An ultrathin graphene filtration membrane and a preparation method thereof

Abstract

The present application relates to a kind of ultra-thin graphene filtration membrane and its preparation method, belong to filtration membrane technical field.The preparation method of the present application includes the following steps, S1, graphene dispersion is added to the vacuum filtration equipment fixed with filter membrane, graphene membrane is deposited on filter membrane by the way of vacuum filtration;S2, the filter membrane that graphene membrane is deposited is immersed in separation liquid to make graphene membrane separate from filter membrane, and ultra-thin graphene filtration membrane is obtained.The preparation method of the present application constructs graphene membrane with ordered and dense structure by vacuum filtration method, thickness can be accurately controlled by graphene deposition amount, and pure stone ultra-thin graphene filtration membrane is obtained by separation liquid, the thermal conductivity of ultra-thin graphene filtration membrane is 1632W / m·k, even after severe friction and folding, it also has excellent no fold performance.After 100 times hard folding cycle, the thermal conductivity only drops by 0.7%.

Description

Technical Field

[0001] This invention belongs to the field of vacuum filtration membrane technology, and particularly relates to an ultrathin graphene vacuum filtration membrane and its preparation method. Background Technology

[0002] With the rapid advancements in electronic device performance over the past few decades, effectively removing heat generated by integrated circuit (IC) chips (such as CPUs and GPUs) has become increasingly important for the continuous, stable, and smooth operation of systems. Since device reliability is exponentially related to operating temperature, a temperature increase of 10°C-15°C can shorten device lifespan by 50%. Graphene, a two-dimensional carbon allotrope, consists of only a single planar layer with conjugated atoms arranged in a honeycomb lattice. Graphene's low atomic mass, strong bonding, simple crystal structure, and low unharmony give it a unique K≈5300W / m·K. Simultaneously, graphene possesses excellent flexibility; these unique properties make it a promising candidate for creating ultra-flexible heat dissipation films for ultra-high-temperature applications.

[0003] There are many methods for graphene film deposition. With the rapid development of chemical vapor deposition (CVD) technology, high-quality single-layer or multi-layer graphene films can be obtained for research or applications. Advanced researchers use thermal CVD to grow single-layer graphene films. When applied to Pt chips, the hotspot temperature was reduced from 394K to 381K. Ultrafast growth technology has driven the scalable preparation of CVD graphene. For example, a one-inch-sized single-crystal graphene can be rapidly grown on a Cu-Ni alloy substrate. Xu et al. developed an ultrafast CVD method using oxygen supply to grow single-crystal graphene. However, the application of CVD graphene films as thermal diffusers still faces obstacles because transferring graphene from the substrate without damaging the lattice structure is relatively difficult. Furthermore, this method is costly, often requiring heating to several thousand degrees Celsius, resulting in enormous energy consumption. Therefore, more and more research is adopting methods such as spraying, drop coating, and screen printing to deposit prepared graphene powder into films, significantly reducing costs. However, the resulting graphene film has problems such as loose structure, uneven film thickness, and poor controllability of surface morphology, all of which have a huge impact on the heat dissipation effect of graphene.

[0004] Vacuum filtration technology involves depositing materials and dispersions onto a filter membrane surface using a vacuum negative pressure method. Due to the van der Waals forces between the deposited layer and the filter membrane, the deposited layer (especially a thin layer) is difficult to separate from the membrane surface. Therefore, this technology is often used to deposit nanomaterials that do not require separation from the filter membrane, and the deposited material is used together with the filter membrane after deposition. During the deposition process, if the deposited layer is thinner in one area than in others, the liquid flow rate increases at that location, thereby accelerating the deposition rate and "filling in" the thin spot. This "self-regulating" mechanism allows for the production of highly smooth and uniform deposited layers with a very compact and ordered structure. Furthermore, under a fixed negative pressure, the thickness of the deposited layer can be precisely controlled by adjusting the amount of nanomaterial used. However, the non-destructive separation of the filtered graphene membrane from the substrate remains a challenge for this method. Currently, the graphene filtration membranes with relatively thick thickness (>5μm) are the ones that can achieve good separation results. For example, the graphene-based heat dissipation membrane prepared by Professor Song's team based on vacuum filtration has a thickness of about 10μm and a thermal conductivity of 150W / m·k; the graphene heat dissipation membrane prepared by Dai et al. based on vacuum filtration has a thickness of more than 20μm and a thermal conductivity of about 300W / m·k.

[0005] However, according to the principle of heat conduction, the thinner the graphene film, the lower the heat transfer loss between layers and the higher the conductivity. Therefore, how to achieve non-destructive and rapid separation and transfer of thin vacuum-filtered deposited layers from the substrate is the key to breakthroughs in the application of vacuum-filtered simultaneous masking in heat dissipation film preparation. However, deposition methods, including spraying, drop coating, screen printing, and inkjet printing, all suffer from varying degrees of problems such as uneven printing lines, loose deposition structures, poor controllability, and significant susceptibility to environmental influences due to the "coffee ring" effect.

[0006] Vacuum filtration allows for precise control of graphene film thickness, resulting in deposited graphene films with uniform surfaces and compact structures, which is highly beneficial for improving thermal conductivity. However, a method for separating graphene films with controllable thickness is currently lacking. Sun et al. obtained graphene films by depositing graphene oxide films and then reducing them. However, the internal graphene oxide cannot fully contact the reducing agent, leading to incomplete reduction, and graphene oxide has poor thermal conductivity. Therefore, a method is needed to non-destructively separate the fully reduced graphene film from the substrate.

[0007] A graphene deposition layer with uniform and controllable thickness and a compact structure was deposited on the filter membrane using a vacuum filtration method. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the problem that the existing technology cannot separate the graphene filtration membrane from the substrate, especially for very thin graphene membranes, and to achieve rapid and non-destructive separation.

[0009] To address the aforementioned technical problems, this invention provides an ultrathin graphene filtration membrane and its preparation method. A graphene membrane with an ordered and dense structure is constructed using a vacuum filtration method, and then a pure ultrathin graphene filtration membrane is obtained using a coagulation bath method. The thermal conductivity of the ultrathin graphene filtration membrane reaches 1632 W / m·K.

[0010] The first objective of this invention is to provide a method for preparing an ultrathin graphene filtration membrane, comprising the following steps:

[0011] S1. Add graphene dispersion to a vacuum filtration device with a fixed filter membrane, and deposit a graphene membrane on the filter membrane by vacuum filtration.

[0012] S2. The filter membrane with graphene deposited on it is immersed in the separation liquid to separate the graphene membrane from the filter membrane, thus obtaining an ultrathin graphene vacuum filtration membrane.

[0013] In one embodiment of the present invention, in S1, the filter membrane is selected from alumina, polyimide or polycarbonate.

[0014] In one embodiment of the present invention, in S1, the preparation of the graphene specifically includes the following steps: dispersing graphene oxide in a triethylene glycol solution to form a graphene oxide dispersion, irradiating it with a laser wavelength of 1000nm-1100nm, and after irradiation, washing and drying to obtain the graphene; the triethylene glycol solution is prepared by mixing triethylene glycol and N,N-dimethylformamide in a volume ratio of 1-10:1-10.

[0015] In one embodiment of the present invention, the concentration of the graphene oxide is 0.5 mg / mL to 2 mg / mL.

[0016] In one embodiment of the present invention, the laser irradiation time is 0.25h-2h, the frequency is 5Hz-20Hz, and the energy density is 300mJ-1200mJ.

[0017] In one embodiment of the present invention, in S1, the concentration of the graphene dispersion is 0.1 μg / mL to 100 mg / mL.

[0018] In one embodiment of the present invention, in S1, the thickness of the graphene film is 30 nm-6 μm.

[0019] In one embodiment of the present invention, in S1, the pressure of vacuum filtration is 0.01MPa-0.15MPa.

[0020] In one embodiment of the present invention, the dispersion and the separation liquid satisfy three conditions: first, the polarity of the separation liquid is less than that of the dispersion liquid; second, the dispersibility of the separation liquid for graphene is weaker than that of the dispersion liquid; and third, the separation liquid and the dispersion liquid are miscible.

[0021] Furthermore, when the dispersion is N,N-dimethylformamide (DMF), the separation liquid is selected from ethanol, methanol, or acetone;

[0022] When the dispersion is isopropanol, the separation liquid is selected from heptane, cyclopentane, or isooctane;

[0023] When the dispersion is acetone, the separation liquid is selected from isopropanol, heptane, cyclopentane or isooctane.

[0024] A second objective of this invention is to provide an ultrathin graphene filtration membrane prepared by the aforementioned preparation method.

[0025] The technical solution of the present invention has the following advantages compared with the prior art:

[0026] (1) The preparation method described in this invention constructs a graphene membrane with an ordered and dense structure through vacuum filtration. The thickness can be precisely controlled by the amount of graphene deposited. Then, a pure ultrathin graphene filtration membrane is obtained through separation liquid. The thermal conductivity of the ultrathin graphene filtration membrane is 1632 W / m·K, and it has excellent crease-free performance even after severe friction and folding. After 100 hard folding cycles, the thermal conductivity only decreases by 0.7%.

[0027] (2) The preparation method described in this invention can uniformly disperse graphene using a suitable dispersant to achieve better deposition results. This is mainly achieved by altering the phase equilibrium of the liquid through a dual-diffusion mass transfer mechanism, disrupting the solvation of the nanoelectrode sheets in the dispersant, causing the dispersant molecules to diffuse outwards while the separation liquid molecules diffuse inwards. This results in the rapid shrinkage and compaction of the nanoelectrode deposition layer. The compact structure not only improves the electrical properties of the deposition layer but also enhances its mechanical properties. With a suitable separation liquid, the dual-diffusion mass transfer process is activated after the three-phase interface comes into contact. Once dual-diffusion mass transfer occurs, the binding energy between the graphene layer and the filter membrane decreases, enabling rapid and non-destructive separation of graphene electrode deposition layers with thicknesses ranging from nanometers to micrometers. Attached Figure Description

[0028] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0029] Figure 1 This is a diagram of the graphene filtration membrane of Example 1 of the present invention;

[0030] Figure 2 This is a test image showing the thinness of the graphene filtration membrane in Example 1 of the present invention.

[0031] Figure 3 The separation mechanism of the graphene filtration membrane of this invention;

[0032] Figure 4 The images shown are SEM images of the graphene membrane prepared in Example 1 of the present invention, wherein (a) is a surface SEM image of the ultrathin graphene filtration membrane of Example 1, (b) is a cross-sectional SEM image of the ultrathin graphene filtration membrane of Example 1, (c) is a cross-sectional SEM image of the graphene membrane of Comparative Example 3, and (d) is a cross-sectional SEM image of the graphene membrane of Comparative Example 4.

[0033] Figure 5 The thermal conductivity of graphene filtration membranes of different thicknesses in Test Example 3 of this invention;

[0034] Figure 6 The thermal conductivity of different graphene films in Test Example 4 of this invention;

[0035] Figure 7 The figures show the flexibility test results of the graphene filtration membranes prepared under different pressure conditions in Test Example 5 of this invention; where (a) is the unfolded image after 100 folds (0.1 MPa), (b) is the unfolded image after 100 folds (0.2 MPa), (c) is the unfolded image after 100 folds (2 MPa), (d) is a magnified image of the corresponding fold (0.1 MPa), (e) is a magnified image of the corresponding fold (0.2 MPa), and (f) is a magnified image of the corresponding fold (2 MPa); the scale bar is 5 μm. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0037] In this invention, unless otherwise stated, the 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.

[0038] In this invention, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0040] Example 1

[0041] The ultrathin graphene filtration membrane and its preparation method of the present invention specifically include the following steps:

[0042] S1. Graphene oxide was dispersed in a triethylene glycol solution (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion with a concentration of 0.5 mg / mL. The dispersion was irradiated with a laser at a wavelength of 1064 nm for 15 min. The laser irradiation frequency was 5 Hz and the energy density was 300 mJ. After irradiation, the dispersion was washed once with water and once with ethanol, and then dried at 60 °C to constant weight to obtain graphene.

[0043] S2. Graphene was dispersed in DMF to form a graphene dispersion with a concentration of 0.1 mg / mL. Alumina was used as a filter membrane, which was fixed in a vacuum filtration funnel. The graphene dispersion was poured into the funnel, and a graphene membrane was deposited on the filter membrane by vacuum filtration (pressure 0.1 MPa). After filtration, the graphene-coated filter membrane was placed in a container, and ethanol was added to separate the graphene membrane from the filter membrane, resulting in a graphene filtration membrane with a thickness of approximately 1.83 μm. Figure 1 As shown, from Figure 1 It can be seen that the graphene filtration membrane has a complete and flat structure.

[0044] Example 2

[0045] The ultrathin graphene filtration membrane and its preparation method of the present invention specifically include the following steps:

[0046] S1. Graphene oxide was dispersed in a triethylene glycol solution (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion with a concentration of 0.5 mg / mL. The dispersion was irradiated with a laser at a wavelength of 1064 nm for 30 min. The laser irradiation frequency was 10 Hz and the energy density was 600 mJ. After irradiation, the dispersion was washed once with water and once with ethanol, and then dried at 60 °C to constant weight to obtain graphene.

[0047] S2. Graphene is dispersed in DMF to form a graphene dispersion with a concentration of 0.5 mg / mL. Alumina is used as a filter membrane, which is fixed in a vacuum filtration funnel. The graphene dispersion is poured into the vacuum filtration funnel, and a graphene membrane is deposited by vacuum filtration (pressure of 0.1 MPa). After filtration, the filter membrane with the deposited graphene membrane is placed in a container, and ethanol is added to separate the graphene membrane from the filter membrane to obtain a graphene filtration membrane with a thickness of 30 nm.

[0048] Example 3

[0049] The ultrathin graphene filtration membrane and its preparation method of the present invention specifically include the following steps:

[0050] S1. Graphene oxide was dispersed in a triethylene glycol solution (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion with a concentration of 1 mg / mL. The dispersion was irradiated with a laser at a wavelength of 1064 nm for 60 min. The laser irradiation frequency was 15 Hz and the energy density was 800 mJ. After irradiation, the dispersion was washed once with water and once with ethanol, and then dried at 60 °C to constant weight to obtain graphene.

[0051] S2. Graphene is dispersed in DMF to form a graphene dispersion with a concentration of 1 mg / mL. Alumina is used as a filter membrane, which is fixed in a vacuum filtration funnel. The graphene dispersion is poured into the vacuum filtration funnel, and a graphene membrane is deposited by vacuum filtration (pressure of 0.1 MPa). After filtration, the filter membrane with the deposited graphene membrane is placed in a container, and ethanol is added to separate the graphene membrane from the filter membrane to obtain a graphene filtration membrane with a thickness of 3 μm.

[0052] Example 4

[0053] The ultrathin graphene filtration membrane and its preparation method of the present invention specifically include the following steps:

[0054] S1. Graphene oxide was dispersed in a triethylene glycol solution (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion with a concentration of 2 mg / mL. The dispersion was irradiated with a laser at a wavelength of 1064 nm for 120 min. The laser irradiation frequency was 20 Hz and the energy density was 1200 mJ. After irradiation, the dispersion was washed once with water and once with ethanol, and then dried at 60 °C to constant weight to obtain graphene.

[0055] S2. Graphene is dispersed in DMF to form a graphene dispersion with a concentration of 10 mg / mL. Alumina is used as a filter membrane, which is fixed in a vacuum filtration funnel. The graphene dispersion is poured into the vacuum filtration funnel, and a graphene membrane is deposited by vacuum filtration (pressure of 0.1 MPa). After filtration, the filter membrane with the deposited graphene membrane is placed in a container, and ethanol is added to separate the graphene membrane from the filter membrane to obtain a graphene filtration membrane with a thickness of 6 μm.

[0056] Example 5

[0057] The ultrathin graphene filtration membrane and its preparation method of the present invention specifically include the following steps:

[0058] S1. Graphene oxide was dispersed in a triethylene glycol solution (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion with a concentration of 0.5 mg / mL. The dispersion was irradiated with a laser at a wavelength of 1064 nm for 15 min. The laser irradiation frequency was 5 Hz and the energy density was 300 mJ. After irradiation, the dispersion was washed once with water and once with ethanol, and then dried at 60 °C to constant weight to obtain graphene.

[0059] S2. Graphene is dispersed in ethanol to form a graphene dispersion with a concentration of 0.1 mg / mL. Alumina is used as a filter membrane, which is fixed in a vacuum filtration funnel. The graphene dispersion is poured into the vacuum filtration funnel, and a graphene membrane is deposited on the filter membrane by vacuum filtration (pressure of 0.1 MPa). After filtration, the filter membrane with the graphene membrane deposited is placed in a container, and methanol is added to separate the graphene membrane from the filter membrane, thus obtaining a graphene vacuum filtration membrane.

[0060] Example 6

[0061] The ultrathin graphene filtration membrane and its preparation method of the present invention specifically include the following steps:

[0062] S1. Graphene oxide was dispersed in a triethylene glycol solution (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion with a concentration of 0.5 mg / mL. The dispersion was irradiated with a laser at a wavelength of 1064 nm for 15 min. The laser irradiation frequency was 5 Hz and the energy density was 300 mJ. After irradiation, the dispersion was washed once with water and once with ethanol, and then dried at 60 °C to constant weight to obtain graphene.

[0063] S2. Graphene is dispersed in acetone to form a graphene dispersion with a concentration of 0.1 mg / mL. Alumina is used as a filter membrane, which is fixed in a vacuum filtration funnel. The graphene dispersion is poured into the vacuum filtration funnel, and a graphene membrane is deposited on the filter membrane by vacuum filtration (pressure of 0.1 MPa). After filtration, the filter membrane with the graphene membrane deposited is placed in a container, and methylamine is added to separate the graphene membrane from the filter membrane, thus obtaining a graphene vacuum filtration membrane.

[0064] Comparative Example 1

[0065] The results are basically the same as in Example 1, except that water was used instead of ethanol, which made it impossible to successfully peel off the graphene film.

[0066] Comparative Example 2

[0067] The results are basically the same as in Example 1, except that DMF was replaced with acetone, which made it impossible to successfully peel off the graphene film.

[0068] Comparative Example 3

[0069] The process is basically the same as in Example 1, except that: S2, the graphene film is prepared by drop coating. Graphene is dispersed in N,N-dimethylformamide to form a graphene dispersion with a concentration of 1 mg / mL. The graphene dispersion is evenly dropped onto a smooth polytetrafluoroethylene plate. The substrate is heated until the solution evaporates to form a graphene film, and then the film is separated from the substrate.

[0070] Comparative Example 4

[0071] The process is basically the same as in Example 1, except that: S2, the graphene prepared by screen printing is dispersed in N,N-dimethylformamide to form a graphene dispersion with a concentration of 1 mg / mL. The graphene dispersion is then screen printed onto a polytetrafluoroethylene plate. After the substrate is heated and the solution evaporates to form a graphene film, the graphene film is separated from the substrate.

[0072] Test Example 1

[0073] The ultrathin graphene filtration membrane prepared in Example 1 was placed on dandelion, and the results were as follows: Figure 2 As shown. From Figure 2 As can be seen, the ultrathin graphene filtration membrane is extremely thin and light, showing no damage or collapse even on the fragile dandelion. This demonstrates that the graphene membrane prepared by the method of this invention is thin and lightweight, which is highly advantageous for the field of electronic devices. Its separation mechanism is as follows: Figure 3 As shown, from Figure 3 As can be seen, immediately after filtration, a large amount of dispersion exists between the graphene layers. Upon placement in the separation liquid, due to the excellent interoperability between the separation liquid and the dispersion liquid, and the greater polarity of the separation liquid, dispersion molecules rapidly escape from the interlayer space and combine with the separation liquid. However, because the separation liquid has poor dispersion properties for graphene, very few molecules enter the interlayer space. Under these conditions, the spacing between layers rapidly decreases, the structure becomes compact, and separation from the substrate is achieved under buoyancy. A suitable dispersant can uniformly disperse graphene, resulting in better deposition effects. This is mainly achieved by altering the phase equilibrium of the liquid through a dual-diffusion mass transfer mechanism, disrupting the solvation of the nanoelectrode sheets in the dispersant, causing dispersant molecules to diffuse outwards while separation liquid molecules diffuse inwards. This results in the rapid shrinkage and compaction of the nanoelectrode deposition layer. The compact structure not only improves the electrical properties of the deposition layer but also enhances its mechanical properties. With a suitable separation liquid, after the three-phase interface comes into contact, a double diffusion mass transfer process is activated. After the double diffusion mass transfer occurs, the binding energy between the graphene layer and the filter membrane decreases, enabling rapid and non-destructive separation of graphene electrode deposition layers with thicknesses ranging from nanometers to micrometers.

[0074] Test Example 2

[0075] The graphene films prepared in Example 1 and Comparative Examples 3-4 were characterized, and the results are as follows: Figure 4 As shown. From Figure 4 As can be seen, the graphene film prepared in Example 1 exhibits a flat structure with a thickness of 1.83 μm, and the graphene sheets are compactly and orderly stacked. The graphene film prepared in Comparative Example 3 has a thickness of 2.23 μm, with loosely stacked graphene sheets and large air gaps between layers. The graphene film prepared in Comparative Example 4 has a thickness of 1.42 μm, and the graphene sheets are relatively loosely stacked.

[0076] Test Example 3

[0077] Based on Example 1, the effect of different graphene filtration membrane thicknesses on thermal conductivity was investigated. The specific experimental procedure was as follows: graphene was dispersed in a DMF dispersion, and then deposited under vacuum at 0.1 MPa to obtain a graphene membrane. The thickness of the graphene membrane was determined by the amount of graphene deposited. When the amount of graphene deposited was 2 g / m... 3 2.85g / m 3 3.85g / m 3 and 4.8g / m 3 The obtained graphene film thicknesses were 1.06 μm, 1.83 μm, 2.78 μm, and 3.84 μm, respectively. Ethanol was then used as the dispersion for separating the graphene film from the substrate, and thermal conductivity was measured. The results are as follows: Figure 5 As shown. From Figure 5 It can be seen that the thermal conductivity is 1488 W / m·K when the film thickness is 1.08 μm; the highest thermal conductivity is 1632 W / m·K at 1.83 μm; 1422 W / m·K at 2.78 μm; and 1231 W / m·K at 3.84 μm. Generally, as the number of stacked graphene layers increases, more scattering occurs during heat transfer, thus the thermal conductivity decreases with increasing film thickness. However, the highest thermal conductivity was obtained when the thickness of the graphene film separated by vacuum filtration was 1.83 μm, which is 3.5% higher than that of the 1.08 μm thickness. This is because, for vacuum filtration, excessively thin graphene films have low density and short filtration times, resulting in more air layers between layers, thus affecting the thermal conductivity.

[0078] Test Example 4

[0079] Based on the above experiments, the thermal conductivity of the graphene films prepared in Example 1 and Comparative Examples 3-4 was compared, and the results are as follows: Figure 6 As shown. From Figure 6 It can be seen that screen printing has a heat output of 945 W / m·K, drop coating has 543 W / m·K, and vacuum filtration has 1632 W / m·K. This is because vacuum filtration can obtain a more dense and ordered graphene arrangement, resulting in a smaller air layer distance for heat transfer between layers and reduced heat loss. Screen printing and drop coating methods have a large number of voids between layers. Figure 4 c-4d).

[0080] Test Example 5

[0081] Based on Example 1, at 2.85 g / m 3 To measure the graphene deposition rate, the flexibility was tested at 0.1 MPa, 0.2 MPa, and 2 MPa, and the results are as follows: Figure 7 As shown. From Figure 7As can be seen, after repeatedly folding the prepared membrane 100 times and unfolding it, the best flexibility was observed at a pressure of 0.1 MPa, with almost no visible creases. This conclusion was also consistent under an optical microscope. This is because the method of this invention can provide an ordered membrane structure, which is highly advantageous for material flexibility. The membrane flexibility is related to the filtration pressure. Excessive pressure leads to tighter interlayer spacing of the graphene layers, resulting in decreased flexibility. Insufficient pressure fails to meet the high thermal conductivity requirement. At a pressure of 0.1 MPa, after 100 hard-folding cycles, the thermal conductivity decreased by only 0.7%, demonstrating the excellent performance of the ultrathin graphene filtration membrane prepared by this invention.

[0082] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing an ultrathin graphene filtration membrane, characterized in that, Includes the following steps, S1. A graphene dispersion is added to a vacuum filtration device with a fixed filter membrane, and a graphene film is deposited on the filter membrane by vacuum filtration. The preparation of the graphene specifically includes the following steps: dispersing graphene oxide in a triethylene glycol solution to form a graphene oxide dispersion, irradiating it with a laser wavelength of 1000nm-1100nm, and after irradiation, washing and drying to obtain the graphene; the triethylene glycol solution is prepared by mixing triethylene glycol and N,N-dimethylformamide in a volume ratio of 1-10:1-10. S2. The filter membrane with graphene deposited on it is immersed in the separation liquid to separate the graphene membrane from the filter membrane, thus obtaining an ultrathin graphene filtration membrane. The dispersion and the separation liquid meet three conditions: first, the polarity of the separation liquid is less than that of the dispersion liquid; second, the dispersibility of the separation liquid for graphene is weaker than that of the dispersion liquid; and third, the separation liquid and the dispersion liquid are miscible.

2. The method for preparing the ultrathin graphene filtration membrane according to claim 1, characterized in that, In S1, the filter membrane is selected from alumina, polyimide, or polycarbonate.

3. The method for preparing the ultrathin graphene filtration membrane according to claim 1, characterized in that, In S1, the concentration of the graphene oxide is 0.5 mg / mL to 2 mg / mL.

4. The method for preparing the ultrathin graphene filtration membrane according to claim 1, characterized in that, In S1, the laser irradiation time is 0.25h-2h, the frequency is 5Hz-20Hz, and the energy density is 300mJ-1200mJ.

5. The method for preparing the ultrathin graphene filtration membrane according to claim 1, characterized in that, In S1, the concentration of the graphene dispersion is 0.1 μg / mL to 100 mg / mL.

6. The method for preparing the ultrathin graphene filtration membrane according to claim 1, characterized in that, In S1, the thickness of the graphene film is 30 nm-6 μm.

7. The method for preparing the ultrathin graphene filtration membrane according to claim 1, characterized in that, In S1, the pressure of vacuum filtration is 0.01MPa-0.15MPa.

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