Preparation method of reduced graphene oxide separation membrane intercalated with heteropoly acid molecular clusters and application thereof

Abstract

This invention relates to the field of membrane separation technology, and discloses a method for preparing a reduced graphene oxide separation membrane intercalated with heteropolyacid molecular clusters and its application. The membrane comprises a substrate and a functional layer deposited on the substrate, wherein the functional layer is a reduced graphene oxide layer intercalated with heteropolyacid molecular clusters. A graphene oxide solution, a heteropolyacid solution, and isopropanol are mixed; the mixed solution is deposited on the surface of the substrate to form a film; the heteropolyacid-graphene oxide film is subjected to in-situ photoreduction to obtain a reduced graphene oxide composite membrane. This invention is the first to use heteropolyacid molecular clusters as intercalating agents. These clusters are uniform in size, structurally stable, and readily soluble in water. After being combined with graphene oxide, they can form uniform and ordered two-dimensional channels, which is crucial for the selective separation of the composite membrane. This invention effectively avoids the problems of poor mass transfer, poor separation, and easy swelling caused by particulate matter filling into two-dimensional materials.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a method for preparing a reduced graphene oxide separation membrane with intercalated heteropolyacid molecular clusters and its application. Background Technology

[0002] Water scarcity and security are among the greatest challenges of the 21st century. Seawater desalination is the most common method for addressing water scarcity, especially drinking water scarcity. To solve this challenge, there is an urgent need to develop low-cost, low-energy-consumption, environmentally friendly, and safe seawater desalination technologies to ensure a sustainable supply of clean water. Compared with traditional desalination technologies, membrane separation desalination technology has significant advantages: it requires less space than traditional adsorption methods; it has excellent separation efficiency and selectivity, resulting in higher water quality.

[0003] In this regard, carbon-based materials such as graphene oxide (GO), with its two-dimensional structure and tunable nanopores or nanochannels, have attracted considerable interest. Graphene oxide (GO) can form membranes exhibiting superpermeability and superselectivity. Furthermore, GO can be obtained from abundant natural graphite using simple methods, which is considered cost-effective.

[0004] During the fabrication of GO membranes, the compression between the layers leads to small interlayer gaps and low flux. Currently, the most common method to improve GO membranes is to intercalate carbon quantum dots, nanowires, or metal-organic frameworks to increase the interlayer spacing and thus improve water flux. However, directly doping these intercalating agents can introduce defects into the membrane, such as uneven intercalation, resulting in impaired mass transfer, poor porosity, poor separation, and easy swelling. Furthermore, GO membranes contain many oxygen-containing functional groups, which easily swell in water and exhibit poor stability. Therefore, reduction methods can be used to remove some of these oxygen-containing functional groups, improving membrane stability and swelling resistance. However, reduction reduces the interlayer spacing, leading to a decrease in flux.

[0005] There is a lack of membrane structures in the current technology that have a high ion rejection rate, allow water to quickly permeate through the interlayer channels during the filtration process, and are resistant to swelling. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and to provide a method for preparing a reduced graphene oxide separation membrane with intercalation of heteropolyacid molecular clusters and its application.

[0007] To achieve the above objectives, the first aspect of the present invention provides a reduced graphene oxide composite film, the composite film comprising a substrate and a functional layer deposited on the substrate, wherein the functional layer is a reduced graphene oxide layer intercalated with heteropolyacid molecular clusters.

[0008] A second aspect of the present invention provides a method for preparing a reduced graphene oxide composite film according to the first aspect, the method comprising the following steps:

[0009] (1) Mix the graphene oxide solution, the heteropolyacid solution and isopropanol;

[0010] (2) The mixed solution obtained in step (1) is deposited on the surface of the substrate to form a film, thereby obtaining a heteropolyacid-graphene oxide film;

[0011] (3) The heteropolyacid-graphene oxide film obtained in step (2) is subjected to in-situ photoreduction to obtain a reduced graphene oxide composite film.

[0012] A third aspect of the present invention provides a reduced graphene oxide composite film prepared according to the preparation method described in the second aspect.

[0013] The fourth aspect of the present invention provides the application of the reduced graphene oxide composite membrane according to the first or third aspect in ion permeation.

[0014] The fifth aspect of the present invention provides an ion permeation device comprising the reduced graphene oxide composite membrane described in the first or third aspect.

[0015] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0016] (1) This invention is the first to use heteropolyacid molecular clusters as intercalating agents. These clusters are uniform in size, structurally stable, and readily soluble in water. When combined with graphene oxide, they can form uniform and ordered two-dimensional channels, which is crucial for the selective separation of the composite membrane. This invention effectively avoids the problems of poor mass transfer, poor separation, and easy swelling caused by the defects brought about by particulate matter filling into two-dimensional materials.

[0017] (2) Under photocatalysis, a reduced graphene oxide layer with intercalated heteropolyacid molecular clusters can be prepared. Due to hydrogen bonding and van der Waals interactions, there is a strong attraction between the heteropolyacid molecular clusters and the reduced graphene oxide. The two combine to form a heteropolyacid molecular cluster / reduced graphene oxide composite, and the prepared film has good stability.

[0018] (3) The composite membrane provided by the present invention has a high ion rejection rate, can allow water to quickly permeate through the interlayer channels during the filtration process, and has high selectivity and anti-swelling properties.

[0019] (4) The preparation method provided by the present invention is green and environmentally friendly, and simple to operate. The prepared reduced graphene oxide composite membrane can be used for ion separation and seawater desalination, and has broad application prospects. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation method described in this invention;

[0021] Figure 2 This is the rGO-PW prepared in Example 4 of the present invention. 12 SEM image of the membrane;

[0022] Figure 3 This is the rGO-PW prepared in Example 4 of the present invention. 12 Optical photograph of the membrane;

[0023] Figure 4 This is the rGO-PW prepared in Example 4 of the present invention. 12 Raman diagram of the membrane;

[0024] Figure 5 This is the rGO-PW prepared in Example 4 of the present invention. 12 HETEM image of the membrane;

[0025] Figure 6 It is a U-shaped permeameter used in ion permeation testing;

[0026] Figure 7 This is the rGO-PW prepared in Example 4 of the present invention. 12 Comparison of the permeation rates of the membrane and the GO membrane prepared in Comparative Example 1 for different salt solutions; where (A) the horizontal axis represents the type of salt; (B) the horizontal axis represents the hydration radius of the cation;

[0027] Figure 8 The rGO-PW prepared in Examples 4-8 of this invention 12 Comparison of membrane permeation rates to NaCl and MgCl2 salt solutions;

[0028] Figure 9 The rGO-PW prepared in Examples 1-4 of this invention 12 Comparison of membrane permeation rates to NaCl and MgCl2 salt solutions;

[0029] Figure 10 The rGO-PW prepared in Examples 1-4 of this invention 12 Schematic diagram of the desalination performance of the membrane and the GO membrane prepared in Comparative Example 1;

[0030] Figure 11 The GO membrane prepared in Comparative Example 1 and the rGO-PW membrane prepared in Example 4 are examples of the present invention. 12 Comparison images of the membrane before and after rinsing and soaking treatments;

[0031] Figure 12 The GO membrane prepared in Comparative Example 1 and the rGO-PW membrane prepared in Example 4 are examples of the present invention. 12 XRD patterns of the membrane in dry and wet conditions;

[0032] Figure 13 This is the rGO-PW prepared in Example 4 of the present invention. 12 Photos of the membrane placed in water for 1 day and 7 days;

[0033] Figure 14 This is the rGO-PW prepared in Example 4 of the present invention. 12 Comparison of the long-term stability of the membrane with that of the GO membrane prepared in Comparative Example 1;

[0034] Figure 15 This is the rGO-PW prepared in Example 4 of the present invention. 12 Comparison of the permeation performance of the membrane for NaCl and MgCl2 after five cycles of membrane recycling. Detailed Implementation

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] The first aspect of the present invention provides a reduced graphene oxide composite film, the composite film comprising a substrate and a functional layer deposited on the substrate, wherein the functional layer is a reduced graphene oxide layer intercalated with heteropolyacid molecular clusters.

[0037] The heteropolyacid molecular clusters used in this invention exist in molecular form. Therefore, their intercalation between graphene oxide sheets results in higher compatibility, fewer defects in the prepared membrane, and a higher degree of two-dimensional order. The strong interaction between the heteropolyacids and rGO controls the interlayer spacing of the separation membrane within the sub-nanometer range, which helps to suppress the expansion of the reduced graphene oxide nanosheets and enhance the stability of the membrane.

[0038] The composite membrane described in this invention has high water permeability and high ion rejection rate, as well as high selectivity and stability.

[0039] In some embodiments of the present invention, the substrate is selected from nylon, polyvinylidene fluoride and polyacrylonitrile.

[0040] In some embodiments of the present invention, the heteropolyacid molecular clusters are selected from at least one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid and borotungstic acid, preferably phosphotungstic acid.

[0041] In some embodiments of the present invention, the mass ratio of reduced graphene oxide to heteropolyacid molecular clusters in the composite membrane is 1:1-10, for example 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, and any value within the range of any two of the above values, preferably 1:8-1:10, and more preferably 1:10. In the present invention, as the heteropolyacid content increases, the interaction between the heteropolyacid and rGO is enhanced, leading to an increase in ion rejection rate.

[0042] In some embodiments of the present invention, the thickness of the functional layer is 35-270 nm, for example 35 nm, 90 nm, 140 nm, 230 nm, 270 nm, and any value within the range of any two of the above values, preferably 90-140 nm, and more preferably 90 nm. In the present invention, if the thickness of the composite membrane is too small, the water flux is large but the salt rejection rate is low; if the thickness of the composite membrane exceeds 90 nm, it has a high salt rejection rate, but due to the large thickness, the water mass transfer resistance is large and the water flux is low.

[0043] In some embodiments of the present invention, the composite membrane has a bilayer spacing d1 and d2, wherein d1 is... d2 is In this invention, if the interlayer spacing is too small, the water permeability is insufficient; if the interlayer spacing is too large, the separation performance decreases. This invention can precisely control the interlayer spacing at the sub-nanometer scale, achieving a comprehensive improvement in both water permeability and separation performance.

[0044] In this invention, Cu Ka radiation is provided. X-ray diffraction (XRD) analysis was performed on a Rigaku XRD-6000 diffractometer to characterize the structure of the prepared film and to further calculate the interlayer spacing (Bragg equation).

[0045] In some embodiments of the present invention, the Raman peak intensity ratio of the composite film is 1.32 (ID / IG).

[0046] The composite membrane prepared by this invention exhibits a high strength ratio (D(1345cm)). -1 ) and G (1595cm -1 Characteristic bands, of which the D band is related to the degree of disorder of amorphous carbon, while the G band is related to the in-plane tensile vibration of the C-C bonds of ordered sp2 carbon in the graphene sheet.

[0047] In this invention, Raman spectroscopy (Renishaw Raman spectrometer) uses an incident laser with a wavelength of 580 nm at a wavelength of 1000-2000 cm⁻¹. -1 Within the scope.

[0048] In some embodiments of the present invention, the water contact angle of the composite membrane is 72.7°. In the present invention, if the water contact angle is too small, the membrane is prone to expansion in water, the interlayer spacing increases, the stability decreases, and it will affect the separation process of the membrane and the mass transfer process within the membrane channels, making it difficult to achieve efficient separation.

[0049] In this invention, the water contact angle is measured using a JC2000D2M static contact angle goniometer.

[0050] A second aspect of the present invention provides a method for preparing a reduced graphene oxide composite film according to the first aspect, the method comprising the following steps:

[0051] (1) Mix the graphene oxide solution, the heteropolyacid solution and isopropanol;

[0052] (2) The mixed solution obtained in step (1) is deposited on the surface of the substrate to form a film, thereby obtaining a heteropolyacid-graphene oxide film;

[0053] (3) The heteropolyacid-graphene oxide film obtained in step (2) is subjected to in-situ photoreduction to obtain a reduced graphene oxide composite film.

[0054] In this invention, depositing the mixed solution into a film followed by in-situ photoreduction enhances the stability and anti-swelling properties of the composite film. Furthermore, this invention does not perform photocatalytic reduction in solution. This is because photocatalytic reduction in solution is prone to aggregation, making it difficult to maintain an ordered layered structure, which is detrimental to improving the film's orderliness and leads to reduced selectivity in the composite film. The in-situ photoreduction method effectively avoids the problems of easy aggregation of graphene oxide during reduction, difficulty in controlling the degree of reduction, and the use of toxic or harmful reducing agents.

[0055] The method not only constructs an ordered two-dimensional layered space and structure, which is beneficial to improving the separation performance of the composite membrane, but also, since the reduced graphene oxide layer intercalated with heteropolyacid molecular clusters is a product obtained by chemical reaction between graphene oxide and heteropolyacid, there is a strong interaction between the two, which effectively improves the stability of the membrane.

[0056] like Figure 1 As shown, isopropanol plays an auxiliary role in the reduction process. Specifically, isopropanol first reduces phosphotungstic acid to reduced phosphotungstic acid (hexapolyblue), and the reduced phosphotungstic acid then reduces graphene oxide (GO) to reduced graphene oxide (rGO) under light irradiation.

[0057] In some embodiments of the present invention, the graphene oxide solution in step (1) is prepared by the following method: graphene oxide powder is prepared from natural graphite as raw material, dissolved in deionized water or ultrapure water and sonicated to obtain graphene oxide solution.

[0058] In some embodiments of the present invention, the graphene oxide powder is prepared by a modified Hummer process.

[0059] In some embodiments of the present invention, the concentration of the graphene oxide solution is 0.01-0.5 mg / mL, preferably 0.1 mg / mL.

[0060] In some embodiments of the present invention, the concentration of the heteropolyacid solution is 0.1-5 mg / mL, preferably 1 mg / mL.

[0061] In some embodiments of the present invention, the volume ratio of the graphene oxide solution to the heteropolyacid solution is 1:0.1-1.3, preferably 1:1.

[0062] In some embodiments of the present invention, the mixing conditions include: being carried out under ultrasonic conditions; and a mixing time of 10 min to 2 h, preferably 0.5 to 1 h.

[0063] In some embodiments of the present invention, the deposition method in step (2) is vacuum filtration.

[0064] In some embodiments of the present invention, the deposition time is 1-6 hours, preferably 3 hours.

[0065] In some embodiments of the present invention, the in-situ light reduction in step (3) is performed under UV light.

[0066] In some embodiments of the present invention, the in-situ light reduction time is 0.5-6 hours, preferably 4 hours.

[0067] A third aspect of the present invention provides a reduced graphene oxide composite film prepared according to the preparation method described in the second aspect.

[0068] The fourth aspect of the present invention provides the application of the reduced graphene oxide composite membrane according to the first or third aspect in ion permeation.

[0069] When the reduced graphene oxide composite membrane described in this invention is used for ion permeation, it can achieve low salt permeability and high selectivity, and therefore can be used for ion separation and seawater desalination.

[0070] When applied to forward osmosis processes, rGO-PW 12 The membrane not only exhibits a high 157.19 mol / m³, but also... -2 h -1 It has a high water flux and also exhibits a value of ~4.74×10⁻⁶. 3 Its ultra-high water-salt selectivity is superior to most membranes reported in the literature.

[0071] The fifth aspect of the present invention provides an ion permeation device comprising the reduced graphene oxide composite membrane described in the first or third aspect.

[0072] The present invention will be described in detail below through embodiments.

[0073] Unless otherwise specified in the following examples and comparative examples, all conditions were performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available products.

[0074] Example 1

[0075] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0076] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0077] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0078] (3) Take 3 mL of the GO dispersion prepared in step (1), and take 3 mL of the PW prepared in step (2). 12 Add 300 μL of isopropanol to 3 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0079] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0080] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 90 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:10 can be obtained. 12 membrane.

[0081] Example 2

[0082] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0083] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0084] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0085] (3) Take 5 mL of the GO dispersion prepared in step (1) and take 5 mL of the PW dispersion prepared in step (2). 12 Add 500 μL of isopropanol to 5 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0086] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0087] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 140 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:10 can be obtained. 12 membrane.

[0088] Example 3

[0089] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0090] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0091] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0092] (3) Take 8 mL of the GO dispersion prepared in step (1) and take 8 mL of the PW prepared in step (2). 12 Add 800 μL of isopropanol to 8 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0093] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0094] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 230 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:10 can be obtained. 12membrane.

[0095] Example 4

[0096] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0097] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0098] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0099] (3) Take 10 mL of the GO dispersion prepared in step (1), and take the PW prepared in step (2). 12 Add 1000 μL of isopropanol to 10 mL of dispersion, and mix the above solution thoroughly (sonicate for 1 h);

[0100] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0101] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 270 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:10 can be obtained. 12 membrane.

[0102] Figure 2 This is a SEM image of the rGO-PW12 membrane prepared in Example 4 of this invention. It can be seen that the rGO-PW12 membrane has a distinct two-dimensional layered membrane structure with stacked layers.

[0103] Figure 3 This is an optical photograph of the rGO-PW12 film prepared in Example 4 of this invention.

[0104] Figure 4 This is the Raman spectroscopy image of the rGO-PW12 membrane prepared in Example 4 of this invention. It can be seen that the Id / Ig value of the rGO-PW12 membrane is increased compared to that of the GO membrane, proving that the GO membrane was successfully reduced.

[0105] Figure 5 This is a HETEM image of the rGO-PW12 film prepared in Example 4 of this invention. It can be seen that heteropolyacid molecular clusters (within the red circle) are uniformly distributed on the rGO nanosheets.

[0106] Comparative Example 1

[0107] The GO film was prepared according to the method of Example 4, except that steps (2) and (3) were not included. The GO dispersion was formed on the surface of the nylon substrate and dried at room temperature for 24 hours to obtain the GO film.

[0108] Example 5

[0109] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0110] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0111] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0112] (3) Take 10 mL of the GO dispersion prepared in step (1), and take the PW prepared in step (2). 12 Add 100 μL of isopropanol to 1 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0113] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0114] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 270 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:1 can be obtained. 12 membrane.

[0115] Example 6

[0116] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0117] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0118] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0119] (3) Take 10 mL of the GO dispersion prepared in step (1), and take the PW prepared in step (2). 12 Add 300 μL of isopropanol to 3 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0120] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0121] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 270 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:3 can be obtained. 12 membrane.

[0122] Example 7

[0123] This embodiment is used to illustrate rGO-PW 12 Membrane preparation.

[0124] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0125] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0126] (3) Take 10 mL of the GO dispersion prepared in step (1), and take the PW prepared in step (2). 12 Add 500 μL of isopropanol to 5 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0127] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0128] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 270 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:5 can be obtained. 12 membrane.

[0129] Example 8

[0130] This embodiment is used to illustrate rGO-PW 12Membrane preparation.

[0131] (1) Take graphene oxide (GO) powder and prepare a GO aqueous solution with a concentration of 0.1 mg / mL in deionized water. Sonicate for 1 h to fully peel off the GO sheets and prepare a GO dispersion.

[0132] (2) Take phosphotungstic acid (PW) 12 Prepare a 1 mg / mL solution of PW in deionized water. 12 Dispersion;

[0133] (3) Take 10 mL of the GO dispersion prepared in step (1), and take the PW prepared in step (2). 12 Add 800 μL of isopropanol to 8 mL of dispersion and mix the above solution thoroughly (sonicate for 1 h);

[0134] (4) The nylon substrate is loaded into the membrane module, and then the mixed solution prepared in step (3) is deposited on the surface of the nylon substrate under pressure to form a film, thus preparing GO-PW. 12 membrane;

[0135] (5) Take the GO-PW obtained in step (4) 12 After irradiating the membrane under a UV lamp for 4 hours, rGO-PW with a thickness of 270 nm and a mass ratio of reduced graphene oxide to heteropolyacid molecular clusters of 1:8 can be obtained. 12 membrane.

[0136] Test Example 1: Membrane Structure Characterization

[0137] (1) Equipped with Cu Ka radiation X-ray diffraction (XRD) analysis was performed on a Rigaku XRD-6000 diffractometer to characterize the structure of the prepared film (see [link to relevant documentation]). Figure 11 ), and further calculate the interlayer spacing of the membrane.

[0138] (2) Raman spectroscopy (Renishaw Raman spectrometer) using an incident laser with a wavelength of 580 nm at a wavelength of 1000-2000 cm⁻¹ -1 Within the scope.

[0139] (3) A JC2000D2M static contact angle measuring instrument was used. Perform water contact angle tests.

[0140] The results are shown in Table 1.

[0141] Table 1

[0142]

[0143] rGO-PW prepared in other embodiments 12The interlayer spacing, ID / IG ratio, and water contact angle of the membrane are the same as those of the rGO-PW membrane prepared in Example 4. 12 The membranes are basically the same, so they will not be listed again.

[0144] As can be seen from the results in Table 1, rGO-PW 12 The interlayer spacing of the membrane is precisely and effectively controlled within the sub-nanometer range. Furthermore, PW was intercalated into GO nanosheets. 12 The decrease in ID / IG value after in-situ photoreduction of polyacid molecular clusters confirms the successful reduction of the GO film, while rGO-PW 12 The decrease in hydrophilicity of the membrane surface means a reduction in oxygen-containing functional groups on the GO sheet surface, i.e., successful reduction of GO.

[0145] Test Example 2: Ion Permeation Test

[0146] The test was conducted using a U-shaped permeameter (e.g.) Figure 6 As shown in the diagram, the membrane is sealed between two chambers. The permeate side of the U-shaped permeate cell is filled with deionized water, while the feed side contains various salt solutions (KCl, NaCl, LiCl, MgCl2, CaCl2, AlCl3) at a concentration of 0.1M. The effective membrane area is 1.77 cm². 2 (Circular discs with a radius of 0.75 cm), all tests were conducted at room temperature. More importantly, to avoid concentration polarization during the testing process, both compartments were magnetically stirred to ensure homogeneous solutions.

[0147] The conductivity on the permeation side was measured using a conductivity meter, and the permeation rate was further calculated as a function of permeation time. The detection limit of the conductivity meter was 0.01 μS, corresponding to salt concentrations in the μM range.

[0148] Figure 7 This indicates that, compared to the GO membrane, the rGO-PW prepared in Example 4... 12 Membrane for K + Na + Li + Ca 2+ Mg 2+ Al 3+ The retention performance was greatly improved (by two orders of magnitude); and as the ion hydration diameter increased, rGO-PW... 12 The membrane exhibited enhanced retention properties, demonstrating its effectiveness in reducing and modifying PW. 12 Following the molecular cluster, rGO-PW 12 The reduction in the effective channel size of the membrane can impede the passage of ions and exhibits superior sieving selectivity for cations with different hydration diameters.

[0149] Figure 8This indicates that the rGO-PW prepared in Examples 4-8 12 The ion retention performance of the membrane varies with rGO and PW. 12 The increase in mass ratio indicates that PW 12 It plays an important role in constructing confined nanochannels to achieve efficient ion screening.

[0150] Figure 9 As the thickness increases, rGO-PW prepared in Examples 1-4 12 The membrane exhibits a continuous decreasing trend in ion permeability due to increased transport resistance, which implies that the stacking of structurally ordered rGO nanosheets is beneficial for subsequent separation.

[0151] Test Example 3: Desalination Performance Test

[0152] The test used a U-shaped apparatus, with 50 mL of 0.1 M NaCl solution on the feed side and 50 mL of 1 M sucrose solution on the permeate side, to conduct a forward osmosis experiment and obtain the water flux value. Water flux (J) w The difference in liquid volume (ΔV) between the feed side and the permeate side is calculated over time (Δt) as follows:

[0153]

[0154] Wherein, A(m) 2 () represents the effective area of ​​the test membrane.

[0155] The results are as follows Figure 10 As shown.

[0156] The salt rejection ratio (R) is calculated by measuring the osmotic ions on the osmotic side, and the formula is as follows:

[0157]

[0158] In the formula, C d and C f These represent the NaCl concentrations on the permeation side and the feed side, respectively.

[0159] The results are shown in Table 2.

[0160] serial number Example 1 Example 2 Example 3 Example 4 NaCl rejection rate, % 98.3 98.9 99.3 99.5

[0161] from Figure 10 As can be seen from Table 2, rGO-PW 12 The membrane achieves a high NaCl rejection rate (98.3%) and a high water flux (157.19 mol m³ / s). -2 h -1 ) and extremely high water-salt selectivity (4.74 × 10⁻⁶) 3 This performance is superior to most membranes reported in the literature.

[0162] Test Example 4 Stability Test

[0163] (1) The GO film prepared in Comparative Example 1 and the rGO-PW prepared in Example 4 were studied by XRD. 12 Swelling properties of membranes in aqueous environments.

[0164] The membrane was immersed in deionized water for 30 minutes. The wetted membrane was then removed and the surface free water was quickly adsorbed with filter paper before XRD testing was performed immediately. The swelling resistance of the separation membrane can be tested by comparing the XRD patterns of the membrane in dry and wet states and the corresponding changes in interlayer spacing.

[0165] from Figure 11 It can be seen that rGO-PW 12 The membrane has good resistance to swelling.

[0166] (2) To further verify the structural stability, the GO film prepared in Comparative Example 1 and the rGO-PW prepared in Example 4 were compared. 12 The membrane underwent rinsing and soaking treatment.

[0167] like Figure 12 As shown, rGO-PW 12 After rinsing with water, the membrane's original structure is well preserved. Conversely, when rinsed with water, large areas of GO can be immediately peeled off from the nylon substrate.

[0168] (3) Long-term stability is crucial for the solution application of graphene oxide-based films. The rGO-PW prepared in Example 4 12 The membrane was very stable and showed no obvious damage or delamination even after being placed in water for 7 days. Figure 13 ).

[0169] (4) Figure 14 Demonstrates the effectiveness of rGO-PW prepared in Example 4 12 The membrane exhibits excellent long-term stability (over 400 hours).

[0170] (5)rGO-PW 12 Membrane recycle performance study: 0.1M NaCl and MgCl2 solutions were used as feed solutions, respectively. After each permeation experiment, the filtration device and membrane were thoroughly rinsed with deionized water. The rGO-PW prepared in Example 4 was compared with... 12 A comparison of the permeation performance of the membrane for NaCl and MgCl2 after five cycles of ion recycling.

[0171] Figure 15 Prove rGO-PW 12 The membrane exhibits good cycle stability.

[0172] PW 12In-situ photoreduction of adjacent rGO sheets inserted into the layered membrane effectively suppressed the expansion of the two-dimensional GO membrane in liquid water. Due to PW 12 The strong interaction between rGO-PW and oxygen functional groups on GO nanosheets 12 Compared to GO membranes, the membrane effectively reduces the permeation rate of salt solutions by two orders of magnitude. Furthermore, the membrane prepared in this invention not only exhibits good stability within 400 hours but also has good reusability.

[0173] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A reduced graphene oxide composite film, characterized in that, The composite film includes a substrate and a functional layer deposited on the substrate, wherein the functional layer is a reduced graphene oxide layer with heteropolyacid molecular clusters intercalated. The preparation method of the reduced graphene oxide composite film includes the following steps: (1) Mix the graphene oxide solution, the heteropolyacid solution, and isopropanol; (2) The mixed solution obtained in step (1) is deposited on the surface of the substrate to form a film, thereby obtaining a heteropolyacid-graphene oxide film; (3) The heteropolyacid-graphene oxide film obtained in step (2) is subjected to in-situ photoreduction to obtain a reduced graphene oxide composite film.

2. The composite membrane according to claim 1, wherein, The substrate is selected from one of nylon, polyvinylidene fluoride and polyacrylonitrile; And / or, the heteropolyacid molecular clusters are selected from at least one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid, and borotungstic acid; And / or, the mass ratio of reduced graphene oxide to heteropolyacid molecular clusters in the composite membrane is 1:1-10; And / or, the thickness of the functional layer is 35-270 nm.

3. The composite membrane according to claim 2, wherein, The mass ratio of reduced graphene oxide to heteropolyacid molecular clusters in the composite membrane is 1:8-1:10; And / or, the thickness of the functional layer is 90-140 nm.

4. The composite membrane according to claim 2, wherein, The mass ratio of reduced graphene oxide to heteropolyacid molecular clusters in the composite membrane is 1:

10. And / or, the thickness of the functional layer is 90 nm.

5. The composite membrane according to claim 1 or 2, wherein, The composite membrane has a bilayer spacing of d1 and d2, where d1 is 14.52 Å and d2 is 7.67 Å; And / or, the Raman peak intensity ratio of the composite film is 1.32 (ID / IG). And / or, the water contact angle of the composite membrane is 72.7°.

6. A method for preparing a reduced graphene oxide composite film according to any one of claims 1-5, characterized in that, The method includes the following steps: (1) Mix the graphene oxide solution, the heteropolyacid solution, and isopropanol; (2) The mixed solution obtained in step (1) is deposited on the surface of the substrate to form a film, thereby obtaining a heteropolyacid-graphene oxide film; (3) The heteropolyacid-graphene oxide film obtained in step (2) is subjected to in-situ photoreduction to obtain a reduced graphene oxide composite film.

7. The method according to claim 6, wherein, The graphene oxide solution in step (1) is prepared by the following method: graphene oxide powder is prepared from natural graphite, dissolved in deionized water or ultrapure water and sonicated to obtain graphene oxide solution; And / or, the concentration of the graphene oxide solution is 0.01-0.5 mg / mL; And / or, the concentration of the heteropolyacid solution is 0.1-5 mg / mL; And / or, the volume ratio of the graphene oxide solution to the heteropolyacid solution is 1:0.1-1.3; And / or, the mixing conditions include: being performed under ultrasonic conditions; and a mixing time of 10 min to 2 h.

8. The method according to claim 7, wherein, The graphene oxide powder was prepared by a modified Hummer method; And / or, the concentration of the graphene oxide solution is 0.1 mg / mL; And / or, the concentration of the heteropolyacid solution is 1 mg / mL; And / or, the volume ratio of the graphene oxide solution to the heteropolyacid solution is 1:1; And / or, the mixing time is 0.5-1 h.

9. The method according to claim 6 or 7, wherein, The deposition method described in step (2) is vacuum filtration; And / or, the deposition time is 1-6 h.

10. The method according to claim 9, wherein, The deposition time was 3 hours.

11. The method according to any one of claims 6 or 7, wherein, The in-situ light reduction described in step (3) is performed under UV light; And / or, the in-situ light restoration time is 0.5-6 h.

12. The method according to claim 11, wherein, The in-situ light restoration time is 4 hours.

13. A reduced graphene oxide composite film prepared by any one of claims 6-12.

14. The application of the reduced graphene oxide composite membrane according to any one of claims 1-5 and 13 in ion permeation.

15. An ion permeation device comprising a reduced graphene oxide composite membrane according to any one of claims 1-5 and 13.

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