Graphene film and preparation method thereof

Abstract

The invention relates to a graphene film and a preparation method thereof. The graphene film is composed of reduced graphene oxide, the reduced graphene oxide has controllable surface functional groups and atomic structures, and the reduced graphene oxide film mainly comprises carbon atoms, oxygen atoms, halogen atoms and nitrogen atoms. Oxygen atoms mainly exist in the form of oxygen functional groups and comprise hydroxyl, epoxy and carbonyl, the content of hydroxyl and epoxy is 11-32%, the content of carbonyl is 3.6-13.6%, and the content of halogen atoms and nitrogen atoms is 1.5-3.9%. According to the present invention, the functional groups and the atomic structure on the surface of the graphene oxide are adjusted, the chemical structure of the graphene is comprehensively controlled, and the new strategy is provided for the regulation of the optical property of the graphene film so as to achieve the modulation of the infrared radiation characteristic of the graphene.

Description

Technical Field

[0001] The present invention relates to the field of new materials and preparation thereof, and in particular to a graphene film and a preparation method thereof. Background Art

[0002] The infrared emissivity control strategy can achieve the infrared stealth requirements under different ambient temperatures. By adjusting the infrared radiation intensity of the target and integrating it with the ambient background radiation, it can significantly reduce the detectability of the target to avoid infrared detection. At the same time, the stability of stealth materials in extreme service environments such as high humidity, high salt fog and other conditions is crucial in practical applications. Stealth materials with wide-range infrared emission characteristics and resistance to extreme environments have become a research hotspot.

[0003] Graphene is composed of carbon atoms in the form of sp 2 The hybrid form forms a two-dimensional atomic lattice with excellent mechanical and electrical properties. As a precursor of graphene, graphene oxide has abundant oxygen-containing functional groups on its surface, which makes it possible to manipulate chemical surface groups, adjust the electronic energy state structure, change the graphene Fermi level and inhibit infrared absorption. In addition, graphene oxide has good solvent processing properties, and large-area graphene films can be prepared by vacuum filtration and scraping assembly. The reduced graphene oxide with oxygen-containing functional groups on the surface is also environmentally stable.

[0004] In recent years, many studies have focused on using graphene and its derivatives to control infrared emissivity. For example: Reference 1 discloses a multilayer graphene electro-induced infrared emissivity dynamic control device, which uses the adjustable response characteristics of graphene in the infrared band, uses an additional power supply to control the voltage to manipulate the insertion and extraction of ionic liquids, modulates the Fermi level of graphene to change the radiation characteristics of the device in the mid-infrared band, and the emissivity is adjustable in the range of 0.25-0.7. Reference 2 discloses a plasma enhanced chemical vapor deposition method to directly grow nitrogen-doped vertical graphene on commercial quartz foam. The graphene nitrogen doping in the graphene lattice is modulated by the graphene E F To a higher conduction band, its infrared emissivity (2.5–25 μm) is reduced from 0.96 to 0.68, suppressing 31% thermal radiation loss. Reference 3 discloses that vacancy and anion defects synergistically regulate the infrared emissivity of carbon nanotube films. Appropriate oxygen vacancies enhance charge transfer, while N / S co-doping behavior can alleviate the lattice contraction caused by vacancy defects, reduce lattice vibration and suppress infrared emission. Its infrared emissivity can be adjusted in the range of 0.33-0.81.

[0005] Related studies including the above literature have studied the infrared emissivity of carbon-based materials such as graphene.

[0006] Although the above research has made significant progress in regulating the infrared emissivity of graphene-based materials, there are still many challenges to be solved. In particular, the extended preparation of low-emissivity graphene films is still limited. 1) The infrared emissivity of carbon materials such as graphene is modulated, but applying voltage to embed ionic liquids into graphene to achieve chemical hybridization of graphene requires careful consideration of the volatility of ionic liquids, inconvenience in storage, and additional energy consumption. 2) The complex process and high energy consumption of introducing heteroatoms to modulate the graphene Fermi level also make it difficult to achieve the extended preparation of low-emissivity infrared stealth graphene films to meet application needs. 3) Due to the lack of consideration of the stacking morphology of nanosheets, it is difficult to prepare graphene film materials with lower emissivity.

[0007] Reference 1: Nature Photonics 2021, 15, 493-498, DOI: 10.1038 / s41566-021-00791-1;

[0008] Reference 2: Journal of the American Chemical Society 2022, 144, 15562-15568, DOI: 10.1021 / jacs.2c04454;

[0009] Reference 3: Advanced Functional Materials 2024, 2402193, DOI: 10.1002 / adfm.202402193.

[0010] In view of this, the present invention is proposed. Summary of the invention

[0011] The present invention provides a novel and simple method, which adopts a strategy of using graphene oxide as a precursor to regulate the surface functional groups and atomic structure, first prepares graphene oxide with appropriate functional group types and quantities, removes oxygen-containing groups on the surface by chemical reduction, and appropriately introduces heteroatoms during the oxidation and reduction process to regulate the optical properties of the graphene film. At the same time, the good orientation of the assembly units of the graphene film is also conducive to further reducing the infrared emissivity of the film. In order to solve the above problems.

[0012] In order to achieve the above objectives, the present invention particularly adopts the following technical solutions:

[0013] The present invention provides a graphene film, wherein the graphene film is composed of reduced graphene oxide, and the reduced graphene oxide has controllable surface functional groups and atomic structure, wherein:

[0014] The reduced graphene oxide film mainly contains carbon, oxygen, halogen and nitrogen atoms.

[0015] The oxygen atoms mainly exist in the form of oxygen functional groups, including hydroxyl, epoxy and carbonyl groups. The content of hydroxyl and epoxy groups is 11-32%, the content of carbonyl groups is 3.6-13.6%, and the content of halogen atoms and nitrogen atoms is 1.5-3.9%.

[0016] Preferably, the atomic ratio of carbon atoms to oxygen atoms in the reduced graphene oxide film is 3.2 to 8.4.

[0017] Preferably, the halogen atom content is 1.5 to 3.9%;

[0018] Preferably, the halogen atom includes a bromine atom or an iodine atom.

[0019] Preferably, the nitrogen atom content is 3.1-3.6%.

[0020] Preferably, the average lateral size of the assembled elementary graphene oxide sheets of the reduced graphene oxide film is 0.6 to 3.2 μm, and the thickness of the reduced graphene oxide film is 0.5 to 4 μm;

[0021] Preferably, the graphene film has one or more of the following properties:

[0022] Conductivity of 2 to 200,000 S / m;

[0023] Infrared emissivity of 0.74 to 0.15;

[0024] Electromagnetic shielding rate of 0-40dB;

[0025] Tensile strength of 100-500MPa.

[0026] The present invention provides a method for preparing the graphene film, comprising the following steps:

[0027] 1) obtaining a graphene oxide dispersion;

[0028] 2) treating the graphene oxide dispersion obtained in step 1) to obtain a graphene oxide film;

[0029] 3) The graphene oxide film obtained in step 2) is subjected to chemical reduction treatment by hydrohalic acid to obtain a graphene film.

[0030] Preferably, in step 1), the concentration of the oxidized graphene oxide dispersion is 0.5 to 60 mg / mL.

[0031] Preferably, the graphene oxide film is formed by vacuum filtration, blade coating, ink direct writing or screen printing.

[0032] Preferably, the hydrohalic acid solution is diluted with a solvent in a ratio ranging from 0.25 to 4, and the solvent is preferably but not limited to deionized water.

[0033] Preferably, in step 2), the reaction temperature is 25-60° C. and the reaction time is 1-12 h.

[0034] Preferably, after the reduction treatment, the method further comprises a step of washing the reduced-oxidized graphene film with ethanol.

[0035] The preparation and chemical reduction steps of graphene oxide of the present invention are used to adjust the surface functional groups and atomic structure of graphene oxide, comprehensively control the chemical structure of graphene, and provide a new strategy for regulating the optical properties of graphene films, thereby achieving modulation of the infrared radiation characteristics of graphene.

[0036] Beneficial effects of the present invention:

[0037] 1) The present invention regulates the oxygen-containing functional groups on the surface of graphene oxide by chemical reduction. The removal effect of the functional groups and the amount of heteroatom introduction are different under different reducing agent concentrations, thereby achieving the control of the surface functional groups and obtaining a graphene film with a wide range of emissivity;

[0038] 2) The present invention provides a new idea for modulating the Fermi level of graphene. Using graphene oxide as a precursor provides the possibility of expanding the preparation of infrared stealth materials. For example, infrared stealth fabrics for human bodies can be further prepared on a large scale. Graphene with different emissivity can be designed into anti-counterfeiting patterns and encrypted information;

[0039] 3) The method for preparing the graphene film with ultra-low infrared emissivity and wide-range adjustable emissivity in the present invention does not involve high energy consumption of introducing heteroatom doping and additional power supply to provide voltage drive. The processing process is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 The figure is a flow chart for preparing a graphene film with controllable infrared radiation characteristics in a specific implementation scheme of the present invention.

[0042] FIG2( a ) is a fitted C1s spectrum of Example 2 based on X-ray photoelectron spectroscopy (XPS);

[0043] Figure 2(b) is the fitted C1s spectrum of Example 3 based on X-ray photoelectron spectroscopy (XPS);

[0044] FIG2( c ) is a fitted C1s spectrum of Example 4 based on X-ray photoelectron spectroscopy (XPS);

[0045] FIG2( d ) is a fitted C1s spectrum of Example 5 based on X-ray photoelectron spectroscopy (XPS).

[0046] FIG3( a ) is an emissivity spectrum of the graphene film obtained in Example 2-5 in the mid-infrared band (2.5-25 μm);

[0047] FIG3( b ) shows the difference in infrared detection temperature of the graphene film obtained in Example 2-5 when heated at different temperatures.

[0048] FIG4( a) is a photograph of graphene fabric obtained in Example 6 and produced on a large scale on polypropylene textiles;

[0049] FIG4( b ) is a visible light optical photograph and an infrared photograph of a person wearing a white T-shirt made of the fabric of Example 6;

[0050] FIG4( c ) is an infrared photograph of a person wearing a white T-shirt made of the fabric of Example 6. ...

[0051] Figure 5 The infrared information encryption pattern designed by combining coatings with different emissivity in Example 7 is shown in FIG. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0053] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints A and B.

[0054] In this specification, the numerical range expressed using "above" or "below" means a numerical range including the number.

[0055] In this specification, the word "may" includes both performing a certain process and not performing a certain process.

[0056] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0057] In this specification, the term "room temperature" or "normal temperature" refers to an ambient temperature of 23±2°C.

[0058] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" or "mass %" used means weight or mass percentage.

[0059] In the present specification, "OH" refers to a hydroxyl group from a "-C-OH" structure, and does not include a hydroxyl group in a carboxyl group; "C=O" refers to a carbonyl structure, including a ketocarbonyl group and a carboxylcarbonyl group.

[0060] In the present specification, the use of “substantially” / “essentially” means that the deviation is not more than 3%, preferably not more than 1%, based on a reference or ideal situation.

[0061] In this specification, unless otherwise stated, "plurality" means that there are two or more.

[0062] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0063] First, the present invention is explained as a whole, as follows:

[0064] The present invention primarily provides a graphene film product with controllable infrared radiation characteristics. Based on the controllable surface functional groups and atomic structure regulation of graphene oxide, by controlling the graphene chemical structure, a new strategy is provided for regulating the optical properties of graphene, and further modulation of the infrared radiation characteristics of graphene is achieved.

[0065] Furthermore, the present invention is mainly based on the following insights:

[0066] Graphene has broad application prospects in the field of electronic devices due to its easy-to-regulate electronic structure, stable chemical properties and ultra-high carrier mobility. Graphene is a semi-metallic material with zero bandgap. The essence of manipulating the graphene bandgap is to destroy the symmetry of the graphene structure. Chemical methods include chemical doping and the introduction of defects. When different proportions of groups are grafted onto graphene, the graphene bandgap will be different. Changing the functional groups and oxidation levels (the ratio of carboxyl, epoxy and hydroxyl groups) can adjust the graphene bandgap. Oxidized graphene has the sp-retaining honeycomb structure.2 structural region, and sp 3 defect regions, the reduced graphene oxide formed by controlled reduction can produce more ordered regions, which can theoretically increase the sp 2 The bonds and ratios of the graphene can be increased and the band gap can be reduced to produce an intermediate gap state; at the same time, when heteroatoms are doped into the graphene lattice, the Fermi level of graphene can be moved to the conduction band. Furthermore, infrared absorption can be suppressed by adjusting the graphene Fermi level. When the Fermi level is greater than half a photon energy, interband transition absorption can be suppressed. Changing the band gap of graphene can adjust the properties of the material, such as refractive index, light absorption, and conductivity; as the Fermi level increases, short-wavelength light absorption can be blocked, giving graphene low-emission characteristics. It should be noted that at this time, the Fermi level of graphene is mainly determined by the grafted surface functional groups and impurity atoms.

[0067] Based on the above understanding, the present invention uses graphene oxide as a precursor, and performs reduction treatment on trace carboxyl graphene oxide obtained by an optimized oxidation method, adjusts the ratio of oxygen-containing functional groups (epoxy and hydroxyl groups) on the surface of graphene oxide, and introduces impurity atoms (nitrogen, bromine) based on the oxidation method and the reduction method. Combined with the Fermi level adjustment strategy, a graphene film with adjustable gradient emissivity of 0.15-0.74 can be prepared. At the same time, it has a multi-level conductive distribution that can be used for electromagnetic shielding. The ultra-low emissivity graphene infrared stealth film also has excellent environmental stability, which can meet the long-term infrared stealth stability in various extreme environments.

[0068] The reduced graphene oxide of the present invention is obtained based on the steps of graphene oxide preparation, film formation and reduction treatment.

[0069] The preparation of graphene oxide in the present invention is based on some typical processing methods:

[0070] The implementation steps based on the improved Hummers method are as follows: 3g of flake graphite and 1.5g of sodium nitrate are stirred evenly in 90mL of concentrated sulfuric acid under ice-water bath conditions, and then 9g of potassium permanganate is slowly added. After the addition of the oxidant is completed, the reaction temperature is controlled to 35°C and reacted for 3h, and then an appropriate amount of deionized water is added. At this time, the reaction temperature is controlled at 85-95°C, 15min, and finally 1L of deionized water is used to terminate the reaction process. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, multiple high-speed centrifugation and gradient centrifugation are performed.

[0071] The implementation steps based on the improved Hofmann method are as follows: 3g of flake graphite is added to a mixed solution of 30mL of concentrated nitric acid and 55mL of concentrated sulfuric acid in an ice-water bath, followed by slow addition of 33g of potassium chlorate, and after the addition of the oxidant, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L of deionized water. The washing method is the same as above.

[0072] The surface functional groups of graphene oxide obtained by the above oxidation method mainly include carboxyl, hydroxyl, epoxy, carbonyl, etc., and a small amount of heteroatom nitrogen will be introduced based on the oxidation system.

[0073] Furthermore, the present invention believes that by chemically reducing graphene oxide, it is possible to achieve the regulation of a multi-gradient ratio of surface oxygen-containing functional groups based on a carbon skeleton, and introduce a small amount of halogen heteroatoms during the reduction process to further regulate the Fermi level and carrier density of graphene.

[0074] The graphene oxide film is obtained by assembling a film using the graphene oxide dispersion obtained by the aforementioned graphite oxidation method.

[0075] In some specific embodiments, the graphene oxide dispersion is configured according to different solid contents. In the present invention, graphene film products of different shapes and thicknesses are prepared in a concentration range of 0.5 to 60 mg / mL.

[0076] The concentration of the present invention can be adjusted by dilution, high-speed centrifuge concentration, or rotary evaporation.

[0077] For dilution, ultrapure water or deionized water may be used without any particular limitation.

[0078] For high-speed centrifugation, a rotation speed of 10,000 rpm or above is usually used.

[0079] For rotary evaporation, the concentration of the dispersion can be further increased.

[0080] The film-forming means of graphene oxide in the present invention can be blade coating, vacuum filtration, ink direct writing and screen printing. From the perspective of the regular orientation of graphene oxide sheets, blade coating and vacuum filtration are preferred.

[0081] There is no particular limitation on the vacuum filtration, and the filter membrane material used may be polytetrafluoroethylene, polyvinylidene chloride, etc.

[0082] For scraping, an automatic coating machine is used, and the substrate used can be polystyrene, polyvinyl chloride, polytetrafluoroethylene, etc.; coatings of different thicknesses are prepared by changing the scraping speed and scraper height.

[0083] For direct ink writing, dispensing machine equipment is used, and the program is designed to print different filigree patterns.

[0084] For screen printing, design patterns and print different designs.

[0085] In addition, for vacuum filtration, the concentration and volume of graphene oxide dispersion are preferably 0.5-2 mg / mL and 5-10 mL; for blade coating, the concentration of graphene oxide is preferably 15-20 mg / mL; for ink direct writing and screen printing processes, the concentration of graphene oxide is preferably 40-60 mg / mL.

[0086] After obtaining the graphene oxide film, it is dried by natural drying at room temperature.

[0087] In the present invention, the above-mentioned graphene oxide film assembly is subjected to reduction treatment. For chemical reduction treatment of graphene oxide film, in a specific embodiment, hydrohalic acid (hydroiodic acid or hydrobromic acid) is used as a reducing agent, and deionized water is used to mix the reducing solution with different concentration ratios to obtain reducing solutions with different concentration gradients, and the volume ratio of deionized water to 48wt% hydrohalic acid is controlled at 0.25 to 4. The concentration conditions are selected according to the required emissivity film, wherein the hydrohalic acid is preferably but not limited to hydrobromic acid or hydroiodic acid.

[0088] As for the temperature of chemical reduction, room temperature reduction and reduction under oven heating conditions are adopted. As for the selection of temperature conditions, it is selected according to the oxidation degree of graphene oxide, and the temperature range is 25-60°C.

[0089] The reduction time is controlled within 1-12 hours. The reduction reaction time is determined according to the oxidation degree of the graphene oxide.

[0090] The reduced graphene oxide obtained by reduction is cleaned by rinsing and soaking in ethanol.

[0091] After the reduced graphene oxide is obtained, it is dried by heating in an oven. The reduced graphene oxide obtained can be treated with any acid, alkali, salt or organic solvent.

[0092] The number of functional groups, atomic types and bonding of the reduced graphene oxide film were determined by X-ray photoelectron spectroscopy (XPS).

[0093] The inventors believe that, with respect to the reduction route of hydrohalic acid, the reduction process of graphene oxide is a process in which the reducing agent diffuses gradually from the outside to the inside of the graphene oxide film. The reduction progress can be determined by XPS analysis of the carbon-oxygen ratio (C / O) of the reduced graphene oxide and the CO, C=C and C=O bonding of C1s. The dominant role of hydrohalic acid is to remove the oxygen-containing functional groups of graphene oxide and increase the sp 2region. Most halogens can be eliminated spontaneously from the reduced graphene oxide film, but there is still a small amount of residual halogen in the completely reduced film, which will produce more carriers for the heteroatom doping effect introduced by the reducing agent. Therefore, the role of chemical doping in the high conductivity and low emission characteristics of reduced graphene oxide cannot be ruled out. The conductivity test was determined by a four-probe, and the emission characteristics were determined by a Fourier infrared tester with an integrating sphere.

[0094] In some specific embodiments, the present invention removes oxygen-containing functional groups on the surface of graphene oxide by chemical reduction, and compared with the open band gap of graphene oxide, the reduced graphene oxide sp 2 The cluster ratio increases, and the atomic structure and chemical state evolve during the reduction process, producing mid-gap states, thereby improving the light absorption behavior in the infrared band.

[0095] In addition, the dense stacking of graphene oxide nanosheets helps to form a complete conductive network after chemical reduction. The smooth surface structure and dense interlayer structure can further improve the reflective properties of the film and reduce the emissivity. Therefore, it is important to optimize and adjust the orientation and dense stacking of nanosheets.

[0096] In addition, heteroatom doping is introduced for the selected graphite oxidation method and the use of reducing agent hydrohalic acid. The type of doping elements, the content of doped heteroatoms, the specific position of atoms, etc. also affect the band gap of graphene. At the same time, the heteroatom doping effect can enhance the carrier density of graphene and improve the conductivity of graphene film. Therefore, under the joint action of functional group removal and heteroatom doping effect, the energy band of graphene is modulated in a wide range. Therefore, optimizing and adjusting the doping of heteroatoms also has an impact on the modulation of the infrared emission characteristics of graphene.

[0097] As the precursor graphene oxide of the present invention, when the carboxyl content is low, it helps to form a dense structure of the graphene oxide film, thereby improving the light reflection behavior of the film; at the same time, it is of great significance for the controllable regulation of oxygen-containing functional groups under mild conditions and further modulation of graphene over a wide range.

[0098] In the reduced graphene oxide film obtained by the present invention, the ratio of carbon atoms to oxygen atoms is in the range of 3.2 to 8.4, preferably 4.8 to 8.4 for obtaining a graphene film with low emissivity, and the oxygen atoms are mainly present in the form of hydroxyl, epoxy and carbonyl groups, wherein the hydroxyl and epoxy groups are 11 to 32%, preferably 11-18%, and the carbonyl group is 3.6 to 13.6%, preferably 3-6%. The content of bromine atoms and nitrogen atoms is 1.5 to 3.9%.

[0099] The graphene film obtained according to the present invention has a wide range of emissivity modulation. In some specific implementation schemes, the emissivity in the 8-14 μm infrared band can be as low as 0.15, and can be controllably adjusted within the range of 0.15-0.74. A high-temperature radiation object at 55°C only displays ~35°C under the cover of a 2 μm thick film; the maximum electrical conductivity can reach 200,000 S / m, and the electromagnetic shielding performance is 40 dB; the tensile strength can reach more than 100 MPa; and the infrared stealth performance and electromagnetic shielding performance are stable for a long time (30 days) in strong acid, strong alkali, simulated seawater, organic solvents, and high humidity and heat environments.

[0100] In addition, scraping and brushing can demonstrate the feasibility of large-scale preparation of infrared stealth films and coatings; the combination of ink direct writing, screen printing and multi-gradient emissivity graphene films can realize the display of information encryption and anti-counterfeiting functions.

[0101] In addition, for the reduced graphene oxide film of the present invention, the thickness of the film can be 0.5 to 4 μm, preferably 2 to 3 μm. For the infrared stealth functional fabric brushed on the fabric substrate, the plane display area can be 1 m 2 above.

[0102] The reduced graphene oxide film provided by the present invention provides low infrared radiation characteristics, which is of great significance in the fields of military infrared camouflage and high electromagnetic protection in extreme environments.

[0103] Example

[0104] The present invention will be further described below through specific examples, wherein the raw materials used in each example or comparative example can be obtained commercially.

[0105] Example 1

[0106] This embodiment relates to a graphene film with controllable infrared radiation characteristics and a preparation method thereof, which specifically includes the following steps:

[0107] The implementation steps of preparing graphene oxide based on the improved Hummers method are as follows: 3g, 300 mesh flake graphite and 1.5g sodium nitrate are stirred evenly in 90mL concentrated sulfuric acid under ice-water bath conditions, and then 9g potassium permanganate is slowly added. After the addition of the oxidant is completed, the reaction temperature is controlled to 35°C for 3h, and then an appropriate amount of deionized water is added. At this time, the reaction temperature is controlled at 85-95 degrees Celsius for 15min, and finally 1L deionized water is used to terminate the reaction process. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0108] The graphene oxide dispersion obtained above was diluted with water to a concentration of 1 mg / mL, 8 mL, ultrasonically treated for 40 min, ultrasonic power 320 W, and the graphene oxide film was assembled by vacuum filtration and dried naturally. The graphene oxide was reduced with hydrobromic acid, and deionized water and 48 wt% hydrobromic acid solution were diluted in a volume ratio of 1:4 to obtain a reduction solution. The graphene oxide film obtained above was reduced with the reduction solution at 60 ° C, and the reaction time was 12 hours.

[0109] The reduced graphene oxide film was cleaned by rinsing with ethanol 2-3 times, soaking for 15 minutes, and drying in an oven at 60°C.

[0110] The reduced graphene oxide film has a carbon-oxygen ratio of 5.4, epoxy and hydroxyl groups account for 14.9%, carbonyl groups account for 13.6%, nitrogen content is 1.63%, bromine content is 2.9%, thickness is 2 microns, its emissivity in the 8-14 micron band is 0.49, and conductivity is 10000 S / m.

[0111] Example 2

[0112] The implementation steps of preparing graphene oxide based on the improved Hofmann method are as follows: 3g, 300-mesh flake graphite is added to a mixed solution of 30mL concentrated nitric acid and 55mL concentrated sulfuric acid under ice-water bath conditions, followed by slow addition of 33g potassium chlorate, and after the addition of the oxidant is completed, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L deionized water. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0113] The graphene oxide dispersion obtained above was diluted with water to a concentration of 1 mg / mL, 8 mL, ultrasonically treated for 40 min, ultrasonic power 320 W, and the graphene oxide film was assembled by vacuum filtration and dried naturally. The graphene oxide was reduced with hydrobromic acid, and deionized water and 48 wt% hydrobromic acid solution were diluted in a volume ratio of 1:1 to obtain a reduction solution. At room temperature, the graphene oxide film obtained above was reduced with the reduction solution for 12 hours.

[0114] The reduced graphene oxide film was cleaned by rinsing with ethanol 2-3 times, soaking for 15 minutes, and drying in an oven at 60°C.

[0115] The reduced graphene oxide film has a carbon-oxygen ratio of 3.2, epoxy and hydroxyl groups account for 32.0%, carbonyl groups account for 4.7%, nitrogen content is 3.5%, bromine content is 1.5%, thickness is 2 microns, its emissivity in the 8-14 micron band is 0.56, and conductivity is 860S / m.

[0116] Example 3

[0117] The implementation steps of preparing graphene oxide based on the improved Hofmann method are as follows: 3g, 300-mesh flake graphite is added to a mixed solution of 30mL concentrated nitric acid and 55mL concentrated sulfuric acid under ice-water bath conditions, followed by slow addition of 33g potassium chlorate, and after the addition of the oxidant is completed, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L deionized water. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0118] The graphene oxide dispersion obtained above was diluted with water to a concentration of 1 mg / mL, 8 mL, ultrasonically treated for 40 min, ultrasonic power 320 W, and the graphene oxide film was assembled by vacuum filtration and dried naturally. The graphene oxide was reduced with hydrobromic acid, and deionized water and 48 wt% hydrobromic acid solution were diluted in a volume ratio of 1:2 to obtain a reduction solution. At room temperature, the graphene oxide film obtained above was reduced with the reduction solution for 12 hours.

[0119] The reduced graphene oxide film was cleaned by rinsing with ethanol 2-3 times, soaking for 15 minutes, and drying in an oven at 60°C.

[0120] The reduced graphene oxide film has a carbon-oxygen ratio of 3.6, epoxy and hydroxyl groups account for 18.4%, carbonyl groups account for 4.7%, nitrogen content is 3.1%, bromine content is 2.1%, thickness is 2 microns, its emissivity in the 8-14 micron band is 0.41, and conductivity is 4340S / m.

[0121] Example 4

[0122] The implementation steps of preparing graphene oxide based on the improved Hofmann method are as follows: 3g, 300-mesh flake graphite is added to a mixed solution of 30mL concentrated nitric acid and 55mL concentrated sulfuric acid under ice-water bath conditions, followed by slow addition of 33g potassium chlorate, and after the addition of the oxidant is completed, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L deionized water. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0123] The graphene oxide dispersion obtained above was diluted with water to a concentration of 1 mg / mL, 8 mL, ultrasonically treated for 40 min, ultrasonic power 320 W, and the graphene oxide film was assembled by vacuum filtration and dried naturally. The graphene oxide was reduced with hydrobromic acid, and deionized water and 48 wt% hydrobromic acid solution were diluted in a volume ratio of 1:3 to obtain a reduction solution. At room temperature, the graphene oxide film obtained above was reduced with the reduction solution, and the reaction time was 12 h.

[0124] The reduced graphene oxide film was cleaned by rinsing with ethanol 2-3 times, soaking for 15 minutes, and drying in an oven at 60°C.

[0125] The reduced graphene oxide film has a carbon-oxygen ratio of 4.8, epoxy and hydroxyl groups account for 17.9%, carbonyl groups account for 3.6%, nitrogen content is 3.6%, bromine content is 3.1%, thickness is 2 microns, its emissivity in the 8-14 micron band is 0.30, and conductivity is 43200 S / m.

[0126] Example 5

[0127] The implementation steps of preparing graphene oxide based on the improved Hofmann method are as follows: 3g, 300-mesh flake graphite is added to a mixed solution of 30mL concentrated nitric acid and 55mL concentrated sulfuric acid under ice-water bath conditions, followed by slow addition of 33g potassium chlorate, and after the addition of the oxidant is completed, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L deionized water. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0128] The graphene oxide dispersion obtained above was diluted with water to a concentration of 1 mg / mL, 8 mL, ultrasonically treated for 40 min, ultrasonic power 320 W, and the graphene oxide film was assembled by vacuum filtration and dried naturally. The graphene oxide was reduced with hydrobromic acid, and deionized water and 48 wt% hydrobromic acid solution were diluted in a volume ratio of 1:4 to obtain a reduction solution. At room temperature, the graphene oxide film obtained above was reduced with the reduction solution for 12 hours.

[0129] The reduced graphene oxide film was cleaned by rinsing with ethanol 2-3 times, soaking for 15 minutes, and drying in an oven at 60°C.

[0130] The reduced graphene oxide film has a carbon-oxygen ratio of 8.4, epoxy and hydroxyl groups account for 11.3%, carbonyl groups account for 5.3%, nitrogen content is 3.3%, bromine content is 3.9%, thickness is 2 microns, its emissivity in the 8-14 micron band is 0.14, and conductivity is 200000 S / m.

[0131] Example 6

[0132] The implementation steps of preparing graphene oxide based on the improved Hofmann method are as follows: 3g, 300-mesh flake graphite is added to a mixed solution of 30mL concentrated nitric acid and 55mL concentrated sulfuric acid under ice-water bath conditions, followed by slow addition of 33g potassium chlorate, and after the addition of the oxidant is completed, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L deionized water. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0133] The graphene oxide dispersion obtained above was concentrated by centrifugation, and the concentration was controlled to 10-15 mg / mL by rotary evaporation, and then applied to the fabric substrate by a coating machine or brush. Hydrobromic acid reduction treatment was performed, and deionized water and 48wt% hydrobromic acid solution were diluted in a volume ratio of 1:4 to obtain a reduction solution. The graphene oxide coating was reduced with the reduction solution at room temperature, and the reaction time was 12 hours.

[0134] The fabric coating can be worn on a human body, so that the infrared image of the human body can be integrated with the room temperature environment to avoid infrared detection.

[0135] Example 7

[0136] The implementation steps of preparing graphene oxide based on the improved Hofmann method are as follows: 3g, 300-mesh flake graphite is added to a mixed solution of 30mL concentrated nitric acid and 55mL concentrated sulfuric acid under ice-water bath conditions, followed by slow addition of 33g potassium chlorate, and after the addition of the oxidant is completed, the reaction temperature is controlled to 25°C for 80h, and finally the reaction is terminated with 1L deionized water. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0137] The graphene oxide dispersion obtained above was concentrated by centrifugation, and the concentration was controlled to be 30-40 mg / mL by rotary evaporation. A screen printing template with an encrypted information unit was designed and produced, and was printed step by step on a polytetrafluoroethylene filter membrane by screen printing. The graphene oxide printed pattern was reduced step by step at room temperature using a reducing solution prepared by diluting deionized water and 48 wt % hydrobromic acid solution in a ratio of 1:4, 1:2, and 1:1, and the reaction time for each step was 12 h.

[0138] The printed pattern can display different digital units at different temperatures and is used for infrared information encryption.

[0139] The test data of the above embodiments are shown in Table 1 below:

[0140] Table 1

[0141] C / O CC / C=C COC / C-OH C=O N Br Emissivity Example 1 5.4 71.5％ 14.9％ 13.6％ 1.6％ 2.9％ 0.49 Example 2 3.2 63.4％ 32.0％ 4.7％ 3.5％ 1.5％ 0.56 Example 3 3.6 76.9％ 18.4％ 4.7％ 3.1％ 2.1％ 0.41 Example 4 4.8 78.6％ 17.9％ 3.6％ 3.6％ 3.1％ 0.30 Example 5 8.4 83.4％ 11.3％ 5.3％ 3.3％ 3.9％ 0.15

[0142] It can be seen from Figure 2(a), Figure 2(b), Figure 2(c) and Figure 2(d) that the carbon-oxygen ratio of the reduced graphene oxide film obtained in Example 1 is 5.4, and the carbon-oxygen ratio of the reduced graphene oxide obtained in Examples 2-5 is 3.2-8.4; based on X-ray photoelectron spectroscopy (XPS) and fitting the C1s spectrum, the weakening of the signal peak intensity of graphene oxide C=O (288.7eV) and CO (286.6eV) can indicate the removal of surface oxygen-containing groups (C-OH, COC) by chemical reduction. Specifically, the C-OH and COC functional groups of Example 2 are 32.0%, and the C=O content is 4.7%; the C-OH and COC functional groups of Example 3 are 18.4%, and the C=O content is 4.7%; the C-OH and COC functional groups of Example 4 are 17.9%, and the C=O content is 3.6%; the C-OH and COC functional groups of Example 5 are 11.3%, and the C=O content is 5.3%; From the above analysis, it can be seen that with the increase of the reducing agent concentration, the oxygen-containing functional groups gradually decrease, especially the C-OH and COC functional groups are significantly removed. This helps the graphene sp 2The increase in the domain ratio reduces the band gap and produces an intermediate gap state. At the same time, the content of bromine atoms is gradually increased to 1.5%, 2.1%, 3.1%, and 3.9% respectively. The increase in the content of doped atoms helps to increase the carrier density and improve the internal conductivity of the graphene film.

[0143] from Figure 3a It can be seen that the infrared emissivity of Example 2, Example 3, Example 4, and Example 5 gradually decreases, and the average emissivity in the 8-14μm infrared detection range is 0.56, 0.41, 0.30, and 0.15, respectively, indicating that the reasonable allocation of the number and proportion of functional groups on the surface of graphene oxide can change the light absorption behavior of the macroscopic film. The rSGO films of Examples 2-5 are cut into "BUCT" patterns, which can show different colors under an infrared camera, providing a basis for infrared anti-counterfeiting. Different emissivities lead to different thermal infrared temperatures, which are Figure 3b It can be seen that when attached to a high-temperature object, Examples 2-5 display different thermal infrared temperatures, and the increasing trend becomes more obvious as the actual temperature increases. For example, at an actual temperature of 82°C, Examples 2, 3, 4, and 5 display infrared temperatures of 66, 60, 53, and 42°C, respectively.

[0144] As shown in Figure 4, the large-area graphene-coated fabric obtained in Example 6 is 0.7*1.5m 2 , and it can be used as a wearable fabric for human body, which has the purpose of infrared invisibility at room temperature. This shows that reduced graphene oxide has the accessibility of large-scale preparation.

[0145] Depend on Figure 5 It can be seen that Example 7 uses programmable information encryption through screen printing. In the visible light range, the digital password pattern of step-by-step printing-restored displays a similar black optical color, which is difficult to distinguish the digital password with the naked eye, and only displays the number "888". When the paper is placed on a 60°C heating plate, some pattern units have high emissivity and are captured as warm colors similar to the paper under an infrared camera, while the remaining units display cold colors, displaying the number "893". When the hot plate is heated to 80°C, another part of the unit pattern is converted into warm colors, and the number decrypted by the cold and warm color difference is "071".

[0146] Example 8

[0147] The implementation steps of preparing graphene oxide based on the improved Hummers method are as follows: 3g, 300 mesh flake graphite and 1.5g sodium nitrate are stirred evenly in 90mL concentrated sulfuric acid under ice-water bath conditions, and then 9g potassium permanganate is slowly added. After the addition of the oxidant is completed, the reaction temperature is controlled to 35°C for 3h, and then an appropriate amount of deionized water is added. At this time, the reaction temperature is controlled at 85-95 degrees Celsius for 15min, and finally 1L deionized water is used to terminate the reaction process. In order to wash the residual impurities such as strong acid and oxidant in the graphene oxide, the reaction product is washed with 10wt% hydrochloric acid solution and deionized water in turn until the product cannot be precipitated and layered in deionized water; then centrifuged at a speed of 14000rpm until the collected lower layer of graphene oxide is weakly acidic.

[0148] The graphene oxide dispersion obtained above was diluted with water to a concentration of 1 mg / mL, 8 mL, ultrasonically treated for 40 min, ultrasonic power 320 W, and the graphene oxide film was assembled by vacuum filtration and dried naturally. The graphene oxide was reduced with hydrobromic acid, and deionized water and 48 wt% hydroiodic acid solution were diluted in a volume ratio of 1:1 to obtain a reduction solution. The graphene oxide film obtained above was reduced with the reduction solution at 25 ° C, and the reaction time was 3 hours.

[0149] The reduced graphene oxide film was cleaned by rinsing with ethanol 2-3 times, soaking for 15 minutes, and drying in an oven at 60°C.

[0150] The reduced graphene oxide film has a carbon-oxygen ratio of 5.1, epoxy and hydroxyl groups account for 13.6%, carbonyl groups account for 14.8%, nitrogen content is 3.02%, iodine content is 1.5%, thickness is 2 microns, its emissivity in the 8-14 micron band is 0.47, and conductivity is 10500S / m.

[0151] In summary, the infrared emission characteristics of reduced graphene oxide are mainly affected by oxygen-containing functional groups. Starting from the controllable surface groups of graphene oxide, the present invention selects appropriate reducing agent reduction conditions to achieve the controlled removal effect of oxygen-containing functional groups, and simultaneously achieves the introduction of appropriate doping atoms and the enhancement of conductivity. This synergistic effect improves the low-emission characteristics of the graphene film, and obtains a graphene film with controllable emissivity adjustment, which can be applied to a variety of scenarios including infrared stealth and information encryption.

[0152] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A graphene film, characterized in that: The graphene film is composed of reduced graphene oxide, and the reduced graphene oxide has controllable surface functional groups and atomic structure, wherein: The reduced graphene oxide film mainly contains carbon, oxygen, halogen and nitrogen atoms; The oxygen atoms mainly exist in the form of oxygen functional groups, including hydroxyl, epoxy and carbonyl groups. The content of hydroxyl and epoxy groups is 11-32%, the content of carbonyl groups is 3.6-13.6%, and the content of halogen atoms and nitrogen atoms is 1.5-3.9%.

2. The graphene film according to claim 1, characterized in that: The atomic ratio of carbon atoms to oxygen atoms in the reduced graphene oxide film is 3.2 to 8.

4.

3. The graphene film according to claim 1, characterized in that: The halogen atom content is 1.5 to 3.9%; Preferably, the halogen atom includes a bromine atom or an iodine atom.

4. The graphene film according to claim 1, characterized in that: The nitrogen atom content is 3.1-3.6%.

5. The graphene film according to claim 1, characterized in that: The average lateral size of the assembled elementary graphene oxide sheets of the reduced graphene oxide film is 0.6 to 3.2 μm, and the thickness of the reduced graphene oxide film is 0.5 to 4 μm; Preferably, the graphene film has one or more of the following properties: Conductivity of 2 to 200,000 S / m; Infrared emissivity of 0.74 to 0.15; Electromagnetic shielding rate of 0-40dB; Tensile strength of 100-500MPa.

6. A method for preparing a graphene film according to any one of claims 1 to 5, comprising the following steps: 1) obtaining a graphene oxide dispersion; 2) treating the graphene oxide dispersion obtained in step 1) to obtain a graphene oxide film; 3) The graphene oxide film obtained in step 2) is subjected to chemical reduction treatment by hydrohalic acid to obtain a graphene film.

7. The preparation method according to claim 6, characterized in that: In step 1), the concentration of the oxidized graphene oxide dispersion is 0.5 to 60 mg / mL.

8. The preparation method according to claim 6, characterized in that: The graphene oxide film is formed under vacuum filtration, scraping molding, ink direct writing or screen printing.

9. The method according to claim 6, characterized in that In step 2), the hydrohalic acid solution is diluted with the solvent in a ratio ranging from 0.25 to 4.

10. The preparation method according to claim 6, characterized in that: In step 2), the reaction temperature is 25-60°C and the reaction time is 1-12h; Preferably, after the reduction treatment, the method further comprises a step of washing the reduced-oxidized graphene film with ethanol.

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