plurality of locations at a graphene monolayer such as graphene monolayer  100 . The reagent may be contacted to the graphene monolayer in any suitable form, such as a solid, a liquid, a gas, a solute in a solution, particles in a suspension, or the like. The reagent may be contacted to the graphene monolayer by any suitable means, such as by: immersion; spin coating; dip coating; selective coating, e.g., applied via an ink-jet type nozzle; sublimation or condensation; chemical vapor deposition; or the like. 
       FIG. 3A  also shows that at graphene monolayer  100 , the reagent represented by R-Het* may be reacted with at least one graphene carbon atom C g  at each of the plurality of locations, e.g., C g    304  and  306 . The reaction forms heteroatom-carbon moieties represented by R-Het-C g    300  and  302  in modified graphene monolayer  100 ′. Modified graphene monolayer  100 ′ may be represented by the formula [R-Het-C g ] p graphene, where p represents the number of locations in the plurality of locations. 
       FIG. 3A  also shows that at graphene monolayer  100 ′, steric interactions between adjacently located R-Het-C g    300  and  302  provide a minimum separation distance  104 . The side view shown in  FIG. 3A  may be compared to the top view shown in  FIGS. 1B and 1C . The R groups, symbolized by the shaded spheres in  FIG. 3A , may be selected to provide a minimum steric radius r R . The phrase “minimum steric radius r R ” means the relative orientation of respective R groups that provides minimum separation distance  104  of at least about 2*r R . The shaded spheres representing the R groups in  FIG. 3A  correspond to circles  105  and  119  shown in  FIGS. 1B ,  1 C,  1 D and  1 E. The minimum steric distance  104  provided by using the R groups may substantially reduce the chance of R-Het-C g  derivitizing adjacent carbon-carbon bonds in graphene. In various examples, the steric interactions may isolate Het-C g  bonds from each other. In various examples, the steric interactions may lead to discrete pore formation, whereby graphene carbon radicals created by removing Het-C g  may be unlikely to combine or rearrange into larger pores. 
     The group represented by R may be one of —R a , —SO 2 R a , —(CO)OR a , or —SiR a R b R c ; where R a , R b , and R c  are each independently alkyl, aryl, heteroaryl, aralkyl, or heteroaralkyl. In various examples, the alkyl, aryl, heteroaryl, aralkyl, and heteroaralkyl groups represented by R a , R b , and R c  may be substituted or unsubstituted. In some examples, the groups represented by R a , R b , and R c  may be unsubstituted. 
     The group Het* may be any heteroatom group which reacts with carbons C g  or carbon-carbon double bonds C g ═C g  in graphene to form heteroatom-carbon moieties, e.g., as represented by R-Het-C g    300  and  302 . Examples of heteroatom groups represented by Het* may include nitrene radical, or an activated oxy group such as oxy radical, oxy anion, hydroxyl, carboxyl, or carboxylate; or the like. Activated heteroatom reagents represented by R-Het* may be prepared by activating precursor compounds represented by R-Het. Various examples of reacting heteroatom groups with graphene are discussed in the descriptions of  FIGS. 5A ,  5 B,  5 C,  5 D, and  5 E. 
       FIG. 3A  also shows that perforated graphene monolayer  106 , including discrete pores  108 , may be formed by removing heteroatom-carbon moieties represented by R-Het-C g    300  and  302  at modified graphene monolayer  100 ′. Discrete pores  108  are characterized by carbon vacancy defects in the graphene monolayer defined by removing the graphene carbon atoms C g  from the plurality of locations such that the graphene monolayer has substantially uniform pore sizes throughout. 
       FIG. 3B  is a conceptual drawing showing additional operations which may be included in a method of forming a plurality of discrete pores  108  in a graphene monolayer  100  to form perforated graphene monolayer  106 . For example,  FIG. 3B  shows an operation of activating a precursor R-Het to form the activated reagent R-Het*. In another example of an additional operation,  FIG. 3B  shows that the heteroatom-carbon moieties represented by R-Het-C g    300  and  302  may be removed by employing additional operations. For example, as shown in  FIG. 3A , the R groups may be removed to provide groups H-Het*-C g    301  and  303 , followed by removal of H-Her-Cg  301  and  303  and passivation with hydrogen to provide discrete pores  108  in perforated graphene monolayer  106 . 
       FIG. 4  depicts an example reaction scheme corresponding to the general scheme shown in  FIG. 3A  and  FIG. 3B . In  FIG. 4 , trimethyl silyl azide  400 , corresponding to R-Het in  FIGS. 3A and 3B , may be first heated or photolyzed to produce the activated trimethyl silyl nitrene radical  402 . For example, graphene  404  may be placed in an evacuated reaction chamber. Trimethyl silyl azide  400  may be degassed and evaporated to a pressure between about 0.1 Torr and about 10 Torr, for example about 1 Torr. The chamber may be heated, for example, between about 150° C. and about 250° C., for example, about 200° C. Trimethyl silyl nitrene radical  402  may be reacted with a carbon carbon double bond in graphene  404  to form the trimethyl silyl aziridine compound  406 , corresponding to R-Het-C g  in  FIGS. 3A and 3B . Referring to  FIG. 3A , the Het group in R-Het-C g    300  and  302  bonds to at least one carbon C g . In the example shown in  FIG. 4 , the nitrene radical bonds to two carbons to form the three-membered aziridine ring in compound  406 . The specific example in  FIG. 4  also shows that the trimethyl silyl group in compound  406 , corresponding to R, may be cleaved, e.g., with a fluoride ion source such as tetrabutyl ammonium fluoride to form the N—H aziridine ring in compound  408 . 
       FIG. 5A  depicts an example reaction scheme corresponding to a portion of the general scheme shown in  FIG. 3A  and  FIG. 3B . Graphene monolayer  500  may be contacted with a plurality of substituted nitrene radicals  501 . A plurality of carbon-carbon double bonds C g ═C g  in graphene monolayer  500  may react with the substituted nitrene radicals  501 . A graphene monolayer may be formed that may be functionalized with a plurality of N—R substituted aziridine groups as represented by aziridine structure  502 . The N—R substituents of the aziridine groups may be cleaved to form an N—H aziridine structure  504 . 
     In various examples, a suitable nitrene precursor group represented by -Het may be azide, —N 3 . In some examples, R-Het* may be prepared as R-nitrene  501  by reacting an azide precursor represented by R—N 3  under thermolytic or photolytic conditions suitable for converting azide to nitrene. In some examples, suitable values for R when -Het is azide may include —R a  or —SiR a R b R c . In various examples, reaction of R-nitrene with graphene produces an N—R aziridine  502  as shown in  FIG. 5A . 
     In some examples, R in aziridine structure  502  may be —SiR a R b R c . In various examples, groups such as —SiR a R b R c  may be cleaved from the substituted aziridine represented by structure  502  by contacting each substituted aziridine  502  with one of: a quaternary ammonium fluoride; an alkyl sulfonic acid; an aryl sulfonic acid; trifluoromethane sulfonic acid; an alkali metal hydroxide; or an oxidant. 
     In various examples, when R may be —(CO)OR a , a suitable nitrene precursor group represented by -Het may be —N—OSO 2 —R f , wherein R f  may be a methanesulfonate, trifluoromethanesulfonate, bromophenylsulfonate, methylphenylsulfonate or nitrophenylsulfonate group. In some examples, R-Het* may be prepared as R-nitrene  501  by reacting a nitrene precursor represented by R a O(CO)—N—OSO 2 —R f  with an amine base such as triethylamine. In various examples, reaction of R-nitrene with graphene produces an N—R aziridine  502  as shown in  FIG. 5A . 
     In various examples, when R may be —(SO 2 )R a′ , a suitable nitrene precursor group represented by -Het may be —NH 2 . In some examples, R a′  may be substituted or unsubstituted alkyl, aryl, heteroaryl, aralkyl, or heteroaralkyl. In various examples, R a′  may be an alkyl, fluoroalkyl, bromophenyl, alkylphenyl or nitrophenyl group, which may be further substituted. In some examples, R-Het* may be prepared as R-nitrene  501  by reacting a nitrene precursor represented by R a —SO 2 —NH 2  with PhI(O(CO)CH 3 ) 2  in the presence of a copper, palladium, or gold catalyst. Example catalysts may include copper acetylacetonate, palladium tetrakis acetylacetonate, gold 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine triflate, or the like. The reaction may be conducted in situ with a graphene monolayer. In some examples, R a —SO 2 —NH 2  may be reacted with PhI(O(CO)CH 3 ) 2  with an alkaline metal hydroxide, e.g., KOH, in an alcohol, e.g. methanol, to form R a —SO 2 —N═IPh. The isolated R a —SO 2 —N═IPh may be then be reacted with a copper, palladium, or gold catalyst such as copper acetylacetonate to produce R-Het* as R-nitrene. In various examples, reaction of R-nitrene with graphene produces an N—R aziridine  502  as shown in  FIG. 5A . 
     In some examples, R in aziridine structure  502  may be —(CO)OR a . In various examples, groups such as —(CO)OR a  may be cleaved from the substituted aziridine represented by structure  502  by contacting each substituted aziridine  502  with one of: an alkali alkylthiolate; a trialkyl silyl iodide; an alkali metal hydroxide; an alkali earth metal hydroxide; potassium carbonate; HBr/acetic acid; sodium bis(2-methoxyethoxy)aluminum hydride; sodium tellurium hydride; a potassium trialkylsiloxide; an alkyl lithium; a quaternary ammonium fluoride; an acyl chloride with sodium iodide; an alkyl sulfonic acid; trifluoromethane sulfonic acid; or an aryl sulfonic acid. 
     In some examples, R in aziridine structure  502  may be —SO 2 R a . In various examples, groups such as —SO 2 R a  may be cleaved from the substituted aziridine represented by structure  502  by contacting each substituted aziridine  502  with one of: HBr and acetic acid; HBr and phenol; HF and pyridine; sodium bis(2-methoxyethoxy)aluminum hydride; an alkali metal arylide salt; an alkali metal in ammonia or iso-propylamine; sodium-potassium alloy adsorbed on silica gel; samarium iodide; perchloric acid in acetic acid; photolysis in the presence of ether; photolysis in the presence of sodium borohydride and dimethoxybenzene; photolysis in the presence of hydrazine; photolysis in the presence of borane:ammonia; photolysis in the presence of sodium borohydride and beta-naphthoxide; or sodium amalgam in the presence of sodium monohydrogen phosphate. 
     In some examples, R in aziridine structure  502  may be —R a . In various examples, groups such as —R a  may be cleaved from the substituted aziridine represented by structure  502  by contacting each substituted aziridine  502  with one of: hydrogen in the presence of catalytic palladium; borane in the presence of catalytic palladium; borane in the presence of catalytic Raney nickel; or hydrogen peroxide followed by tetrasodium 5,10,15,20-tetra(4-sulfophenyl) porphyrinatoiron(II). 
       FIG. 5B  depicts an example reaction scheme corresponding to a portion of the general scheme shown in  FIG. 3A  and  FIG. 3B  which may be employed for forming pores containing single carbon vacancy defects. In various examples, N—H aziridine moieties represented by structural formula  504  may be heated. In some examples, N—H aziridine moieties represented by structural formula  504  may be heated in the presence of hydrogen gas. Suitable temperatures range from between about 700° C. to about 900° C., in various examples between about 750° C. to about 850° C., or in some examples about 800° C. Suitable reaction times range from about 1 minute to about 12 hours, in various examples from about 10 minutes to about 4 hours, in some examples from about 15 minutes to about 2 hours, or in other examples, about 30 minutes. In various examples, suitable hydrogen gas conditions range from a pressure of hydrogen from about 1 Torr to about 7600 Torr; in some examples from about 1 Torr to about 760 Torr; or in other examples, from about 10 Torr to about 100 Torr, for example, 50 Torr. Other suitable hydrogen gas conditions may include a flow of hydrogen gas from about 1 sccm to about 25 sccm, in various examples from about 1 sccm to about 5 sccm, or in some examples about 3 sccm. The N—H group and one Cg may be thermolytically cleaved from the surface of structure  504 . Passivation with hydrogen may provide structure  506 , a graphene monolayer with a pore defined by the removal of a single graphene carbon Cg. Perforated graphene structure  506  corresponds to the single-carbon vacancy defect of discrete pore  108 , for example as depicted in perforated graphene monolayer  106  in  FIG. 1C . 
       FIG. 5C  depicts an example reaction scheme corresponding to a portion of the general scheme shown in  FIG. 3A  and  FIG. 3B  which may be employed for forming pores containing double carbon vacancy defects. In various examples, the N—H aziridine moieties represented by structure  504  may be hydrolyzed to produce beta-amino alcohol moieties each represented by structural formula  508 . The hydrolysis reaction may be conducted by contacting structure  504  with a basic aqueous solution of an alkali metal hydroxide or an alkaline earth metal oxide or hydroxide. The hydrolysis reaction may employ the basic aqueous solution in a concentration range from about 0.1 molar to about 10 molar, for example, about 1 molar. In various examples, the hydrolysis reaction may be conducted at a temperature between: about 0° C. and about 100° C.; about 10° C. and about 90° C.; about 20° C. and about 80° C.; or about 25° C. and about 75° C.; The hydrolysis reaction may be followed by rinsing with water and/or an aqueous buffer solution, for example, a pH 7 buffer solution. 
     Following the hydrolysis reaction, the plurality of N—H aziridine moieties represented by structural formula  508  may be heated under hydrogen to a temperature between about 750° C. and about 900° C. to produce the plurality of pores in the graphene monolayer as a plurality of double-carbon vacancy defects each represented by structural formula  510 . The Cg-NH 2  and Cg-OH groups may be may be thermolytically cleaved from the surface of beta-amino alcohol structure  508 . Thermolytic cleavage may evolve one or more gases, for example, hydrogen cyanide, hydrogen, carbon monoxide, ammonia, water, or the like. Passivation with hydrogen may be employed to provide structure  510 , a graphene monolayer with a pore defined by the removal of two graphene carbons Cg. Perforated graphene structure  510  corresponds to the double-carbon vacancy defect of discrete pore  122 , for example as depicted in perforated graphene monolayer  120  in  FIG. 1E . 
       FIG. 5D  depicts an example reaction scheme corresponding to a portion of the general scheme shown in  FIG. 3A  and  FIG. 3B , which employs a 1,2 diether to form a 1,2 diol intermediate compound represented by structure  514 . Graphene monolayer  500  may be contacted with an activated oxy reagent represented by R-Het*, wherein R may be —R a . The activated oxy reagent represented by R-Het* may be prepared by combining a suitable precursor of an activated oxy reagent represented by R-Het with an activating reagent, such as a trivalent iodosoaryl reagent. Suitable iodosoaryl reagents may include, for example, iodosobenzene tetrafluoroborate, iodosobenzene hexafluoroantimonate, iodosobenzene hexafluorophosphate, or the like. 
     Trivalent iodosoaryl reagents may be prepared by combining a chloroform solution of (diacetoxyiodo)benzene with an aqueous solution of a suitable acid, e.g., tetrafluoroboric acid, hexafluoroantimonic acid, or hexafluorophosphoric acid. The mixture may be evaporated under vacuum at 40° C. to 50° C. The product, e.g., iodosobenzene tetrafluoroborate, iodosobenzene hexafluoroantimonate, or iodosobenzene hexafluorophosphate, may be crystallized by adding a small amount of water. 
     Suitable precursors of activated oxy reagents represented by R-Het, wherein R may be —R a  may include alcohols of formula R—OH, salts of R—O −  with alkaline metal cations, salts of R—O −  with alkaline earth metal cations, or the like. Carbon-carbon double bond C g ═C g  in graphene monolayer  500  may react in the presence of the trivalent iodosoaryl reagent and R-Het* to form a graphene monolayer functionalized with a 1,2-diether represented by structure  512 . 
     In various examples, the RO ether groups may be cleaved from structure  512  to form the 1,2 diol intermediate compound represented by structure  514 . In various examples, 1,2 diether structure  512  may be reacted with one or more of hydrobromic acid, hydroiodic acid, boron tribromide, or aluminium trichloride. 
       FIG. 5E  depicts an example reaction scheme corresponding to a portion of the general scheme shown in  FIG. 3A  and  FIG. 3B , which employs a 1,2 diester moiety to form the 1,2 diol intermediate compound represented by structure  514 . 
     Referring to  FIG. 5E , in various examples, graphene monolayer  500  may be reacted with a trivalent iodosoaryl reagent and a carboxyl precursor R-Het, wherein R may be —R a . 
     In various examples, the trivalent iodosoaryl reagent may include, for example, iodosobenzene tetrafluoroborate, iodosobenzene hexafluoroantimonate, or iodosobenzene hexafluorophosphate, prepared as described under the description for  FIG. 5D . 
     In various examples, suitable carboxyl precursors of activated oxy reagents represented by R-Het, wherein R may be —R a  may include: carboxylic acids of formula R—CO 2 H; salts of R—CO 2   −  with alkaline metal cations; salts of R—CO 2  with alkaline earth metal cations; or the like. Carbon-carbon double bond C g ═C g  in graphene monolayer  500  may react with the trivalent iodosoaryl reagent and the carboxyl precursor represented by R-Het to form a graphene monolayer functionalized with a 11,2-diester moiety represented by structure  518 . 
     Referring to  FIG. 5E , in various examples, the iodosylaryl reagent and the carboxyl precursor R-Het may together form a complex corresponding to R-Het*. For example, R-Het* may represent (bis(R—CO 2 )iodo(III))benzene, which may be formed by reacting benzene, potassium peroxodisulfate, elemental iodine, and R-Het ═R—CO 2 H in the presence of concentrated sulfuric acid. In various examples, graphene monolayer  500  may be reacted with bis(R—CO 2 )iodo(III))benzene and a copper(I) or copper(II) salt of: trifluoromethanesulfonate; perchlorate; methanesulfonate; sulfonate; methylphenylsulfonate; bromophenylsulfonate; nitrophenylsulfonate; or the like. Carbon-carbon double bond C g ═C g  in graphene monolayer  500  may react with the bis(R—CO 2 )iodo(III))benzene to form a graphene monolayer functionalized with a 1,2-diester moiety represented by structure  518 . 
     Referring to  FIG. 5E , in various examples, the RCO 2 -Cg carboxyl groups in 1,2-diester moiety  518  may be hydrolyzed to form the 1,2 diol compound represented by structure  514 . In various examples, suitable conditions may include contacting 1,2-diester moiety  518  with an acid or base under conditions suitable for hydrolyzing the 1,2-diester moiety  518  to form the 1,2 diol compound represented by structure  514 . In various examples, suitable acids may include HF, HCl, HBr, HI, H 2 SO 4 , phosphoric acid, methanesulfonic acid, trifluoromethanesulfonic acid, methylphenylsulfonic acid; bromophenylsulfonic acid; nitrophenylsulfonic acid, or the like. In various examples, suitable conditions may include contacting 1,2-diester moiety  518  with a base, for example, an alkaline metal hydroxide, an alkaline earth metal hydroxide, an alkaline earth metal oxide, or the like. In some other examples, a suitable base may include a quaternary ammonium hydroxide, for example, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, or the like. In various examples, a quaternary ammonium salt may be added, for example, tetrabutylammonium sulfate, tetraethylammonium bromide, or the like. In various examples, suitable conditions may include providing a source of water. In various examples, suitable conditions may include a biphasic system including an aqueous phase and an organic phase, where the organic phase may include tetrahydrofuran, dioxane, diethyl ether, or the like. In various examples, suitable conditions may include heating between about 20° C. and about 100° C. In various examples, wherein a biphasic system may be employed, suitable conditions may include heating between about 20° C. and about the boiling temperature of the organic phase, e.g., tetrahydrofuran. 
     Referring again to  FIG. 5D  and  FIG. 5E , in various examples, the 1,2 diol intermediate compound represented by structure  514  may be thermolytically cleaved and passivated to provide structure  516 , a graphene monolayer with a pore defined by the removal of two graphene carbons Cg. The 1,2 diol intermediate compound represented by structure  514  may be heated. In some examples, 1,2 diol intermediate compound represented by structure  514  may be heated in the presence of hydrogen gas. Suitable temperatures range from between about 700° C. to about 900° C., in various examples between about 750° C. to about 850° C., or in some examples about 800° C. Suitable reaction times range from about 1 minute to about 12 hours, in various examples from about 10 minutes to about 4 hours, in some examples from about 15 minutes to about 2 hours, or in other examples, about 30 minutes. In various examples, suitable hydrogen gas conditions range from a pressure of hydrogen from about 1 Torr to about 7600 Torr; in some examples from about 1 Torr to about 760 Torr; or in other examples, from about 10 Torr to about 100 Torr, for example, 50 Torr. Other suitable hydrogen gas conditions may include a flow of hydrogen gas from about 1 sccm to about 25 sccm, in various examples from about 1 sccm to about 5 sccm, or in some examples about 3 sccm. The two Cg-OH groups may be thermolytically cleaved from the surface of structure  514 . Thermolytic cleavage may evolve one or more species, for example, hydrogen, hydroxyl, carbon monoxide, carbon dioxide, water, or the like. Passivation with hydrogen may be employed to provide structure  516 , a graphene monolayer with a pore defined by the removal of two graphene carbons Cg. Perforated graphene structure  516  corresponds to the double-carbon vacancy defect of discrete pore  122 , for example as depicted in perforated graphene monolayer  120  in  FIG. 1D . 
     Example embodiments may also include methods of making an example perforated graphene monolayer or an example membrane that may include an example perforated graphene monolayer as described herein. These methods may be implemented in any number of ways, including the structures described herein. One such way may be by machine operations, of devices of the type described in the present disclosure. Another optional way may be for one or more of the individual operations of the methods to be performed in conjunction with one or more human operators performing some of the operations while other operations may be performed by machines. These human operators need not be collocated with each other, but each can be only with a machine that performs a portion of the program. In some other examples, the human interaction may be automated such as by pre-selected criteria that may be machine automated. 
       FIG. 6  is a flow diagram showing operations that may be used in making an example perforated graphene monolayer, such as perforated graphene monolayers  106  or  120 , or corresponding membranes such as membrane  200  in accordance with at least some embodiments described herein. 
     A method of making an example perforated graphene monolayer such as  106  or  120  may include one or more operations, actions or functions as illustrated by one or more of blocks  622 ,  624 ,  626 ,  628 , and/or  630 . The method may begin with an operation  622 , “CONTACT R-HET* TO PLURALITY OF LOCATIONS AT GRAPHENE MONOLAYER”, such as graphene monolayer  100 . The reagent may be contacted to the graphene monolayer in any suitable form, such as a solid, a liquid, a gas, a solute in a solution, particles in a suspension, or the like. The R-Het* reagent may be contacted to the graphene monolayer by any suitable apparatus or method, such as by employing: a solution coating apparatus; a spin coating apparatus; a dip coating apparatus; selective coating apparatus, e.g., applied via a pressurized fluid applicator, e.g., an ink-jet type nozzle; sublimation or condensation using a condenser, a vacuum chamber, and/or a heater; chemical vapor deposition; or the like. Controller device  610  may operate “MIXER/REACTOR/R-HET* ADDITION/APPLICATOR” machine  792  to perform operation  622 . Machine  792  may include one or more mixing functions, such as mechanical stirring, heating, ultrasonication for dissolving and/or reacting reagents as described above. Machine  792  may also include one or more application or coating functions for contacting reagents such as R-Het* to the graphene. At operation  622 , manufacturing controller  790  may instruct machine  792  with parameters regarding, for example, the extent of mechanical stirring or reaction based on the reagents employed. Operation  622  may be continued until a desired point may be reached, e.g., the reaction has proceeded for a sufficient length of time to functionalize the surface of the graphene monolayer. 
     In some examples, the R-Het* reagent may be prepared in the presence of the graphene monolayer by activating a R-Het* precursor to form an activated heteroatom such as R-nitrene, [RO] or [RCO 2 ], as discussed above under  FIGS. 5A ,  5 B,  5 C,  5 D, and  5 E. In various examples, suitable reagent activator apparatus may include one or more of: a resistive heating element; an infrared laser; an ultraviolet light source; and/or one or more reagent reservoirs, e.g., a reaction chamber configured to contact a precursor compound R-Het and a trivalent iodosoaryl compound; or the like. 
     Referring again to  FIG. 6 , the method may include an operation  624 , “PROVIDE SEPARATION DISTANCE BETWEEN LOCATIONS”, such as separation distances  104  or  118 . In various examples, the separation distance may be provided by selecting an R group with the desired amount of steric bulk, where the separation distance may be at least about twice the minimum steric radius r R  of group R. In some examples, the separation distance may be increased, for example, by running the reaction at a low concentration of R-Het* such that the surface of the graphene monolayer may be sparsely reacted. In some examples, the separation distance may be modulated indirectly by contacting graphene monolayer with R-Het* at selected locations via patterned application of R-Het* using a pressurized fluid applicator, or the like. 
     The method may include an operation  626 , “REACT EACH R-HET* WITH GRAPHENE CARBON AT EACH LOCATION”. In some examples, the reaction may occur upon contact of R-Het* with the graphene monolayer. In other examples, a R-Het may be activated at selected sites at the graphene monolayer. For example, when R-Het may be R-azide, an ultraviolet light source such as an ultraviolet lamp, an ultraviolet light emitting diode, or a collimated light source such as an ultraviolet laser may be used to photolytically generate R-Het* as R-nitrene. In some examples, a collimated light source such as an ultraviolet laser may be used to photolytically generate R-Het* as R-nitrene at specific sites on the graphene monolayer. Controller device  610  may operate “HEATER/PHOTOLYZER” machine  794 , optionally in conjunction with machine  792  to perform operations  624  and  626 . Controller device  610  may provide machine  792  and/or machine  794  with parameters regarding, for example, the location and patterning of applying the R-Het* reagent, the location and patterning of activating the R-Het* reagent from a R-Het precursor, e.g. by photolytic activation, heating, or the like. Operation  624  may be continued until a desired point may be reached, e.g., the graphene monolayer has had sufficient time to react to the desired level of functionalization. 
     The method may include an operation  628 , “FORM PORES BY CREATING CARBON VACANCY DEFECTS UNDER PASSIVATION CONDITIONS”, such as pores  108  and  122 . In some examples, pores such as  108  and  122  may be formed by heating a precursor such as aziridine  504 , beta amino alcohol  508 , 1,2 diol  514 , or the like. Suitable apparatus components for forming pores  108  and  122  may include a heater, such as a resistive heating element or an infrared laser. Suitable apparatus components for forming pores  108  and  122  may also include a hydrogen source, e.g., a reaction chamber configured to apply a partial pressure of hydrogen or a flow of hydrogen while heating may be conducted. Controller device  610  may also operate “HEATER/PHOTOLYZER” machine  794 , optionally in conjunction with “HYDROGEN PASSIVATION SOURCE”  796  to perform operation  628 . Operation  628  may be continued until a desired point may be reached, e.g., the functionalized graphene monolayer has had sufficient time to react to form and passivate the discrete pores, such as pores  108  or  122 . 
     The method may include an operation  630 , “CONTACT GRAPHENE WITH PORES TO PERMEABLE SUPPORT SUBSTRATE”. Operation  630  may include preparing a perforated graphene monolayer as described herein from a graphene monolayer produced on copper foil, e.g., 25 micrometer thick copper foil. Operation  630  may also include one or more actions such as: depositing and curing a layer of a suitable transfer polymer on the perforated graphene monolayer; etching to remove the copper foil; washing the resulting perforated graphene monolayer/cured polymer; contacting the perforated graphene monolayer surface to a suitable permeable substrate; redepositing and curing a second layer of polymer; washing the combined polymer layers away with a solvent such as acetone; and the like. Suitable polymers for operation  630  may include, for example, polymethyl methacrylates. Suitable apparatus for operation  630  may include apparatus for coating the polymethyl methacrylate, e.g., solution coaters, spin coaters, dip coaters, and the like. Suitable apparatus for operation  630  may also include a curing oven or ultraviolet light source for curing the polymethyl methacrylate. Additional suitable apparatus for operation  630  may include etching and washing chambers. Further suitable apparatus for operation  630  may include apparatus for contacting the perforated graphene monolayer surface to a suitable permeable substrate, such as a contact press. At operation  630 , the processor (e.g., processor  610 ) may control applicator, mixer, and reactor functions of machine  792  to transfer the perforated graphene monolayer to a permeable substrate such as  302 , to form a membrane such as  300 . Operation  630  may include one or more functions such as: melt processing; solvent evaporation; reduced pressure solvent evaporation; spin coating; dip coating; spray coating; solvent casting; doctor blading; removal of solvent under supercritical conditions; polymerization in situ from precursors of the polymer; curing or crosslinking the polymer in situ; contact printing; metal etching; polymer etching/dissolution; or the like. 
     In various examples, operations described herein may include contacting reagents to the graphene monolayer or perforated graphene monolayer. For example, operation  622  may include contacting a reagent R-Het* to a graphene monolayer; operation  630  may include contacting and curing a polymer to the perforated graphene monolayer; and the like. Such methods may include one or more techniques such as: melt processing; solvent evaporation; reduced pressure solvent evaporation; spin coating; dip coating; spray coating; ink-jet style printing; solvent casting; doctor blading; removal of solvent under supercritical conditions; polymerization in situ from precursors of the polymer; curing or crosslinking the polymer in situ, or the like. Specific details of suitable polymer processing conditions may be selected based on the particular R-Het* or polymer. For example, typical solution casting methods employ high boiling solvents of the polymer in question. 
     The operations included in the process of  FIG. 6  described above are for illustration purposes. A process of making an example perforated graphene monolayer or membrane as described herein may be implemented by similar processes with fewer or additional operations. In some examples, the operations may be performed in a different order. In some other examples, various operations may be eliminated. In still other examples, various operations may be divided into additional operations, or combined together into fewer operations. Although illustrated as sequentially ordered operations, in some implementations the various operations may be performed in a different order, or in some cases various operations may be performed at substantially the same time. 
       FIG. 7  is a block diagram of an automated machine  700  that may be used for making an example perforated graphene monolayer, in accordance with at least some embodiments described herein. As illustrated in  FIG. 7 , “MANUFACTURING CONTROLLER”  790  may be coupled to machines that may be used to carry out the operations described herein, for example, “MIXER/REACTOR/R-HET* ADDITION/APPLICATOR”  792 , “HEATER/PHOTOLYZER”  794 , “HYDROGEN PASSIVATION SOURCE”  796 , and/or “SUPPORT SUBSTRATE APPLICATOR”  798 . 
     Manufacturing controller  790  may be operated by human control, or may be directed by a remote controller  770  via network  710 . Data associated with controlling the different processes of making the perforated graphene monolayers and membranes thereof may be stored at and/or received from data stores  780 . 
       FIG. 8  illustrates a general purpose computing device that may be used to control the automated machine  700  of  FIG. 7  or similar manufacturing equipment in making an example perforated graphene monolayer or membrane thereof, in accordance with at least some embodiments described herein. In a basic configuration  802 , computing device  800  typically may include one or more processors  804  and a system memory  806 . A memory bus  808  may be used for communicating between processor  804  and system memory  806 . 
     Depending on the desired configuration, processor  804  may be of any type including but not limited to a microprocessor (μP), a microcontroller (μC), a digital signal processor (DSP), or any combination thereof. Processor  804  may include one more levels of caching, such as a level cache memory  812 , a processor core  814 , and registers  816 . Example processor core  814  may include an arithmetic logic unit (ALU), a floating point unit (FPU), a digital signal processing core (DSP Core), or any combination thereof. An example memory controller  818  may also be used with processor  804 , or in some implementations memory controller  815  may be an internal part of processor  804 . 
     Depending on the desired configuration, system memory  806  may be of any type including but not limited to volatile memory (such as RAM), non-volatile memory (such as ROM, flash memory, etc.) or any combination thereof. System memory  806  may include an operating system  820 , one or more manufacturing control applications  822 , and program data  824 . Manufacturing control application  822  may include a control module  826  that may be arranged to control automated machine  700  of  FIG. 7  and any other processes, methods and functions as discussed above. Program data  824  may include, among other data, material data  828  for controlling various aspects of the automated machine  700 . This described basic configuration  802  is illustrated in  FIG. 8  by those components within the inner dashed line. 
     Computing device  800  may have additional features or functionality, and additional interfaces to facilitate communications between basic configuration  802  and any required devices and interfaces. For example, a bus/interface controller  830  may be used to facilitate communications between basic configuration  802  and one or more data storage devices  832  via a storage interface bus  834 . Data storage devices  832  may be removable storage devices  836 , non-removable storage devices  838 , or a combination thereof. Examples of removable storage and non-removable storage devices include magnetic disk devices such as flexible disk drives and hard-disk drives (HDD), optical disk drives such as compact disk (CD) drives or digital versatile disk (DVD) drives, solid state drives (SSD), and tape drives to name a few. Example computer storage media may include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. 
     System memory  806 , removable storage devices  836  and non-removable storage devices  838  may be examples of computer storage media. Computer storage media may include, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which may be used to store the desired information and which may be accessed by computing device  800 . Any such computer storage media may be part of computing device  800 . 
     Computing device  800  may also include an interface bus  840  for facilitating communication from various interface devices (e.g., output devices  842 , peripheral interfaces  844 , and communication devices  866  to basic configuration  802  via bus/interface controller  830 . Example output devices  842  may include a graphics processing unit  848  and an audio processing unit  850 , which may be configured to communicate to various external devices such as a display or speakers via one or more NV ports  852 . Example peripheral interfaces  544  may include a serial interface controller  854  or a parallel interface controller  856 , which may be configured to communicate with external devices such as input devices (e.g., keyboard, mouse, pen, voice input device, touch input device, etc.) or other peripheral devices (e.g., printer, scanner, etc.) via one or more I/O ports  858 . An example communication device  866  may include a network controller  860 , which may be arranged to facilitate communications with one or more other computing devices  862  over a network communication link via one or more communication ports  864 . 
     The network communication link may be one example of a communication media. Communication media may typically be embodied by computer readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and may include any information delivery media. A “modulated data signal” may be a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media may include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, radio frequency (RF), microwave, infrared (IR) and other wireless media. The term computer readable media as used herein may include both storage media and communication media. 
     Computing device  800  may be implemented as a portion of a physical server, virtual server, a computing cloud, or a hybrid device that may include any of the above functions. Computing device  800  may also be implemented as a personal computer including both laptop computer and non-laptop computer configurations. Moreover computing device  800  may be implemented as a networked system or as part of a general purpose or specialized server. 
     Networks for a networked system including computing device  800  may comprise any topology of servers, clients, switches, routers, modems, Internet service providers, and any appropriate communication media (e.g., wired or wireless communications). A system according to embodiments may have a static or dynamic network topology. The networks may include a secure network such as an enterprise network (e.g., a LAN, WAN, or WLAN), an unsecure network such as a wireless open network (e.g., IEEE 802.11 wireless networks), or a world-wide network such (e.g., the Internet). The networks may also comprise a plurality of distinct networks that may be adapted to operate together. Such networks may be configured to provide communication between the nodes described herein. By way of example, and not limitation, these networks may include wireless media such as acoustic, RF, infrared and other wireless media. Furthermore, the networks may be portions of the same network or separate networks. 
       FIG. 9  illustrates a block diagram of an example computer program product that may be used to control the automated machine of  FIG. 7  or similar manufacturing equipment in making an example perforated graphene monolayer or example membrane thereof, arranged in accordance with at least some embodiments described herein. In some examples, as shown in  FIG. 9 , computer program product  900  may include a signal bearing medium  902  that may also include machine readable instructions  904  that, when executed by, for example, a processor, may provide the functionality described above with respect to  FIG. 6  through  FIG. 8 . For example, referring to processor  790 , one or more of the tasks shown in  FIG. 9  may be undertaken in response to instructions  904  conveyed to the processor  790  by medium  902  to perform actions associated with making an example perforated graphene monolayer or example membrane thereof as described herein. Some of those instructions may include, for example, one or more instructions for: contacting R-Het* to a plurality of locations at a graphene monolayer; providing a separation distance between locations; reacting each R-Het* with at least one graphene carbon atom; forming a plurality of discrete pores in the graphene monolayer; and/or contacting the perforated graphene monolayer to a permeable substrate. 
     In some implementations, signal bearing medium  902  depicted in  FIG. 9  may encompass a computer-readable medium  906 , such as, but not limited to, a hard disk drive, a Compact Disc (CD), a Digital Versatile Disk (DVD), a digital tape, memory, etc. In some implementations, signal bearing medium  902  may encompass a recordable medium  908 , such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations, signal bearing medium  902  may encompass a communications medium  910 , such as, but not limited to, a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). For example, computer program product  900  may be conveyed to the processor  904  by an RF signal bearing medium  902 , where the signal bearing medium  902  may be conveyed by a wireless communications medium  910  (e.g., a wireless communications medium conforming with the IEEE 802.11 standard). While the embodiments will be described in the general context of program modules that execute in conjunction with an application program that runs on an operating system on a personal computer, those skilled in the art will recognize that aspects may also be implemented in combination with other program modules. 
     Generally, program modules may include routines, programs, components, data structures, and other types of structures that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that embodiments may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and comparable computing devices. Embodiments may also be practiced in distributed computing environments where tasks may be performed by remote processing devices that may be linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     Embodiments may be implemented as a computer-implemented process (method), a computing system, or as an article of manufacture, such as a computer program product or computer readable media. The computer program product may be a computer storage medium readable by a computer system and encoding a computer program that comprises instructions for causing a computer or computing system to perform example process(es). The computer-readable storage medium can for example be implemented via one or more of a volatile computer memory, a non-volatile memory, a hard drive, a flash drive, a floppy disk, or a compact disk, and comparable media. 
     Throughout this specification, the term “platform” may be a combination of software and hardware components for providing a configuration environment, which may facilitate configuration of software/hardware products and services for a variety of purposes. Examples of platforms may include, but are not limited to, a hosted service executed over a plurality of servers, an application executed on a single computing device, and comparable systems. The term “server” generally refers to a computing device executing one or more software programs typically in a networked environment. However, a server may also be implemented as a virtual server (software programs) executed on one or more computing devices viewed as a server on the network. More detail on these technologies and example operations is provided below. 
     An example membrane may include a graphene monolayer with a plurality of discrete pores that are chemically perforated therein. Each of the plurality of discrete pores may have a substantially uniform pore size characterized by one or more carbon vacancy defects in the graphene monolayer such that the graphene monolayer may have substantially uniform pore sizes throughout. 
     In various examples, each of the plurality of discrete pores may be characterized by at least about two carbon vacancy defects in the graphene monolayer. In further examples, the graphene monolayer may be characterized by a separation selectivity of: H 2  to CH 4  of at least 200:1. In various examples, the plurality of discrete pores may be characterized by a minimum separation of at least about 4 angstroms. 
     In some examples, the membrane may further include a permeable substrate that contacts the graphene monolayer, wherein the permeable substrate may include one or more of polyethylene, polypropylene, polyester, polyurethane, polystyrene, polyolefin, aramide, aromatic polyester, carbon fiber, polysulfone, polyethersulfone, a metal mesh, and/or porous ceramic. 
     An example method may include contacting a compound represented by R-Het* to a plurality of locations at the graphene monolayer. Het* may be nitrene or activated oxy. R may be one of —R a , —SO2R a , —(CO)OR a , or —SiR a R b R c . R a , R b , and R c  may be independently aryl or heteroaryl. Some example methods may also include providing a separation distance of at least r R  between adjacent locations in the plurality of locations, wherein r R  may be a minimum steric radius of R. Various example methods may also include reacting the compound represented by R-Het* with at least one graphene carbon atom C g  at each of the plurality of locations to form a plurality p of heteroatom-carbon moieties at the graphene monolayer represented by [R-Het-C g ] p graphene. The method may also include forming a plurality of discrete pores in the graphene monolayer by removing a plurality of the heteroatom-carbon moieties represented by R-Het-C g , The plurality of discrete pores may be characterized by a plurality of carbon vacancy defects in the graphene monolayer defined by removing the graphene carbon atoms C g  from the plurality of locations. The graphene monolayer may have substantially uniform pore sizes throughout. 
     In various examples, Het* may be nitrene; and each of the plurality of heteroatom-carbon moieties at the graphene monolayer may be a substituted aziridine represented by structural formula  502 : 
     
       
         
         
             
             
         
       
     
     In some examples, the method may further include preparing R-Het* by reacting an azide precursor represented by R—N 3  under thermolytic or photolytic conditions suitable for converting azide to nitrene, wherein Het* may be nitrene. 
     In further examples, the method may also include preparing R-Het* by reacting an azide precursor represented by R—N—OSO 2 —R f  with a base, wherein R f  may be a mesylate, triflate, brosylate, tosylate or nosylate group, wherein Het* may be nitrene and R may be —(CO)OR a . 
     In various examples, the method may further include cleaving a plurality of the R groups to produce a plurality of N—H aziridine moieties at the graphene monolayer that may each be represented by structural formula  504 : 
     
       
         
         
             
             
         
       
     
     In some examples of the method, wherein R may be —SiR a R b R c  and the plurality of R groups may be cleaved by contacting each substituted aziridine represented by structural formula I with one of: a quaternary ammonium fluoride; an alkyl sulfonic acid; an aryl sulfonic acid; trifluoromethane sulfonic acid; an alkali metal hydroxide; or an oxidant. 
     In further examples of the method, wherein R may be —(CO)OR a  and the plurality of R groups may be cleaved by contacting each substituted aziridine represented by structural formula I with one of: an alkali alkylthiolate; a trialkyl silyl iodide; an alkali metal hydroxide; an alkali earth metal hydroxide; potassium carbonate; HBr/acetic acid; sodium bis(2-methoxyethoxy)aluminum hydride; sodium tellurium hydride; a potassium trialkylsiloxide; an alkyl lithium; a quaternary ammonium fluoride; an acyl chloride with sodium iodide; an alkyl sulfonic acid; trifluoromethane sulfonic acid; or an aryl sulfonic acid. 
     In various examples of the method, wherein R may be —SO 2 R a  and the plurality of R groups may be cleaved by contacting each substituted aziridine represented by structural formula I with one of: HBr and acetic acid; HBr and phenol; HF and pyridine; sodium bis(2-methoxyethoxy)aluminum hydride; an alkali metal arylide salt; an alkali metal in ammonia or iso-propylamine; sodium-potassium alloy adsorbed on silica gel; samarium iodide; perchloric acid in acetic acid; photolysis in the presence of ether; photolysis in the presence of sodium borohydride and dimethoxybenzene; photolysis in the presence of hydrazine; photolysis in the presence of borane:ammonia; photolysis in the presence of sodium borohydride and beta-naphthoxide; or sodium amalgam in the presence of sodium monohydrogen phosphate. 
     In some examples, wherein R may be —R a , the plurality of R groups may be cleaved by contacting each substituted aziridine represented by structural formula I with one of: hydrogen in the presence of catalytic palladium; borane in the presence of catalytic palladium; borane in the presence of catalytic Raney nickel; or hydrogen peroxide followed by tetrasodium 5,10,15,20-tetra(4-sulfophenyl) porphyrinatoiron(II). 
     In further examples, the method may also include heating the plurality of N—H aziridine moieties represented by structural formula  504  in the presence of hydrogen gas to a temperature between about 750° C. and about 900° C. to produce the plurality of pores in the graphene monolayer as a plurality of single-carbon vacancy defects, that may each be represented by structural formula  506 : 
     
       
         
         
             
             
         
       
     
     In various examples, the method may further include: hydrolyzing the plurality of N—H aziridine moieties represented by structural formula  504  to produce a plurality of beta-amino alcohol moieties at the graphene monolayer that may each be represented by structural formula  508 ; and heating the plurality of N—H aziridine moieties represented by structural formula  508  under hydrogen to a temperature between about 750° C. and about 900° C. to produce the plurality of pores in the graphene monolayer as a plurality of double-carbon vacancy defects that may each be represented by structural formula  510 : 
     
       
         
         
             
             
         
       
     
     In some examples of the method, wherein: R may be —R a ; Het* may be activated oxy; and each of the plurality of heteroatom-carbon moieties at the graphene monolayer may be a compound represented by structural formula  512  or a compound represented by structural formula  518 : 
     
       
         
         
             
             
         
       
     
     In further examples, the method may also include preparing R-Het* by contacting a trivalent iodosoaryl reagent with one of: R a —OH; an alkaline metal salt of R a —O − ; an alkaline earth metal salt of R a —O − ; R a —CO 2 H; an alkaline metal salt of R a —CO 2   − ; or an alkaline earth metal salt of R a —CO 2   − . In various examples, the trivalent iodosoaryl reagent may be iodosobenzene tetrafluoroborate, iodosobenzene hexafluoroantimonate, or iodosobenzene hexafluorophosphate. 
     In some examples, the method may further include: reacting the compound represented by structural formula  512  with one or more of hydrobromic acid, hydroiodic acid, boron tribromide, or aluminium trichloride; or reacting the compound represented by structural formula  518  with an acid or base, thereby forming a compound that may be represented by structural formula  514 : 
     
       
         
         
             
             
         
       
     
     In further examples, the method may also include: heating the compound represented by structural formula  514  under hydrogen to a temperature between about 750° C. and about 900° C. to produce the plurality of pores in the graphene monolayer as a plurality of double-carbon vacancy defects that may each be represented by structural formula  510 : 
     
       
         
         
             
             
         
       
     
     In various examples, the method may further include: contacting the graphene monolayer with a permeable substrate, wherein the permeable substrate includes one or more of polyethylene, polypropylene, polyester, polyurethane, polystyrene, polyolefin, aramide, aromatic polyester, carbon fiber, polysulfone, polyethersulfone, a metal mesh, and/or porous ceramic. 
     An example method of separating a compound from a fluid mixture may include providing a fluid mixture that contains a first compound and a second compound. Some example methods may also include providing a membrane that includes a graphene monolayer that may be chemically perforated by a plurality of discrete pores. Each of the plurality of discrete pores may be characterized by one or more carbon vacancy defects such that the graphene monolayer has substantially uniform pore sizes throughout. Each of the plurality of discrete pores may be characterized by a diameter that may be selective for passage of the first compound compared to the second compound. Various example methods may also include contacting the fluid mixture to a first surface of the graphene monolayer. Example methods may further include directing the first compound through the plurality of discrete pores to separate the first compound from the second compound. 
     In various examples of the method of separating a compound from a fluid mixture, the first compound may be smaller than the second molecule. 
     In some examples, the method of separating a compound from a fluid mixture may further include directing the first compound through the plurality of discrete pores by employing a gradient across the graphene monolayer, wherein the gradient may be one or more of temperature, pressure, concentration, electric field, or electrochemical potential. 
     In further examples, the method of separating a compound from a fluid mixture may also include separating the first compound from the second compound at a separation selectivity of between about 200:1 and about 10^23:1. 
     In various examples of the method of separating a compound from a fluid mixture, wherein the first compound may be one of helium, neon, argon, xenon, krypton, radon, hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, sulfur dioxide, hydrogen sulfide, a nitrogen oxide, a C1-C4 alkane, a silane, water, an organic solvent, or a haloacid. 
     The present disclosure also generally describes an example membrane. An example membrane may be prepared by a process that includes contacting a compound represented by R-Het* to a plurality of locations at a graphene monolayer. Het* may be nitrene or activated oxy. R may be one of —R a , —SO2R a , —(CO)OR a , or —SiR a R b R c . R a , R b , and R c  may be independently aryl or heteroaryl. Some example membranes may be prepared by a process that also includes providing a separation distance of at least r R  between adjacent locations in the plurality of locations, wherein r R  may be a minimum steric radius of R. The example membrane may be prepared by a process that further includes reacting the compound represented by R-Her with at least one graphene carbon atom C g  at each of the plurality of locations to form a plurality p of heteroatom-carbon moieties at the graphene monolayer represented by [R-Het-C g ] p graphene. The example membrane may be prepared by a process that also includes forming a plurality of discrete pores in the graphene monolayer by removing a plurality of the heteroatom-carbon moieties represented by R-Het-C g . The plurality of discrete pores may be characterized by a plurality of carbon vacancy defects in the graphene monolayer defined by removing the graphene carbon atoms C g  from the plurality of locations. The graphene monolayer may have substantially uniform pore sizes throughout. 
     The present disclosure also generally describes system for preparing a graphene membrane with substantially uniform pores. The system may include: a reagent activator for preparing an activated reagent from a precursor reagent; a reagent applicator configured to contact the activated reagent to a plurality of locations at a graphene monolayer; a reaction chamber configured to hold the graphene monolayer; a heater configured to thermally cleave a plurality of heteroatom-carbon moieties at the graphene monolayer to form a perforated graphene monolayer; and a support substrate applicator configured to contact the perforated graphene monolayer to a support substrate. 
     In various examples of the system, the reagent activator may include one or more of: a resistive heating element; an infrared laser; an ultraviolet light source; and/or a reaction chamber configured to contact the precursor compound and a trivalent iodosoaryl compound. 
     In some examples of the system, the reagent applicator may include one or more of: a solution coater; a spin coater; a dip coater; a pressurized fluid applicator; a reagent reservoir; a vacuum chamber; a condenser; and/or a chemical vapor deposition chamber. 
     In further examples of the system, the heater may include one or more of: a hydrogen source; a resistive heating element; and/or an infrared laser. 
     In various examples of the system, the support substrate applicator may include one or more of: a solution coater, a spin coater, a dip coater, a curing oven an ultraviolet light source an etching chamber, a washing chamber, and/or a contact press. 
     The terms “a” and “an” as used herein mean “one or more” unless the singular is expressly specified. For example, reference to “a base” may include a mixture of two or more bases, as well as a single base. 
     As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which “about” is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which the term is used, “about” will mean up to, plus or minus 10% of the particular term. 
     As used herein, the terms “optional” and “optionally” mean that the subsequently described circumstance may or may not occur, so that the description may include instances where the circumstance occurs and instances where it does not. 
     As used herein, “substituted” refers to an organic group as defined below (e.g., an alkyl group) in which one or more bonds to a hydrogen atom contained therein may be replaced by a bond to non-hydrogen or non-carbon atoms. Groups not explicitly stated to be one of substituted or unsubstituted may be either substituted or unsubstituted. Substituted groups also may include groups in which one or more bonds to a carbon(s) or hydrogen(s) atom may be replaced by one or more bonds, including double or triple bonds, to a heteroatom. A substituted group may be substituted with one or more substituents, unless otherwise specified. In some embodiments, a substituted group may be substituted with 1, 2, 3, 4, 5, or 6 substituents. Examples of substituent groups may include: halogens (i.e., F, Cl, Br, and I); hydroxyls; alkoxy, alkenoxy, aryloxy, aralkyloxy, heterocyclyloxy, and heterocyclylalkoxy groups; carbonyls (oxo); carboxyls; esters; urethanes; oximes; hydroxylamines; alkoxyamines; aralkoxyamines; thiols; sulfides; sulfoxides; sulfones; sulfonyls; sulfonamides; amines; N-oxides; hydrazines; hydrazides; hydrazones; azides; amides; ureas; amidines; guanidines; enamines; imides; iso-cyanates; iso-thiocyanates; cyanates; thiocyanates; imines; nitro groups; nitriles (i.e., CN); and the like. 
     Substituted ring groups such as substituted cycloalkyl, aryl, heterocyclyl and heteroaryl groups also may include rings and ring systems in which a bond to a hydrogen atom may be replaced with a bond to a carbon atom. Substituted cycloalkyl, aryl, heterocyclyl and heteroaryl groups may also be substituted with substituted or unsubstituted alkyl, alkenyl, and alkynyl groups as defined below. 
     Alkyl groups may include straight chain and branched chain alkyl groups having from 1 to 12 carbon atoms, and typically from 1 to 10 carbons or, in some examples, from 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of straight chain alkyl groups may include groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups may include, but are not limited to, iso-propyl, iso-butyl, sec-butyl, tert-butyl, neopentyl, iso-pentyl, and 2,2-dimethylpropyl groups. Representative substituted alkyl groups may be substituted one or more times with substituents such as those listed above and may include, without limitation, haloalkyl (e.g., trifluoromethyl), hydroxyalkyl, thioalkyl, aminoalkyl, alkylaminoalkyl, dialkylaminoalkyl, alkoxyalkyl, carboxyalkyl, and the like. 
     Cycloalkyl groups may include mono-, bi- or tricyclic alkyl groups having from 3 to 12 carbon atoms in the ring(s), or, in some embodiments, 3 to 10, 3 to 8, or 3 to 4, 5, or 6 carbon atoms. Exemplary monocyclic cycloalkyl groups may include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. In some embodiments, the cycloalkyl group has 3 to 8 ring members, whereas in other embodiments, the number of ring carbon atoms ranges from 3 to 5, 3 to 6, or 3 to 7. Bi- and tricyclic ring systems may include both bridged cycloalkyl groups and fused rings, such as, but not limited to, bicyclo[2.1.1]hexane, adamantyl, decalinyl, and the like. Substituted cycloalkyl groups may be substituted one or more times with non-hydrogen and non-carbon groups as defined above. However, substituted cycloalkyl groups also may include rings that may be substituted with straight or branched chain alkyl groups as defined above. Representative substituted cycloalkyl groups may be mono-substituted or substituted more than once, such as, but not limited to, 2,2-, 2,3-, 2,4-, 2,5- or 2,6-disubstituted cyclohexyl groups, which may be substituted with substituents such as those listed above. 
     Aryl groups may be cyclic aromatic hydrocarbons that do not contain heteroatoms. Aryl groups herein may include monocyclic, bicyclic and tricyclic ring systems. Aryl groups may include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, fluorenyl, phenanthrenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodiments, aryl groups contain 6-14 carbons, and in others from 6 to 12 or even 6-10 carbon atoms in the ring portions of the groups. In some embodiments, the aryl groups may be phenyl or naphthyl. “Aryl groups” may include groups containing fused rings, such as fused aromatic-aliphatic ring systems (e.g., indanyl, tetrahydronaphthyl, and the like). “Aryl groups”, unless explicitly stated to be one of substituted or unsubstituted, may be either unsubstituted or substituted with other groups, such as alkyl or halo groups, bonded to one of the ring members. Representative substituted aryl groups may be mono-substituted or substituted more than once. For example, monosubstituted aryl groups include, but are not limited to, 2-, 3-, 4-, 5-, or 6-substituted phenyl or naphthyl groups, which may be substituted with substituents such as those listed above. 
     Aralkyl groups may be alkyl groups as defined above in which a hydrogen or carbon bond of an alkyl group may be replaced with a bond to an aryl group as defined above. In some embodiments, aralkyl groups contain 7 to 16 carbon atoms, 7 to 14 carbon atoms, or 7 to 10 carbon atoms. Substituted aralkyl groups may be substituted at the alkyl, the aryl or both the alkyl and aryl portions of the group. Representative aralkyl groups may include but are not limited to benzyl and phenethyl groups and fused (cycloalkylaryl)alkyl groups such as 4-indanylethyl. Representative substituted aralkyl groups may be substituted one or more times with substituents such as those listed above. 
     Heterocyclyl groups may include aromatic (also referred to as heteroaryl) and non-aromatic ring compounds containing 3 or more ring members of which one or more may be a heteroatom such as, but not limited to, N, O, and S. In some embodiments, the heterocyclyl group contains 1, 2, 3 or 4 heteroatoms. In some embodiments, heterocyclyl groups may include mono-, bi- and tricyclic rings having 3 to 16 ring members, whereas other such groups have 3 to 6, 3 to 10, 3 to 12, or 3 to 14 ring members. Heterocyclyl groups encompass aromatic, partially unsaturated and saturated ring systems, such as, for example, imidazolyl, imidazolinyl and imidazolidinyl groups. The phrase “heterocyclyl group” may include fused ring species including those comprising fused aromatic and non-aromatic groups, such as, for example, benzotriazolyl, 2,3-dihydrobenzo[1,4]dioxinyl, and benzo[1,3]dioxolyl. “Heterocyclyl group” also may include bridged polycyclic ring systems containing a heteroatom such as, but not limited to, quinuclidyl. A “Heterocyclyl group”, unless explicitly stated to be one of substituted or unsubstituted, may be either unsubstituted or substituted with other groups, such as alkyl, oxo or halo groups, bonded to one of the ring members. Heterocyclyl groups may include, but are not limited to, aziridinyl, azetidinyl, pyrrolidinyl, imidazolidinyl, pyrazolidinyl, thiazolidinyl, tetrahydrothiophenyl, tetrahydrofuranyl, dioxolyl, furanyl, thiophenyl, pyrrolyl, pyrrolinyl, imidazolyl, imidazolinyl, pyrazolyl, pyrazolinyl, triazolyl, tetrazolyl, oxazolyl, iso-xazolyl, thiazolyl, thiazolinyl, iso-thiazolyl, thiadiazolyl, oxadiazolyl, piperidyl, piperazinyl, morpholinyl, thiomorpholinyl, tetrahydropyranyl, tetrahydrothiopyranyl, oxathiane, dioxyl, dithianyl, pyranyl, pyridyl, pyrimidinyl, pyridazinyl, pyrazinyl, triazinyl, dihydropyridyl, dihydrodithiinyl, dihydrodithionyl, homopiperazinyl, quinuclidyl, indolyl, indolinyl, iso-indolyl, azaindolyl (pyrrolopyridyl), indazolyl, indolizinyl, benzotriazolyl, benzimidazolyl, benzofuranyl, benzothiophenyl, benzthiazolyl, benzoxadiazolyl, benzoxazinyl, benzodithiinyl, benzoxathiinyl, benzothiazinyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl, benzo[1,3]dioxolyl, pyrazolopyridyl, imidazopyridyl (azabenzimidazolyl), triazolopyridyl, iso-xazolopyridyl, purinyl, xanthinyl, adeninyl, guaninyl, quinolinyl, iso-quinolinyl, quinolizinyl, quinoxalinyl, quinazolinyl, cinnolinyl, phthalazinyl, naphthyridinyl, pteridinyl, thianaphthyl, dihydrobenzothiazinyl, dihydrobenzofuranyl, dihydroindolyl, dihydrobenzodioxinyl, tetrahydroindolyl, tetrahydroindazolyl, tetrahydrobenzimidazolyl, tetrahydrobenzotriazolyl, tetrahydropyrrolopyridyl, tetrahydropyrazolopyridyl, tetrahydroimidazopyridyl, tetrahydrotriazolopyridyl, and tetrahydroquinolinyl groups. Representative substituted heterocyclyl groups may be mono-substituted or substituted more than once, such as, but not limited to, pyridyl or morpholinyl groups, which may be 2-, 3-, 4-, 5-, or 6-substituted, or disubstituted with various substituents such as those listed above. 
     Heteroaryl groups may be aromatic ring compounds containing 5 or more ring members, of which one or more may be a heteroatom such as, but not limited to, N, O, and S. Heteroaryl groups include, but are not limited to, groups such as pyrrolyl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, iso-xazolyl, thiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, thiophenyl, benzothiophenyl, furanyl, benzofuranyl, indolyl, azaindolyl (pyrrolopyridinyl), indazolyl, benzimidazolyl, imidazopyridinyl (azabenzimidazolyl), pyrazolopyridinyl, triazolopyridinyl, benzotriazolyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl, imidazopyridinyl, iso-xazolopyridinyl, thianaphthyl, purinyl, xanthinyl, adeninyl, guaninyl, quinolinyl, iso-quinolinyl, tetrahydroquinolinyl, quinoxalinyl, and quinazolinyl groups. Heteroaryl groups include fused ring compounds in which rings may be aromatic such as indolyl groups and include fused ring compounds in which only one of the rings may be aromatic, such as 2,3-dihydro indolyl groups. “Heteroaryl groups” may include fused ring compounds. “Heteroaryl groups” unless explicitly stated to be substituted or to be unsubstituted, may be either unsubstituted or substituted with other groups bonded to one of the ring members, such as alkyl groups. Representative substituted heteroaryl groups may be substituted one or more times with various substituents such as those listed above. 
     Heteroaralkyl groups may be alkyl groups as defined above in which a hydrogen or carbon bond of an alkyl group may be replaced with a bond to a heteroaryl group as defined above. Substituted heteroaralkyl groups may be substituted at the alkyl, the heteroaryl or both the alkyl and heteroaryl portions of the group. Representative substituted heteroaralkyl groups may be substituted one or more times with substituents such as those listed above. 
     Groups described herein having two or more points of attachment (i.e., divalent, trivalent, or polyvalent) within the compound of the technology may be designated by use of the suffix, “ene.” For example, divalent alkyl groups may be alkylene groups, divalent aryl groups may be arylene groups, divalent heteroaryl groups may be heteroarylene groups, and so forth. 
     Alkoxy groups may be hydroxyl groups (—OH) in which the bond to the hydrogen atom may be replaced by a bond to a carbon atom of a substituted or unsubstituted alkyl group as defined above. Examples of linear alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, and the like. Examples of branched alkoxy groups include, but are not limited to, iso-propoxy, sec-butoxy, tert-butoxy, iso-pentoxy, iso-hexoxy, and the like. Examples of cycloalkoxy groups include, but are not limited to, cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, cyclohexyloxy, and the like. Representative substituted alkoxy groups may be substituted one or more times with substituents such as those listed above. 
     The term “amine” (or “amino”), as used herein, refers to NR 5 R 6  groups, wherein R 5  and R 6  may be independently hydrogen, or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, heterocyclylalkyl or heterocyclyl group as defined herein. In some embodiments, the amine may be alkylamino, dialkylamino, arylamino, or alkylarylamino. In other embodiments, the amine may be NH 2 , methylamino, dimethylamino, ethylamino, diethylamino, propylamino, iso-propylamino, phenylamino, or benzylamino. The term “alkylamino” may be defined as NR 7 R 8 , wherein at least one of R 7  and R 8  may be alkyl and the other may be alkyl or hydrogen. The term “arylamino” may be defined as NR 9 R 10 , wherein at least one of R 9  and R 10  may be aryl and the other may be aryl or hydrogen. 
     The term “halogen” or “halo,” as used herein, refers to bromine, chlorine, fluorine, or iodine. In some embodiments, the halogen may be fluorine. In other embodiments, the halogen may be chlorine or bromine. 
     There is little distinction left between hardware and software implementations of aspects of systems; the use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software may become significant) a design choice representing cost vs. efficiency tradeoffs. There are various vehicles by which processes and/or systems and/or other technologies described herein may be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle; if flexibility is paramount, the implementer may opt for a mainly software implementation; or, yet again alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. 
     The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples may be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g. as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. 
     The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, systems, or components, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. 
     In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Versatile Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). 
     Those skilled in the art will recognize that it is common within the art to describe devices and/or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and/or processes into data processing systems. That is, at least a portion of the devices and/or processes described herein may be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system generally includes one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops. 
     A typical manufacturing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems. The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated may also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being “operably couplable”, to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically connectable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). 
     Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into sub-ranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. For example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. 
     The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.