Porous hydrophobic reduced graphene oxide membrane as well as preparation method and application thereof

Abstract

The invention relates to a porous hydrophobic reduced graphene oxide membrane as well as a preparation method and application thereof, the preparation method comprises the following steps: mixing glycine and a graphene oxide dispersion liquid, heating and reducing to obtain a reduced graphene oxide dispersion liquid; selecting a hydrophilic substrate with a pore structure, and enabling the reduced graphene oxide dispersion liquid to form a film on the hydrophilic substrate to obtain a reduced graphene oxide film; performing oxygen plasma etching on the reduced graphene oxide film subjected to heating reduction by taking a porous metal film as a mask plate to obtain a porous reduced graphene oxide film; and performing hydrophobic treatment on the porous reduced graphene oxide film by using plasma to obtain the porous hydrophobic reduced graphene oxide film. The porous hydrophobic reduced graphene oxide film provided by the invention can realize accurate regulation and control of thickness and pore diameter and large-area preparation, and is low in preparation cost and simple in process; in membrane distillation, high water flux can be generated, meanwhile, high salt rejection rate can be achieved, and the membrane has good application prospects in the field of seawater desalination.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials and functional thin films, and particularly relates to a porous hydrophobic reduced graphene oxide membrane, a preparation method thereof, and an application thereof. Background Art

[0002] The global fresh water crisis is an important issue widely concerned in the 21st century. As a technology that has been developed for more than 50 years, seawater desalination is still regarded as the primary solution to solve the fresh water crisis. According to the "2022 National Seawater Utilization Report", as of the end of 2022, 150 seawater desalination projects have been installed in China, and the estimated project scale is 2,357,048 tons / day, an increase of 500,615 tons / day compared with 2021. As a new membrane separation technology, membrane distillation can obtain clean water from high-salinity seawater and industrial wastewater through thermal driving. Compared with the traditional reverse osmosis technology, it has less demanding requirements for the concentration of the feed liquid, and the membrane distillation process has a high desalination rate and can obtain high-quality product water. At present, hydrophobic polytetrafluoroethylene filter membranes are often used in membrane distillation technology, but due to their low porosity, the water flux is low, and the cost of hydrophobic polytetrafluoroethylene filter membranes is high.

[0003] Since the discovery of graphene, two-dimensional materials have received extensive attention due to their unique properties. At present, two-dimensional layered membranes are obtained by stacking two-dimensional nanosheets layer by layer, and the nanoscale confinement channels therein can achieve ultrafast transport and precise separation of ions and molecules. CN110420567A and CN115888419A respectively report hydrophobic graphene oxide membranes and graphene membranes with ultra-high dye rejection rates. In the field of seawater desalination, graphene oxide membranes also have good application prospects. Water enters from the surface defects of the graphene oxide membrane and is transported in the interlayer channels. During this process, the oxygen-containing functional groups on the surface of the graphene oxide membrane can not only accelerate the transport of water, but also adsorb metal ions, reducing the ion permeation. However, the hydrophilicity of the surface of the graphene oxide membrane inhibits the diffusion of water vapor, and the too-long interlayer channels of the membrane increase the transport resistance of water molecules, which will both lead to a decrease in water flux. Therefore, hydrophobic treatment of the membrane and shortening the transport path of water molecules are crucial for improving the water flux of membrane distillation.

[0004] Based on the above, the technology needs to be improved. Summary of the Invention

[0005] Aiming at the deficiencies and defects of the above-mentioned prior art, the purpose of the present invention is to provide a porous hydrophobic reduced graphene oxide membrane, a preparation method thereof, and an application thereof, so as to solve the technical problems that the hydrophilicity of the surface of the graphene oxide membrane in the prior art and the too-long interlayer channels of the membrane lead to poor water separation performance.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, a method for preparing a porous hydrophobic reduced graphene oxide membrane is provided, which includes:

[0008] Step 1: Mix glycine with a graphene oxide dispersion liquid, and obtain a reduced graphene oxide dispersion liquid through heat reduction.

[0009] Step 2: Select a hydrophilic substrate with a pore structure, and form a film of the reduced graphene oxide dispersion liquid on the hydrophilic substrate to obtain a reduced graphene oxide membrane.

[0010] Step 3: Use a porous metal thin film as a mask plate to perform oxygen plasma etching on the reduced graphene oxide membrane to obtain a porous reduced graphene oxide membrane.

[0011] Step 4: Use plasma to perform hydrophobic treatment on the porous reduced graphene oxide membrane to obtain the porous hydrophobic reduced graphene oxide membrane.

[0012] Optionally, in Step 1, the mass ratio of glycine to graphene oxide in the graphene oxide dispersion liquid is 100 - 125:10 - 25.

[0013] Optionally, in Step 1, the heat reduction is carried out by ultrasonic and heat stirring for reduction, wherein the ultrasonic time is 10 - 30 min, the temperature of heat stirring is 90 - 100 °C, and the time of heat stirring is 20 - 24 h.

[0014] Optionally, the hydrophilic substrate in Step 2 is an anodic aluminum oxide membrane, a polyethersulfone membrane, or a mixed cellulose ester membrane, and the pore diameter of the hydrophilic substrate is 100 - 200 nm.

[0015] Optionally, in Step 2, the method for forming a film of the reduced graphene oxide dispersion liquid on the hydrophilic substrate is one of suction filtration, spin coating, knife coating, and dip coating, and the thickness of the reduced graphene oxide membrane obtained by using 0.125 - 1 mg of reduced graphene oxide is 50 - 400 nm.

[0016] Optionally, the pore diameter of the porous metal thin film in Step 3 is 5 - 400 nm.

[0017] Optionally, the power of the oxygen plasma etching in Step 3 is 50 - 100 W, and the oxygen plasma etching time for a reduced graphene oxide membrane with a thickness of 50 - 400 nm is 5 - 40 min.

[0018] Optionally, the plasma in Step 4 is sulfur hexafluoride plasma or fluorine plasma, the power of the hydrophobic treatment is 50 - 100 W, and the time is 5 - 40 min.

[0019] In a second aspect of the present invention, there is provided a porous hydrophobic reduced graphene oxide membrane, which is prepared by the preparation method described in the present invention.

[0020] In a third aspect of the present invention, there is provided an application of a porous hydrophobic reduced graphene oxide membrane as described in the present invention in the field of seawater desalination.

[0021] Compared with the prior art, the beneficial technical effects of the present invention include:

[0022] (Ⅰ) The preparation method of the present invention can achieve precise control of the thickness and pore size of the porous hydrophobic reduced graphene oxide membrane. The thickness control range is 50 - 400 nm, and the pore size control range is 60 - 400 nm. Moreover, large-area preparation of the porous hydrophobic reduced graphene oxide membrane can be realized, indicating that the porous hydrophobic reduced graphene oxide membrane prepared by the present invention has the potential for application in the field of seawater desalination.

[0023] (Ⅱ) The preparation method of the present invention can obtain a porous reduced graphene oxide membrane with an array of pores having a pore size of 60 - 400 nm by using a porous metal thin film and oxygen plasma etching, and there are no structural defects, which enables rapid transmission of water molecules in the porous reduced graphene oxide membrane.

[0024] (Ⅲ) The preparation method of the present invention performs hydrophobic treatment on the porous reduced graphene oxide membrane, endowing the membrane with superhydrophobic properties, which is beneficial to the diffusion of water vapor during the membrane distillation process. Description of the Drawings

[0025] Figure 1 is a schematic diagram of the preparation process of a porous hydrophobic reduced graphene oxide membrane provided by an embodiment of the present invention;

[0026] Figure 2 is a scanning electron microscope (SEM) image of the porous hydrophobic reduced graphene oxide membrane prepared in Example 1. Detailed Embodiments

[0027] The present invention provides a porous hydrophobic reduced graphene oxide membrane and its preparation method and application. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] An embodiment of the present invention provides a preparation method of a porous hydrophobic reduced graphene oxide membrane, as Figure 1 shown, which specifically includes:

[0029] Step 1: Mix glycine with a graphene oxide dispersion liquid, and obtain a reduced graphene oxide dispersion liquid through heat reduction;

[0030] Step 2: Select a hydrophilic substrate with a pore structure, and form a film of the reduced graphene oxide dispersion on the hydrophilic substrate (such as by vacuum filtration) to obtain a reduced graphene oxide film;

[0031] Step 3: Use a porous metal film (such as a porous gold film) as a mask to perform oxygen plasma etching on the reduced graphene oxide film to obtain a porous reduced graphene oxide film;

[0032] Step 4: Use plasma to perform a hydrophobic treatment on the porous reduced graphene oxide film to obtain a porous hydrophobic reduced graphene oxide film with pores and hydrophobicity (preferably array pores).

[0033] In the embodiment of the present invention, glycine is first mixed with the graphene oxide dispersion liquid, and after heating reduction, a reduced graphene oxide dispersion liquid is obtained (the reduced graphene oxide has fewer layers). This is because glycine can bind to the surface of graphene oxide through its polar groups, stabilize the dispersion state of graphene oxide, and help to better disperse graphene oxide in an aqueous solution, avoiding the aggregation of graphene sheets, thereby obtaining the reduced graphene oxide dispersion liquid. Then, a reduced graphene oxide film is prepared on a hydrophilic substrate with a pore structure. By using this method, a large-area reduced graphene oxide film can be prepared as needed, and the reduced graphene oxide film obtained by this method is beneficial to the regulation of the hydrophilicity of the film. The hydrophilic substrate with a pore structure in this embodiment has hydrophilic channels. During the membrane distillation process, the hydrophilic channels have a capillary tension effect and act as a water pump, which is beneficial to improving the water flux of the membrane distillation. Then, a porous metal film is used as a mask to perform oxygen plasma etching on the reduced graphene oxide film to obtain a porous reduced graphene oxide film, and the precise regulation of the pore diameter of the porous reduced graphene oxide film can be achieved. Finally, the obtained porous reduced graphene oxide film is subjected to a hydrophobic treatment using plasma, so that the film obtains superhydrophobic performance, which is beneficial to the diffusion of water vapor during the membrane distillation process.

[0034] In the embodiment of the present invention, in order to make the structure of the membrane stable, reduced graphene oxide is obtained by means of heating reduction. The reduced graphene oxide inherits the good mechanical properties of graphene oxide. By etching and hydrophobic treatment of the reduced graphene oxide film formed by the reduced graphene oxide, a hydrophobic and porous reduced graphene oxide film (i.e., a porous hydrophobic reduced graphene oxide film) is obtained. This not only increases the diffusion channels of water molecules, but also the hydrophobic interface helps the diffusion of water vapor. Therefore, it shows a high water flux and salt rejection rate in membrane distillation.

[0035] In one embodiment, in order to avoid excessive or insufficient reduction of graphene oxide, through experiments, it is obtained that the mass ratio of glycine to graphene oxide in step one is 100 - 125:10 - 25. It should be noted that the graphene oxide dispersion of the present invention is preferably an aqueous solution of graphene oxide, wherein the concentration of graphene oxide is preferably 0.25 mg / mL. The above concentration is not limited, and the concentration of the graphene oxide dispersion can also be adjusted as needed.

[0036] In one embodiment, in step one, the thermal reduction is carried out by ultrasonic and heating stirring.

[0037] In one embodiment, in step one, in order to avoid excessive or insufficient reduction of graphene oxide, the ultrasonic time is 10 - 30 min, the temperature of heating stirring is 90 - 100 °C (such as 95 °C), and the time of heating stirring is 20 - 24 h.

[0038] In one embodiment, in order to enable water to transfer quickly, the hydrophilic substrate in step two uses anodic aluminum oxide membrane, polyethersulfone membrane or mixed cellulose ester membrane, and the pore size of the hydrophilic substrate is 100 - 200 nm. The pore size of the hydrophilic substrate can specifically be selected as 100 nm, 150 nm, 200 nm, etc., but is not limited thereto.

[0039] In one embodiment, in step two, the method of forming a film of the reduced graphene oxide dispersion on the hydrophilic substrate is one of suction filtration, spin coating, blade coating, dip coating. The thickness of the reduced graphene oxide film obtained by using 0.125 - 1 mg of reduced graphene oxide is 50 - 400 nm.

[0040] In one embodiment, in order to make the reduction more thorough, step two further includes performing a thermal reduction treatment on the reduced graphene oxide film.

[0041] In one embodiment, in order to improve the evaporation rate of water molecules, the pore size of the porous metal film in step three is 5 - 400 nm, such as 5 nm, 10 nm, 20 nm, 40 nm, 100 nm, 200 nm, 300 nm, 400 nm, etc., but is not limited thereto.

[0042] In one embodiment, the porous metal film can be formed by evaporation coating on the anodic aluminum oxide membrane, or can be directly evaporated on the reduced graphene oxide film. In order to precisely control the pore size, it is possible to choose to deposit the porous metal film on the anodic aluminum oxide membrane. In order to achieve large-scale preparation, it is possible to choose to directly evaporate a porous metal film with a thickness of 2 - 5 nm (such as a porous gold film) on the reduced graphene oxide film. Since the thin porous metal film with a thickness of 2 - 5 nm is not continuous and has defects, a porous metal film can be directly formed on the reduced graphene oxide film.

[0043] Among them, the method of evaporating a porous metal thin film on an anodic aluminum oxide film specifically includes the steps of: evaporating a metal thin film on the anodic aluminum oxide film with a porous structure, and then soaking it in a sodium hydroxide solution for 20 - 40 min to dissolve the anodic aluminum oxide film, thereby obtaining a porous metal thin film.

[0044] In one embodiment, in order to etch regular and uniform array holes on the reduced graphene oxide film, the power of the oxygen plasma etching in step three is 50 - 100 W (such as 50 W, 60 W, 80 W, 100 W, etc.), and the oxygen plasma etching time of the reduced graphene oxide film with a thickness of 50 - 400 nm is 5 - 40 min.

[0045] In one embodiment, in step four, sulfur hexafluoride plasma or fluorine plasma is used to perform a hydrophobic treatment on the porous reduced graphene oxide film, and the power of the hydrophobic treatment is 50 - 100 W, and the time is 5 - 40 min.

[0046] The embodiment of the present invention also provides a porous hydrophobic reduced graphene oxide film, which is prepared by the above - mentioned preparation method of the porous hydrophobic reduced graphene oxide film.

[0047] The embodiment of the present invention also provides an application of the porous hydrophobic reduced graphene oxide film in the field of seawater desalination.

[0048] The porous hydrophobic reduced graphene oxide film of the embodiment of the present invention not only increases the diffusion channels of water molecules, but also the hydrophobic interface helps the diffusion of water vapor, so it shows a high water flux and salt rejection rate in membrane distillation.

[0049] The present invention will be further described below through specific embodiments.

[0050] Example 1

[0051] 1. The preparation method of a porous hydrophobic reduced graphene oxide film in this embodiment is as follows:

[0052] Step 1: Mix 125 mg of glycine with a graphene oxide dispersion solution with a concentration of 0.25 mg / mL (containing 25 mg of graphene oxide), perform ultrasonic treatment for 30 min, and heat and stir in an oil bath at 95 °C for 24 h to obtain a reduced graphene oxide dispersion solution;

[0053] Step 2: Adopt the method of vacuum filtration to form a film of the reduced graphene oxide dispersion solution on the surface of a polyethersulfone membrane with a pore size of 100 nm to obtain a reduced graphene oxide film;

[0054] Step 3: Evaporate a gold film on an anodic aluminum oxide membrane with a pore diameter of 80 nm, and soak it in a 4M sodium hydroxide solution for 30 min to dissolve the anodic aluminum oxide membrane, thereby obtaining a porous gold film. Use the porous gold film as a mask plate to perform oxygen plasma etching on the reduced graphene oxide membrane. The power of the plasma etching is 50 W and the time is 20 min to obtain a porous reduced graphene oxide membrane with a thickness of 200 nm;

[0055] Step 4: Perform hydrophobic treatment on the porous reduced graphene oxide membrane with sulfur hexafluoride plasma. The power is 100 W and the time is 40 min to obtain a porous hydrophobic reduced graphene oxide membrane.

[0056] 2. Verification of the structure of the porous hydrophobic reduced graphene oxide membrane

[0057] The porous hydrophobic reduced graphene oxide membrane prepared in Example 1 was tested by scanning electron microscopy. The results are as Figure 2 shown. The results show that regular and uniformly distributed array pores are presented on the membrane surface. The pore diameter range of the array pores is 60 - 100 nm, indicating that array pores are successfully etched on the surface of the reduced graphene oxide membrane by oxygen plasma.

[0058] 3. Application: Water flux and salt rejection performance of the porous hydrophobic reduced graphene oxide membrane in membrane distillation

[0059] The porous hydrophobic reduced graphene oxide membrane with a pore diameter of 60 - 100 nm and a thickness of 200 nm prepared in Example 1 was placed in a self-built membrane distillation device for experiments. The feed liquid used a 3.5 wt% NaCl solution (simulating seawater), and the water bath temperature was set at 75 °C, and the water evaporation side water bath temperature was set at 18 °C. At the same time, a thermometer was used to monitor the actual temperature in real time. The actual temperature corresponding to 75 °C / 18 °C was 65 °C / 25 °C. By detecting the ionic conductivity of the water collected on the condensation side in real time, it was found that the ionic conductivity did not change significantly, indicating that the prepared porous hydrophobic reduced graphene oxide membrane had no obvious structural defects and could achieve excellent salt rejection effect. In addition, by measuring the mass of the water collected on the condensation side, the water flux of the porous hydrophobic reduced graphene oxide membrane in this membrane distillation process was 180 - 300 LMH. While ensuring a 100% salt rejection rate for sodium ions, the porous hydrophobic reduced graphene oxide membrane prepared in Example 1 could also achieve a relatively high water flux.

[0060] Example 2

[0061] Compared with Example 1, in this example, the mass of glycine in Step 1 is 100 mg. This example can prepare a reduced graphene oxide dispersion substantially the same as that in Example 1. Due to the decrease in the glycine content, the reduction degree of the reduced graphene oxide is slightly reduced, but the impact on the performance of the membrane is small. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation are basically the same as those in Example 1.

[0062] Example 3

[0063] Compared with Example 1, in this example, the mass of graphene oxide participating in the reaction in Step 1 is 10 mg. This example can prepare a reduced graphene oxide dispersion substantially the same as that in Example 1. Due to the decrease in the mass of graphene oxide, the reduction degree of the reduced graphene oxide increases slightly, but the impact on the performance of the membrane is small. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation are basically the same as those in Example 1.

[0064] Example 4

[0065] Compared with Example 1, in this example, the ultrasonic time in Step 1 is 10 min. This example can prepare a reduced graphene oxide dispersion substantially the same as that in Example 1. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation are basically the same as those in Example 1.

[0066] Example 5

[0067] Compared with Example 1, in this example, the ultrasonic time in Step 1 is 20 min. This example can prepare a reduced graphene oxide dispersion substantially the same as that in Example 1. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation are basically the same as those in Example 1.

[0068] Example 6

[0069] Compared with Example 1, the difference in this example is that the heating temperature in Step 1 is 90 °C. This example can prepare a reduced graphene oxide dispersion that is basically the same as that in Example 1. Due to the decrease in the heating temperature, the reduction degree of the reduced graphene oxide is slightly reduced, but the impact on the performance of the membrane is small. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example are basically the same as those in Example 1.

[0070] Example 7

[0071] Compared with Example 1, the difference in this example is that the heating temperature in Step 1 is 100 °C. This example can prepare a reduced graphene oxide dispersion that is basically the same as that in Example 1. Due to the increase in the heating temperature, the reduction degree of the reduced graphene oxide slightly increases, but the impact on the performance of the membrane is small. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example are basically the same as those in Example 1.

[0072] Example 8

[0073] Compared with Example 1, the difference in this example is that the heating and stirring time in Step 1 is 20 h. This example can prepare a reduced graphene oxide dispersion that is basically the same as that in Example 1. Due to the decrease in the stirring time, the reduction degree of the reduced graphene oxide is slightly reduced, but the impact on the test performance of the membrane is small. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example are basically the same as those in Example 1.

[0074] Example 9

[0075] Compared with Example 1, the difference in this example is that the substrate used in Step 2 is an anodic aluminum oxide membrane. This example can prepare a reduced graphene oxide dispersion that is basically the same as that in Example 1. The porous hydrophobic reduced graphene oxide membrane can also be successfully prepared according to the subsequent steps. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example are basically the same as those in Example 1.

[0076] Example 10

[0077] Compared with Example 1, in this example, the difference is that the substrate used in Step 2 is a mixed cellulose ester membrane. This example can prepare a reduced graphene oxide dispersion that is basically the same as that in Example 1. According to the subsequent steps, a porous hydrophobic reduced graphene oxide membrane can also be successfully prepared. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation are basically the same as those in Example 1.

[0078] Example 11

[0079] Compared with Example 1, in this example, the difference is that the mass of the reduced graphene oxide obtained in Step 2 is 0.125 mg, and the oxygen plasma etching time in Step 3 is 5 min. Due to the different mass of the reduced graphene oxide and the oxygen plasma etching time in this example, a porous hydrophobic reduced graphene oxide membrane with a thickness of 50 nm can be prepared. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation is slightly higher than that in Example 1, and the salt rejection rate is basically the same.

[0080] Example 12

[0081] Compared with Example 1, in this example, the difference is that the mass of the reduced graphene oxide obtained in Step 2 is 1 mg, and the oxygen plasma etching time in Step 3 is 40 min. Due to the different mass of the reduced graphene oxide and the oxygen plasma etching time in this example, a porous hydrophobic reduced graphene oxide membrane with a thickness of 400 nm can be prepared. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation is slightly lower than that in Example 1, and the salt rejection rate is basically the same.

[0082] Example 13

[0083] Compared with Example 1, in this example, the difference is that the substrate used for evaporating and depositing the gold film in Step 3 is anodic aluminum oxide membrane with a pore size of 400 nm. This example can prepare a porous hydrophobic reduced graphene oxide membrane with a pore size of 400 nm. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation is lower than that in Example 1, and the salt rejection rate is basically the same.

[0084] Example 14

[0085] Compared with Example 1, in this example, the difference is that in Step 3, a metal thin film (porous gold film) is directly evaporated on the reduced graphene oxide film. Since the metal thin film on the reduced graphene oxide film is ultrathin and there are a large number of pores on the surface, a porous hydrophobic reduced graphene oxide film with a pore size of 5 nm can be prepared using the porous gold film as a mask plate. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide film, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide film prepared in this example in membrane distillation are basically the same as those in Example 1. At the same time, this example simplifies the preparation process of the porous reduced graphene oxide film and enables the large-scale preparation of the porous reduced graphene oxide film.

[0086] Example 15

[0087] Compared with Example 1, in this example, the difference is that in Step 4, the porous reduced graphene oxide film is treated with fluorine plasma for hydrophobic treatment with a power of 100 W and a time of 40 min, and a porous hydrophobic reduced graphene oxide film is obtained. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide film, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide film prepared in this example in membrane distillation are basically the same as those in Example 1.

[0088] Example 16

[0089] Compared with Example 1, in this example, the difference is that in Step 4, the power of the hydrophobic treatment is 50 W, and a porous hydrophobic reduced graphene oxide film is obtained. Through the membrane distillation test on the film, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide film prepared in this example in membrane distillation are basically the same as those in Example 1.

[0090] Example 17

[0091] Compared with Example 1, in this example, the difference is that in Step 4, the power of the hydrophobic treatment is 75 W, and a porous hydrophobic reduced graphene oxide film is obtained. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide film, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide film prepared in this example in membrane distillation are basically the same as those in Example 1.

[0092] Example 18

[0093] Compared with Example 1, in this example, the difference is that in Step 4, the time of the hydrophobic treatment is 20 min, and a porous hydrophobic reduced graphene oxide film is obtained. Through the membrane distillation test on the porous hydrophobic reduced graphene oxide film, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide film prepared in this example in membrane distillation are basically the same as those in Example 1.

[0094] Example 19

[0095] Compared with Example 1, in this example, the time for hydrophobic treatment in Step 4 is 30 min, and a porous hydrophobic reduced graphene oxide membrane is obtained. Through the membrane distillation test of the porous hydrophobic reduced graphene oxide membrane, it is found that the water flux and salt rejection rate of the porous hydrophobic reduced graphene oxide membrane prepared in this example in membrane distillation are basically the same as those in Example 1.

[0096] Comparative Example 1

[0097] Compared with Example 1, in this comparative example, the mass of glycine in Step 1 is 80 mg. In this comparative example, due to the small mass of glycine, the reduction degree of reduced graphene oxide is small, which causes the structure of the subsequent prepared porous hydrophobic reduced graphene oxide membrane to be unstable.

[0098] Comparative Example 2

[0099] Compared with Example 1, in this comparative example, the ultrasonic time in Step 1 is 60 min. In this comparative example, due to the too long ultrasonic time, the reduced graphene oxide is small, and there will be a large number of defects in the reduced graphene oxide membrane obtained after the stacking of reduced graphene oxide, which is not conducive to the subsequent experiments.

[0100] Comparative Example 3

[0101] Compared with Example 1, in this comparative example, the heating temperature in Step 1 is 120 °C. In this comparative example, due to the too high heating temperature, the reduction degree of reduced graphene oxide is too large, which will lead to the decline of the mechanical properties of the prepared porous hydrophobic reduced graphene oxide membrane and affect the membrane distillation effect during the test.

[0102] Comparative Example 4

[0103] Compared with Example 1, in this comparative example, the heating and stirring time in Step 1 is 16 h. In this comparative example, due to the short heating and stirring time, the reduction degree of reduced graphene oxide is small, which causes the structure of the subsequent prepared porous hydrophobic reduced graphene oxide membrane to be unstable.

[0104] Comparative Example 5

[0105] Compared with Example 1, in this comparative example, the power of oxygen plasma etching in Step 3 is 100 W. In this comparative example, due to the too large power of oxygen plasma etching, large-scale irregular hole defects will be caused on the surface of the reduced graphene oxide membrane, seriously damaging the structure of the membrane.

[0106] Comparative Example 6

[0107] This comparative example is different from Example 1 in that the oxygen plasma etching time in Step 3 of this comparative example is 60 min. In this comparative example, due to the too long oxygen plasma etching time, the structure of the membrane will also be damaged.

[0108] Comparative Example 7

[0109] This comparative example is different from Example 1 in that the power of the sulfur hexafluoride plasma hydrophobization treatment in Step 4 of this comparative example is 40 W. In this comparative example, due to the small power of the sulfur hexafluoride plasma hydrophobization treatment, the hydrophobic effect of the porous hydrophobic reduced graphene oxide membrane is not good.

[0110] Comparative Example 8

[0111] This comparative example is different from Example 1 in that the time of the sulfur hexafluoride plasma hydrophobization treatment in Step 4 of this comparative example is 4 min. In this comparative example, due to the short time of the sulfur hexafluoride plasma hydrophobization treatment, the hydrophobic performance of the porous hydrophobic reduced graphene oxide membrane is also low, which affects the subsequent membrane distillation experiment.

[0112] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description. All such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a porous hydrophobic reduced graphene oxide membrane, characterized in that, Including: Step 1: Mix glycine with a graphene oxide dispersion liquid, and obtain a reduced graphene oxide dispersion liquid through heating reduction. Step 2: Select a hydrophilic substrate with a pore structure, and form a film of the reduced graphene oxide dispersion liquid on the hydrophilic substrate to obtain a reduced graphene oxide film. Step 3: Use a porous metal film as a mask plate to perform oxygen plasma etching on the reduced graphene oxide film to obtain a porous reduced graphene oxide film. Step 4: Use plasma to perform hydrophobic treatment on the porous reduced graphene oxide film to obtain the porous hydrophobic reduced graphene oxide film.

2. The preparation method according to claim 1, wherein In Step 1, the mass ratio of glycine to graphene oxide in the graphene oxide dispersion liquid is 100 - 125:10 - 25.

3. The preparation method according to claim 1, characterized in that, In Step 1, the heating reduction is carried out by ultrasonic and heating stirring. The ultrasonic time is 10 - 30 min, the temperature of heating stirring is 90 - 100 °C, and the time of heating stirring is 20 - 24 h.

4. The preparation method according to claim 1, characterized in that, The hydrophilic substrate in Step 2 is an anodic aluminum oxide membrane, a polyethersulfone membrane or a mixed cellulose ester membrane, and the pore diameter of the hydrophilic substrate is 100 - 200 nm.

5. The preparation method according to claim 1, characterized in that, In Step 2, the method of forming a film of the reduced graphene oxide dispersion liquid on the hydrophilic substrate is one of suction filtration, spin coating, blade coating, dip coating. The thickness of the reduced graphene oxide film obtained by using 0.125 - 1 mg of reduced graphene oxide is 50 - 400 nm.

6. The preparation method according to claim 1, characterized in that, The pore diameter of the porous metal film in Step 3 is 5 - 400 nm.

7. The preparation method according to claim 1, characterized in that, In Step 3, the power of the oxygen plasma etching is 50 - 100 W, and the oxygen plasma etching time of the reduced graphene oxide film with a thickness of 50 - 400 nm is 5 - 40 min.

8. The preparation method according to claim 1, characterized in that, In Step 4, the plasma is sulfur hexafluoride plasma or fluorine plasma, the power of the hydrophobic treatment is 50 - 100 W, and the time is 5 - 40 min.

9. A porous hydrophobic reduced graphene oxide membrane, characterized in that, Prepared by the preparation method described in any one of claims 1 - 8.

10. Application of a porous hydrophobic reduced graphene oxide film as described in claim 9 in the field of seawater desalination.

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