Porous composite membranes, methods for making porous composite membranes, gas separation systems, methods for separating H2 from gas streams, and processes for reducing H2O swelling in graphene oxide-based hydrogen membranes

Abstract

The present invention relates to a porous composite membrane comprising: graphene oxide sheets; and nanoparticles bound to the surface of the graphene oxide sheets solely by electrostatic and / or van der Waals interactions. The present invention also relates to a method for producing the porous composite membrane, a gas separation system comprising the porous composite membrane, the use of the porous composite membrane in a process for separating H from a gas stream, and a process for reducing HO swelling in the graphene oxide sheets.

Description

[Background technology]

[0001] Priority

[0002] This international application claims priority to U.S. Patent Application No. 16 / 892,666, filed June 4, 2020, the entire contents of which are incorporated herein by reference.

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a porous composite membrane based on graphene oxide with improved moisture stability and resistance to water swelling, a method for its manufacture and its uses, in particular the use of the porous composite membrane in gas separation systems and processes for separating H from gas streams.

[0005] In this specification, numbers in brackets ([ ]) refer to the list of references provided at the end of the specification.

[0006] Background of the Invention

[0007] Graphene oxide (GO), inexpensively produced by the controlled oxidation and exfoliation of graphite, has recently emerged as a promising 2D nanomaterial for creating high-performance membranes for critical applications. GO has long been known for its ability to form ultra-hydrogen-permeable membranes with high selectivity (α) for hydrogen (H) over many gas species, including carbon dioxide. In the early 2010s, ultrathin graphene oxide (GO) was proposed as a stepping stone for the separation of hydrogen and carbon dioxide via membrane separation processes. Selectivities of up to 1000 and permeabilities in the triple digits (~000 GPU) have been reported. These performances are ideal for highly efficient H separation and can achieve the purity levels required for immediate use in fuel cells.

[0008] However, GO is highly hygroscopic and tends to swell in the presence of moisture. This means that absorbed water enters the GO channels, expanding the interlayer spacing (d-spacing). Thus, GO membranes become highly hygroscopic and swell in the presence of moisture, resulting in a significant loss of sieving (separation) performance. When GO membranes are exposed to a humid environment, the hydrated GO sheets become negatively charged, promoting delamination of the membrane and resulting in deactivation due to electrostatic repulsion. Thus, water swelling significantly impairs the separation performance of laminated GO membranes. This significant swelling is the Achilles' heel of GO membranes and remains an unresolved issue in the practical implementation of this exciting technology.

[0009] As indicated above, there is an unmet need for GO-based membranes with improved moisture stability and resistance to water swelling, as well as methods for imparting water stability and resistance to water swelling to GO-based membranes. Summary of the Invention [Means for solving the problem]

[0010] Summary of the Invention

[0011] It is therefore an object of the present invention to provide a graphene oxide-based porous composite membrane with improved moisture stability and resistance to water swelling.

[0012] By improving known GO-based membranes, the present invention - a graphene oxide sheet; - nanoparticles bound to the surface of the graphene oxide sheet solely by electrostatic and / or van der Waals interactions; A porous composite membrane is presented, comprising:

[0013] The present invention further provides a method for producing a porous composite membrane of the present invention, comprising the steps of: (i) providing a dispersion of graphene oxide sheets in an aqueous solvent; (ii) providing a dispersion of nanoparticles in an aqueous solvent; (iii) mixing the graphene oxide dispersion with the nanoparticle dispersion to form a graphene oxide particle composite dispersion; and (iv) filtering the dispersion obtained in step (iii) through a porous support substrate to produce a substrate-supported graphene oxide-nanoparticle composite film.

[0014] In another aspect, the present invention further provides a gas separation system comprising a porous composite membrane in fluid communication with a gas stream comprising a separable mixture of at least two gases comprising H2, said porous composite membrane comprising: - a graphene oxide sheet; - nanoparticles bound to the surface of the graphene oxide sheets solely by electrostatic and / or van der Waals interactions.

[0015] In yet another aspect, the present invention provides a method for separating H from a gas stream, comprising permeating a mixture of at least two separable gases through a porous composite membrane as defined in claim 1, wherein said mixture of gases contains at least H.

[0016] In yet another aspect, the present invention also provides a process for reducing HO swelling in graphene oxide-based membranes, the process comprising attaching nanoparticles through electrostatic and / or van der Waals bonding interactions to the graphene oxide sheets that make up the graphene oxide-based hydrogen membrane. [Brief explanation of the drawings]

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To illustrate exemplary embodiments of the present invention, negatively charged nanoparticles (e.g., ND - , POSS - ) are provided as comparative data, while the data shown for pristine GO films and GO-based composite films with positively charged nanoparticles (e.g., ND+ , POSS + Data are presented for GO-based composite membranes with

[0019] [Figure 1A] Figures 1A-1K provide information about the observed microstructure of GO-based composite membranes according to the present invention. Figure 1A. Schematic of the GOαND+ composite structure for efficient H2 separation from CO2. i. Stacking of GO nanosheets as an ordered stacked membrane; ii. Less ordered stacked GO sheets resulting from the introduction of ND+ into the GO structure; iii. GO sheets swell upon water adsorption, disrupting the membrane microstructure; iv. ND+ retains the GOαND+ microstructure under humid conditions; v. Molecular depiction of the electrostatic intermolecular interactions between GO sheets and ND+ particles. Carbon atoms are indicated by solid gray markers, while oxygen and hydrogen atoms are indicated by solid and hollow markers, respectively. [Figure 1B] Figure B-1. AFM image of GO sheet. The inset shows the height profile of the GO sheet. Figure B-2. AFM image of GO30ND+. The inset shows the height profile of the GO sheet with ND+s. [Figure 1C] TEM image of ND+ particles deposited on GO at 30% ND+ loading. Scale bar is 50 nm. [Figure 1D] Interparticle distance of ND+ decorating the GO surface at 30% ND loading. [Figure 1E] Cross-sectional TEM image of the interface between GO and ND+ in a GO30ND+ film. The scale bar is 10 nm. [Figure 1F] Surface and cross-sectional FESEM images of the vacuum-filtered GO membrane. The inset shows a surface SEM of the AAO support. The scale bar is 200 nm in both Figure 1F and G. [Figure 1G] Surface and cross-sectional FESEM images of the vacuum-filtered GO membrane. The inset shows a surface SEM of the AAO support. The scale bar is 200 nm in both Figure 1F and G. [Figure 1H]Surface and cross-sectional SEM of vacuum-filtered GO30ND+ membrane. Scale bar is 200 nm. [Figure 1I] Surface and cross-sectional SEM of vacuum-filtered GO30ND+ membrane. Scale bar is 200 nm. [Figure 1J] Figure 1J. Normalized H2 permeability. [Figure 1K] Figure 1K. Normalized H2 / CO2 selectivity of GO and GOαND+ membranes over time under equimolar hydration (RH: 85%) equimolar H2 / CO2 mixture.

[0020] [Figure 2A] Figures 2A–2F show the observed in-plane size of GO sheets. SEM images (Figures 2A–2C) and the corresponding size distributions (Figures 2D–2F) estimated using ImageJ software by taking the square root of the area of ​​SGO (Figures 2A and 2D), GO (Figures 2B and 2E), and LGO (Figures 2C and 2F). Three types of GO sheets with average in-plane sizes of 0.2 μm, 3 μm, and 10 μm were synthesized. The average in-plane size of GO sheets was determined from scanning electron microscope (SEM) images, and the corresponding size distributions were estimated using ImageJ software from over 120 sheets. To prepare AFM samples, 1 μg / mL dispersions of SGO, GO, and LGO were dropped onto the surface of a silicon wafer and air-dried for 24 hours. [Figure 2B] Same as above [Figure 2C] Same as above [Figure 2D] Same as above [Figure 2E] Same as above [Figure 2F] Same as above

[0021] [Figure 3A] Figures 3A-3B provide information on the observed size distribution of ND+ particles. Dynamic light scattering of a 5 mg / mL ND+ dispersion in water showed a diameter of approximately 3 nm (Figure 3A), consistent with data obtained from TEM images (Figure 3B). In the TEM images, the scale bar is 5 nm. [Figure 3B] Same as above

[0022] [Figure 4A] Figures 4A-4C provide information on the observed size distributions of the negatively charged ND (ND-) particles used in Comparative Example 2 (Figure 4A), and the negatively and positively charged POSS particles used in Comparative Example 3 and Example 4, respectively (Figures 4B and 4C). All samples were measured by dynamic light scattering of 5 mg / mL dispersions in water. The negatively charged dispersed POSS (POSS-) particles exhibited an average size of approximately 4 nm in water (Figure 4B), similar to ND- (Figure 4A). The positively charged POSS (POSS+) particles exhibited an average size of approximately 7 nm (Figure 4C). [Figure 4B] Same as above [Figure 4C] Same as above

[0023] [Figure 5] Figures 5A-D show digital images of the GO film (Figure 5A) and the GOαND+ composite films: GO10ND+ film (Figure 5B), GO20ND+ film (Figure 5C), and GO30ND+ film (Figure 5D). All GOαND+ composite films showed relatively high transparency, indicating good dispersion of ND+ within the GO framework.

[0024] [Figure 6A] Figures 6A–6H show 2D and 3D height AFM images of the GO-based film surfaces: GO film (Figure 6A–B), GO10ND+ film (Figure 6C–D), GO20ND+ film (Figure 6E–F), and GO30ND+ film (Figure 6G–H). The scan area is 10 μm × 10 μm. The relevant surface roughness parameters are listed in Table 1. [Figure 6B] Same as above [Figure 6C] Same as above [Figure 6D] Same as above [Figure 6E] Same as above [Figure 6F] Same as above [Figure 6G] Same as above [Figure 6H] Same as above

[0025] [Figure 7A] Figures 7A-7D show surface SEM images of GO-based films: GO (Figure 7A), GO10ND+ (Figure 7B), GO20ND+ (Figure 7C), and GO30ND+ (Figure 7D). The insets are SEM images of the AAO support itself. With the addition of ND+ particles, the surface microstructure gradually changes to a coarse morphology. The presence of a coarse microstructure without significant aggregation of ND+ particles confirmed the uniform dispersion of ND+ particles, even at a relatively high loading of 30 wt%. [Figure 7B] Same as above [Figure 7C] Same as above [Figure 7D] Same as above

[0026] [Figure 8A] Figures 8A-8D show the relatively long-term separation of an equimolar H2 / CO2 mixture through the GO-based membrane at room temperature and under humid conditions (RH: 85%) between the GO-based membrane of the present invention and the GO-POSS composite membrane of Comparative Example 2. Figure 8 shows the H2 permeability of the GOαND+ (Figure 8A) and GOαPOSS- (Figure 8B) composite membranes and the H2 / CO2 selectivity of the GOαND+ (Figure 8C) and GOαPOSS- (Figure 8D) composite membranes under a continuous supply of an equimolar H2 / CO2 mixture under humid conditions (RH: 85%). [Figure 8B] Same as above [Figure 8C] Same as above [Figure 8D] Same as above

[0027] [Figure 9A]Figures 9A–9H provide information on the physicochemical properties of GO-based membranes. Figure 9A shows the zeta potential values ​​of GO, GOαND+, GOαND-, GOαPOSS+, and GOαPOSS- composites at various loadings at pH 7; the inset shows the zeta potential values ​​of ND+ / - and POSS+ / - dispersions at pH 7. Figure 9B shows the XRD patterns of GOαND+ membranes with various ND+ particle loadings. Figure 9C shows the H2 permeability and H2 / CO2 ideal selectivity of GO and GO30ND+ membranes with various thicknesses. Figure 9D shows the H2 / CO2 separation performance of the GO-ND+ composite membranes of the present invention (circles, numbers indicate the ND+ content in the membrane) compared with a state-of-the-art GO-based H2 separation membrane (squares) known in the art. 1:[1], 2:[2], 3:[3], 4:[4], 5:[5], 6:[6], 7:[7], 8:[8], 9:[9], 10:

[10] , 11:

[11] , 12:

[12] , 13:

[13] . The inset shows the change in membrane H separation performance by adding different types of nanofillers (i.e., ND+ and POSS- at various loadings). Figure 9E compares the H / CO separation performance of our GO-ND+ composite membrane (circles, numbers indicate the ND+ content in the membrane) with that of state-of-the-art H separation membranes other than GO-based materials. COF (pentagon):

[14] , inorganic (diamond): 1:

[15] , 2:

[16] , 3:

[17] , 4:

[18] , 5:

[19] , 6:

[20] , MXene (hexagon):

[21] , MOF (triangle): 1:

[22] , 2:

[23] , 3:

[24] , 4:

[25] , 5:

[26] , 6:

[24] , 7:

[27] , 8:

[28] , 9:

[29] , 10:

[30] , 11:

[31] . Figures 9F–G show the H permeability and H / CO selectivity of composite membranes containing various types of nanofillers (i.e., ND+ / − and POSS+ / −) at various loadings under an equimolar H / CO mixture feed. Figure 9H shows the permeability (left y-axis) of H (filled circles) and CO (filled triangles) through the GO30ND+ membrane, as well as the H / CO selectivity (open squares) obtained from mixed gas feeds of CO with different H contents. [Figure 9B] Same as above [Figure 9C] Same as above [Figure 9D] Same as above [Figure 9E] Same as above [Figure 9F] Same as above [Figure 9G] Same as above [Figure 9H] Same as above

[0028] [Figure 10] Figure 10 shows the FTIR spectra of ND particles, GO, and GOαND composite films. GO exhibited typical peaks corresponding to CO (alkoxy / alkoxide, 1046 cm-1), CO (carboxy, 1410 cm-1), C=C (aromatic, 1627 cm-1), C=O (carboxy / carbonyl, 1726 cm-1), and -OH (3300 cm-1). The ND spectrum exhibited relevant absorption peaks at 1720 cm-1 and 1000–1350 cm-1, corresponding to the stretching of C=O and CO or COC vibrations, respectively, consistent with literature findings. The carbonyl band at 1726 cm-1 shifted to a broader lower-wavelength peak at 1636 cm-1 upon incorporation of ND particles, demonstrating hydrogen bonding between GO and ND+.

[0029] [Figure 11A] Figures 11A-11C show a comparison of XPS analysis of the GO film (Figure 11A) and the GO30ND+ film (Figures 11B-C). The XPS of the GO30ND+ film showed a decrease in the O / C ratio compared to the GO sample. A significant decrease in the intensity of C=O was also observed compared to the GO film (see Table 4). This is attributed to hydrogen bonding between oxygen-containing groups on the GO sheet surface and the ND+ particles. While no nitrogen peaks were observed in the GO film, the GO30ND+ film exhibited 1.5% nitrogen, detected at 399.1 eV (C-NH-C) and 401.1 eV (C-N). [Figure 11B] Same as above [Figure 11C] Same as above

[0030] [Figure 12]Figure 12 shows the Raman spectra of ND+, GO, and GOαND+ composite films. The D and G peaks near 1345 cm-1 and 1590 cm-1 are characteristic of defective graphitic carbon and sp2-hybridized aromatic carbon in pure GO films. The ID / IG ratios of GO and GOαND+ films are very similar. However, in the GOαND+ film, the D and G bonds are slightly wider than in pristine GO, confirming a disordered structure due to the intercalation of ND+ and GO sheets. The addition of ND+ slightly shifts the D and G peaks, reaching a low of ~1342 cm-1 and a high of ~1591 cm-1 in GO30ND+, which is presumably due to electrostatic interactions between GO and ND+.

[0031] [Figure 13] Figure 13 shows a comparison of the mechanical properties of the GO-based composite film of the present invention with those of a pure GO-based film and a GOαPOSS-composite film. The stiffness (vertical bars) and Young's modulus (squares) of the GOαND+ film were improved by 100 MPa and 25% compared to the pure GO film, indicating good interaction between GO and ND+. However, the nanoindentation mechanical properties of the GOαPOSS-composite were reduced compared to the pure GO film, mainly due to the formation of aggregates and poor interaction with the GO framework. Error bars represent the standard error of 20 indentations.

[0032] [Figure 14A] Figures 14A-14C show a comparison of gas adsorption isotherms. N adsorption isotherms at 77 K for the GO and GO30ND+ films (Figure 14A), and CO, H, and N adsorption isotherms at 298 K for the GO (Figure 14B) and GO30ND+ films (Figure 14C). Both the GO and GO30ND+ films showed predominant CO adsorption over H and N. Notably, the CO adsorption of GO30ND+ was much higher than that of the pure GO film, confirming that the ND+ particles effectively suppressed the re-stacking of GO sheets. [Figure 14B] Same as above [Figure 14C] Same as above

[0033] [Figure 15A]Figures 15A–15K show a comparison of stability data for ND+-loaded GO membranes. Figure 15A shows photographs of GO and GO30ND+ membranes soaked in water: i. polyethersulfone (PES) support; ii. as-prepared GO membrane; iii. GO membrane soaked in water after 1 day; iv. as-prepared GO30ND+ membrane; and v. GO30ND+ membrane soaked in water after 1 day. The scale bar is 2 cm. Figure 15B shows the normalized H2 / CO2 selectivity (open symbols) and normalized H2 permeability (filled symbols) of the GO membrane (square), GO5ND+ membrane (diamond), GO10ND+ membrane (circle), GO20ND+ membrane (upward-pointing triangle), and GO30ND+ membrane (downward-pointing triangle) under six consecutive wet (85% RH) / dry (0% RH) cycles and an equimolar H2 / CO2 gas mixture supply. Figures 15C-D show XRD patterns of GO and GOαND+ membranes in the dry state, after exposure to humidity (RH: 33%; RH: 85%), and after immersion in water. Figures 15E-F show surface and cross-sectional FESEM images of GO membranes after wet / dry cycle measurements. Figure 15G shows the H permeability loss relative to the dry feed value for GO and GOαND+ membranes with various ND+ loadings under various relative humidity feeds (RH: 12, 33, 75, and 85%). The inset shows the H / CO selectivity values. Figure 15H shows the H / CO selectivity loss relative to the dry feed value for GO and GOαND+ membranes (with different loadings) under various relative humidity feeds (RH: 12, 33, 75, and 85%). The inset shows the H permeability value in the GPU. Figure 15I shows the H2 permeability (top graph, inverted solid triangles) and O2 permeability (second graph from the top, upright solid triangles) of GO30ND+ under six consecutive wet (85% RH) / dry (0% RH) cycles and an equimolar H2 / CO2 mixed gas feed, as well as the H2 / O2 selectivity of the GO membrane (open squares) and GO30ND+ (open triangles). Figure 15J shows the H2 permeability loss and H2 / CO2 selectivity loss of the GO, GO30ND+, GO30ND-, GO30POSS+, and GO30POSS- membranes under a wet feed (85% RH) versus the dry feed values.Figure 15K shows the PM0.3 removal rates of the polyethersulfone support, GO membrane, and GOαND+ membrane before and after immersion for 2 to 8 hours. [Figure 15B] Same as above [Figure 15C] Same as above [Figure 15D] Same as above [Figure 15E] Same as above [Figure 15F] Same as above [Figure 15G] Same as above [Figure 15H] Same as above [Figure 15I] Same as above [Figure 15J] Same as above [Figure 15K] Same as above

[0034] [Figure 16A] Figures 16A-16B show a comparison of the FTIR (Figure 16A) and XRD patterns (Figure 16B) of POSS particles, GO films, and GO α-POSS films. The POSS particles exhibited an absorption peak at 1107 cm-1, which was attributed to the stretching of the Si-O vibration band. The peaks of the GO-mixed POSS films remained almost unchanged compared to those of the pure components (Figure 16A). The XRD peaks shifted to the left with the addition of POSS particles, indicating an increase in the interlayer spacing of the GO sheets (Figure 16B). The insertion of negatively charged POSS particles between GO sheets enhanced the electrostatic repulsion between the layers, resulting in an increase in the channel size. The crystalline structure of the GO α-POSS films was determined by wide-angle X-ray diffraction (WAXD, Rigakuraint XRD). Using a CuKα anode, the sample was scanned at a rate of 10° / min over the 2θ range of 5–40° at a voltage of 40 kV and a current of 200 mA. [Figure 16B] Same as above

[0035] [Figure 17] 17 shows an exemplary surface SEM image of a GO20POSS-film (Comparative Example 2). The aggregation of particles within the GO system can be observed from the SEM image, indicating poor interaction between the POSS- and GO sheets.

[0036] [Figure 18] Figure 18 shows the stability data for GOαPOSS-membranes: H / CO selectivity (open markers) and H permeability (filled markers) of GO, GO10POSS-membranes, and GO30POSS-membranes under continuous wet (RH: 85%) / dry (RH: 0%) cycling with an equimolar H / CO mixture.

[0037] [Figure 19] Figure 19 shows an example of a schematic device for a Wicke-Kallenbach permeation system for gas separation measurements. MFC: mass flow controller, GC: gas chromatograph (Shimadzu GC-2014) equipped with a thermal conductivity detector (TCD).

[0038] [Figure 20A] Figures 20A-20D show TEM observations of ND particles decorating the GO surface and the interparticle distance. Figures 20A and 20C: 10 wt% ND+ on GO sheets. Figures 20B and 20D: 20 wt% ND+ on GO sheets. Scale bars are 50 nm for both Figures 20A and 20B. ND+ particles and GO-ND composites were reexamined under TEM using samples subjected to the same process conditions (e.g., concentration, shaking / sonication) to prepare laminated films. When ND+ and GO sheets were mixed and shaken, ND+ uniformly decorated the GO surface (Figures 20A-20B). Based on software-assisted image analysis, we found that more than 50% of the particles were 10-40 nm apart, reaching up to 120 nm (Figures 20C-D). [Figure 20B] Same as above [Figure 20C] Same as above [Figure 20D] Same as above

[0039] See Figure 20: ND on GO + The distribution of about 250 ND + The particles were analyzed by measuring their diameter. +The selection of was determined by a predetermined gray level threshold of the TEM image. The obtained values ​​were plotted on a histogram and fitted with a Gaussian function.

[0040] Dispersion D is the TEM image 1 First, 10 × 10 equidistant horizontal and vertical grid lines were overlaid on the TEM image. Next, adjacent NDs were + The free path spacing between the samples was precisely measured. The number of measurements, N, was approximately 200 for each sample. These values ​​were then plotted on a histogram and fitted to a log-normal distribution function.

number

[0041] The variance D was calculated using the following formula:

number

number

[0042] In the range of μ±0.1μ, the dispersion D 0.1 becomes:

number

[0043] In the range of μ±0.2μ, the dispersion D 0.2 becomes:

number

[0044] D 0.1 and D 0.2Higher values ​​of indicate that more interval data fall within the ranges of μ ± 0.1μ and μ ± 0.2μ, respectively, which is indicative of ND + This means a more uniform distribution of particles.

[0045] [Table A]

[0046] [Figure 21] Figure 21 shows the gas permeation of the GO30ND+ membrane versus temperature for equimolar H2 / CO2 feed gas. This figure shows the effect of temperature on the H2 / CO2 selectivity of the GO30ND membrane, measured under dry conditions. The temperature dependence of CO2 permeation is higher than that of H2 permeation. As the temperature increases, the adsorption of CO2 molecules is significantly hindered. Because the adsorption of CO2 molecules restricts their transport through the GO membrane channels, the CO2 flux is higher at higher temperatures, increasing by approximately 4.7 times for CO2 (from ~17.7 to ~82.7 GPU). However, H2 molecules show little affinity for the GO surface, decreasing by ~1.3 times for H2 (from ~3532.5 to ~4497.0 GPU). Permeance (GPU) is shown by the filled symbols (circles and triangles), and H2 / CO2 selectivity is shown by the open squares.

[0047] [Figure 22A] Figures 22A-22B show the XRD patterns of the heat-treated GO-only (Figure 22A) and GO30ND+ (Figure 22B) membranes. The GO membrane showed a slight decrease in interlayer spacing, while the interlayer spacing value of the GO30ND+ membrane remained unchanged at 80 °C, but both began to decrease at 120 °C. These results are consistent with the increase in permeability and decrease in selectivity in the membranes with increasing temperature. [Figure 22B] Same as above

[0048] [Figure 23A]Figures 23A–23D show the effect of cyclic wetting tests on the morphology of GO films (Figures 23A–23B) and GO30ND+ films (Figures 23C–23D). To visualize the undesirable reorganization of GO films under wetting, we compared the morphologies of GO and GO30ND+ films after cyclic wetting tests. The GO film began to swell and delaminate from the support (Figure 23A). Specifically, after the cyclic wetting test (Figure 23B), small (~200 nm) circular protrusions were observed on the GO film, which, after a certain point, led to catastrophic results. In the case of the GO30ND+ film, neither delamination nor protrusions were observed (Figures 23C–D). Note that Figures 23A and 23B are the same as Figures 15F and 15E, respectively. The figures are provided as Figures 23A and 23B to illustrate the difference from the SEM images of the GO30ND+ film after cyclic measurements. [Figure 23B] Same as above [Figure 23C] Same as above [Figure 23D] Same as above

[0049] [Figure 24A] Figures 24A-24B show the H permeability (Figure 24A) and H / CO selectivity (Figure 24B) of GO and GOαND+ membranes (with different loadings) under various relative humidity feeds (RH: 12, 33, 75, and 85%). [Figure 24B] Same as above DETAILED DESCRIPTION OF THE INVENTION

[0050] definition

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Generally, the names used herein and the experimental methods described below are those well known and commonly used in the art.

[0052] To facilitate understanding of the present invention, several terms and phrases are defined below.

[0053] As used herein except in the claims, the terms "a," "an," "the," and / or "said" mean one or more. As used herein in the claims, when used with the terms "comprise," "comprises," and / or "comprising," the terms "a," "an," "the," and / or "said" can mean one or more. As used in this specification and claims, the terms "having," "has," "is," "have," "including," "includes," and / or "include" have the same meaning as "comprise," "comprises," and / or "comprising."

[0054] By the phrases "combinations thereof," "mixtures thereof," and the use of "and / or" after a list, as part of a list, a list in a table, the use of "such as" as part of a list, the phrase "such as," and / or a parenthetical list including "for example" or "i.e.", any combination (e.g., any subset) of the listed components in a series, as well as combinations and / or mixtures of related species and / or embodiments not directly listed but described herein, are also contemplated. Such related genera, subgenera, species, and / or embodiments described herein are contemplated as "selected from at least one of," "mixtures thereof," and / or "combinations thereof," both in the form of the individual components as claimed, and as the mixtures and / or combinations as claimed.

[0055] As used herein, the term "graphene oxide" refers to an exfoliated graphite oxide product without departing from the conventional meaning of the term in the art. It refers to a compound containing carbon, oxygen, and hydrogen in appropriate proportions, and graphene oxide may contain carbon as the primary component, constituting more than about 50 wt%, more than about 60 wt%, more than about 70 wt%, more than about 80 wt%, more than about 90 wt%, more than about 95 wt%, or more than about 99 wt% of the total weight of the graphene oxide. Graphene oxide may also contain oxygen-containing functional groups, such as epoxy, hydroxyl, or carboxyl groups.

[0056] Graphene oxide for use in the present invention can be produced by any means known in the art. For example, graphene oxide can be obtained by oxidizing graphene (preferably a single, planar, two-dimensional, honeycomb-lattice carbon material). For example, graphite oxide can be produced from graphite flakes (e.g., natural graphite flakes) by treating them with potassium permanganate and sodium nitrate in concentrated sulfuric acid. This method is known as the Hummers process. Another method is the Brodie process, which involves adding potassium chlorate (KClO) to a slurry of graphite in fuming nitric acid. Individual graphene oxide (GO) sheets can then be exfoliated by using ultrasonic forces to break down the graphite oxide in water or other polar solvents, and the added salts can be removed from the bulk residue by centrifugation and, optionally, dialysis.

[0057] The term "nanodiamond" as used herein refers to diamond or particles thereof having a nanometer-scale size, e.g., a size (e.g., cross-sectional dimension) of less than about 999 nm, less than about 900 nm, less than about 800 nm, less than about 700 nm, less than about 600 nm, less than about 500 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, less than about 100 nm, or less than about 50 nm. Nanodiamonds are not particularly limited in their shape, color, grade, composition, surface chemical modification, etc. Furthermore, nanodiamonds may contain carbon as a component, for example, greater than about 50 wt%, greater than about 60 wt%, greater than about 70 wt%, greater than about 80 wt%, greater than about 90 wt%, greater than about 95 wt%, or greater than about 99 wt% of their total weight. Exemplary embodiments of the present invention provide composite materials comprising graphene oxide and at least one nanodiamond. In particular, the nanodiamonds may be non-covalently bound to the surface of the graphene oxide. For example, nanodiamonds may be bound to the surface of graphene oxide via electrostatic and / or van der Waals interactions.

[0058] As used herein, "zeta potential," when referring to the surface charge of a GO flake or particle, does not depart from the conventional meaning of the term in electrochemistry and refers to the potential difference between the surface of the GO flake or particle and a fixed layer of fluid attached to the surface of the GO flake or particle. Zeta potential is typically affected by the nature of the material surface and the properties of the fluid in contact with the material surface (e.g., pH, ion concentration, ionic force, etc.). Zeta potential can be measured using an electrokinetic analyzer. Zeta potential can be measured using the Smoluchowski model.

[0059] Unless otherwise specified, the term "average diameter" as used herein refers to the average of the longest dimensions of each particle in the population.

[0060] As used herein, the term "fluid communication" means that a fluid can pass through a first component and reach and pass through a second or other component, whether the components are physically connected or arranged in series.

[0061] As used herein, the term "microscale" and the related prefix "micro" are intended to mean an item having at least one dimension that is equal to or greater than one micrometer and less than one millimeter.

[0062] As used herein, the term "nanoscale" and the related prefix "nano" (eg, "nanoparticle") are intended to mean less than 1 micrometer in length.

[0063] The term "nanoparticle" includes, for example, "nanospheres," "nanorods," "nanocups," "nanowires," "nanoclusters," "nanofibers," "nanolayers," "nanotubes," "nanocrystals," "nanobeads," "nanobelts," and "nanodisks." Nanoparticles that can be used in the context of the present invention may be solid particles of nanoscale size.

[0064] The terms "weight percent," "wt%," "wt-%," "percent by weight," "wt %," and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition multiplied by 100.

[0065] As used herein, "about" refers to any inherent measurement error or rounding of numerical values ​​(e.g., calculations of measurements, ratios, etc.), and therefore the term "about" can be used with any value and / or range. As used herein, the term "about" can refer to a ±5% variation of the specified value. For example, "about 50" percent can, in some embodiments, have a variation of 45 to 55 percent. In the case of integer ranges, the term "about" can include one or two integers greater than and / or less than the stated integer. Unless otherwise indicated herein, the term "about" is intended to include values ​​near the stated range (e.g., weight %, temperature) that are equivalent with respect to the functionality of the associated individual component, composition, or embodiment.

[0066] As used herein, the term "and / or" means any one of the items, any combination of the items, or all of the items with which this item is associated.

[0067] As will be understood by those of ordinary skill in the art, all numbers, including those expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and the like, are approximate and are understood to be modified in all instances as necessary by the term "about." These values ​​may vary depending on the desired properties sought to be obtained by the skilled artisan utilizing the teachings set forth herein. It is also understood that such values ​​inherently contain variations necessarily resulting from the standard deviation found in their respective testing measurements.

[0068] As will be understood by those skilled in the art, for all purposes, particularly in terms of providing a written description, all ranges described herein encompass all possible subranges and combinations of subranges, as well as the individual values ​​(e.g., integers) comprising the ranges. A recited range (e.g., weight percent, temperature, etc.) includes each specific value, integer, decimal, or unit within the range. Any recited range is fully descriptive and can be readily recognized as being divisible into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, it is recognized that each range discussed herein can be readily divided into a lower third, middle third, upper third, etc.

[0069] Also, as will be understood by those skilled in the art, all terms such as "up to," "at least," "greater than," "less than," "greater than," and "more than" are inclusive of the recited numbers, and such terms refer to ranges that can then be subdivided into subranges as described above. Similarly, all ratios described herein also include all subratios that fall within the broader ratio. Thus, the specific values ​​listed for radicals, substituents, and ranges are merely exemplary, and they do not exclude other defined values ​​or other values ​​within the defined ranges for radicals and substituents.

[0070] Those skilled in the art will also readily understand that when members of a group are grouped in a general manner, such as a Markush group, the invention encompasses not only the entire group listed as a whole, but also each member of the group individually, and all possible subgroups of the main group. Moreover, for all purposes, the invention includes the main group itself and the main group absent one or more group members. Thus, the invention contemplates the explicit exclusion of one or more elements of any listed group. Thus, provisos may be applied to any of the disclosed categories or embodiments, whereby any one or more of the described elements, species, or embodiments may be excluded from such category or embodiment, e.g., as used in an express negative limitation.

[0071] The methods, systems, devices, and compositions of the present invention may comprise, consist essentially of, or consist of the components and ingredients of the present invention as well as other components described herein. As used herein, "consisting essentially of" means that the methods, systems, devices, and compositions may include additional steps, components, or ingredients, but only if the additional steps, components, or ingredients do not materially alter the basic and novel characteristics of the claimed methods, systems, devices, and compositions.

[0072] Throughout the description and claims of this specification, the terms "comprise" and "contain" and variations thereof mean "including, but not limited to," and are not intended to exclude (and do not exclude) other elements, additives, components, integers, or steps. Throughout the description and claims of this specification, the singular includes the plural unless the context requires otherwise. In particular, where the indefinite article is used, the specification should be understood to contemplate the plural as well as the singular, unless the context requires otherwise.

[0073] It is to be understood that any feature, integer, property, compound, chemical moiety, or chemical group described in connection with a particular aspect, embodiment, or example of the invention may also be applied to any other aspect, embodiment, or example described herein, unless inconsistent. All features disclosed herein (including the accompanying claims, abstract, and drawings) and / or all disclosed method steps or steps may be combined in any combination, except where at least some of such features and / or steps are mutually exclusive combinations. The invention is not limited to the details of the foregoing embodiments or examples. The invention extends to any novel one or any novel combination of features disclosed herein (including the accompanying claims, abstract, and drawings), or any novel one or any novel combination of any disclosed method steps.

[0074] Detailed Description of Preferred Embodiments of the Invention

[0075] The present disclosure is described with respect to specific embodiments. However, it will be readily apparent to those skilled in the art that various modifications, rearrangements, and substitutions can be made without departing from the spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

[0076] For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to exemplary embodiments illustrated in the drawings, and specific language will be used to describe the drawings. It will be understood, however, that the scope of the present disclosure is not intended to be limited by the drawings. Any alterations and further modifications of the features of the invention exemplified herein, and any further applications of the principles of the present disclosure exemplified herein, that would be understood by those skilled in the art and in possession of this disclosure, are deemed to be within the scope of the present disclosure.

[0077] The term "exemplary" is used herein to mean "serving as, for example, or as an illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. The term "example" may be used synonymously with the term "exemplary."

[0078] Illustrative embodiments are described below. For purposes of clarity, not all features of an actual embodiment are described in this specification. Of course, it will be understood that in developing such an actual embodiment, implementation-specific decisions must be made to conform to system- and business-related constraints to achieve the particular goals of the developer, which will vary from implementation to implementation. Moreover, it will be understood that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0079] The present GO-based composite membranes, systems, and processes overcome one or more of the aforementioned problems typically associated with conventional GO-based membrane technologies and processes. Specifically, the present GO-based composite membranes exhibit improved water stability and resistance to water swelling. Unique features of this and other GO-based composite membranes are described below and illustrated in the accompanying drawings.

[0080] The GO-based composite membranes, systems, and processes, both in terms of structure and operation, can be understood from the accompanying drawings in conjunction with the accompanying description. Several embodiments of the GO-based composite membranes, systems, and processes are shown in Figures 1-24. Various components, parts, and features of different embodiments may be combined with one another and / or substituted for one another, all of which should be understood to be within the scope of the present application, even if not all variations and specific embodiments are shown in the drawings. It should also be understood that, unless otherwise stated, mixing and matching of features, elements, and / or functions between various embodiments is expressly contemplated herein, such that one skilled in the art would understand from this disclosure that features, elements, and / or functions of one embodiment may be incorporated into another embodiment, as appropriate.

[0081] As discussed above, there is an unmet need for GO-based membranes with improved humidity (moisture) stability and resistance to water swelling, and for methods of imparting water stability and resistance to water swelling to GO-based membranes.

[0082] The present invention solves this problem by providing a porous composite membrane comprising: -Graphene oxide sheet -Nanoparticles bound to the surface of graphene oxide sheets solely through non-covalent interactions

[0083] Non-covalent interactions include electrostatic interactions and / or van der Waals interactions. As used herein, the term "van der Waals interactions" generally refers to any non-covalent interaction between materials. Van der Waals forces include dipole-dipole forces, dipole-induced dipole forces, and London dispersion forces. Hydrogen bonds are dipole-dipole forces and are included in van der Waals forces.

[0084] The composite film may include multiple stacked graphene oxide sheets, and nanoparticles may be intercalated between the stacked graphene oxide sheets. Regarding the characterization of GO sheets, a series of characterization experiments can be performed to understand the characteristic shape, functionality, and other physicochemical properties of GO sheets. These experiments can include calculations related to a zeta potential analyzer for charge, Raman spectroscopy for G / D ratio, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) for functional groups, X-ray diffraction (XRD) for crystal structure, and atomic force microscopy (AFM), SEM, and transmission electron microscopy (TEM) for size and shape. In particular, SEM and AFM techniques can be used to measure the size of GO flakes and the thickness of the film.

[0085] The graphene oxide sheets in the composite film of the present invention may have an interlayer distance or d-spacing of approximately 0.6 to 1.2 nm. For example, the distance between GO sheets may be in the range of 0.7 to 1.0 nm, e.g., 0.8 to 0.9 nm. The d-spacing can be determined by powder X-ray diffraction (XRD) using Bragg's law: d = λ / 2 sin(θ) (1), where θ is half the diffraction angle and λ is the wavelength of the X-ray source. As the reader will understand, the d-spacing or lattice spacing refers to the distance between parallel planes of GO. In principle, XRD measures the average spacing between layers or atomic columns. Therefore, the interlayer distance or d-spacing of GO reported herein refers to the average value. Typically, the interlayer space between stacked GO sheets contains hydrophilic and hydrophobic domains. The hydrophilic domains between GO sheets are generally located at the edges and / or basal planes of the GO sheets, where oxygen functional groups are present. Due to their affinity for hydrophilic domains, water molecules may intercalate into the hydrophilic domains of stacked GO sheets. Without wishing to be bound by any particular theory, it is believed that intercalation of nanoparticles between GO stacks creates or stabilizes regions within the GO sheet stacks where the hydrophobicity of the internal pore walls restricts the permeation of water molecules, thereby imparting a less water-affinity and greater resistance to water swelling to the GO-based composite membrane. The graphene oxide sheets may have an average planar size of about 200 nm to 15 μm, e.g., 1 to 10 μm, e.g., about 1 to 6 μm. The planar size of the graphene oxide sheets can be measured using SEM. For example, nanoparticles possess an overall positive charge, particularly on their outer surfaces, which form electrostatic / van der Waals interactions with the graphene oxide sheet surface. This positive charge is believed to facilitate electrostatic and / or van der Waals interactions between the graphene oxide surface and the nanoparticles.Without wishing to be bound by any particular theory, the presence of positively charged nanoparticles on the surface of the GO sheets is believed to neutralize the negative charge of the stacked GO sheets (GO sheets are uncharged in the dry state, but after exposure to water, the surface of the GO sheets becomes negatively charged, primarily due to deprotonation of hydroxyl groups), stabilizing the resulting film against moisture. For example, the nanoparticles may have a positive charge with a zeta potential of 30 mV or more at pH 7. The zeta potential of nanoparticles can be measured using an electrokinetic analyzer. Suitable positively charged nanoparticles include, for example, positively charged nanodiamonds, cationic POSS particles, cationic dyes, metal cations, and double hydroxides. Nanoparticles usable in the context of the present invention may be different from clay nanoparticles or MOF nanoparticles.

[0086] Additional nanoparticles that can be used in the context of the present invention may include metal nanocrystals such as Ag nanocrystals, porphyrins such as meso-(p-hydroxyphenyl)porphyrin nanocrystals, and / or melamine nanoparticles. The adsorption of metal nanoparticles, porphyrins, and melamine onto GO sheet surfaces via noncovalent bonds has been described, for example, in references [32-34] (two-dimensional assembly of GO sheets with metal nanoparticles, porphyrins, and melamine via noncovalent bonding of nanoparticles on the GO surface). However, these reports do not consider the possibility of applying noncovalent adsorption phenomena to three-dimensional GO-based composite structures, let alone their use as membranes with sieving capabilities. GO-based membranes of the present invention can be prepared according to the teachings of the present disclosure using metal nanocrystals such as Ag nanocrystals, porphyrins such as meso-(p-hydroxyphenyl)porphyrin nanocrystals, and / or melamine as nanoparticles. For example, the methods described in the Examples may be used by substituting Ag nanocrystals, porphyrin nanoparticles, and / or melamine nanoparticles for NDs.

[0087] The nanoparticles may have an average diameter of about 3-10 nm, e.g., 3-5 nm, e.g., about 3 nm or about 4 nm. If the nanoparticles have an irregular shape, routine averaging can be performed to determine the average diameter. Known methods for measuring nanoparticle diameter, average diameter, and size distribution can be used. For example, the average diameter of nanoparticles can be measured using light scattering and transmission electron microscopy (Carvalho, Patricia M., et al., "Application of light scattering technology to nanoparticle development. Chemistry 6 (2018): 237."), which includes routine statistical analysis using models such as the cumulant method (see

[35] ) for nanoparticles that do not all have the same size and / or geometric shape.

[0088] For example, about 5-40 wt% of nanoparticles may be assembled on the surface of the graphene oxide sheet through electrostatic and / or van der Waals interactions, where the wt% is expressed based on the total weight of the graphene oxide sheet and nanoparticles. For example, about 5-35 wt%, about 5-30 wt%, about 10-30 wt%, or about 20-30 wt% of nanoparticles may be used and assembled on the surface of the graphene oxide sheet through electrostatic and / or van der Waals interactions to form a GO-based porous composite membrane according to the present invention.

[0089] The nanoparticles may be carbonaceous nanoparticles (i.e., composed of carbon atoms). This is particularly advantageous due to the affinity of carbonaceous materials with graphene oxide. For example, the nanoparticles may comprise nanodiamonds. Nanodiamonds are carbon structures that can carry a positive charge and are therefore particularly suitable for reduction in order to practice the present invention. In this disclosure, nanodiamonds are referred to as "ND" to indicate the presence of a positive charge. + ". When nanodiamonds are prepared to carry an overall negative charge, they can be abbreviated as "ND- " is written as "ND + and N.D. - are commercially available, for example, in the form of a colloidal aqueous dispersion. For example, ND, which is commercially available under the trade name NanoAmando® + and N.D. - A colloidal aqueous dispersion can be used. Without wishing to be bound by any particular theory, nanodiamonds (NDs) characterized by an sp3 / sp2 core / shell structure and a positive surface charge are + ) enhances the water stability of GO films by reducing the electrostatic repulsion between hydrated GO sheets, thereby suppressing random re-stacking and aggregation of GO sheets in the presence of moisture and strengthening the overall film structure.

[0090] Generally, nanodiamonds as used herein can be formed by the detonation reaction of graphite and can be formed into fine nanoparticles having a size of about 3-10 nm, e.g., about 3-5 nm, e.g., about 3 nm or about 4 nm.

[0091] The porous GO-based composite membrane of the present invention may have a thickness in the range of, for example, 20 to 200 nm, or 25 to 150 nm, or 30 to 120 nm.

[0092] The porous GO-based composite membranes according to the present invention exhibit particularly advantageous properties with respect to water stability, resistance to water swelling, mechanical strength, and separation performance.

[0093] Porous GO-based composite films according to the present invention typically exhibit H permeabilities of, for example, >1300 GPU, or ≥1800 GPU, or ≥2400 GPU, or ≥3500 GPU when measured at 25±3° C. under dry conditions with a film thickness of 30-120 nm. As used herein, "dry conditions" understands a relative humidity in the range of less than 20% RH and atmospheric pressure.

[0094] The porous GO-based composite membrane of the present invention exhibits an ideal gas selectivity α when measured under dry conditions with a membrane thickness in the range of 30 to 120 nm at 25±3°C and a continuous supply of an equimolar H2 / CO2 mixture. H2 / CO2 It may show >200.

[0095] The porous GO-based composite films of the present invention may exhibit, for example, an H permeability of >750 GPU, or >1300 GPU, or ≥1800 GPU, or ≥2000 GPU, or ≥2400 GPU, or ≥3300 GPU when measured in a continuous supply of an equimolar H / CO mixture at 25±3°C under 85% relative humidity conditions with a film thickness in the range of 30-120 nm.

[0096] The porous GO-based composite films of the present invention may exhibit, for example, ≥2x, or ≥3x, or ≥4x, or ≥5x, or ≥6x, or ≥7x H permeability compared to a pure graphene oxide film of equal thickness (0% nanoparticles by weight) when measured under a continuous supply of an equimolar H / CO mixture at 25±3°C under 85% relative humidity conditions with film thicknesses ranging from 30-120 nm.

[0097] The porous GO-based composite membranes of the present invention, when measured at 25±3°C under humidity conditions of 85% relative humidity with a membrane thickness in the range of 30-120 nm and with a continuous supply of an equimolar H2 / CO2 mixture, may exhibit an H2 permeability of, for example, ≥60%, or ≥65%, or ≥70%, or ≥75%, or ≥80%, or ≥85%, or ≥90%, or ≥95%, compared to the H2 permeability of membranes measured under conditions of the same temperature, membrane thickness, and equimolar H2 / CO2 mixture.

[0098] The porous GO-based composite membranes of the present invention, when measured at 25±3°C under humidity conditions of 85% relative humidity with a membrane thickness in the range of 30 to 120 nm and with a continuous supply of an equimolar H2 / CO2 mixture, exhibit a H2 / CO2 selectivity (α) of, for example, ≥ 50%, or ≥ 60%, or ≥ 70%, or ≥ 80%, or ≥ 90%, compared to the H2 / CO2 selectivity of membranes measured under conditions of the same temperature, same membrane thickness, and same equimolar H2 / CO2 mixture. H2 / CO2) can be shown.

[0099] The porous GO-based composite films of the present invention can exhibit hardness, for example, of ≥ 610 MPa, or ≥ 630 MPa, or ≥ 650 MPa, or ≥ 670 MPa, or ≥ 690 MPa, or ≥ 700 MPa, or ≥ 710 MPa, when measured using nanoindentation with a Berkovich three-sided pyramidal diamond tip (100 nm radius) at 25 ± 3 °C under a load of 0.05 mN, with the measurement error reported based on a standard error of 20 indentations.

[0100] The porous GO-based composite membranes of the present invention can exhibit a Young's modulus (Young's modulus) of, for example, ≥ 15 GPa, or ≥ 16 GPa, or ≥ 17 GPa, or ≥ 18 GPa, or ≥ 19 GPa, or ≥ 20 GPa; or ≥ 21 GPa, when measured using nanoindentation with a Berkovich three-sided pyramidal diamond tip (100 nm radius) at 25 ± 3 °C under a load of 0.05 mN, with the measurement error reported based on the standard error of 20 indentations.

[0101] As noted above, the porous composite membranes of the present invention can find use in any application in which porous GO-based membranes find use. An application of particular interest is gas separation, particularly H2 separation from gas mixtures. Thus, in any of the variations described herein, the porous GO-based composite membranes of the present invention can be GO-based composite hydrogen membranes, particularly water-resistant GO-based composite hydrogen membranes.

[0102] Preparation of composite membranes

[0103] In another aspect, the present invention provides a method for producing a porous composite membrane according to the present invention, the method comprising: (i) providing a dispersion of graphene oxide sheets, e.g., single-layer graphene oxide sheets, in an aqueous solvent; (ii) providing a dispersion of nanoparticles in an aqueous solvent; (iii) mixing the graphene oxide dispersion and the nanoparticle dispersion to prepare a dispersion of graphene oxide-nanoparticle composites; (iv) filtering the dispersion obtained in step (iii) through a porous support substrate to produce a substrate-supported graphene oxide-nanoparticle composite film.

[0104] Fabrication of graphene oxide-nanoparticle composite films supported on porous membranes can also be achieved using spray coating, casting, dip coating techniques, load coating, inject printing, or any other thin film coating technique.

[0105] The aqueous solvents in steps (i) and (ii) may be the same or different. The aqueous solvents in steps (i) and (ii) may each independently comprise water or an alcohol / water mixture, e.g., water. The alcohol may comprise methanol, ethanol, isopropanol, 1-butanol, tert-butanol, ethylene glycol, etc., or a mixture of two or more thereof. The aqueous solvents in steps (i) and (ii) may be the same aqueous solvent, selected from water or an alcohol / water mixture, e.g., water. For example, the aqueous solvent in steps (i) and (ii) is water at a pH of 6-7.

[0106] Step (i) may include any method known in the art for dispersing graphene oxide. For example, step (i) may include sonicating a dispersion of graphene oxide in an aqueous solvent, where the aqueous solvent is as defined in any variation herein.

[0107] Similarly, step (ii) can include any method known in the art for dispersing nanoparticles, including carbonaceous nanoparticles such as nanodiamonds. Such methods can include, for example, bath ultrasonic dispersion, ultrasonic probe dispersion, ultrasonic agitation, high speed homogenizer, or high pressure homogenizer.

[0108] The method for producing a porous composite membrane according to the present invention may further comprise the step of drying the substrate-supported graphene oxide-nanoparticle composite membrane obtained in step (iv). For example, this can be carried out under vacuum at a temperature of about 50-70°C to remove excess aqueous solvent.

[0109] The dispersion of step (iii) may contain nanoparticles in an amount of, for example, about 5-40 wt %, or about 5-35 wt %, or about 5-30 wt %, or about 10-30 wt %, or about 20-30 wt %, where wt % is expressed based on the total weight of the graphene oxide sheets plus nanoparticles.

[0110] Gas Separation Systems and Processes

[0111] As mentioned above, the porous composite membranes of the present invention can be used in any application where GO-based membranes are used. A particular area of ​​interest is gas separation, particularly H2 separation from gas mixtures. Thus, in any of the variations described herein, the GO-based composite membranes of the present invention can be GO-based composite hydrogen membranes, particularly water-resistant GO-based composite hydrogen membranes.

[0112] Thus, in another aspect, the present invention provides a gas separation system comprising a porous composite membrane of the present invention in fluid communication with a gas stream comprising at least two separable gas mixtures comprising H2, the porous composite membrane comprising: - a graphene oxide sheet, and - nanoparticles bound to the surface of graphene oxide sheets solely by electrostatic and / or van der Waals interactions;

[0113] In the gas separation system according to the present invention, the porous composite membrane may be disposed on a porous support substrate. The porous support substrate may be any suitable support substrate. The porous support substrate may be a woven fabric material or a porous membrane.

[0114] For example, if present, the porous support substrate material may be an inorganic material. Thus, the porous material (e.g., the porous support substrate) may comprise a ceramic. For example, the porous support substrate material may be alumina, zeolite, or silica.

[0115] If present, the porous support substrate material may be a polymer material. Thus, the porous support substrate material may be a porous polymer support, for example, a flexible porous polymer support. The porous material (e.g., the porous support substrate) may comprise a polymer. The polymer may comprise a synthetic polymer.

[0116] For example, the porous support substrate may comprise a ceramic or polymeric porous support, including porous ceramic materials such as alumina-based or silica-based porous ceramics, and hydrophilic polymeric materials such as polysulfone (PS), polyethersulfone (PES), polyvinylidene fluoride (PVDF), or polyacrylonitrile.

[0117] If present, the porous support substrate may have a thickness of tens of microns or less, may be less than about 1 mm thick, or may be less than about 100 microns thick. For example, the porous support substrate may have a thickness of 50 microns or less, or 10 microns or less. In exemplary embodiments, the thickness may be greater than about 1 micron, although in some cases the thickness may be less than about 1 micron.

[0118] The porous support substrate should be sufficiently porous so as not to hinder the movement / permeation of solutes, but should have pores small enough so that the graphene oxide sheets cannot enter the pores. For example, the pore size may be less than 1 μm, e.g., less than 500 nm or less than 200 nm. Typically, the pore size is greater than 1 nm, e.g., greater than 10 nm.

[0119] Gas separation systems according to the present invention can include porous composite membranes, as generally defined herein and in various variations. For example, a porous composite membrane can include multiple stacked graphene oxide sheets, and nanoparticles can be intercalated between the stacked graphene oxide sheets. Gas separation systems according to the present invention featuring stacked GO sheets can be configured to allow molecules such as H2 gas to flow through the nanochannels between the GO layers, while rejecting undesired solutes by size exclusion and / or charge effects.

[0120] A gas separation system according to the present invention may comprise a porous composite membrane having a hardness of, for example, ≥ 610 MPa, or ≥ 630 MPa, or ≥ 650 MPa, or ≥ 670 MPa, or ≥ 690 MPa, or ≥ 700 MPa, or ≥ 710 MPa, when measured using nanoindentation at 25 ± 3°C with a Berkovich three-sided pyramidal diamond tip (100 nm radius) under a load of 0.05 mN.

[0121] A gas separation system according to the present invention may comprise a porous composite membrane having a Young's modulus of, for example, ≥ 15 GPa, or ≥ 16 GPa, or ≥ 17 GPa, or ≥ 18 GPa, or ≥ 19 GPa, or ≥ 20 GPa, or ≥ 21 GPa, when measured using nanoindentation at 25 ± 3 °C with a Berkovich three-sided pyramidal diamond tip (100 nm radius) under a load of 0.05 mN.

[0122] A gas separation system according to the present invention can comprise multiple GO-based composite membranes according to the present invention, which may be arranged in parallel (to increase the flux capacity of the process / device) or in series.

[0123] The gas separation system may be, for example, the system shown in Figure 19. A gas separation system according to the present invention may include: a separation unit having an inlet, a circulating component outlet (retentate component outlet) and a permeate component outlet; - a gas stream comprising at least two separable gas mixtures containing at least H2, the gas stream being in fluid communication with an inlet of the separation unit; - at least one porous composite membrane according to the invention as defined herein generally and in the variants, configured in the separation unit such that only the permeate component can flow from the inlet to the permeate component outlet after first passing through the porous composite membrane, and the circulating component flows from the inlet to the circulating component outlet without passing through the porous composite membrane; - a circulating component collector in fluid communication with the circulating component outlet of the separation unit; and - a permeate collector in fluid communication with the permeate outlet of the separation unit.

[0124] As mentioned above, the GO-based composite membranes according to the present invention can find use as H separation membranes. Thus, the gas separation system according to the present invention can be used with gas mixtures of at least two separable gases, including at least H.

[0125] In another aspect, the present invention provides a method for separating H from a gas stream, comprising passing at least two separable gas mixtures through a porous composite membrane of the present invention, wherein said gas mixture contains at least H.

[0126] The porous composite membranes of the present invention are suitable for separating H from any gas mixture containing hydrogen gas. For example, the composite membranes of the present invention can be used to separate H gas from H / CO, H / ammonia, H / O, H / N, H / CH, or H / CHCH mixtures. For example, the gas stream can be natural gas. The use of the porous composite membranes of the present invention in separating H from H / O gas mixtures is particularly interesting because O and H are produced by the electrolysis of water. Reduced swelling in water In yet another aspect, the present invention relates to a process for reducing water swelling in graphene oxide-based hydrogen membranes, the process comprising bonding nanoparticles and graphene oxide sheets comprising the graphene oxide-based hydrogen membrane electrostatically and / or by van der Waals bonding interactions. --------------------------

[0127] All of the above-mentioned variations, particularly the various elements that make up the GO-based composite membranes of the present invention, are understood to apply mutatis mutandis to the above sections on "Manufacture of Composite Membranes," "Gas Separation Processes and Systems," and "Processes for Reducing Water Swelling," and to the compositions / methods / processes / systems / applications defined in this disclosure. This includes all variations described in the "Detailed Description of Certain Preferred Embodiments of the Invention" section herein, including descriptions of a) graphene oxide, b) nanoparticles, c) nanodiamonds, d) membrane separation properties (e.g., permeability, gas selectivity), and e) membrane mechanical properties (e.g., hardness, Young's modulus), all of which apply mutatis mutandis to the compositions / methods / processes / systems / applications defined in this disclosure, including the above sections on "Manufacture of Composite Membranes," "Gas Separation Processes and Systems," and "Processes for Reducing Water Swelling."

[0128] equivalent

[0129] The following representative examples are intended to help illustrate the invention and are not intended to, and should not be construed as, limiting the scope of the invention. Indeed, various modifications and many further embodiments of the invention, in addition to those shown and described herein, will become apparent to those skilled in the art from the entire contents of this document, including the examples below and reference to the scientific and patent literature cited herein. Moreover, it should be understood that the contents of these references are incorporated herein by reference to help illustrate the state of the art.

[0130] The following examples contain important additional information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and the equivalents thereof. [Example]

[0131] Example

[0132] The composite membranes and methods for making composite membranes of the present invention can be further understood by the examples which illustrate some of the ways in which these composite materials may be made or used. However, it will be understood that these examples do not limit the invention. Variations of the invention, whether now known or further developed, are considered to be within the scope of the invention, as described herein and claimed below.

[0133] Abbreviation

[0134] GO: graphene oxide

[0135] ND: Nanodiamond

[0136] ND + : Positively charged nanodiamonds

[0137] ND - :Negatively charged nanodiamonds

[0138] POSS - : Octa(tetramethylammonium) functionalized polyhedral oligomeric silsesquioxane, negatively charged.

[0139] POSS + : Octa(tetramethylammonium) functionalized polyhedral oligomeric silsesquioxane, positively charged.

[0140] GOαND + Film: GO-nanodiamond composite film according to the present invention, α is the ND in the composite film + It represents the weight concentration of particles.

[0141] GOαND - Membrane: GO-ND - Composite membrane, α is ND in the composite membrane - It represents the weight concentration of particles.

[0142] GOαPOSS - Membrane: GO-POSS - composite film, α represents the weight concentration of negatively charged polyhedral oligomeric silsesquioxane particles in the composite film.

[0143] GOαPOSS + Membrane: GO-POSS of the present invention + composite film, α represents the weight concentration of positively charged polyhedral oligomeric silsesquioxane particles in the composite film.

[0144] material

[0145] Graphite powder was obtained from Qingdao Nanshu Graphite Co., Ltd.

[0146] Aqueous colloidal solutions of positively and negatively charged nanodiamond (ND) particles with an average size of 3.8±0.7 nm (2.5 wt %) in water, "NanoAmando®", were obtained from Nano Carbon Research Institute Co., Ltd. (Japan), respectively.

[0147] C 32 H 96 N8O 20 Si8 (negatively charged) and C 24 H 72 Cl8N8O 12 Octa(tetramethylammonium)-functionalized and octa(ammonium)-functionalized water-soluble polyhedral oligomeric silsesquioxane (POSS) particles with the formula Si8 (positively charged) were obtained from Hybrid Plastics, Inc. (Hattiesburg, US), respectively.

[0148] 10 mL of the GO dispersion, ND dispersion, and POSS dispersion were freeze-dried, and the concentrations of the original dispersions were precisely measured using an ultramicrobalance.

[0149] characteristics

[0150] 4000~600cm -1 The as-prepared films were characterized by FTIR spectroscopy (Shimadzu IRTracer-100 spectrometer, Japan) in the λ range. X-ray diffraction (XRD) patterns were obtained using BL02B2 at SPring-8 (λ = 0.999190 Å) at the Japan Synchrotron Radiation Research Institute (JASRI). The crystalline structure of the films was determined by wide-angle XRD analysis (Rigaku Smartlab). Using a CuKα anode, the samples were scanned at a rate of 10° / min over the 2θ range of 4–40° at a voltage of 40 kV and a current of 200 mA. X-ray photoelectron spectroscopy (XPS) measurements were performed using an X-ray photoelectron spectrometer (ESCA-3400, Shimadzu). To correct for the chemical shift of each element, the binding energy of the impurity carbon (1s) peak (C1s peak) was adjusted to 284.6 eV. Raman microspectroscopy was performed using a 532 nm excitation laser at 20–25 mV (Horiba, XploRa, Japan).

[0151] The morphology of the films was observed by field emission scanning electron microscopy (FESEM, Hitachi S-4800). Transmission electron microscopy (TEM) images were collected on a JEOL JEM 1400 plus (120 kV) and JEM-2200FS setup (JEOL) (200 kV). The samples were freeze-fractured in liquid nitrogen and briefly sputter-coated with osmium to prevent electron charging. The morphology of the GO-based films was measured by atomic force microscopy (AFM, NanoWizard III, JPK Instruments, Japan) in tapping mode.

[0152] SEM and AFM measurements were also performed to measure the horizontal (plane) size and thickness of the GO nanosheets.

[0153] The particle size distribution and zeta potential value of the membrane precursor were measured using a Malvern Zetasizer Nano instrument (Malvern Panalytical).

[0154] The H2 / CO2 and N2 adsorption isotherms of the membranes were recorded at 298 K or 77 K up to 1 bar using a BELSORP-Max (BEL Japan). The samples were subjected to dynamic vacuum (10 -5 The mixture was degassed offline at 80°C under 10 bar for 24 hours.

[0155] Young's modulus (E) and indentation hardness (H) were measured at room temperature using a nanoindenter tester (ENT2100, Elionix) equipped with a Berkovich three-sided pyramidal diamond tip (100 nm radius) under a load of 0.05 mN. The as-prepared or hydrophilic films (and air-dried films) were investigated for PM0.3 removal rates using a handheld particle counter KC-51 (Rion). Removal rates were calculated based on the average of three separate measurements for various film samples.

[0156] Gas Permeation Test

[0157] Gas permeability measurements were performed using a homemade membrane permeation / separation setup (Figure 19). Membrane gas permeability measurements were performed at atmospheric pressure using a Wicke-Kallenbach cell (Figure 19). To avoid damage to the selective layer, the edges of the membrane disk were covered with aluminum tape pre-coated with rubber pads before starting the measurements. For single-gas and mixed-gas measurements, the volumetric flow rates of the feed gas were maintained at 50 mL / min and 100 mL / min, respectively, using a digital mass flow controller (Horiba, Japan). A constant volumetric flow rate of 50 mL / min of argon was used as a sweep gas to eliminate concentration polarization on the permeate side. To avoid physical damage to the GO-based membrane, the membrane surface was covered with airtight tape before the gas permeation test (pore size ∼6 mm). The pressure gradient between the feed and permeate sides of the membrane was negligible.

[0158] For the hydration gas permeation test, an equimolar H2 / CO2 mixture was passed through a gas bubbler and humidity sensor placed in front of the permeation cell and filled with saturated solutions of LiCl (12% RH), MgCl2 (33% RH), NaCl (75% RH), and water (85% RH). For the simulated water splitting test, a flow rate of 90 mL min-1 was used. -1 A mixture of H2:O2 (2:1) was passed through a water bubbler (85% RH) beforehand and passed through the permeation cell. The gas permeation behavior of the membrane at various temperatures was investigated in a temperature-controlled chamber. The membrane was maintained at each temperature for at least 3 hours. The composition of the permeated gas was analyzed using a calibrated gas chromatograph (Shimadzu GC-2014).

[0159] The gas permeability (Pi, GPU) was calculated using the following formula:

[0160]

number

[0161] where Ni is the permeation rate of component i, mol s -1 where Dpi is the transmembrane pressure difference Pa of component i, and A (m2) is the membrane area.

[0162] Ideal selectivity (αi / j) is defined as the permeability of gas "i" relative to the permeability of gas "j" and is given by:

[0163]

number

[0164] In the case of a mixed gas, the selectivity αi / j was defined as the molar ratio of the two components on the permeate side and the feed side.

[0165]

number

[0166] where x and y are the volume fractions of the corresponding components on the feed and permeate sides, respectively.

[0167] Example 1 - GO-ND + Composite membrane production

[0168] Synthesis of GO

[0169] Single-layer graphene oxide (GO) was prepared by a modified hammerhead method. Briefly, 1 g of graphite powder (mesh size 50, Qingdao Nanshu Graphite Co., Ltd.) was added to a 9:1 (v / v) mixture of concentrated H2SO4 / H3PO4 (120:14 mL) in an ice bath and stirred for 20 min. Next, 6 g of KMnO4 was gradually added to the reaction medium, and the mixture was stirred at 50 °C for 4 h, 8 h, and 24 h for large GO (LGO), (medium) GO, and small GO (SGO), respectively. The reaction mixture was cooled to room temperature and slowly poured into 150 mL of cold water (0–2 °C). Subsequently, 2 mL of 30% HO2 was added dropwise until the solution turned pale yellow. The product was filtered using 10% aqueous HCl (750 mL) and thoroughly washed with distilled water until the pH value reached 6–7.

[0170] 10 mL of the GO dispersion was freeze-dried, and the concentration of the original dispersion was precisely measured using an ultramicrobalance.

[0171] Membrane preparation

[0172] The as-prepared hammerhead product was sonicated (Branson 1510E-MT) at 40 W for 1 hour to exfoliate the GO sheets. Following sonication, the resulting dispersion was centrifuged twice at 5,000 rpm (30 minutes each) to remove large, unexfoliated flakes. The supernatant was then centrifuged at 10,000 rpm for 40 minutes to remove small GO flakes, yielding a GO dispersion. Unexfoliated particles were removed from the LGO dispersion by a 3-minute ultrasonic bath treatment, followed by 20 minutes of centrifugation at 3,000 rpm. Centrifugation at 5,000 rpm for 30 minutes was then repeated, and the precipitate was collected. For SGO, 4 hours of sonication and 1 hour of 10,000 rpm were performed, and the supernatant was collected. To obtain uniform membranes, a predetermined amount of GO dispersion was pre-diluted to 0.001 mg / mL and then passed through an anodized aluminum oxide (AAO) filter (pore size: 20 nm, diameter: 25 mm, Whatman) or polyethersulfone (PES, pore size: 30 nm, diameter: 25 mm, Sterlitech) by vacuum filtration (GCD-051X, ULVAC vacuum pump) at a vacuum pressure of 10 Pa. The as-prepared ND positively charged + The dispersion was centrifuged at 10,000 rpm for 1 hour to remove aggregates. + The suspension (5–35 wt%) was added to the diluted GO dispersion and stirred for 10 min. The composite GOαND was then isolated by vacuum filtration. + Immediately before film deposition, the obtained GO-ND + The dispersion was subjected to a mild ultrasonic bath treatment at 23 W for 10 min. The total mass of GO and GOαND was kept the same for all samples (0.03 mg). The resulting membranes were dried under vacuum at 60 °C for 24 h to remove residual water before further characterization. For PM0.3 removal, the GO-based membranes (total mass: ~0.01 mg) were vacuum filtered onto a polyethersulfone substrate (100 kDa, diameter: 25 mm, Synder).

[0173] Comparative Example 2 For comparison, a certain amount of negatively charged POSS particles was first dispersed in water and ultrasonicated for 5 hours. - A membrane was prepared.

[0174] Comparative Example 3 For comparison, negatively charged ND (ND - Example 1 was re-run using the 2000-kJ / kg 2000 k ...

[0175] Example 4 For comparison, Comparative Example 2 was re-run with positively charged POSS particles.

[0176] result

[0177] GO membranes were prepared on both ceramic and polymer supports by applying a common vacuum filtration method to dispersions of single-layer GO sheets (Figure 1B-1, Figure 2). (Note: The in-plane size of GO sheets plays an important role in controlling the 2D channels for selective gas molecule transport.) The average in-plane size of GO sheets was obtained by scanning electron microscopy (SEM) imaging. To prepare SEM samples, a 1 μg / mL GO dispersion was dropped onto the surface of an AAO wafer and air-dried for 24 hours. The in-plane size of GO sheets was calculated from the average size of over 120 sheets, as shown in Figure 2.

[0178] Before vacuum filtration, the GO dispersion was treated with 3 nm NDs. + ND to the membrane by adding + (Fig. 3). - ), and positive charge (POSS + ) and negative charge (POSS - Polyhedral oligomeric silsesquioxane (POSS) nanoparticles with a high loading ratio (i.e., 30 wt. % of ND) were also used as comparative fillers (Figure 4). + Filling) and ND +The GOαND films were finely dispersed on the isolated GO surface (Fig. 1C, Fig. 20, and related notes), with an average particle-to-particle distance of approximately 10 nm (Fig. 1D). + where α (α = 5, 10, 20, 30, and 35) is the ND based on the total mass of the film. + The scanning electron microscope (SEM) and atomic force microscope (AFM) images of the GO-only film (Figures 1F, 1G, and Figures 5-7) showed a smooth surface without visible defects. However, the surface roughness of the composite film was significantly higher than that of the ND film. + It increased with the addition of particles (Fig. 1H, Fig. 6, and Fig. 7, and Table 1).

[0179] [Table 1]

[0180] H 2 Transmittance

[0181] Pristine GO membranes fabricated on ceramic supports were found to perform similarly to or slightly better than those reported in the literature, with initial H permeability of approximately 1150 GPU and ideal gas selectivity for CO of ~282 (Tables 2 and 3). However, when exposed to a water-saturated equimolar mixed gas feed, GO membrane performance dramatically deteriorated over a 100-hour test at room temperature. Permeability and selectivity decreased by 55% and 70%, respectively (Figures 1J-K and 8). In contrast, GO30ND + exhibited three times the level of H permeability (up to 3741 GPU) of the pristine GO membrane, with a relatively small decrease in ideal gas selectivity (α H2 / CO2 However, the most striking feature is that when extensively tested with a wet gas feed, GO30ND + The decrease in membrane permeability and selectivity was only ∼5% and ∼10%, respectively.

[0182] [Table 2] a. Gas permeability was determined based on the average of three separate measurements of various membrane samples. GPU is the gas permeability unit, 1 GPU = 3.35 x 10 -10 mol m -2 s -1 Pa -1 .

[0183] [Table 3] a. Ideal gas selectivity data was determined based on the average of three separate measurements of various membrane samples.

[0184] The result was ND. + It was shown that this could stabilize the performance of GO-based membranes.

[0185] Composite film morphology - GO / ND + interaction

[0186] ND + The interaction between the GO sheets and the cellulose acetate was investigated in detail.

[0187] ND + The particles are positively charged (+45 mV), whereas the GO sheets carry a net negative charge (-48 mV) at pH = 7 (Figure 9A), which allows ND to attach to the GO structure via strong electrostatic interactions. + This allows for proper assembly of ND + The results showed that the lamination properties of the GO laminates were changed, but the composite films were formed by electrostatic interactions and the interaction between the GO sheets and the ND. + The particles remained intact due to hydrogen bonds between them. + The hydrogen bonding in the film is verified by the significant bond peak shift in the FTIR spectrum (Figure 10). X-ray photoelectron spectroscopy (XPS) spectra of C1s and N1s reveal that ND in the GO mixture + The presence of was confirmed (see Figure 11 and Table 4).

[0188] [Table 4]

[0189] GO samples and GOαNDs + X-ray diffraction of the sample was particularly clear. The sharp peak of the GO film at 2θ = 6.15° suggests highly ordered stacking of GO stacks with a d-spacing of 0.93 nm (Figure 9B). The intensity of the peak was ND + The GO stacking order was disrupted by the introduction of ND. + The addition of GO30ND slightly shifted the peak, and the corresponding d-spacing was + The film reached 0.89 nm. + Particles or POSS + The combination of nanoparticles and GO induces a charge compensation effect (Figure 9A), which contributes to a decrease in the d-spacing in the resulting GO stacks due to the weakening of the interlayer electrostatic repulsion (Figure 9B). + The bending of the flexible GO sheets due to the incorporation of particles leads to a narrower interlayer spacing (Figure 9E). In addition to the XRD peak intensity, the peak width can also be correlated with the size of the GO stacks. Positively charged ND particles (ND + When ND penetrated between the GO stacks, the negative charge effect was reduced (Figure 9A), the interlayer electrostatic repulsion weakened, and the channel size narrowed. In addition to the XRD peak intensity, the peak width can also be correlated with the size of the GO stacks. The average crystallite width and the number of GO layers in each stack are inversely proportional to the width of the diffraction peak according to the Debye-Scherer equation (Note: Table 5). A significant decrease in GO crystallite size was observed when ND + This was observed with increasing GO content (Table 5), which reflects the breakdown of the laminated GO stacks and the formation of more grain boundaries within the composite film. + The disruption of GO stacks by the addition of particles was shown (Fig. 12). The functional groups on the surface of GO are responsible for the formation of a good, compact structure, whereas the spherical NDs in solution are not. + The presence of particles prevents the individual GO sheets from stacking again (Figure 12).

[0190] [Table 5] Note: Table 5. X-ray diffraction of GO / ND composites provides quantitative insight into the average layer spacing and number of GO layers (number of layers and average width) per well-stacked domain, as well as useful information about the crystallite size in the composite. d-spacing (1), crystallite width (2), and stacking (3) were calculated using the following equations: The X-ray diffraction peaks of GO-based films correspond to the interlayer spacing of GO sheet stacks and can be calculated using the Bragg equation.

[0191] Bragg's law: d=λ / 2sin(θ) (1) where θ is half the diffraction angle and λ is the wavelength of the X-ray source.

[0192] The peak width of the GO-based films reflects the average size of the GO domains (crystallites) in each sample, which separate at grain boundaries and large lattice defects. Using the Debye-Scherer equation, the average crystalline width (D) of the GO domains can be determined.

[0193] D=0.89λ / βcos(θ) (2) where D is the crystallite width and β is the full width at half maximum (FWHM) of the diffraction peak in radians.

[0194] The average number of GO layers per domain (N) provides insight into the degree of re-stacking ability of GO nanosheets after incorporation of ND particles. A combination of the Bragg and Debye-Scherer equations (1) and (2) was used to calculate the average number of layers in GO stacks.

[0195] N=D / d+1 (3) where D and d are the crystallite width and interlayer spacing, respectively.

[0196] Mechanical properties of composite membranes

[0197] GOαND + It was also found that both the Young's modulus and hardness of the film were improved by ~25% compared to the pristine GO film (Figure 13). + The Young's modulus and hardness of the films were ≥ 15 GPa and ≥ 610 MPa, respectively. The improved mechanical properties are desirable for practical applications and long-term operation of the films. + This can be explained by a favorable interaction between

[0198] Gas Separation

[0199] Primarily, this section will focus on the separation of H2 and CO2. However, other industrially important hydrogen gas combinations (H2 / O2, H2 / N2, H2 / CH4, and H2 / C2H6) have been tested and performed equally well, as summarized in Tables 2 and 3 (see supra).

[0200] Gas diffusion in GO membranes occurs between the edges of adjacent sheets and the interlaminar channels. Therefore, not only the membrane thickness but also the planar dimensions of the GO sheets (Figure 2) are important for producing high-flux membranes. Increasing membrane thickness enhances the molecular sieving effect and increases selectivity. + When the overall ratio of GO to NH₂ remains unchanged, the effective permeability of all gases decreases in thicker membranes (Figure 9C). The H₂ permeability of the membrane with the thinnest platelet size (approximately 200 nm, Figure 2) is 60% and 240% higher than that of membranes with average sheet sizes of 3 μm and 10 μm, respectively. The higher tortuosity of the relatively large sheets reduces the gas diffusivity, but this more than doubles the selectivity of the membrane with the largest GO sheets, improving the sieving ability. Also, the ND + A membrane combining GOαND + ) A similar trend was observed (Tables 2 and 3).

[0201] The cross-section of the GO film in Figure 1G shows a highly packed morphology with a uniform thickness of approximately 38 ± 6 nm. + The addition of particles (30 wt%) increased the film thickness to 75 ± 8 nm (Figure 1I). + The thickness of GO and ND in the vacuum filtered solution + The initial concentration of GOαND is affected by this. While not wishing to be bound by any particular theory, it is believed that as the thickness increases, there is more free space between the packed GO stacks. With this in mind, we can reliably determine the selectivity of GOαND. + Report the membrane permeability with respect to the system thickness. + The addition of increasing amounts of particles significantly and controlled the gas permeability improvement, while the selectivity remained at the same level as the GO membrane, especially at low filler concentrations, i.e., up to 30 wt% (Fig. 9D - inset). + The H2 permeability of the membrane was observed to be ~3741 GPU (α H2 / CO2 = 212), an exceptional increase in permeability of ~300% was observed compared to the pure GO film (Fig. 9D and Tables 2 and 3). Without wishing to be bound by any particular theory, it is believed that the decrease in the number of GO layers and the shrinkage of the crystallite width of the GO stacks are responsible for the increase in permeability (Table 5). N2 adsorption tests show that the addition of 30 wt% ND + The addition of particles increased the pore volume to 0.036 cm for pure GO membranes. 3 / g to 0.17cm 3 / g, which enhances gas diffusion in the composite membrane (Figure 14A). + The increase in thickness of the GO film from 38±6 nm unfilled to 75±8 nm (Figures 1G and 1I) is evidence that the addition of fillers opens up the structure. In general, when compared across a wide range of inorganic materials, including silica, MOFs

[23] , COFs

[14] , and MXenes

[21] , GO30ND +The membrane exhibits both exceptional H permeability (>3700 GPU) and H / CO selectivity (>200) (Figure 9E and Table 6). In previous studies, the insertion of various particles into GO stacks induced higher permeability at the expense of a significant decrease in selectivity. However, we were able to achieve negligible selectivity loss while maintaining very high permeability.

[0202] [Table 6]

[0203] The gas separation properties of the membrane were evaluated under mixed gas feed conditions. When an equimolar H2 / CO2 feed mixture was used, the GO30ND + The H2 permeability and H2 / CO2 selectivity of the membrane decreased by 6% and 13%, respectively (Table 7, Figure 9H).

[0204] [Table 7]

[0205] The decrease in membrane permeability and selectivity under mixed gas conditions is generally attributed to the partial inhibition of H molecular transport by highly adsorbed CO molecules (Figure 14B-C). This is expected to be exacerbated by a high CO feed concentration. Thus, a 25% and 45% decrease in H permeability and selectivity is observed for a 20:80 H / CO feed mixture (Figure 9H). However, considering that the absolute permeability and selectivity of the membrane material are in the highest range, this loss in performance under more realistic conditions is acceptable. It is important to consider the temperature window over which a gas separation membrane can operate in various application scenarios. Therefore, we demonstrate that GO30ND exhibits excellent performance at high temperatures. +Membranes were tested. A general trend was observed in which higher gas permeabilities for both CO and H molecules were observed as the temperature increased. However, the H / CO selectivity tended to decrease, as the system favored CO flux due to a significant decrease in CO adsorption at higher temperatures (Figure 21). Nevertheless, these membranes were functional up to 80°C, as minimal changes in the spacing of the membrane interlayers were evident up to this temperature (Figure 22).

[0206] Stable against water, humidity and aerosols

[0207] ND against humidity + Compelling evidence for the stabilizing properties of GO30ND + This can be confirmed by immersion in water (Figure 15A), where relatively thick GO films (~200 nm) prepared over a relatively large area by vacuum filtration on a polyethersulfone support appear to collapse upon immersion in liquid water, whereas GO30ND + The film is stable for the same period. + A more stringent stability test of the stabilizing effect was also performed, demonstrating it by repeatedly exposing the membrane to wet and dry feeds of a H2 / CO2 mixture (relative humidity 85%) (Figure 15B). The pristine GO membrane failed to maintain its performance after one full cycle of exposure and became completely permeable to both gases. Interestingly, the membrane's performance further deteriorated upon exposure to a second dry gas feed, suggesting that significant and irreversible structural restructuring occurs in the presence of hygroscopic materials in both wet and dry environments. Structural disruption was confirmed based on changes in d-spacing values ​​(Figure 15C), delamination of the GO selective layer from the AAO (Figure 15E), and the appearance of blisters (protrusions) on the GO membrane surface under humid conditions (Figure 15F). On the other hand, GOαND +The membranes exhibited relatively large reversibility in membrane properties when exposed to wet and dry gases. The stability of the composite membranes was also evident by the preservation of interlayer spacing and overall membrane structure under humid conditions (Figures 15D and 23). Data presented in Figures 1J-K show membrane permeability at 85% relative humidity, ND + While the content enhances stability, the variation in membrane permeability and selectivity is directly related to humidity level (Figures 15G-H and 24). This quasi-reversible variation in membrane performance under cycling or constant humidity conditions is due to the ND + This suggests that the GO stacks within the membrane are non-covalently stabilized.

[0208] Inserted positive charge ND + The impact of

[0209] In the context of the present invention, in an exemplary embodiment, GO-based composite membranes were fabricated under neutral or near-neutral solution conditions (pH 6-7). Destabilization under wet conditions was minimized, likely due to the restricted movement of GO stacks caused by electrostatic repulsion between negatively charged GO sheets. + The effect of intercalating between GO stacks is to partially neutralize the negative charges of the GO sheets, thereby alleviating the strong repulsion of the GO layers.

[0210] To investigate the generalizability of the charge compensation effect, we investigated another type of positively charged particle, POSS. + As a negative control, ND - and POSS - GO films incorporating various loadings of POSS were also prepared (Figures 2F and 2G). - The addition of (-30 mV) was tested in Comparative Example 2. - The material was characterized in the same sequence (Figure 9A), and the results showed that it contained GO sheets and POSS, as confirmed by FTIR and WXRD data (Figure 16). -The interaction between the nanofillers and GOαPOSS was shown to be weak. - The mechanical properties of the composite films were found to be poor (Figure 13), which was associated with severe aggregation of particles within the GO framework (SEM images in Figure 17). + Unlike the composite membrane, GOαPOSS - The gas selectivity of the membrane was much lower than that of the pure GO membrane due to the formation of significant aggregation and nonselective interfacial defects (Tables 2 and 3). - The structure was found to exhibit unstable performance under humid gas feed or under continuous dehydration-hydration cycles in equimolar H2 / CO2 mixtures (Figures 8B and 18).

[0211] GOαPOSS - The results obtained with the membranes are consistent with previous reports of GO-based membranes in which foreign particles have been inserted into the GO sheets (e.g., MOF additives have been inserted into the GO system). The insertions consistently resulted in increased permeability but decreased selectivity (Figure 9D and Table 6). - The same is observed in Comparative Example 2 with the addition of filler.

[0212] This is the GOαND described in Example 1. + This is in stark contrast to the facts observed in the GOαND system according to the present invention. + The system's high performance is due to the positively charged ND + The concept becomes stronger that the degree of interaction of an additive can be correlated with the degree of chemical similarity with its surrounding environment.

[0213] The weak interaction between the negatively charged particles and the GO flakes was confirmed by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WXRD), and severe aggregation (Figures 16 and 17). - (Figure 13) The poor mechanical properties of POSS - This also suggests that there is no strong interaction between the GO layer and the GOαND. +Unlike membranes, GOαPOSS - and GOαND - The H2 / CO2 selectivity of ND significantly decreases to 30 and 74, respectively, under equimolar H2 / CO2 mixed feed (Figure 2G). Destabilization under humid conditions is minimized by restricting the movement of GO stacks due to electrostatic repulsion between negatively charged GO sheets. + and POSS + The insertion of particles into the GO stack partially neutralized the negative charge of the GO sheets, alleviating the strong repulsion of the layers (Figure 2A). The lack of electrostatic stabilization is responsible for the GOαPOSS - and GOαND - Due to the lack of a ionic surfactant in the system, these membranes showed inconsistent performance under humidified gas feed (Figure 15J) or under continuous drying-hydration cycling of equimolar H2 / CO2 mixtures (Figure 18). It has been reported that charged clays and other ions can be stabilized by thicker (18-20 μm) GO sheets against dissolution in water. In this study, positively charged NDs were found to be stable when membranes were fabricated under near-neutral solution conditions (pH 6-7). + The intercalation of between GO stacks partially neutralized the negative charges of the GO sheets and alleviated the strong repulsion of the layers.

[0214] Furthermore, the improvement of the water decomposition product (H2 / O2 mixture ~ 66% H2) resulted in GOαND + As shown in Figure 15I and Table 8, the application range of the GO30ND membrane was expanded. + The H2 / O2 selectivity of the membrane reached ~42 and remained unchanged over a series of wet / dry cycle measurements. Despite a higher H2 / O2 selectivity of ~84, the GO membrane became nonselective under one full cycle. Therefore, ND + The addition of GOαND is an effective strategy to overcome the instability of H-purified GO films caused by water splitting. Because water can exist in molecular or aerosol form, the resistance of the films to macroscale restructuring was confirmed by examining aerosol transport through films significantly aged by liquid exposure (Figure 15K). +The base material not only blocked PM0.3 aerosol particles with 99% efficiency but also demonstrated stability in the presence of water, whereas the PM0.3 removal rate for a GO membrane pretreated in water in an accelerated degradation test dropped to 40%.

[0215] [Table 8]

[0216] conclusion

[0217] In summary, the examples are based on the synthesis of positively charged nanodiamonds (ND + ) or POSS + We demonstrate the use of nanoparticles, which neutralize the negative charge of the stacked GO sheets and stabilize the resulting film against moisture. Pure GO films lost all sieving ability under forced humidity cycling tests, while GOαND + The composite membranes were found to retain up to about 90% of their stability under the same conditions. Specifically, the examples demonstrate the stability of GO-based membranes to adverse humid conditions while maintaining the membrane's overall high performance for H2 / CO2 separation. This is due to the sp3 / sp2 core / shell structure and positive surface charge, or POSS, charge. + Positively charged nanodiamonds (NDs) are characterized by nanoparticles. + This was achieved by the insertion of a positively charged ND + or POSS + The nanoparticles reduce the electrostatic repulsion between hydrated GO sheets, allowing stable and GO-compatible structures to intercalate between the GO stacks and strengthen the film structure, thereby suppressing random re-stacking and aggregation of GO sheets in the presence of moisture (Fig. 1A).

[0218] ND + The addition of POSS was shown to improve permeability by a factor of three (~3700 GPU) over the pure membrane, without dramatically affecting the overall hydrogen selectivity (e.g., αH / CO ~ 210) of the membrane. +The addition of nanoparticles also showed robust results.

[0219] In contrast, similarly sized but negatively charged nanodiamonds (ND - ) or polyhedral oligomeric silsesquioxanes (POSS - ) additives were found not to increase the swelling resistance of GO-based films.

[0220] Thus, this example demonstrates the benefit of adding positively charged nanoparticles, e.g., carbonaceous nanoparticles, to significantly improve the specific separation performance of the negatively charged GO membrane while stabilizing it against moisture and increased destabilization of the membrane's separation performance. + or POSS + This was demonstrated by nanoparticles.

[0221] All references throughout this application, e.g., patent documents, patent publications, and non-patent documents, including issued or granted patents or their equivalents, or other written sources, are incorporated by reference in their entirety, as if individually incorporated by reference, to the extent that each reference is at least partially consistent with the disclosure of this application (e.g., a partially conflicting reference is incorporated except for the partially conflicting portion of the reference).

[0222] All patents and publications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this invention pertains. The references cited herein are incorporated by reference to demonstrate the state of the art, and it is intended that this information may be used herein, if necessary, to exclude (e.g., disclaim) specific embodiments that fall within the prior art. For example, if a composition is claimed, it should be understood that compositions known in the prior art, including specific compositions disclosed in the documents disclosed herein, are not intended to be included in the claim.

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Claims

1. - a graphene oxide sheet; nanoparticles bound to the surface of said graphene oxide sheets solely by electrostatic and / or van der Waals interactions, The nanoparticles have a positive charge with a zeta potential of 30 mV or more at pH 7. Porous composite membrane.

2. 10. The porous composite membrane of claim 1, wherein the composite membrane comprises a plurality of stacked graphene oxide sheets, and the nanoparticles are intercalated between the stacks of the graphene oxide sheets.

3. 3. The porous composite membrane of claim 1, wherein the graphene oxide sheets have an average size in the plane of 200 nm to 15 μm.

4. 4. The porous composite membrane of claim 1, wherein the nanoparticles have an average diameter of 3 nm to 10 nm.

5. 5. The porous composite membrane of claim 1, wherein nanoparticles are assembled on the surface of the graphene oxide sheets by electrostatic and / or hydrogen bonding interactions in an amount of 5-40 wt. %, expressed based on the total weight of the graphene oxide sheets plus nanoparticles.

6. 6. The porous composite membrane of claim 1, wherein the nanoparticles comprise nanodiamonds.

7. 7. The porous composite membrane according to claim 2, wherein at least a portion of the interlayer distance between stacks of the graphene oxide sheets is 0.6 nm or less.

8. A method for producing the porous composite membrane according to any one of claims 1 to 7, comprising: (i) providing a dispersion of graphene oxide sheets in an aqueous solvent; (ii) providing a dispersion of nanoparticles in an aqueous solvent having a positive charge with a zeta potential of 30 mV or greater at pH 7; (iii) mixing the graphene oxide dispersion and the nanoparticle dispersion to prepare a graphene oxide nanoparticle composite dispersion; and (iv) filtering the dispersion obtained in step (iii) through a porous support substrate to produce a substrate-supported graphene oxide-nanoparticle composite film; A method for producing a porous composite membrane, comprising:

9. 9. The method according to claim 8, wherein the aqueous solvent in steps (i) and (ii) is one and the same aqueous solvent selected from water or an alcohol / water mixture.

10. 10. The method according to claim 8, wherein the aqueous solvent in steps (i) and (ii) is water at a pH of 6 to 7.

11. H ２ 1. A gas separation system comprising a porous composite membrane in fluid communication with a gas stream comprising at least two separable gas mixtures containing The porous composite membrane is - a graphene oxide sheet; nanoparticles bound to the surface of said graphene oxide sheets solely by electrostatic and / or van der Waals interactions, The nanoparticles have a positive charge with a zeta potential of 30 mV or more at pH 7. Gas separation system.

12. The gas separation system of claim 11 , wherein the porous composite membrane is disposed on a porous support substrate.

13. 13. The gas separation system of claim 12, wherein the porous support substrate comprises a ceramic or polymeric porous support substrate containing a porous ceramic material of an alumina-based or silica-based porous ceramic, and a hydrophilic polymer material of polysulfone (PS), polyethersulfone (PES), a fluoropolymer such as polyvinylidene fluoride (PVDF), or polyacrylonitrile.

14. 14. A gas separation system according to any one of claims 11 to 13, The porous composite membrane comprises: (i) a hardness of 610 MPa or greater, as measured by nanoindentation at 25±3°C using a Berkovich three-sided pyramidal diamond tip (100 nm radius) under a load of 0.05 mN, with the measurement error based on a standard error of 20 indentations; and (ii) a Young's modulus of 15 GPa or greater, as measured by nanoindentation at 25±3° C. using a Berkovich three-sided pyramidal diamond tip (100 nm radius) under a load of 0.05 mN, with the measurement error being based on a standard error of 20 indentations; Gas separation system.

15. 15. A gas separation system according to any one of claims 11 to 14, comprising: a separation unit having an inlet, a circulating component outlet, and a permeate component outlet; - At least H ２ a gas stream in fluid communication with the inlet of the separation unit, the gas stream comprising at least two separable gas mixtures containing at least one porous composite membrane according to claim 1 configured in said separation unit such that only a permeate component can flow from said inlet to said permeate component outlet after first passing through said porous composite membrane, and a circulating component can flow from said inlet to said circulating component outlet without passing through said porous composite membrane; a circulating component collector in fluid communication with the circulating component outlet of the separation unit; and a permeate collector in fluid communication with the permeate outlet of the separation unit.

16. 8. A method for producing a porous composite membrane comprising passing at least two separable gas mixtures through the porous composite membrane of claim 1, wherein the gas mixture comprises at least H ２ from a gas stream containing H ２ A method for separating

17. H in graphene oxide-based hydrogen membranes ２ 1. A process for reducing O-swell, comprising: Attaching positively charged nanoparticles with a zeta potential of 30 mV or more at pH 7 to the graphene oxide sheets constituting the graphene oxide-based hydrogen membrane by electrostatic and / or van der Waals interactions.

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