Patent Publication Number: US-2022212148-A1

Title: Apparatuses, methods, and systems for fabricating graphene membranes

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/860,829 filed on Jun. 13, 2019, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This document relates to graphene membranes. More specifically, this document relates to apparatuses and methods for fabricating graphene membranes. 
     BACKGROUND 
     US Patent Application Publication No. 2016/0339160 A1 (Bedworth et al.) discloses various systems and methods relating to two-dimensional materials such as graphene. A membrane includes a cross-linked graphene platelet polymer that includes a plurality of cross-linked graphene platelets. The cross-linked graphene platelets include a graphene portion and a cross-linking portion. The cross-linking portion contains a 4 to 10 atom link. The cross-linked graphene platelet polymer is produced by reaction of an epoxide functionalized graphene platelet and a (meth)acrylate or (meth)acrylamide functionalized cross-linker. 
     SUMMARY 
     The following summary is intended to introduce the reader to various aspects of the detailed description, but not to define or delimit any invention. 
     Apparatuses for fabricating graphene membranes are disclosed. According to some aspects, an apparatus for fabricating a graphene membrane includes a first section having a first fluid chamber for housing a suspension of graphene platelets in a fluid. A second section is positionable adjacent the first section. The second section includes a second fluid chamber, and a porous support housed in the second fluid chamber for supporting a porous substrate. When the first section is positioned adjacent the second section and the porous substrate is supported by the porous support, the first fluid chamber and the second fluid chamber are in fluid communication via the porous substrate. The apparatus further includes a pressurizer for creating a pressure differential between the first fluid chamber and the second fluid chamber and thereby forcing the fluid through the porous substrate and into the second fluid chamber and lodging the graphene platelets in the pores of the porous substrate. 
     In some examples, the porous support includes a first layer having pores of a first size, a second layer having pores of a second size larger than the first size, and a third layer having pores of a third size larger than the second size. The first layer can include a sheet of at least one of cellulose, a fabric, and a polymer. The second layer can include a first sub-layer of a sintered polymer or a porous metal, and a second sub-layer of a sintered polymer or a porous metal. 
     In some examples, the pressurizer is configured to pressurize the first fluid chamber. The pressurizer can include a hydraulic cylinder, a compressed air cylinder, or a high-pressure water pump. 
     In some examples, the pressurizer includes a vacuum apparatus for creating a vacuum in the second fluid chamber. 
     In some examples, the apparatus further includes an ultrasonic transducer in the first fluid chamber. 
     In some examples, the apparatus further includes a substrate support frame having a first piece and a second piece. The porous substrate can be securable between the first piece and the second piece. The substrate support frame can be maneuverable to position the porous substrate on the porous support. 
     In some examples, when the first section is positioned adjacent the second section and the porous substrate is supported by the porous support, the substrate support frame is outboard of the first fluid chamber and the second fluid chamber. 
     In some examples, the apparatus further includes at least one sensor for sensing a parameter of the suspension, and/or the fluid, and/or the graphene platelets. 
     Methods for fabricating graphene membranes are also disclosed. According to some aspects, a method for fabricating a graphene membrane includes a) positioning a porous substrate across a porous support. The porous substrate has a first surface and a second surface, and the porous substrate is positioned so that the first surface faces away from the porous support and the second surface faces towards the porous support. The method further includes b) applying a suspension of graphene platelets in a fluid to a first fluid chamber, to contact the first surface of the porous substrate with the suspension; and c) applying a pressure differential across the porous substrate to force the graphene platelets into the pores of the porous substrate and force the fluid through the porous substrate. 
     In some examples, step c) includes pressurizing the first fluid chamber. In some examples, step c) includes applying a vacuum to the porous support. 
     In some examples, the method includes sonicating the suspension during step b) and/or step c). 
     In some examples, the method further includes, prior to step a), mounting the porous substrate in a substrate support frame. Step a) can include maneuvering the substrate support frame to position the porous substrate across the porous support. The method can further include, after step c), removing the substrate support frame and the porous substrate from the porous support. 
     In some examples, the method further includes, during step c), sensing a parameter of the suspension and/or the fluid. 
     In some examples, step c) includes passing the fluid through a first layer, a second layer, and a third layer of the porous support. 
     Systems for fabricating graphene membranes are also disclosed. According to some aspects, a system for fabricating a graphene membrane includes an apparatus and a control sub-system. The apparatus includes a first section having a first fluid chamber for housing a suspension of graphene platelets in a fluid. The apparatus further includes a second section that is positionable adjacent the first section and having a second fluid chamber and a porous support housed in the second fluid chamber for supporting a porous substrate. When the first section is positioned adjacent the second section and the porous substrate is supported by the porous support, the first fluid chamber and the second fluid chamber are in fluid communication via the porous substrate. The apparatus further includes at least one sensor for sensing a parameter of the suspension and/or the fluid. The apparatus further includes a pressurizer for creating a pressure differential between the first fluid chamber and the second fluid chamber and thereby forcing the fluid through the porous substrate and into the second fluid chamber and lodging the graphene platelets in the pores of the porous substrate. The control sub-system can receive information from the sensor and can control the apparatus based on the received information 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings included herewith are for illustrating various examples of articles, methods, and apparatuses of the present specification and are not intended to limit the scope of what is taught in any way. In the drawings: 
         FIG. 1  is a perspective view of a system for fabricating a graphene membrane; 
         FIG. 2  is a perspective view of the substrate support frame of the system of  FIG. 1 ; 
         FIG. 3  is a cross-section taken along line  3 - 3  in  FIG. 1 ; and 
         FIG. 4  is an enlarged view of the encircled region in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Various apparatuses or processes or compositions will be described below to provide an example of an embodiment of the claimed subject matter. No embodiment described below limits any claim and any claim may cover processes or apparatuses or compositions that differ from those described below. The claims are not limited to apparatuses or processes or compositions having all of the features of any one apparatus or process or composition described below or to features common to multiple or all of the apparatuses or processes or compositions described below. It is possible that an apparatus or process or composition described below is not an embodiment of any exclusive right granted by issuance of this patent application. Any subject matter described below and for which an exclusive right is not granted by issuance of this patent application may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim or dedicate to the public any such subject matter by its disclosure in this document. 
     Generally disclosed herein are apparatuses, methods, and systems for fabricating graphene membranes. More specifically, disclosed herein apparatuses, methods, and systems for fabricating graphene membranes, where the graphene membranes include a porous substrate, and graphene platelets lodged in the pores of the porous substrate and/or deposited as a layer on the surface(s) of the porous substrate. Such graphene membranes are disclosed, for example, in international patent application (PCT) publication no. WO 2020/000086A1 (Flint et al.), U.S. patent application Ser. No. 16/542,456 (Flint et al.), and U.S. patent application Ser. No. 16/810,918 (Oguntuase), each of which is incorporated herein by reference in its entirety. Such graphene membranes may be used, for example, in water filtration and purification, or to form conductive surfaces (e.g. for use in batteries). 
     In general, the apparatuses disclosed herein can allow for a suspension of graphene platelets in a fluid to be applied to a porous substrate, and for a pressure differential to be created across the porous substrate, so that the suspension is forced into the pores of the porous substrate. The fluid can pass through the pores, while the graphene platelets are trapped in the pores, to create the membrane (i.e. where the membrane includes the porous substrate and the graphene platelets lodged in the pores of the porous substrate and/or deposited as a layer on the surface(s) of the porous substrate). 
     As used herein, the term “platelet” refers to a structure that includes one or multiple (e.g. at least two and up to nine) sheets of graphene. Preferably, platelets include two, or three sheets of graphene. A platelet can be, for example, up to 15 nanometers thick, with a diameter of up to 100 microns. As used herein, the term ‘graphene platelet’ can refer to a platelet of pure graphene (i.e. non-functionalized graphene) and/or a platelet of functionalized graphene. Functionalized graphene can include, for example, hydroxylated graphene (also referred to as graphene oxide), aminated graphene, and/or hydrogenated graphene. Functionalization of the graphene can create pores in the graphene, which can allow for flow of filtrates, and can create a desired spacing between graphene sheets. For example, in platelets of non-functionalized graphene, the interlayer spacing may be approximately 0.34 nm. In platelets of functionalized graphene, e.g. graphene that is functionalized as hydroxylated graphene (also known as graphene oxide), the interlayer spacing may be approximately 0.83 nm. 
     As used herein, the term “porous substrate” refers to a sheet-like material having pores extending therethrough, from a first surface thereof to a second surface thereof. The pores can have a diameter of, for example, less than or equal to 0.03 microns. Preferably, the pores are at most 5 times larger in diameter than the diameter of the graphene platelets. The substrate can have a thickness (i.e. between the first surface and the second surface) of, for example, less than 1 mm. In some examples the substrate is a polymer, such as but not limited to polytetrafluoroethylene (Teflon®), polysulfone (PsF) (also referred to as polyether sulfone), cellulose, and/or polyester. In some examples, the substrate is an acid-treated polymer, for example polysulfone treated with sulfuric acid. In some examples, the substrate is an acid-treated and ion-treated polymer, for example polysulfone may be treated with sulfuric acid and then with a solution of metal ions (e.g. aluminum or calcium ions). In some examples, the substrate is non-polymeric, such as a woven cotton. 
     A first example of an apparatus for fabricating a graphene membrane will now be described. Referring to  FIG. 1 , the apparatus  100  generally includes a first section  102 , a second section  104 , a pressurizer  106 , and a substrate support frame  108 . In the example shown, the first section  102  is an upper section, and the second section  104  is a lower section; however, in alternative examples, the first  102  and second  104  sections may be otherwise positioned (e.g. as a left-side section and a right-side section). 
     Referring also to  FIG. 2 , in use, a porous substrate  110  (which ultimately becomes part of the graphene membrane) is supported by the substrate support frame  108 . The substrate support frame  108  has a first piece  112  and a second piece  114 , between which the porous substrate  110  is securable (e.g. using bolts). The substrate support frame  108  can be used to ease handling of the porous substrate  110  and to prevent or minimize physical damage to the porous substrate  110 . The substrate support frame  108  generally holds the porous substrate  110  flat (i.e. it can prevent bending, folding, and/or crimping). 
     Referring back to  FIG. 1 , in use, the substrate support frame  108  can facilitate positioning of the porous substrate  110  between the first section  102  and the second section  104 , so that the porous substrate  110  is sandwiched between the first section  102  and the second section  104 , with a first surface  116  of the porous substrate  110  facing towards the first section  102  and away from the second section  104 , and a second surface  118  (shown in  FIGS. 3 and 4 ) of the porous substrate  110  facing towards the second section  104  and away from the first section  102 . 
     Referring now to  FIG. 3 , the first section  102  includes an outer wall  120  (also referred to herein as a “first outer wall”) that defines a fluid chamber  122  (also referred to herein as a “first fluid chamber”). In use, as will be described in further detail below, the fluid chamber  122  houses a suspension of graphene platelets in a fluid. 
     In the example shown, the first section  102  includes a pair of fluid inlet ports  126  and an air escape port  127 . In alternative examples, the first section  102  may include another number of fluid inlet ports, such as one fluid inlet port, and the fluid inlet ports may be in another position. The fluid inlet ports  126  may be opened and closed by a valve (not shown). Furthermore, the first section  102  may include another number of air escape ports, such as more than one air escape port, and the air escape port may be in another position. The air escape port  127  may be opened and closed by a valve (not shown). 
     The first section  102  can further include an ultrasonic transducer (not shown) for sonicating the suspension of graphene platelets, which can help to pack the graphene platelets into the pores of the porous substrate  110  (as described in further detail below). 
     Referring still to  FIG. 3 , the second section  104  includes an outer wall  128  (also referred to herein as a “second outer wall”) that defines a fluid chamber (also referred to herein as a “second fluid chamber”). The second fluid chamber is not visible in the figures, as it is filled with a porous support  136 , described below. In use, the second section  104  is positionable adjacent to the first section  102  so that the first outer wall  120  bears against the second outer wall  128 , via the porous substrate  110 . The second section  104  can further be secured to the first section  102 , for example by clamping or bolting the first outer wall  120  to the second outer wall  128 . 
     Referring still to  FIG. 3 , the second fluid chamber has a drain port  134 . In alternative examples, additional drain ports can be provided (e.g. four drain ports). 
     Referring still to  FIG. 3 , the second section  104  further includes a porous support  136 , which is housed within the second fluid chamber. In use, during fabrication of a graphene membrane, the porous support  136  supports the porous substrate  110  of the graphene membrane, so that when a pressure differential is applied across the porous substrate  110 , the porous substrate does not tear or rip or break or stretch or otherwise incur damage. Furthermore, in use, when the first section  102  is positioned adjacent the second section  104  and the porous substrate  110  is supported by the porous support  136 , the first fluid chamber  122  and the second fluid chamber are in fluid communication via the porous substrate  110 ; 
     In the example shown, the porous support  136  includes several layers, namely a first layer  138 , a second layer  140 , and a third layer  142 . Each layer is porous, with the pore sizes larger than those of the porous substrate  110 , and becoming larger going from the first layer  138  layer to the third layer  142 . For example, the first layer  138  may have pore sizes on the scale of microns, the second layer  140  may have pore sizes on the scale of millimeters, and the third layer  142  may have pore sizes on the scale of inches. 
     In some examples, the first layer  138  includes a sheet of, for example, cellulose, fabric, and/or various polymers or other materials. In some examples, the first layer  138  includes more than one sheet of material. The first layer  138  can be in contact with and physically support the porous substrate  110  during fabrication of the graphene membrane. 
     In the example shown, the second layer  140  includes two sub-layers: a first sub-layer  144  and a second sub-layer  146 . The first sub layer  144  and second sub-layer  146  can include, for example, porous materials such as sintered polymers, sintered metals, zeolites, and/or ceramics. In some particular examples, the first sub-layer  144  and second sub-layer  146  each include a plexiglass sheet with holes drilled therethrough, with the holes of the first sub-layer  144  being smaller than the holes of the second sub-layer  146 . In use, the second layer  140  can contact and physically support the first layer  138 , distribute forces caused by the pressure differential (described in more detail below), and direct fluid away from the porous substrate  110  (i.e. downwardly, in the example shown). 
     In the example shown, the third layer  142  generally serves to drain the second layer  140 , and can be made from various materials having large pores, such as drilled plexiglass. 
     Referring still to  FIG. 3 , the pressurizer  106  can be any device or apparatus or assembly that in use, can create a pressure differential between the first section  102  and the second section  104  (i.e. between the first fluid chamber  122  and the second fluid chamber, across the porous substrate  110 ), to force the fluid of the suspension through the porous substrate  110  and into second fluid chamber and lodge the graphene platelets in the pores of the porous substrate  110 . In the example shown, the pressurizer  106  is a hydraulic cylinder (shown schematically) that is connected to the first section  102 , for pressurizing the fluid chamber  122  of the first section  102 , while the second fluid chamber remains at atmospheric pressure (or below atmospheric pressure, e.g. using a vacuum apparatus). In alternative examples the pressurizer can be, for example, a compressed air cylinder, or a mechanical screw, or a high-pressure water pump, or a compressor. Alternatively, the pressurizer can be a vacuum apparatus and can create a vacuum in the second fluid chamber, while the first fluid chamber  122  remains at atmospheric pressure (or above atmospheric pressure). While in the example shown, the hydraulic cylinder moves vertically to pressurize the first fluid chamber  122 , in alternative examples, a hydraulic cylinder can move horizontally. 
     Referring back to  FIG. 1 , in the example shown, the apparatus  100  is part of a system that includes a control sub-system  148 . The control sub-system  148  can receive information from the apparatus  100  and/or can control the apparatus  100 . For example, the apparatus  100  can include various sensors, such as pressure sensors and/or pH sensors and/or conductivity sensors and/or flow sensors. The control sub-system  148  can receive information from the sensors. Such information can relate, for example, to the pressure differential across the porous substrate  110 , a concentration of ions in a suspension within the first fluid chamber  122  and/or second fluid chamber, a conductivity of the suspension within the first fluid chamber  122  and/or second fluid chamber, a flow rate across the porous substrate  110 , and/or a conductivity of the porous substrate  110 . Furthermore, the control sub-system  148  can control the apparatus  100  based on the received information. For example, the control sub-system  148  can control the pressure differential induced by the pressurizer  106 , and/or the entry of fluid into the upper fluid chamber based on the information. In the example shown, a sensor is shown schematically at  150  in  FIG. 3 . 
     A method of fabricating a graphene membrane will now be described. The method will be described with reference to the apparatus  100 ; however, the method is not limited to the apparatus  100 , and the apparatus  100  is not limited to operation by the method. In general, the method can include a) positioning the porous substrate  110  across the porous support  136  so that the first surface  116  faces away from the porous support  136  and the second surface  118  faces towards the porous support  136 ; b) applying a suspension of graphene platelets in a fluid to the fluid chamber  122  of the first section  102 , to contact the first surface  116  of the porous substrate  110  with the suspension; and c) applying a pressure differential across the porous substrate  110  to force the graphene platelets into the pores of the porous substrate  110  and force the fluid through the porous substrate  110 . 
     More specifically, in use, the porous substrate  110  may first be mounted in the substrate support frame  108 , by securing the porous substrate  110  between the first  112  and second  114  pieces of the substrate support frame  108 , as shown in  FIG. 2 . The apparatus  100  may then be assembled as shown in  FIG. 3 , with the substrate support frame positioned  108  outboard of the first fluid chamber  122  and the second fluid chamber, and with the porous substrate  110  sandwiched between the first outer wall  120  and the second outer wall  128  and supported by the porous support  136 . This can be achieved by opening the apparatus  100  (i.e. separating the first section  102  and second section  104 ), maneuvering the substrate support frame  108  to lay the porous substrate  110  on the second section  104 , closing the apparatus  100  (positioning the first section  102  adjacent the second section  104 ), and securing the first section  102  to the second section  104 . 
     A suspension of graphene platelets in a fluid can then be applied to the first fluid chamber  122 , so that the suspension is in contact with the first surface  116  of the porous substrate  110 . For example, the suspension can be loaded into the first fluid chamber  122  via one of the fluid inlet ports  126 . 
     A mentioned above, the suspension includes graphene platelets suspended in a fluid. The fluid can be, for example, a liquid or a gas. For example, the fluid can be or can include a liquid such as water, an alcohol, and/or an organic solvent (e.g. N-Methyl-2-pyrrolidone (NMP)). Alternatively, the fluid can be or can include a gas such as nitrogen gas, carbon dioxide, noble gases, water vapor, and/or hydrogen gas. In addition to the graphene platelets, various other materials can be suspended in or dissolved in the fluid. The additional materials can be micro- or nano-sized. For example, the suspension can include carbons (e.g. graphite and/or carbon nanotubes), ceramics (such as oxides, carbides, carbonates, and/or phosphates), metals (such as aluminum and/or iron), semiconductors, lipids, and/or polymers. 
     A pressure differential can then be applied across the porous substrate  110 . As mentioned above, this can be achieved by pressurizing the first fluid chamber  122  and/or applying a vacuum to the second fluid chamber. In the example shown, the pressurizer  106  pressurizes the first fluid chamber  122 . Referring to  FIG. 4 , as the pressure differential is applied, the suspension will be forced towards the second section  104 . Particularly, as the pressure differential is applied, the fluid  152  (shown schematically) of the suspension will pass through the pores  154  of the porous substrate  110 , while the graphene platelets  156  will become lodged within the pores  154 , leaving behind a graphene membrane (i.e. a membrane that includes the porous substrate  110  with the graphene platelets  156  lodged within the pores  154  and/or on the first surface  116  of the porous substrate). Optionally, while the pressure differential is being applied, the suspension can be sonicated, in order to facilitate tight packing of the graphene platelets  156  within the pores  154 . 
     After passing through the pores  154 , the fluid  152  will pass into the second section  104 , and through the first layer  138 , second layer  140 , and third layer  142  of the porous support  136 . The fluid can then be drained via the drain port  134 . 
     Optionally during pressurization, the control sub-system  148  can be used to receive information from the apparatus  100 , and/or to control the apparatus  100 . 
     Optionally, additional suspensions can be applied to the substrate. For example, a first suspension of a first type of graphene platelets (e.g. aminated graphene platelets) can be applied to the porous substrate  110 . Then, a second suspension of a second type of graphene platelets (e.g. oxidized graphene platelets) can be applied to the porous substrate. This can result in a graphene membrane that includes several sub-layers of graphene. 
     Upon completion of fabrication of the membrane (e.g. when all of the fluid  152  of the suspension has passed from the first fluid chamber  122  into the second fluid chamber), the apparatus  100  can be disassembled (i.e. by separating the first section  102  and the second section  104 ), and the substrate support frame  108  and the graphene membrane (which includes the porous support  110  with the graphene platelets  156  lodged within the pores  154  of the porous substrate  110  and/or deposited as a layer on the porous substrate  110 ) can together be removed from the first section  102  and second section  104 . The membrane can then optionally be removed from the substrate support frame  108 , or can remain in the substrate support frame  108  for further processing steps. 
     In some examples, rather than loading the suspension into the first fluid chamber  122 , the suspension can be made in the first fluid chamber  122 . For example, the fluid and the graphene platelets can be added to the first fluid chamber  122  separately, and then combined in the first fluid chamber  122 . 
     While the above describes a batch process for fabricating a graphene membrane, the apparatus  100  may alternatively be operated in a semi-batch fashion that approximates or simulates continuous operation. For example, the porous substrate  110  and the substrate support frame  108  can move through the first section  102  and second section  104 , across the porous support  136 . Furthermore, several of the apparatuses  100  may be operated in parallel or in series. When operating in series, each subsequent apparatus  100  can be used to deposit additional graphene platelets  156  onto/into the porous substrate  110 , or to deposit additional materials onto/into the porous substrate  110 . For example, the first apparatus in a series can deposit aminated graphene platelets into/onto the porous substrate  110 , while the second apparatus in the series can deposit oxidized graphene platelets into/onto the porous substrate  110 . 
     Optionally, the various parts of the apparatus  100  can be configured for removal, replacement, and cleaning. 
     While the above description provides examples of one or more processes or apparatuses or compositions, it will be appreciated that other processes or apparatuses or compositions may be within the scope of the accompanying claims. 
     To the extent any amendments, characterizations, or other assertions previously made (in this or in any related patent applications or patents, including any parent, sibling, or child) with respect to any art, prior or otherwise, could be construed as a disclaimer of any subject matter supported by the present disclosure of this application, Applicant hereby rescinds and retracts such disclaimer. Applicant also respectfully submits that any prior art previously considered in any related patent applications or patents, including any parent, sibling, or child, may need to be re-visited.