Method for preparing high-orientation and high-reflectivity graphene film through vapor pressure assisted stretching reduction

Abstract

The invention belongs to the technical field of material science and engineering, and relates to a method for preparing a high-orientation high-reflectivity graphene film through vapor pressure assisted stretching reduction, and the method comprises the following steps: carrying out isotropic stretching and vapor treatment on a graphene oxide film at the same time, namely heating a mixed solution of a hydrogen iodide aqueous solution and ethanol until the mixed solution is vaporized, and carrying out heat preservation at 90-120 DEG C for 6-24 hours, the volume ratio of the hydrogen iodide aqueous solution to the ethanol is 1: (2-5). According to the method, the graphene film is subjected to isotropic tensile stress in the reduction process, so that wrinkles and ripples generated by thermal fluctuation and interlayer spacing change are effectively eliminated, and the flatness of the graphene sheet layer is improved.

Description

Technical Field

[0001] The invention belongs to the field of material science and engineering technology, and relates to a method for preparing a high-oriented and high-reflectivity graphene film by steam pressure-assisted stretching and reduction. Background Art

[0002] As a new type of material, graphene macro-assembly film has shown great application potential in electronic devices, energy catalysis, thermal radiation management, aerospace and other fields due to its unique physical and chemical properties, such as light weight, high electrical conductivity, high thermal conductivity and good mechanical properties.

[0003] The flatness of graphene sheets, the close stacking between sheets, and the order of interlayer stacking in graphene macroscopic assembled films have a crucial impact on their performance. Specifically, the flatness of the sheets directly affects the in-plane transmission efficiency of quasiparticles (such as electrons and phonons) on the sheets, including the ballistic transmission and scattering transmission of electrons, and the ballistic fluctuation and scattering process of phonons. The close stacking between sheets has a significant impact on the inter-sheet transmission of quasiparticles, mainly involving the tunneling effect and thermal excitation transmission mechanism of electrons, as well as the coupled transmission and interface scattering process between phonons. If the stacking domains are disordered or there are a large number of dislocations, electrons and phonons will encounter frequent interface scattering and defect scattering during transmission, which will not only hinder the effective transmission of quasiparticles, but also introduce potential barriers in the material, thereby reducing the electrical and thermal conductivity of the graphene macroscopic assembled films. Therefore, achieving high flatness of graphene sheets, close stacking between sheets, and ordered orientation of stacking domains is the key to improving the mechanical properties, electrical conductivity, and thermal conductivity of graphene macroscopic assembled films.

[0004] Traditional methods for preparing graphene macroscopic assembled films, such as vacuum filtration, pouring evaporation, scraping, spraying, and layer-by-layer self-assembly, usually face many challenges, such as wrinkles between graphene sheets. When wrinkles exist in graphene sheets, the order of the sheet stacking domain will be destroyed, which will make it difficult for the sheets to be tightly stacked, resulting in disordered orientation of the sheets, which ultimately manifests as insufficient surface flatness of the film.

[0005] In order to solve the defects of traditional technology, patent application CN111807355B first obtains a self-supporting GO film by vacuum filtration of GO (graphene oxide) solution, and then immerses the GO film in ethanol for orientation under orthogonal biaxial external force traction, and then places it in a mixed solution of hydroiodic acid and ethanol for chemical reduction, thereby obtaining a graphene macroscopic assembly film. Patent application CN112174120A discloses a method for preparing a high-strength and high-conductivity graphene film, which adds a chemical cross-linking step on the basis of patent application CN111807355B to obtain a high-strength and high-conductivity graphene macroscopic assembly film. However, the flatness of the graphene sheets of the graphene macroscopic assembly films of the above two patents needs to be further improved. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art and to provide a method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching and reduction.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, wherein the graphene oxide film is isotropically stretched and steam treated at the same time, wherein the steam treatment is to heat a mixture of an aqueous hydrogen iodide solution and ethanol until vaporized and then keep the mixture at 90-120° C. for 6-24 hours, wherein the volume ratio of the aqueous hydrogen iodide solution to the ethanol is 1:2-5;

[0009] The thickness of the graphene oxide film is 5-100 μm;

[0010] When the thickness of the graphene oxide film is ≤10 μm, the device used for isotropically stretching and steam treating the graphene oxide film at the same time includes a solvent pool a and a heating device a; the top of the solvent pool a is a vertically arranged cylinder a, the cylinder a is divided into an upper and lower layer and is detachably connected by 2m membrane fixing screws a, m>2, and the 2m membrane fixing screws a are evenly distributed around the circumference of the central axis of the cylinder a; the heating device a is used to heat the solvent pool a;

[0011] When the thickness of the graphene oxide film is greater than 10 μm, the device used for simultaneously isotropically stretching and steam treating the graphene oxide film includes a solvent pool b, a heating device b, a deformable tube and a regulator; the bottom of the deformable tube is sealed and connected to the top of the solvent pool b, the top of the deformable tube is a vertically arranged cylinder b, the cylinder b is divided into two layers, the upper and lower layers are detachably connected by 2m membrane fixing screws b, m>2, and the 2m membrane fixing screws b are evenly distributed around the circumference of the central axis of the cylinder b; the regulator is used to control the radial outward expansion of the cylinder b along the cylinder b; the heating device b is used to heat the solvent pool b.

[0012] like Figure 8 As shown, during the heat preservation process, hydrogen iodide vapor performs nucleophilic reduction on the graphene oxide film fixed above, and the vapor pressure generated by ethanol vapor exerts outward pressure on the graphene oxide film. The vapor pressure acts evenly on the surface of the graphene oxide film. The graphene oxide film is subjected to isotropic tensile stress while being reduced. As the reduction reaction proceeds, the wrinkles and ripples caused by thermal fluctuations and changes in interlayer spacing are eliminated, while gases such as carbon dioxide generated by deoxygenation are squeezed out during the stretching process. At the same time, ethanol molecules enter the film and play a plasticizing role, further releasing some wrinkles and folds. Therefore, the stacking order between graphene sheets increases, and the size and stacking density of the sheet stacking domain increase, thereby improving the flatness and orientation of the graphene film.

[0013] The volume ratio of the aqueous hydrogen iodide solution to ethanol is 1:2-5. As the volume ratio of the aqueous hydrogen iodide solution to ethanol changes, the ratio of the hydrogen iodide reducing vapor and ethanol vapor generated during the reduction process changes. The change in the hydrogen iodide vapor content can adjust the degree of reduction of the graphene oxide film, and the change in the ethanol vapor ratio can adjust the stress applied to the film surface. If the volume ratio of ethanol is too high, the relative content of hydrogen iodide will decrease, thereby reducing the reduction efficiency, and the vapor pressure will increase during the reduction process, which may cause excessive expansion or contraction of the film surface and interior, and may eventually cause cracking or other deformation of the film. In addition, it may also cause uneven distribution of iodine ions on the film surface, affecting the uniformity of reduction in the film, thereby damaging the overall quality of the film. If the volume ratio of ethanol is too low, the generated vapor pressure will be insufficient, the stress on the film surface will be reduced, and it will be difficult to fully suppress the shrinkage caused by the reduction of the film.

[0014] The insulation temperature is 90-120℃. As the insulation temperature increases, the reaction rate and reduction uniformity of hydrogen iodide vapor reduction are enhanced, and the vapor pressure of ethanol vapor and the uniformity of stress distribution on the membrane plane are enhanced; if the insulation temperature is too high, the volatilization rate of the steam will be accelerated, resulting in uneven stress distribution generated by the steam in the membrane, which may further induce thermal stress damage and ultimately cause deformation or even cracking of the membrane; in addition, under high temperature conditions, the graphene membrane may also experience adverse phenomena such as sintering and cracking; if the insulation temperature is too low, the concentration of iodine ions escaping from the membrane will be reduced, affecting the full reduction of the membrane; at the same time, the vapor pressure of ethanol will also decrease accordingly, and it will not be able to exert sufficient stress on the membrane surface, thereby affecting the reduction effect and final quality of the membrane.

[0015] The holding time is 6-24h. The steam stretching reduction degree of the graphene oxide film can be adjusted by adjusting the holding time. If the holding time is too long, the stress of the film will gradually accumulate at high temperature, which may cause cracks or other deformations inside or on the surface of the film, thereby affecting the mechanical properties of the film. At the same time, long-term reaction will increase the chance of oxygen or other gas components in the use environment participating in side reactions, thereby causing degradation of the film. In addition, too long holding time will also lead to increased process costs. If the holding time is too short, it will lead to uneven and insufficient reduction of the film, and the regulating effect of ethanol vapor stress cannot be fully exerted, resulting in uneven stress distribution on the surface of the film, which is prone to tiny cracks and uneven deformation.

[0016] As the preferred technical solution:

[0017] A method for preparing a highly oriented and highly reflective graphene film by steam pressure-assisted stretching reduction as described above, wherein the regulator comprises a displacement bracket, a pressing plate, an upper bracket, a limiting structure and a lower bracket;

[0018] The displacement bracket is a conical cap-shaped structure with the tip at the top, comprising 2n inclined rods I, n>2, the upper ends of the 2n inclined rods I are simultaneously connected to the center of the lower surface of the pressing plate, and the lower ends are evenly distributed around a point o, the point o is located on the central axis of the pressing plate, and the pressing plate is coaxial with the cylinder b;

[0019] The upper support includes 2n horizontal rods, which are radially distributed around point o. The two ends of the horizontal rods are respectively marked as end a and end b. End a is closer to point o than end b. The ends a of the 2n horizontal rods are respectively hinged to the lower ends of the 2n oblique rods I in a one-to-one correspondence.

[0020] The limiting structure restricts the 2n horizontal rods to move only along their own length direction;

[0021] The b ends of two adjacent horizontal rods are each connected by an arc bar, and at least one set of opposite arc bars is composed of three sections: left, middle and right. The middle section is composed of a separated inner layer and outer layer. The outer layer of the middle section is fixedly connected to the left section, and the inner layer of the middle section is fixedly connected to the right section. All the arc bars form a circular ring, and the circular ring extends vertically downward to form a circular tube.

[0022] The lower support includes 2n oblique rods II, which are distributed in an umbrella shape around the central axis of the cylinder b. The angle between the oblique rods II and the central axis of the cylinder b is 100-105°. The lower layer of the cylinder b extends radially outward and is connected to the upper ends of the 2n oblique rods II, and the lower ends of the 2n oblique rods II are connected to the circular tube.

[0023] In the method for preparing a highly oriented and highly reflective graphene film by steam pressure-assisted stretching reduction as described above, the regulator also includes a height measuring bracket, which is vertically arranged on one side of the pressing plate and fixedly connected to the upper bracket.

[0024] In the method for preparing a highly oriented and highly reflective graphene film by steam pressure-assisted stretching reduction as described above, the graphene oxide film is prepared by a filtration method, a casting method or a scraping method.

[0025] The method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction as described above, wherein the grain size height (i.e., the ordered stacking domain height) of the highly oriented and highly reflective graphene film is 3.42-6 nm, the ordered stacking domain accounts for more than 70%, the half-peak width of the XRD diffraction peak is less than 3°, the Herman's orientation parameter S is greater than 0.6, the surface roughness (within 30 μm) is less than 15 nm, the surface reflectivity (within 480-1050 nm) is not less than 25%, and the conductivity is 2×10 4 -2.5×10 5 S·m -1 , tensile strength exceeds 330MPa.

[0026] Beneficial effects:

[0027] (1) The present invention prepares a graphene film by a steam pressure-assisted stretching reduction method. During the reduction process, the graphene film is subjected to isotropic tensile stress, which effectively eliminates wrinkles and ripples caused by thermal fluctuations and changes in interlayer spacing, and improves the flatness of the graphene sheet. At the same time, gases such as carbon dioxide generated by deoxidation are squeezed out during the stretching process, which increases the stacking order between graphene sheets and improves the size of the sheet stacking domain and the stacking density.

[0028] (2) The graphene film produced by the present invention has the advantages of high orientation, high reflectivity, high conductivity, high tensile strength and low surface roughness, and has broader application prospects in the fields of electronic devices, energy catalysis, thermal radiation management, aerospace and so on. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The X-ray diffraction data of the graphene films of Example B1 and Comparative Examples 2 to 4 (corresponding to Figure 1 Middle a, Figure 1 The data in a were obtained by testing with a D8 Advance X-ray diffractometer, where the tube voltage was set to 40 kV and the tube current was set to 40 mA) and the ordered stacking domain area, interlayer spacing, and ordered stacking domain height (corresponding to Figure 1 b) Comparison diagram; in the diagram, VS-GFm corresponds to the product of Example B1, NS-GFm corresponds to the product of Example 2, SS-GFm corresponds to the product of Example 3, and DS-GFm corresponds to the product of Example 4;

[0030] Figure 2 : is a SEM comparison diagram of the graphene film of Example B1 and Comparative Examples 2 to 4; wherein, Figure 2 Where a is the surface of the graphene film of Comparative Example 2, Figure 2 e in the figure is the cross section of the graphene film of comparative example 2, Figure 2 b is the surface of the graphene film of Comparative Example 3, Figure 2 f is the cross section of the graphene film of Example 3. Figure 2 In the figure c is the surface of the graphene film of Comparative Example 4, Figure 2 g is the cross section of the graphene film of Example 4, Figure 2 Where d is the surface of the graphene film of Example B1, Figure 2 where h is the cross section of the graphene film of Example B1;

[0031] Figure 3 It is a comparison chart of the reflectivity in the visible-near infrared band of the graphene films of Example B1 and Comparative Examples 2 to 4;

[0032] Figure 4 is a top view of the isotropic stretching and steam treatment device in Example A1 of the present invention;

[0033] Figure 5 It is a three-dimensional comparison diagram of the surface morphology of the graphene films of Example B1 and Comparative Examples 2 to 4;

[0034] Figure 6 : is a comparison diagram of the root mean square data of the graphene films of Example B1 and Comparative Examples 2 to 4;

[0035] Figure 7 It is a comparison diagram of the image standard deviation curves of the graphene films of Example B1 and Comparative Examples 2 to 4;

[0036] Figure 8 Schematic diagram of the topological structure change of graphene oxide film before and after the steam pressure assisted stretching reduction process;

[0037] Fig. 9 Schematic diagram of an isotropic stretching and steam treatment device in Example A1 of the present invention;

[0038] Fig.10 Schematic diagram of the isotropic stretching and steam treatment device in Example A2 of the present invention; in the figure, 45° is the initial angle; S is the length of the inclined rod I of the displacement bracket; H is the initial height of the displacement bracket, that is, the vertical distance between the pressing plate and the upper bracket; △H is the maximum pressing displacement; △L is the maximum stretching displacement;

[0039] Fig.11 is a top view of the regulator in Example A2 of the present invention;

[0040] Fig.12 It is a side view of the middle section of the arc strip in the upper support of the present invention;

[0041] Among them, 1-solvent pool a, 2-cylinder a, 3-membrane fixing screw a, 4-arc bar, 5-solvent pool b, 6-height measuring bracket, 7-limiting structure, 8-membrane fixing screw b, 9-deformable tube, 10-displacement bracket, 11-pressing plate, 12-upper bracket, 13-lower bracket. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0043] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0044] Grain size height: According to Scherrer formula (L c=Kλ / βcosθ), substituting the Scherrer constant K (K value is 0.9), the ray wavelength λ, the angle of the diffraction peak in the ordered stacking domain θ and the half-peak width β of the XRD diffraction peak to calculate the grain size height L c .

[0045] Proportion of ordered stacking domains: fit the diffraction peaks to obtain the ordered stacking domain diffraction peaks and the disordered stacking domain diffraction peaks, calculate the ratio of the ordered stacking domain diffraction peak area to the entire diffraction peak, and obtain the proportion of ordered stacking domains.

[0046] Half-width of XRD diffraction peak: According to the Bragg law equation (nλ=2dsinθ), substitute the ray wavelength λ, diffraction angle θ and diffraction order n (usually 1) to calculate the interlayer spacing d (between 0.36-0.37nm); the difference in the diffraction angle 2θ at half the peak value of the diffraction peak is the half-width of the XRD diffraction peak.

[0047] Herman's orientation parameter S: The scattering image is obtained by the small angle X-ray scattering instrument (SAXS) at the BL16B1 beamline of the Shanghai Light Source Synchrotron Radiation Facility to obtain the scattering intensity distribution of the diffraction spot. As a variable, the scattering intensity I( ), the weighted average of the scattering intensity at different azimuths is obtained by integration or summation According to Herman's orientation parameter calculation formula (S = The orientation parameter S is obtained.

[0048] Surface roughness: The surface morphology of the graphene film was measured by atomic force microscopy (Bruker, model: Dimension FastScan / Icon) to obtain a three-dimensional image. The root mean square roughness (i.e., surface roughness) data and image standard deviation curve were obtained through software analysis. The entire test process was carried out within a range of 30 μm.

[0049] Surface reflectivity: The surface reflectivity of the graphene film was tested by a microscopic spectroscopy system (Fuxiang Optics, spectrometer detection module: PG2000-Pro spectrometer), with a test band of 480-1050nm.

[0050] Electrical conductivity: The electrical conductivity of the graphene film was measured by a four-probe conductivity tester.

[0051] Tensile strength: The tensile strength of the graphene film was tested by an electronic universal material testing machine (INSTRON 5969).

[0052] The preparation process of the graphene oxide aqueous solution used in the following embodiments is: graphene oxide (purity ≥ 99%, carbon-oxygen ratio of 2-3:1, thickness < 5nm) is uniformly dispersed in water by stirring and ultrasonic method to obtain a graphene oxide aqueous solution of a specific concentration.

[0053] Example A1

[0054] The apparatus used for isotropically stretching and steam treating graphene oxide films with a thickness of ≤10 μm is as follows: Fig. 9 , Figure 4 As shown, it includes a solvent tank a1 and a heating device a;

[0055] The top of the solvent pool a1 is a vertically arranged cylinder a2, which is divided into two layers, upper and lower, and is detachably connected by 2m membrane fixing screws a3, m>2, and the 2m membrane fixing screws a3 are evenly distributed around the circumference of the central axis of the cylinder a2;

[0056] The heating device a is used to heat the solvent tank a1.

[0057] Example A2

[0058] The apparatus used for isotropic stretching and steam treatment of graphene oxide films with a thickness of >10 μm, such as Fig.10 , Fig.11 As shown, it includes a solvent tank b 5, a heating device b, a deformable tube 9 and a regulator;

[0059] The bottom of the deformable tube 9 is sealed and connected to the top of the solvent pool b 5. The top of the deformable tube 9 is a vertically arranged cylinder b. The cylinder b is divided into two layers, upper and lower, and is detachably connected by 2m membrane fixing screws b 8, m>2, and the 2m membrane fixing screws b 8 are evenly distributed around the circumference of the central axis of the cylinder b.

[0060] The heating device b is used to heat the solvent pool b 5;

[0061] The regulator is used to control the outward expansion of the cylinder b along the radial direction of the cylinder b;

[0062] The regulator includes a displacement bracket 10, a pressing plate 11, an upper bracket 12, a limiting structure 7, a lower bracket 13 and a height measuring bracket 6;

[0063] The displacement bracket 10 is a conical cap-shaped structure with the tip at the top, comprising 2n inclined rods I, n>2, the upper ends of the 2n inclined rods I are simultaneously connected to the center of the lower surface of the pressing plate 11, and the lower ends are evenly distributed around a point o, the point o is located on the central axis of the pressing plate 11, and the pressing plate 11 is coaxial with the cylinder b;

[0064] The upper support 12 includes 2n horizontal rods, which are radially distributed around point o. The two ends of the horizontal rods are respectively marked as end a and end b. End a is closer to point o than end b. End a of the 2n horizontal rods is hinged to the lower ends of the 2n oblique rods I in a one-to-one correspondence.

[0065] The limiting structure 7 restricts the 2n horizontal rods to move only along their own length direction;

[0066] like Fig.11 , Fig.12 As shown, the ends b of two adjacent horizontal rods are connected by an arc bar 4, at least one group of relative arc bars 4 is composed of three sections: left, middle and right. The middle section is composed of a separated inner layer and outer layer. The outer layer of the middle section is fixedly connected to the left section, and the inner layer of the middle section is fixedly connected to the right section. All the arc bars 4 form a circular ring, which extends vertically downward to form a circular tube.

[0067] The lower support 13 includes 2n oblique rods II, which are distributed in an umbrella shape around the central axis of the cylinder b. The angle between the oblique rods II and the central axis of the cylinder b is 100-105°. The lower layer of the cylinder b extends radially outward and is connected to the upper ends of the 2n oblique rods II, and the lower ends of the 2n oblique rods II are connected to the circular tube.

[0068] Example B1

[0069] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, the specific steps of which are as follows:

[0070] (1) Preparation of raw materials;

[0071] Graphene oxide aqueous solution: concentration 1 mg g -1 ;

[0072] A mixture of hydrogen iodide aqueous solution and ethanol: the concentration of the hydrogen iodide aqueous solution (i.e., the percentage of the mass of hydrogen iodide to the total mass of hydrogen iodide and water) is 45wt%, and the volume ratio of the hydrogen iodide aqueous solution to the ethanol is 1:3;

[0073] The apparatus used for isotropic stretching and steam treatment was the apparatus described in Example A2, with n being 4, m being 3, the height of the solvent pool b being 10 cm, the volume being 96 mL, and the angle between the inclined rod II and the central axis of the cylinder b being 102°;

[0074] (2) Preparation of graphene oxide film;

[0075] The graphene oxide aqueous solution was filtered using a Celgard 3501 membrane as a filter membrane, and then dried at 40°C for 24 hours, and the filter membrane was removed to obtain a graphene oxide membrane with a thickness of 15 μm.

[0076] (3) Preparation of highly oriented and highly reflective graphene films;

[0077] When the graphene oxide film obtained in step (2) is isotropically stretched and steam-treated, 25 mL of a mixture of hydrogen iodide aqueous solution and ethanol is first added to the solvent pool b, and then the graphene oxide film is fixed between the upper and lower cylinders b by the film fixing screws b and the film fixing screws b are adjusted to keep the graphene oxide film taut. The film is then heated by the heating device b until the hydrogen iodide and ethanol are both vaporized. At the same time, the pressing plate is pressed downward and kept warm at 90°C for 24 hours (the maximum tensile displacement of the graphene oxide film after the end of the insulation is 2 mm). After post-treatment (taking the film, rinsing with ethanol, and drying in a vacuum oven at 60°C), a highly oriented and high reflectivity graphene film is obtained.

[0078] The final highly oriented and highly reflective graphene film has a grain size height of 5.83 nm, an ordered stacking domain ratio of 87%, an XRD diffraction peak half-width of 1.38°, a Herman's orientation parameter S of 0.7, a surface roughness of 13.9 nm, a surface reflectivity of 30%, and a conductivity of 2×10 5 S·m -1 , the tensile strength is 580MPa.

[0079] Comparative Example 1

[0080] A method for preparing a graphene film is basically the same as that of Example B1, except that the mixed solution of hydrogen iodide aqueous solution and ethanol is replaced by an equal volume of hydrogen iodide aqueous solution (with a concentration of 45 wt %).

[0081] The final graphene film has a grain size height of 3.08 nm, a half-peak width of the XRD diffraction peak of 4.5°, a Herman's orientation parameter S of 0.59, a surface roughness of 30.3 nm, and a surface reflectivity of 20%.

[0082] Compared with Example B1, the flatness of the graphene sheets of the graphene film in Comparative Example 1, the tight stacking between the sheets and the ordered orientation of the stacking domain are significantly deteriorated. This is mainly because only an aqueous solution of hydrogen iodide is used in Comparative Example 1, and the high volatility of ethanol is not used to enhance the vapor pressure of the solution. Since hydrogen iodide is a strong acid, it will be completely ionized in water, which reduces the evaporation tendency of water, resulting in a small overall vapor pressure. The lower vapor pressure cannot eliminate the wrinkles and ripples caused by thermal fluctuations and changes in interlayer spacing during the reduction process. When wrinkles exist, the order of the sheet stacking domain will be destroyed, which will make it difficult for the sheets to stack tightly, resulting in disordered orientation of the sheets, which ultimately manifests as insufficient flatness of the membrane surface.

[0083] Comparative Example 2

[0084] A method for preparing a graphene film is basically the same as Example B1, except that the graphene oxide film is not fixed between the upper and lower cylinders b by the film fixing screws b, but is only placed on the top of the solvent pool a.

[0085] The final graphene film has a grain size height of 3.33nm, an ordered stacking domain ratio of 65%, an XRD diffraction peak half-width of 2.41°, a Herman's orientation parameter S of 0.55, a surface roughness of 43.9nm, and a surface reflectivity of 18%.

[0086] Compared with Example B1, in Comparative Example 2, the flatness of the graphene sheets of the graphene film, the tight stacking between the sheets, and the ordered orientation of the stacking domains are significantly deteriorated. This is because after the reduction of the graphene oxide film without stretching, the sheets shrink, resulting in intensified corrugations, folds, and wrinkles. There are more wrinkles between the sheets, resulting in disordered stacking between the layers. The orientation degree of the graphene film is low, which ultimately manifests as insufficient flatness of the film surface.

[0087] Comparative Example 3

[0088] A method for preparing a graphene film is basically the same as that in Example B1, except that m in the device described in Example A2 is 1.

[0089] The final graphene film has a grain size height of 2.21nm, an ordered stacking domain ratio of 56%, an XRD diffraction peak half-width of 3.64°, a Herman's orientation parameter S of 0.5, a surface roughness of 32nm, and a surface reflectivity of 20%.

[0090] Comparative Example 4

[0091] A method for preparing a graphene film is basically the same as that in Example B1, except that m in the device described in Example A2 is 2.

[0092] The final graphene film has a grain size height of 6.03nm, an ordered stacking domain ratio of 62%, an XRD diffraction peak half-width of 1.33°, a Herman's orientation parameter S of 0.6, a surface roughness of 22.7nm, and a surface reflectivity of 27%.

[0093] Compared with Example B1, the flatness of the graphene sheets of the graphene films in Comparative Examples 3 and 4, the tight stacking between the sheets, and the ordered orientation of the stacking domains are significantly deteriorated. This is because Comparative Examples 3 and 4 cannot suppress the shrinkage of the film in all directions during reduction; at the same time, the vapor stress distribution of the film due to vapor pressure is uneven, and isotropic stress cannot be generated in the film, and outward pressure cannot be uniformly applied to the graphene oxide film, resulting in insufficient isotropic tensile stress on the graphene oxide film during the reduction process, and the wrinkles and ripples caused by thermal fluctuations and changes in interlayer spacing are difficult to be completely eliminated, and gases such as carbon dioxide generated by deoxygenation cannot be well squeezed out during the stretching process.

[0094] Comparison of X-ray diffraction data, ordered stacking domain area, interlayer spacing, and ordered stacking domain height of the graphene films of Example B1 and Comparative Examples 2 to 4 Figure 1 As shown, SEM contrast Figure 2 As shown, the reflectivity comparison between visible and near infrared bands is Figure 3 As shown, the three-dimensional comparison of surface morphology is Figure 5 As shown, the RMS data is Figure 6 As shown, the image standard deviation curve is compared with Figure 7 shown; from Figure 2 It can be seen that the graphene film layers of Comparative Examples 2 to 4 all have wrinkles, folds or gaps, while the high-oriented and high-reflectivity graphene film layer of Example B1 appears compact and flat.

[0095] Comparative Example 5

[0096] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction is basically the same as that in Example B1, the only difference is that in the mixed solution of hydrogen iodide aqueous solution and ethanol, the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:7.

[0097] The final highly oriented and highly reflective graphene film has a grain size height of 2.25 nm, a half-peak width of the XRD diffraction peak of 3.57°, a Herman's orientation parameter S of 0.63, a surface roughness of 40.5 nm, and a surface reflectivity of 15%.

[0098] Compared with Example B1, the flatness of the graphene lamellae of the graphene film in Comparative Example 5, the tight stacking between the lamellae, and the ordered orientation of the stacking domain are significantly deteriorated. This is because in Comparative Example 5, the volume ratio of the aqueous hydrogen iodide solution to ethanol in the mixed solution of the aqueous hydrogen iodide solution and ethanol is 1:7, and the volume proportion of ethanol is too high, resulting in a decrease in the relative content of hydrogen iodide, thereby reducing the reduction efficiency, making it impossible for the graphene film to be fully reduced during the reduction process, affecting the flatness of the lamellae and the orderliness of the stacking domain. The high volume proportion of ethanol increases the vapor pressure during the reduction process, causing excessive expansion or contraction of the surface and interior of the film, destroying the tight stacking between the lamellae and the overall structure of the graphene film. In addition, the high volume proportion of ethanol leads to uneven distribution of iodide ions on the surface of the film, affecting the uniformity of reduction in the film, and further damaging the overall quality of the film.

[0099] Comparative Example 6

[0100] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction is basically the same as that in Example B1, except that the holding temperature in step (3) is 80°C.

[0101] The final highly oriented and highly reflective graphene film has a grain size height of 3.08nm, an ordered stacking domain ratio of 67%, an XRD diffraction peak half-width of 2.62°, a Herman's orientation parameter S of 0.55, a surface roughness of 20nm, and a surface reflectivity of 26%.

[0102] Compared with Example B1, the flatness of the graphene lamellae of the graphene film in Comparative Example 6, the tight stacking between the lamellae, and the ordered orientation of the stacking domain are significantly deteriorated. This is because the insulation temperature in Comparative Example 6 is too low. The low insulation temperature leads to a decrease in the concentration of iodine ions escaping from the membrane, which affects the full reduction of the membrane, making it impossible to repair and regularize the lamellae structure of the graphene film, thereby affecting the flatness of the lamellae and the order of the stacking domain. The low insulation temperature causes the vapor pressure of ethanol to decrease accordingly, and it is impossible to apply sufficient stress to the membrane surface, which in turn affects the reduction effect of the membrane, resulting in insufficient tight stacking between the lamellae and poor ordered orientation of the stacking domain, which ultimately affects the overall quality of the graphene film.

[0103] Comparative Example 7

[0104] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction is basically the same as that in Example B1, except that the holding time in step (3) is 4 hours.

[0105] The final highly oriented and highly reflective graphene film has a grain size height of 3.59nm, an ordered stacking domain ratio of 53.5%, an XRD diffraction peak half-width of 2.24°, a Herman's orientation parameter S of 0.58, a surface roughness of 30.3nm, and a surface reflectivity of 8%.

[0106] Compared with Example B1, the flatness of the graphene lamellae of the graphene film in Comparative Example 6, the tight stacking between the lamellae, and the ordered orientation of the stacking domain are significantly deteriorated. This is because the insulation time in Comparative Example 7 is too short. Too short insulation time will lead to uneven and insufficient reduction of the film, making it impossible for the lamellae structure of the graphene film to be fully regularized and repaired, affecting the flatness of the lamellae and the orderliness of the stacking domain. Too short insulation time makes it impossible to fully exert the regulating effect of ethanol vapor stress, resulting in uneven stress distribution on the film surface, destroying the tight stacking between the lamellae and the ordered orientation of the stacking domain, and ultimately affecting the overall quality of the graphene film.

[0107] Example B2

[0108] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, the specific steps of which are as follows:

[0109] (1) Preparation of raw materials;

[0110] Graphene oxide aqueous solution: concentration 0.5 mg g -1 ;

[0111] A mixture of hydrogen iodide aqueous solution and ethanol: the concentration of hydrogen iodide aqueous solution is 45wt%, and the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:2;

[0112] The apparatus used for isotropic stretching and steam treatment was the apparatus described in Example A1, m was 3, the height of the solvent pool a was 8 cm, and the volume was 25 mL;

[0113] (2) Preparation of graphene oxide film;

[0114] The graphene oxide aqueous solution was filtered using a Celgard 3501 membrane as a filter membrane, and then dried at 35°C for 12 hours, and the filter membrane was removed to obtain a graphene oxide membrane with a thickness of 5 μm.

[0115] (3) Preparation of highly oriented and highly reflective graphene films;

[0116] When the graphene oxide film obtained in step (2) is isotropically stretched and steam-treated, 15 mL of a mixture of hydrogen iodide aqueous solution and ethanol is first added to the solvent pool a, and then the graphene oxide film is fixed between the upper and lower layers of cylinders a by the film fixing screw a and the film fixing screw a is adjusted to keep the graphene oxide film taut. The film is then heated by the heating device a until the hydrogen iodide and ethanol are both vaporized and then kept at 90° C. for 6 h. After post-treatment (taking the film, rinsing with ethanol, and drying in a vacuum oven at 40° C.), a highly oriented and high reflectivity graphene film is obtained.

[0117] The final highly oriented and highly reflective graphene film has a grain size of 6 nm, an ordered stacking domain ratio of 90%, an XRD diffraction peak half-width of 1.2°, a Herman's orientation parameter S of 0.8, a surface roughness of 12.5 nm, a surface reflectivity of 34%, and a conductivity of 2.5×10 5 S·m -1 , the tensile strength is 450MPa.

[0118] Example B3

[0119] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, the specific steps of which are as follows:

[0120] (1) Preparation of raw materials;

[0121] Graphene oxide aqueous solution: concentration 7 mg g -1 ;

[0122] A mixture of hydrogen iodide aqueous solution and ethanol: the concentration of hydrogen iodide aqueous solution is 45wt%, and the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:3;

[0123] The apparatus used for isotropic stretching and steam treatment was the apparatus described in Example A2, with n being 3, m being 4, the height of the solvent pool b being 12 cm, the volume being 167 mL, and the angle between the inclined rod II and the central axis of the cylinder b being 103°;

[0124] (2) Preparation of graphene oxide film;

[0125] After the graphene oxide aqueous solution was cast using a quartz watch glass as a casting substrate, it was dried at 45° C. for 18 h, and the substrate was removed to obtain a graphene oxide film with a thickness of 50 μm;

[0126] (3) Preparation of highly oriented and highly reflective graphene films;

[0127] When the graphene oxide film obtained in step (2) is isotropically stretched and steam-treated, 32.5 mL of a mixture of hydrogen iodide aqueous solution and ethanol is first added to the solvent pool b, and then the graphene oxide film is fixed between the upper and lower cylinders b by the film fixing screws b and the film fixing screws b are adjusted to keep the graphene oxide film taut. The film is then heated by the heating device b until both the hydrogen iodide and the ethanol are vaporized. At the same time, the pressing plate is pressed downward and kept warm at 120° C. for 15 h (the maximum tensile displacement of the graphene oxide film after the end of the insulation is 1.5 mm). After post-treatment (taking the film, rinsing with ethanol, and drying in a vacuum oven at 60° C.), a highly oriented and high reflectivity graphene film is obtained.

[0128] The final highly oriented and highly reflective graphene film has a grain size height of 5.78 nm, an ordered stacking domain ratio of 74.7%, an XRD diffraction peak half-width of 1.39°, a Herman's orientation parameter S of 0.69, a surface roughness of 12.1 nm, a surface reflectivity of 35%, and a conductivity of 4×10 4 S·m -1 , the tensile strength is 450MPa.

[0129] Example B4

[0130] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, the specific steps of which are as follows:

[0131] (1) Preparation of raw materials;

[0132] Graphene oxide aqueous solution: concentration 8 mg g -1 ;

[0133] A mixture of hydrogen iodide aqueous solution and ethanol: the concentration of hydrogen iodide aqueous solution is 45wt%, and the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:5;

[0134] The apparatus used for isotropic stretching and steam treatment was the apparatus described in Example A2, with n being 4, m being 3, the height of the solvent pool b being 12, the volume being 167 mL, and the angle between the inclined rod II and the central axis of the cylinder b being 105°;

[0135] (2) Preparation of graphene oxide film;

[0136] After the graphene oxide aqueous solution was cast using a quartz watch glass as a casting substrate, it was dried at 40° C. for 24 hours, and the substrate was removed to obtain a graphene oxide film with a thickness of 100 μm;

[0137] (3) Preparation of highly oriented and highly reflective graphene films;

[0138] When the graphene oxide film obtained in step (2) is isotropically stretched and steam-treated, 50 mL of a mixture of hydrogen iodide aqueous solution and ethanol is first added to the solvent pool b, and then the graphene oxide film is fixed between the upper and lower cylinders b by the film fixing screws b and the film fixing screws b are adjusted to keep the graphene oxide film taut. The film is then heated by the heating device b until the hydrogen iodide and ethanol are both vaporized, and the pressing plate is pressed downward and kept warm at 105° C. for 24 h (the maximum tensile displacement of the graphene oxide film after the end of the insulation is 1 mm). After post-treatment (taking the film, rinsing with ethanol, and drying in a vacuum oven at 50° C.), a highly oriented and high reflectivity graphene film is obtained.

[0139] The final highly oriented and highly reflective graphene film has a grain size height of 4.38 nm, an ordered stacking domain ratio of 72%, an XRD diffraction peak half-width of 1.84°, a Herman's orientation parameter S of 0.65, a surface roughness of 13 nm, a surface reflectivity of 30%, and a conductivity of 3.5×10 4 S·m -1 , the tensile strength is 380MPa.

[0140] Example B5

[0141] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, the specific steps of which are as follows:

[0142] (1) Preparation of raw materials;

[0143] Graphene oxide aqueous solution: concentration 20 mg g -1 ;

[0144] A mixture of hydrogen iodide aqueous solution and ethanol: the concentration of hydrogen iodide aqueous solution is 45wt%, and the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:2;

[0145] The apparatus used for isotropic stretching and steam treatment was the apparatus described in Example A2, with n being 3, m being 4, the height of the solvent pool b being 12 cm, the volume being 167 mL, and the angle between the inclined rod II and the central axis of the cylinder b being 100°;

[0146] (2) Preparation of graphene oxide film;

[0147] The graphene oxide aqueous solution was scraped onto a glass substrate using a scraper, and then dried at 40° C. for 12 h, and the substrate was removed to obtain a graphene oxide film with a thickness of 70 μm.

[0148] (3) Preparation of highly oriented and highly reflective graphene films;

[0149] When the graphene oxide film obtained in step (2) is isotropically stretched and steam-treated, 45 mL of a mixture of hydrogen iodide aqueous solution and ethanol is first added to the solvent pool b, and then the graphene oxide film is fixed between the upper and lower cylinders b by the film fixing screws b and the film fixing screws b are adjusted to keep the graphene oxide film taut. The film is then heated by the heating device b until the hydrogen iodide and ethanol are both vaporized, and the pressing plate is pressed downward at the same time and kept warm at 90°C for 24 hours (the maximum tensile displacement of the graphene oxide film after the end of the insulation is 1 mm). After post-treatment (taking the film, rinsing with ethanol, and drying in a vacuum oven at 40°C), a highly oriented and high reflectivity graphene film is obtained.

[0150] The final highly oriented and highly reflective graphene film has a grain size height of 3.55 nm, an ordered stacking domain ratio of 78%, an XRD diffraction peak half-peak width of 2.5°, a Herman's orientation parameter S of 0.72, a surface roughness of 13.5 nm, a surface reflectivity of 27%, and a conductivity of 3×10 4 S·m -1 , the tensile strength is 360MPa.

[0151] Example B6

[0152] A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, the specific steps of which are as follows:

[0153] (1) Preparation of raw materials;

[0154] Graphene oxide aqueous solution: concentration 40 mg g -1 ;

[0155] A mixture of hydrogen iodide aqueous solution and ethanol: the concentration of hydrogen iodide aqueous solution is 45wt%, and the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:5;

[0156] The apparatus used for isotropic stretching and steam treatment was the apparatus described in Example A2, with n being 4, m being 3, the height of the solvent pool b being 12 cm, the volume being 167 mL, and the angle between the inclined rod II and the central axis of the cylinder b being 100°;

[0157] (2) Preparation of graphene oxide film;

[0158] The graphene oxide aqueous solution was scraped onto a glass substrate using a scraper, and then dried at 40° C. for 24 h, and the substrate was removed to obtain a graphene oxide film with a thickness of 95 μm.

[0159] (3) Preparation of highly oriented and highly reflective graphene films;

[0160] When the graphene oxide film obtained in step (2) is isotropically stretched and steam-treated, 45 mL of a mixture of hydrogen iodide aqueous solution and ethanol is first added to the solvent pool b, and then the graphene oxide film is fixed between the upper and lower cylinders b by the film fixing screws b and the film fixing screws b are adjusted to keep the graphene oxide film taut. The film is then heated by the heating device b until the hydrogen iodide and ethanol are both vaporized, and the pressing plate is pressed downward at the same time and kept warm at 90°C for 24 hours (the maximum tensile displacement of the graphene oxide film after the end of the insulation is 5 mm). After post-treatment (taking the film, rinsing with ethanol, and drying in a vacuum oven at 50°C), a highly oriented and high reflectivity graphene film is obtained.

[0161] The final highly oriented and highly reflective graphene film has a grain size height of 3.42 nm, an ordered stacking domain ratio of 75%, an XRD diffraction peak half-peak width of 2.62°, a Herman's orientation parameter S of 0.7, a surface roughness of 14.1 nm, a surface reflectivity of 25%, and a conductivity of 2×10 4 S·m -1 , the tensile strength is 340MPa.

Claims

1. A method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction, characterized in that: At the same time, the graphene oxide film is isotropically stretched and steam-treated, wherein the steam treatment is to heat a mixture of hydrogen iodide aqueous solution and ethanol until vaporization and then keep the mixture at 90-120° C. for 6-24 hours, wherein the volume ratio of hydrogen iodide aqueous solution to ethanol is 1:2-5; The thickness of the graphene oxide film is 5-100 μm; When the thickness of the graphene oxide film is ≤10 μm, the device used for isotropically stretching and steam treating the graphene oxide film at the same time includes a solvent pool a and a heating device a; the top of the solvent pool a is a vertically arranged cylinder a, the cylinder a is divided into an upper and lower layer and is detachably connected by 2m membrane fixing screws a, m>2, and the 2m membrane fixing screws a are evenly distributed around the circumference of the central axis of the cylinder a; the heating device a is used to heat the solvent pool a; When the thickness of the graphene oxide film is greater than 10 μm, the device used for simultaneously isotropically stretching and steam treating the graphene oxide film includes a solvent pool b, a heating device b, a deformable tube and a regulator; the bottom of the deformable tube is sealed and connected to the top of the solvent pool b, the top of the deformable tube is a vertically arranged cylinder b, the cylinder b is divided into two layers, the upper and lower layers are detachably connected by 2m membrane fixing screws b, m>2, and the 2m membrane fixing screws b are evenly distributed around the circumference of the central axis of the cylinder b; the regulator is used to control the radial outward expansion of the cylinder b along the cylinder b; the heating device b is used to heat the solvent pool b.

2. The method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction according to claim 1, characterized in that: The regulator includes a displacement bracket, a pressing plate, an upper bracket, a limiting structure and a lower bracket; The displacement bracket is a conical cap-shaped structure with the tip at the top, comprising 2n inclined rods I, n>2, the upper ends of the 2n inclined rods I are simultaneously connected to the center of the lower surface of the pressing plate, and the lower ends are evenly distributed around a point o, the point o is located on the central axis of the pressing plate, and the pressing plate is coaxial with the cylinder b; The upper support includes 2n horizontal rods, which are radially distributed around point o. The two ends of the horizontal rods are respectively marked as end a and end b. End a is closer to point o than end b. The ends a of the 2n horizontal rods are respectively hinged to the lower ends of the 2n oblique rods I in a one-to-one correspondence. The limiting structure restricts the 2n horizontal rods to move only along their own length direction; The b ends of two adjacent horizontal rods are each connected by an arc bar, and at least one set of opposite arc bars is composed of three sections: left, middle and right. The middle section is composed of a separated inner layer and outer layer. The outer layer of the middle section is fixedly connected to the left section, and the inner layer of the middle section is fixedly connected to the right section. All the arc bars form a circular ring, and the circular ring extends vertically downward to form a circular tube. The lower support includes 2n oblique rods II, which are distributed in an umbrella shape around the central axis of the cylinder b. The angle between the oblique rods II and the central axis of the cylinder b is 100-105°. The lower layer of the cylinder b extends radially outward and is connected to the upper ends of the 2n oblique rods II, and the lower ends of the 2n oblique rods II are connected to the circular tube.

3. The method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction according to claim 2, characterized in that: The regulator also includes a height measuring bracket, which is vertically arranged on one side of the pressing plate and fixedly connected to the upper bracket.

4. The method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction according to claim 1, characterized in that: The graphene oxide membrane is prepared by a suction filtration method, a casting method or a scraping method.

5. The method for preparing a highly oriented and highly reflective graphene film by steam pressure assisted stretching reduction according to claim 1, characterized in that: The grain size of the highly oriented and highly reflective graphene film is 3.42-6nm, the proportion of ordered stacking domains exceeds 70%, the half-peak width of the XRD diffraction peak is less than 3°, and the Herman's orientation parameter S The surface roughness is less than 15nm, the surface reflectivity is not less than 25%, and the conductivity is 2×10 4 -2.5×10 5 S·m -1 , tensile strength exceeds 330MPa.

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