NANOPOROUS GRAPHENE MEMBRANE

Abstract

A nanoporous graphene membrane fabrication method is formed using an array of sacrificial nanopillars of removable materials are printed onto a substrate, and subsequent growth of graphene. After serial deposition of overlayers of even dissimilar nature, the sacrificial nanostructures are dissolved, leaving nanoporous graphene membrane with nanopores, channels and cavities of nanoscale dimension and geometry designed and controlled, enabling untapped and unique functions in different technological areas such as filtration, electronics, and molecular sensors.

Claims

1. A method for fabrication of a nanoporous graphene membrane, comprising: printing nanopillars of removable material on a substrate; growing a graphene layer on the substrate to surround the nanopillars; and removing the nanopillars to produce the nanoporous graphene membrane.

2. The method of claim 1, wherein the substrate comprises a material selected from one or more of Ni, Cu and transition metals, thereby facilitating and/or catalysing graphene growth.

3. The method of claim 1, wherein the removable material printed as nanopillars is removable by one or more of a solvent, heat, chemical treatment, and physical treatment.

4. The method of claim 1, wherein the printing the nanopillars comprises: printing or depositing the nanopillars using 3D printing, nano-imprint, dip-pen lithography, laser writing and any printing technique, at an aspect ratio having a height-to-width ratio of 3 to 100.

5. The method of claim 1, wherein the nanopillars have a diameter in a range from 1 nm to 1000 nm, and a height in a range from 100 nm to 10,000 nm.

6. The method of claim 1, wherein the nanopillars have at least one of a cylindrical shape, conical shape, and spherical shape.

7. The method of claim 1, further comprising synthesizing a graphene overlayer.

8. The method of claim 1, further comprising synthesizing a graphene overlayer by chemical vapor deposition.

9. The method of claim 1, further comprising: depositing a supporting layer onto the graphene layer, wherein the supporting layer comprises a metal, or a combination of metal and another material.

10. The method of claim 1, further comprising: depositing a supporting layer onto the graphene layer, wherein the supporting layer comprises a non-metal, or a combination of a non-metal and another material.

11. The method of claim 1, further comprising: depositing a supporting layer onto the graphene layer, wherein the supporting comprises an organic material or an organic material and another material.

12. The method of claim 1, further comprising: depositing a supporting layer onto the graphene layer, wherein the supporting layer comprises as a non-organic material or a non-organic material and another material.

13. The method of claim 1, further comprising: depositing an additional overlayer or a stack of overlayers onto the graphene layer or a supporting layer, wherein the additional overlayer comprises a metal, or a combination of metal and another material.

14. The method of claim 1, further comprising: depositing additional an overlayer or a stack of overlayers onto the graphene layer or a supporting layer, wherein the additional overlayer comprises a non-metal, or a combination of a non-metal and another material.

15. The method of claim 1, further comprising: depositing additional an overlayer or a stack of overlayers onto the graphene layer or @ supporting layer, wherein the additional overlayer comprises an organic material or an organic material and another material.

16. The method of claim 1, further comprising: depositing additional an overlayer or a stack of overlayers onto the graphene layer or a supporting layer, wherein the additional overlayer comprises a non-organic material or a non-organic material and another material.

17. A nanoporous membrane comprising: a multi-layered structure consisting of single or multiple functional overlayers fabricated using the method of claim 1.

18. A nanoporous membrane for wearable and implantable bioartificial kidney, comprising: a multi-layered structure consisting of single or multiple functional overlayers fabricated using the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The descriptions that follow are further understood when read with the appended drawings. There are shown in the drawings exemplary embodiments of the disclosed technology for illustration purpose. The invention is not limited to the specific methods, compositions, and devices disclosed. Further, the drawings are not necessarily drawn to scale or proportion.

[0023] FIG. 1 is a schematic diagram illustrating a fabrication process of free-standing nanoporous graphene membrane using the disclosed technique.

[0024] FIG. 2 is a schematic diagram illustrating the fabrication process of supported nanoporous graphene membrane using the disclosed technique.

[0025] FIG. 3 is a scanning electron micrograph (SEM) image showing an example of photoresist nanopillars prepared by 3D printing.

DETAILED DESCRIPTION

Overview

[0026] The disclosed technique was devised to overcome the problems and challenges concerning the fabrication of nanoporous graphene membranes. The following detailed description with reference to the drawings illustrates the spirit and essence of the disclosed technique. The illustrative embodiments and examples in the description, drawing, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit of the subject matter presented here.

[0027] The disclosed technology pertains to a nanoporous membrane fabrication method and related applications. An array of sacrificial nanopillars of removable materials are printed onto a substrate that can facilitate or catalyze graphene synthesis, for instance, Ni and Cu. Graphene is then synthesized on the substrate surface through chemical vapor deposition (CVD) techniques. Depending on the nature of substrate and processing condition, monolayer and/or few-layer (thin film) graphene can be prepared. Afterwards, when the sacrificial nanostructures are dissolved, a free-standing nanoporous graphene membrane is formed. If a supported graphene is required, another supporting layer can be further deposited onto the graphene formed after graphene synthesis. The supporting layer can be metal, non-metal, organic, inorganic and biomaterial, or a combination of these materials. Further, additional layers for extra functions or properties can be deposited.

[0028] In one configuration, the material printed as nanopillars is a removable material. The nanopillar layer may be removed by solvent, by heat, chemical treatment, physical treatment, or a combination of these techniques. The supporting layer deposited onto the graphene/substrate with nanopillars can be metal, non-metal, organic, inorganic and biomaterial, or a combination of these materials. The overlayer can be deposited by spincasting, chemical deposition and physical deposition. The resulting nanoporous graphene membrane may be used to provide one or more layers functionalized for different purposes such as, but not limited to, drug delivery, antibacterial, antimicrobial, electrical, and optical functions.

[0029] The nanopillars can be printed or deposited using 3D printing, nano-imprint, dip-pen lithography, laser writing or any other suitable printing technique. The printing technique used can be any technique capable of printing a high-aspect ratio nanopillar, and may have high-aspect ratio ranges from a height-to-width ratio of 3 to 100.

[0030] In another configuration, the nanopillar may have a preferred diameter from 1 nm to 1000 nm, and may have a preferred height from 100 nm to 10,000 nm. The nanopillars may be provided with a cylindrical shape, conical shape, or spherical shape.

[0031] The technique may be used for preparing a surface functionalizing an inner wall of nanocavities of the nanoporous membrane, by preparing the nanopillars on a substrate, and exposing the nanopillars on the substrate to a solution containing the self-assemble molecules. The self-assemble molecules in this technique may have one end attached with a chemical functional moiety bestowing the desired surface property that can self-assemble onto the nanopillar surface. The other end is attached with a chemical functional moiety that can self-assemble onto the overlayer surface exposed during removal of nanopillars. The overlayer or overlayers may then be deposited, and nanopillars are removed, to produce the nanoporous membrane with a functionalized inner wall surface.

[0032] One end of the self-assemble molecule is attached with a chemical moiety bestowing the desired surface property, and can bind onto the nanopillar surface via weak chemical and/or physical interactions such as but not limited to electrostatic interaction, ionic bonds, weak chemical bonds; these interactions between the self-assemble molecules and the surface of nanopillars can be broken by chemical and/or physical treatment. The ending chemical moiety and/or its adjacent chemical functional groups that attach onto the surface of the nanopillar possesses a desired surface and chemical property of the final inner wall of a pore. The other end of the self-assemble molecules left hanging on the surface of the nanopillars that possesses another chemical functional moiety can bind strongly with the material of the overlayer to be deposited.

[0033] In another configuration, surface functionalizing of an inner wall of nanocavities of the nanoporous membrane is performed by preparing the nanopillars on a substrate, in which the precursor solution or material to be printed or deposited as nanopillars on the substrate, is mixed with self-assemble molecules before being printed or deposited onto the substrate surface. The self-assemble molecules have one end attached with a chemical functional moiety that can strongly bind with the overlayer material to be deposited and can attach firmly onto the overlayer material on the inner surface of the pore during removal of nanopillars to produce the nanoporous membrane with the functionalized surface on the inner wall. The other end of the self-assemble molecule is attached with a chemical functional moiety bestowing the desired surface property and is left hanging on the inner wall surface of the pore after removal of nanopillars to produce the nanoporous membrane. The overlayer or overlayers are then deposited and nanopillars are removed to produce the nanoporous membrane with the functionalized surface on the inner wall.

[0034] The nanoporous membrane may be used to fabricate a wearable and implantable bioartificial kidney, in which the bioartificial kidney has a multi-layered structure consisting of single or multiple functional overlayers. The nanoporous membrane may be used to provide one or more layers functionalized for different purposes such as, but not limited to, drug delivering, antibacterial, antimicrobial, or electrically conducting functions.

Fabrication Process

[0035] FIG. 1 is a schematic drawing illustrating a basic fabrication process of the disclosed technique. On a supporting substrate 100, nanoscale cylindrical or conical pillars 101 can be 3D-printed or fabricated using lithographic techniques, leaving gaps and cavities in between. Compared with lithographic techniques, 3D-printing may have advantages in the disclosed technique because of its ease and lower cost of operation. It also offers a higher degree of freedom and flexibility in designing the nanoscale features. Advantageously, 3D-printing achieves high-aspect ratio nanoscale structures, which is difficult with conventional lithographic techniques. It is noted that this does not mean that the method of preparing the removable layer 101 is limited to 3D-printing. The choice of preparation method does not affect the legitimacy of the disclosed technique within the scope of the present disclosure.

[0036] The substrate 100 serves as a support for subsequent preparation of nanopillars, and to facilitate or catalyze graphene synthesis. In non-limiting examples, substrate 100 is made of Ni, Cu or transition metal or others, that can facilitate or catalyze graphene synthesis, which can be amorphous, polycrystalline, or single-crystalline form. Graphene layer 102 is then synthesized on the substrate surface through CVD methods. Depending on the nature of substrate and processing condition, monolayer and/or few-layer graphene can be prepared, different CVD methods can used.

[0037] Nanopillars 101 are then dissolved or removed by one or more of a solvent, heat, chemical treatment, and physical treatment. After removal of nanopillars 101, free-standing nanoporous graphene membrane is obtained by a further removal of substrate 100, which is achieved one or more of a solvent, heat, chemical treatment, and physical treatment. If substrate 100 and nanopillars 101 are of the same or similar materials, the dissolution or removal of substrate 100 and nanopillars 101 can be performed simultaneously.

[0038] FIG. 2 is a schematic diagram illustrating the fabrication process of supported nanoporous graphene membrane using the disclosed technique. If a supported nanoporous graphene membrane is required, an additional overlayer 103 is deposited onto the graphene layer before removal of nanopillars 101. The supporting overlayer 103 can be metal, non-metal, organic, inorganic and biomaterial, or a combination of these materials. After subsequent removal of substrate 100 and nanopillars 101, supported nanoporous graphene membrane is obtained.

[0039] In another configuration, additional overlayers of materials can be deposited one by one on top of or replacing supporting layer 103, as a stack of multi-layers. The stack can include one or more overlayers of different material nature with different characteristics or functions if they do not react with each other. As such, thin film devices can be constructed around the nanopillars printed or deposited. After subsequent removal of substrate 100 and nanopillars 101, nanoporous multi-layered graphene membrane is obtained.

[0040] Advantageously, nanopillars 101 may be made of dissolvable material that can removed by solvent, by heat, or other appropriate treatment. By way of non-limiting example, it can be poly methyl methacrylate (PMMA) that can be removed by a suitable solvent such as acetone. For some materials used in nanopillar layer 101, heat or UV curing may be required to obtain nanopillars strong enough to survive subsequent processes.

[0041] After this final treatment, the dimension of the 3D-printed nanopillar would dictate the dimension and morphology of the nanocavity to be constructed. For example, if 100 nm wide circular nanopillars are 3D-printed, cylindrical nanochannels with a diameter of around 100 nm are formed in the nanoporous membrane. As such, there is extremely high manufacturing flexibility and control of the dimension of the nanocavity required in the nanoporous membrane. Hitherto, an advanced commercial 3D printer can already achieve a line width of 50 nm.

[0042] FIG. 3 is a scanning electron micrograph (SEM) image showing a non-limiting example of photoresist nanopillars prepared by 3D printing. The SEM shows a non-limiting example of a 3?3 array of photoresist nanopillars 3D printed on a silicon substrate. The array has three rows of nanopillars of three diameters: 1125 nm, 750 nm, and 500 nm. All of them have a height of 2 ?m.

[0043] On the other hand, these nanocavities created will be surrounded by the graphene layer and stacked overlayers left behind, which can be pre-designed to serve as an active component, e.g., electrodes, antennas, heat circuit, etc.

Applications

[0044] Depending on the size of pore, nanoporous graphene can find different applications in different areas.

[0045] Nanoporous graphene with a few to several tens of nm can be used for molecular diagnostics. Nanoporous graphene with pores of size up to several hundred nm or even ?m can be used as permeation membrane. They can also find substantial potential in energy devices, e.g., supercapacitors and lithium-ion batteries. If the pore size, morphology, density, and distribution of nanoporous graphene can be controlled, and integrated into specific device structures, more advanced and sophisticated applications can be realized.

[0046] Graphene is well known as a semimetal with a zero bandgap. With periodic pore array, the corresponding nanoporous graphene will become a topological metasurface exhibiting a topological bandgap, and is expected to be applicable for further development into ultra-low power consumption, highly integrated, and robust active photonic systems at deep-subwavelength scale for applications in quantum communications and information processing.

[0047] Further, nanoporous graphene find pronounced applications in plasmonic sensing devices. A special double-sided plasmonic metasurface with nanoporous graphene for simultaneous biomolecular separation and SERS detection has been reported.

[0048] The present disclosure of fabrication of nanoporous graphene membrane with controllable pore size, morphology, density and distribution can significantly accelerate the development and realization of potential of nanoporous graphene membrane in both conventional and advanced applications.

CLOSING STATEMENT

[0049] The descriptions and examples herein are intended as non-limiting examples to serve to demonstrate the disclosed technology and can be modified by one having ordinary skill in the art to which the claimed invention pertains within the scope of the subject matter of the claimed invention. On the other hand, the present invention is not limited by the examples disclosed in the specification of the subject application, and the scope of the present invention should be interpreted based on the claims, and to include all techniques that are within the equivalent scope.

[0050] From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration. The present invention is not limited necessarily to the embodiments specifically disclosed, but that substitutions, modifications, and variations may be made to the present invention and its uses without departing from the spirit and scope of the invention. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.