An ultrathin asymmetric structure graphene separation membrane and a preparation method and application thereof

Abstract

The application discloses an ultrathin asymmetric structure graphene separation membrane and a preparation method thereof, and the method comprises the following steps: obtaining a graphene separation membrane; performing first soaking on the graphene separation membrane in an alkaline aqueous solution to activate functional groups on the edges of graphene nanopores, and then performing flushing to obtain an activated separation membrane; performing second soaking on the activated separation membrane in a chloroacetic acid solution, then adding sodium hydroxide to perform a modification reaction, and then performing flushing after the reaction to obtain an ultrathin asymmetric structure graphene separation membrane. The ultrathin asymmetric structure graphene separation membrane prepared in the application has uniform pore size and ultrahigh surface charge density, and can be applied to the field of ion transportation in a membrane separation process.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials technology, and in particular to a method for preparing and applying an ultrathin asymmetric graphene separation membrane. Background Technology

[0002] Reverse electrodialysis, used to extract the mixed Gibbs free energy generated at the interface between brine and freshwater (salinity gradient energy), is an effective method for obtaining clean and sustainable energy. As a core component of reverse electrodialysis, ion-selective separation membranes with cation / anion selective transport capabilities play a crucial role in controlling the directional and selective transport of ions, directly determining the efficiency of salinity gradient energy generation. To ensure efficient and selective ion transport, an ideal ion-selective separation membrane should possess high ion permeability and ion selectivity. During ion transport, ion permeability is inversely proportional to the thickness of the separation membrane. Atomic-thin two-dimensional nanoporous separation membranes, due to their ultrathin thickness, possess the shortest ion transport path and the lowest ion transport resistance, and are considered ideal materials for constructing ultra-high ion permeability. However, currently developed atomic-thin two-dimensional separation membranes are only at the conceptual verification stage of single-pore research, making it difficult to meet practical application requirements.

[0003] The ion permeability of atomically thin two-dimensional separation membranes exhibits a linear relationship with the number of nanopores (N) (G m =N*G s In other words, extending the current single-pore proof-of-concept to porous research will significantly improve ion permeability, enabling the achievement of high instantaneous power generation to meet practical applications. In salinity gradient power generation, ion-selective separation membranes primarily achieve effective separation of sub-nanometer-sized cations and anions at the molecular level through size exclusion and electrostatic interactions. However, the expansion from single-pore to porous membranes inevitably encounters problems such as uneven pore size distribution and difficulty in controlling charge density, leading to ion leakage and affecting the ion selectivity of the separation membrane and the efficiency of salinity gradient power generation.

[0004] Therefore, it is necessary to develop a separation membrane for obtaining salinity gradient energy. Summary of the Invention

[0005] The purpose of this invention is to provide an ultrathin asymmetric graphene separation membrane and its preparation method. This invention utilizes a template-assisted etching and surface functionalization process to prepare an ultrathin, asymmetric nanoporous graphene separation membrane with a narrow pore size distribution and high surface charge density. This separation membrane possesses uniform pore size and ultra-high surface charge density, making it suitable for ion transport in membrane separation processes. It exhibits extremely high ion selectivity and energy conversion efficiency under concentration gradients between seawater and river water, greatly promoting the application of atomically thin two-dimensional materials in the salinity gradient energy field.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect of the present invention, a method for preparing an ultrathin asymmetric graphene separation membrane is provided, the method comprising:

[0008] Obtain a graphene separation membrane;

[0009] The graphene separation membrane was first immersed in an alkaline aqueous solution to activate the functional groups at the edge of the graphene nanopores, and then rinsed to obtain an activated separation membrane.

[0010] The activated separation membrane was immersed in chloroacetic acid solution for a second time, and then sodium hydroxide was added for modification reaction. After the reaction was completed, it was rinsed to obtain an ultrathin asymmetric graphene separation membrane.

[0011] In a second aspect of the invention, an ultrathin asymmetric graphene separation membrane prepared by the method is provided.

[0012] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0013] 1. The ultrathin asymmetric graphene separation membrane prepared in this invention has a uniform pore size (ranging from 1 to 2 nm) and an ultra-high surface charge density (reaching -3 mC / m). 2 It can be applied to the field of ion transport in membrane separation processes.

[0014] 2. The ultrathin asymmetric graphene separation membrane constructed in this invention has a fast transmission rate and ultra-high ion rectification characteristics during ion transport.

[0015] 3. The ultrathin asymmetric graphene separation membrane constructed in this invention has extremely high ion selectivity and energy conversion efficiency under the concentration gradient of seawater and river water, which greatly promotes the application of atomically thin two-dimensional materials in the field of salinity gradient energy. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of ion separation of the ultrathin asymmetric structure obtained in Example 1 of the present invention.

[0018] Figure 2This is a SEM image of the ultrathin asymmetric graphene separation membrane prepared in Example 1 of the present invention.

[0019] Figure 3 This is a TEM image of the ultrathin asymmetric graphene separation membrane prepared in Example 1 of the present invention.

[0020] Figure 4 This is an IV curve of the ultrathin asymmetric graphene separation membrane in Example 2 of the present invention during ion transport.

[0021] Figure 5 The graph shows the performance of the ultrathin asymmetric graphene separation membrane in salt gradient energy acquisition, as described in Application Example 1 of this invention. Detailed Implementation

[0022] The present invention will be described in detail below with reference to specific embodiments and examples, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0023] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, 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 pertains. In the event of any conflict, this specification shall prevail.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be obtained by purchasing them from the market or by existing methods.

[0025] Therefore, according to a typical embodiment of the present invention, a method for preparing an ultrathin asymmetric graphene separation membrane is provided, the method comprising:

[0026] Step S1: Obtain the graphene separation membrane;

[0027] Step S1 specifically includes: etching graphene grown on copper foil by CVD with 1 M ferric chloride solution, followed by immersion in water for washing, growing a layer of mesoporous silicon oxide on the surface of the graphene film, etching with oxygen plasma (the pressure used in the etching is 10 Pa and the power is 50 W), then removing the mesoporous silicon by etching with 10% HF solution, and finally rinsing to obtain a graphene separation membrane.

[0028] Step S2: The graphene separation membrane is first immersed in an alkaline aqueous solution to activate the functional groups at the edge of the graphene nanopores, and then rinsed to obtain an activated separation membrane.

[0029] In step S2

[0030] The alkaline aqueous solution is selected from 8% to 12% KOH aqueous solution or 8% to 12% NaOH aqueous solution.

[0031] The first soaking time is 60–150 minutes, and the temperature is 25℃ ± 5℃. If the soaking time is too short, the activation will be incomplete; if it is too long, the reactants will not be completely washed away.

[0032] Step S3: The activated separation membrane is immersed in chloroacetic acid solution for a second time, and then sodium hydroxide is added for modification reaction. After the reaction is completed, it is rinsed to obtain an ultrathin asymmetric graphene separation membrane.

[0033] The concentration of the chloroacetic acid solution is 8% to 12%. If the concentration of the chloroacetic acid solution is too low, the modification will be incomplete; if it is too high, the modification efficiency will be affected.

[0034] The concentration of sodium hydroxide is 8% to 12%.

[0035] The second soaking time is 10–50 minutes, and the temperature is 25℃±5℃. If the soaking time is too short, the modification will be incomplete; if it is too long, the modification efficiency will be affected.

[0036] The modification reaction takes 3 to 6 hours and is carried out at a temperature of 25℃ ± 5℃.

[0037] The reaction principle of this invention is as follows: hydroxyl and epoxy groups at the edges of graphene nanopores are converted into carboxyl functional groups using a modified Hummers method. The high charge density subnanopores functionalized with carboxyl groups allow K... + Achieving rapid ion transport with minimal resistance while effectively blocking Cl... - The asymmetric structure endows the separation membrane with a rectification characteristic similar to that of an ion diode, effectively mitigating concentration polarization of ions on the membrane surface and further improving ion selectivity. This ultrathin asymmetric graphene separation membrane exhibits high K0 under the salinity gradient of seawater and river water. + It improves selectivity, energy conversion efficiency, and salinity gradient energy conversion capability. This effectively compensates for the current shortcomings of two-dimensional atomic thin-film-based methods in salinity gradient energy acquisition.

[0038] According to another typical embodiment of the present invention, an ultrathin asymmetric graphene separation membrane obtained by the method is provided.

[0039] The following will provide a detailed description of an ultrathin asymmetric graphene separation membrane and its preparation method, in conjunction with embodiments, comparative examples, and experimental data.

[0040] Example 1: Preparation method of ultrathin asymmetric graphene separation membrane

[0041] This invention provides a method for preparing an ultrathin asymmetric graphene separation membrane, comprising the following steps:

[0042] Step 1: Prepare an ultrathin asymmetric graphene separation membrane using a template-assisted method. The specific process is as follows: Graphene grown on copper foil by CVD is etched with 1 M ferric chloride solution, then soaked and washed with water to grow a layer of mesoporous silicon oxide on the surface of the graphene membrane. The membrane is then etched by plasma, followed by HF etching to remove the mesoporous silicon oxide, and finally rinsed to obtain the graphene separation membrane.

[0043] Step 2: Immerse the separation membrane in a 10% KOH aqueous solution for 2 hours to activate the functional groups at the edge of the graphene nanopores;

[0044] Step 3: Rinse the activated separation membrane three times with ultrapure water to remove residual KOH from the surface; then soak it in a 10% chloroacetic acid solution for 30 min, add 10% sodium hydroxide to the solution, and react at room temperature for 4 h; rinse three times with ultrapure water to remove unreacted compounds from the surface of the composite membrane. The ultrathin asymmetric graphene separation membrane obtained in Example 1 is as follows... Figure 1 As shown.

[0045] Example 2: Preparation method of ultrathin asymmetric graphene separation membrane

[0046] This invention provides a method for preparing an ultrathin asymmetric graphene separation membrane, comprising the following steps:

[0047] Step 1: Prepare an ultrathin asymmetric graphene separation membrane using a template-assisted method. The specific process is as follows: Graphene grown on copper foil by CVD is etched with 1 M ferric chloride solution, then soaked and washed with water to grow a layer of mesoporous silicon oxide on the surface of the graphene membrane. The membrane is then etched by plasma, followed by HF etching to remove the mesoporous silicon oxide, and finally rinsed to obtain the graphene separation membrane.

[0048] Step 2: Immerse the separation membrane in 8% KOH aqueous solution for 60 min to activate the functional groups at the edge of the graphene nanopores;

[0049] Step 3: Rinse the activated separation membrane three times with ultrapure water to remove residual KOH on the surface; then soak it in 8% chloroacetic acid solution for 10 min, add 8% sodium hydroxide to the above solution, and react at room temperature for 3 h; rinse three times with ultrapure water to remove unreacted compounds on the surface of the composite membrane.

[0050] Example 3: Preparation method of ultrathin asymmetric graphene separation membrane

[0051] This invention provides a method for preparing an ultrathin asymmetric graphene separation membrane, comprising the following steps:

[0052] Step 1: Prepare an ultrathin asymmetric graphene separation membrane using a template-assisted method. The specific process is as follows: Graphene grown on copper foil by CVD is etched with 1 M ferric chloride solution, then soaked and washed with water to grow a layer of mesoporous silicon oxide on the surface of the graphene membrane. The membrane is then etched by plasma, followed by HF etching to remove the mesoporous silicon oxide, and finally rinsed to obtain the graphene separation membrane.

[0053] Step 2: Immerse the separation membrane in a 12% KOH aqueous solution for 150 min to activate the functional groups at the edge of the graphene nanopores;

[0054] Step 3: Rinse the activated separation membrane three times with ultrapure water to remove residual KOH on the surface; then soak it in 12% chloroacetic acid solution for 50 min, add 12% sodium hydroxide to the above solution, and react at room temperature for 6 h; rinse three times with ultrapure water to remove unreacted compounds on the surface of the composite membrane.

[0055] Experimental Example 1: Characterization and Performance Testing of Ultrathin Asymmetric Graphene Separation Membranes

[0056] 1. The ultrathin asymmetric graphene separation membrane obtained in Example 1 was tested using scanning electron microscopy (SEM) and transmission electron microscopy. The results are as follows: Figure 1 , 2 As shown in Figures 3 and 4, we have successfully prepared a graphene separation membrane with an ultrathin asymmetric structure.

[0057] 2. The IV curves of the ultrathin asymmetric graphene separation membrane obtained in Example 1 were tested using a Keithley 6487 at temperatures ranging from -0.2 V to 0.2 V. The test results are as follows: Figure 4 and 5 As shown, the ultrathin graphene separation membrane prepared in Example 1 has excellent ion transport performance, rectification characteristics and salt gradient energy conversion performance.

[0058] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0059] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0060] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an ultrathin asymmetric graphene separation membrane, characterized in that, The method includes: Graphene grown on copper foil by CVD was etched with 1 M ferric chloride solution, then soaked and washed with water to grow a layer of mesoporous silicon oxide on the surface of the graphene film. The film was then etched with oxygen plasma at a pressure of 10 Pa and a power of 50 W. The mesoporous silicon oxide was then removed by etching with 10% HF solution and then rinsed to obtain a graphene separation membrane. The graphene separation membrane was first immersed in an alkaline aqueous solution to activate the functional groups at the edge of the graphene nanopores, and then rinsed to obtain an activated separation membrane. The activated separation membrane was immersed in chloroacetic acid solution for a second time, and then sodium hydroxide was added for modification reaction. After the reaction was completed, it was rinsed to obtain an ultrathin asymmetric graphene separation membrane.

2. The method according to claim 1, characterized in that, The alkaline aqueous solution is selected from 8% to 12% KOH aqueous solution or 8% to 12% NaOH aqueous solution.

3. The method according to claim 1, characterized in that, The first soaking time is 60 to 150 minutes, and the temperature is 25℃ ± 5℃.

4. The method according to claim 1, characterized in that, The concentration of the chloroacetic acid solution is 8% to 12%.

5. The method according to claim 1, characterized in that, The concentration of sodium hydroxide is 8% to 12%.

6. The method according to claim 1, characterized in that, The second soaking time is 10 to 50 minutes, and the temperature is 25℃ ± 5℃.

7. The method according to claim 1, characterized in that, The modification reaction takes 1 to 6 hours and is carried out at a temperature of 25℃ ± 5℃.

8. An ultrathin asymmetric graphene separation membrane prepared by the method according to any one of claims 1-7.

9. The application of the ultrathin asymmetric graphene separation membrane of claim 8 in the preparation of ion transport vehicles for obtaining salinity gradient energy.

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