A photothermal synergistic phase change composite film based on gradient carbon-based heterostructure and its preparation method

Abstract

The application relates to a photothermal synergic phase change composite film based on a gradient type carbon-based heterostructure and a preparation method thereof. 2 The core innovation comprises the following points: 1) the electronic tunneling effect between the hybrid orbitals and the metal d orbitals excites local plasmon resonance, and the photothermal conversion efficiency is improved; 2) the phonon confinement effect of the hierarchical carbon-based topological skeleton suppresses the heat relaxation energy loss; and 3) the micro-nano porous structure is used to regulate the dynamics of the core material, and the controllable release of thermal energy in a wide temperature range is realized. The material and a high polymer binder are compounded and calendered through an interpenetrating network to form a flexible functional film, the preparation process is simple, the material exhibits the synergic performance of efficient thermal energy storage and release in the fields of wearable devices, battery thermal control and building energy saving, and the problems of low photothermal conversion efficiency, large heat loss and poor temperature range adaptability of traditional phase change materials are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nanomaterials and composite phase change materials, and particularly relates to a light-heat synergistic phase change composite film based on gradient carbon-based heterostructure and a preparation method thereof. BACKGROUND

[0002] Solar energy, as a clean, renewable and green energy, has been widely used in photovoltaic, photocatalysis, water purification and other fields. However, the inherent intermittency and variability of solar radiation pose a major challenge to the widespread use of solar energy. Storing solar energy in the form of heat through phase change materials has great prospects because they have high energy density and stable phase change temperature, which can promote continuous energy release even in the absence of solar radiation. However, single phase change materials are limited by their low solar absorption rate and poor light-heat conversion ability. In order to solve these limitations, it is necessary to integrate efficient light-heat materials into phase change materials.

[0003] Among various light-heat materials such as nanocarbon materials, metal-based materials and organic materials, nanocarbon materials have great potential in improving the energy storage efficiency of phase change materials. This potential is attributed to their strong light-heat conversion ability, high thermal conductivity, good stability and low toxicity. In particular, the sp 2 Hybridization of carbon atoms forms a planar π-electron cloud structure, which enables nanocarbon materials to effectively convert solar energy into heat energy through non-radiative transitions of π-electrons. In addition, the conjugated system generated by sp 2 Hybridization of carbon atoms forms a planar π-electron cloud structure, which enables nanocarbon materials to effectively convert solar energy into heat energy through non-radiative transitions of π-electrons. In addition, the conjugated system generated by sp However, traditional carbon materials face challenges such as poor light-heat responsiveness, complex pore structure and difficulty in adjusting multi-level pores. Metal-organic framework derived carbon materials generally retain the explicit network pore structure and unique morphology of their precursors, with unique advantages such as abundant adsorption sites, adjustable hierarchical porosity and excellent stability. In addition, metal nanoparticles with catalytic activity can convert amorphous carbon into graphitized carbon, and reduce the emissivity of these metal nanoparticles to carbon-based materials through localized surface plasmon resonance effect. The mutual coupling between metal nanoparticles and high graphitized carbon further enhances the light-heat performance. However, how to achieve effective contact between phase change materials and metal-coupled high graphitized carbon synergistically enhanced sites remains a major challenge. Therefore, developing a material with fast light-heat response ability, diverse and adjustable pore structure, and thus achieving effective contact between phase change materials and metal-coupled high graphitized carbon synergistically enhanced sites, is crucial for significantly improving the light-heat performance of phase change materials. SUMMARY

[0004] The application aims to provide a light-heat synergic phase change composite film based on gradient carbon-based heterostructure and a preparation method thereof. A gradient heterostructure metal-coupled high-graphitized carbon hybrid carrier is constructed by using in-situ confined growth technology, molecular-level carbon precursor coordination regulation and pyrolysis strategy, and three-dimensional confined encapsulation of a phase change material is successfully realized. Then, the phase change material is combined with a polymer binder to form an interpenetrating network structure, and a light-heat synergic phase change composite film is obtained through directional calendering. The prepared phase change composite film has a simple and efficient preparation process and is suitable for large-scale production, can effectively improve the light-heat response capacity, promote the efficient storage and utilization of solar energy, and has a wide application prospect.

[0005] The application provides a light-heat synergic phase change composite film based on gradient carbon-based heterostructure and a preparation method thereof.

[0006] (1) In a metal organic framework material MOF(A), a MOF(A,B) precursor containing two metal components is obtained by adsorbing exogenous metal ions B;

[0007] (2) The MOF(A,B) precursor containing two metal components prepared in step (1) is carbonized at high temperature under an inert atmosphere, and the metal nanoparticles not covered by carbon are etched with an acid solution to obtain a gradient heterostructure metal-coupled high-graphitized carbon hybrid carrier;

[0008] (3) The gradient heterostructure metal-coupled high-graphitized carbon hybrid carrier prepared in step (2) and a hydroxyl-containing organic phase change material are added into an ethanol solution according to a mass ratio of 4:1 to 1:4, ultrasonic treatment is performed for 20-60 min to ensure complete contact and sufficient mixing, and drying is performed in a vacuum oven at 30-100 DEG C for 12-24 h to obtain a composite phase change material;

[0009] (4) The composite phase change material prepared in step (3) and a polymer binder are added into an agate mortar according to a mass ratio of 10:1 to 5:1, and are mixed and pressed to form a phase change composite film.

[0010] The MOF(A,B) precursor containing two metal components is synthesized by the following method:

[0011] (a) A zinc-containing metal salt and an amino-containing organic ligand are dispersed in a DMF solvent according to a molar ratio of 1:2 to 2:1 to form a homogeneous mixed solution;

[0012] (b) Triethylamine is added to the homogeneous mixed solution of step (a) to adjust the pH value of the system to 7-8, and a colloidal suspension is obtained after stirring;

[0013] (c) sequentially centrifuging the colloidal suspension, washing the colloidal suspension with DMF solvent for 3-5 times, washing the colloidal suspension with methanol solvent for 3-5 times, and then drying the colloidal suspension at 60-80°C under vacuum for 12-24h to obtain MOF(A) powder;

[0014] (d) dispersing the MOF(A) powder and a metal salt with catalytic properties in DMF solvent to obtain a mixed solution, and controlling the concentration of the metal salt with catalytic properties in the mixed solution to be 25-125mg / mL;

[0015] (e) ultrasonically dispersing the mixed solution of step (d) for 20-60min, and then reacting the mixed solution under stirring for 2-5h, centrifuging the reaction product, and drying the reaction product at 60-80°C under vacuum for 12-24h to finally obtain MOF(A,B) precursor containing two metal components.

[0016] The gradient heterostructure metal-coupled high-graphitized carbon hybrid carrier is synthesized by the following method:

[0017] (a) placing the MOF(A,B) precursor containing two metal components in an inert atmosphere, and programming the temperature to 900-1200°C at a temperature increasing rate of 1-5°C / min, and then carbonizing the MOF(A,B) precursor at the temperature for 2-6h;

[0018] (b) immersing the carbonized product of step (a) in a 6-12M hydrochloric acid solution, and performing chemical etching on the carbonized product at room temperature for 6-24h to remove free metal nanoparticles not coated by carbon layers;

[0019] (c) repeatedly washing the etched product of step (b) with deionized water until the filtrate is neutral to completely remove residual acid and metal ions and obtain a purified product;

[0020] (d) drying the purified product of step (c) at 60-80°C under vacuum for 12-24h to finally obtain the gradient heterostructure metal-coupled high-graphitized carbon hybrid carrier.

[0021] The metal salt containing zinc suitable for the present application includes but is not limited to one or more of zinc nitrate, zinc sulfate, zinc acetate, and zinc chloride; and the organic ligand containing amino groups includes but is not limited to one or more of 2-amino terephthalic acid, 3-amino-1,2,4-triazole, and 2-amino biphenyl-4,4'-dicarboxylic acid.

[0022] The metal salt with catalytic properties suitable for the present application includes but is not limited to one or more of nickel nitrate, nickel sulfate, nickel acetate, nickel chloride, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, iron nitrate, iron chloride, iron sulfate, and iron acetate.

[0023] The hydroxyl-containing organic phase change material suitable for the present invention includes any combination of one or more of n-octanol, n-decanol, octanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, cetearyl alcohol, behenyl alcohol, and polyethylene glycol.

[0024] The polymer binder suitable for the present invention includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyvinyl alcohol, polyacrylic acid, polyimide, epoxy resin, polyurethane, and polyacrylonitrile.

[0025] The beneficial effects of the present invention are as follows: the method of the present invention is used to successfully construct a gradient heterostructure metal-coupled highly graphitized carbon hybrid carrier, and realize the three-dimensional confined encapsulation of phase change materials, thereby stably obtaining a photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure. By designing a heterogeneous interface structure of graphitized carbon shells encapsulating metal nanocrystals, the graphite sp 2 The electron tunneling effect between the hybrid orbital and the metal d orbital produces a localized surface plasmon enhancement effect, significantly improving the photothermal conversion efficiency; at the same time, the phonon confinement effect of the graded carbon skeleton significantly reduces the thermal relaxation loss of the phase change material. In addition, the alcohol phase change material containing hydroxyl groups exhibits the highest kinetic energy and diffusion coefficient after encapsulation. The gradient heterostructure metal coupled with the highly graphitized carbon hybrid carrier effectively broadens the phase transition temperature and heat release time of the composite phase change material, achieving a wide temperature range and long-term heat energy release of the composite phase change film. This preparation method is simple, efficient and suitable for large-scale production. It can effectively improve the photothermal response capability, promote the efficient storage and utilization of solar energy, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the TEM spectrum of the carrier material obtained in Example 1 of the present invention.

[0027] Figure 2 This is the XRD pattern of the support material obtained in Example 1 of the present invention.

[0028] Figure 3 This is the XRD pattern of the composite phase change material obtained in Example 1 of the present invention.

[0029] Figure 4 This is the DSC spectrum of the composite phase change material obtained in Example 1 of the present invention.

[0030] Figure 5 This is the DSC spectrum of the composite phase change material obtained in Example 1 of the present invention after 200 cycles.

[0031] Figure 6 This is the photothermal temperature change curve of the phase change composite film obtained in Example 1 of the present invention.

[0032] Figure 7The photothermal temperature change curve of the phase change composite film obtained in Embodiment 2 of the present application.

[0033] Figure 8 The photothermal temperature change curve of the phase change composite film obtained in Embodiment 3 of the present application. DETAILED DESCRIPTION

[0034] The principles and features of the present application are described below, and the examples are only used to explain the present application, and are not used to limit the scope of the present application.

[0035] Embodiment 1

[0036] (1) Preparation of a gradient heterostructure nickel-coupled high-graphitized carbon hybrid carrier material:

[0037] Zinc nitrate hexahydrate and 2-amino terephthalic acid were dispersed in a DMF solvent in a molar ratio of 2:1 to form a homogeneous mixed solution, then a triethylamine solution was added to adjust the pH value of the system to 7, and a colloidal suspension was obtained after stirring. The colloidal suspension was subjected to centrifugal separation, DMF solvent washing 3 times and methanol solvent washing 3 times in sequence, and then dried at 80°C under vacuum conditions for 24h to obtain MOF(Zn) powder; the MOF(Zn) powder and nickel nitrate were dispersed in a DMF solvent, and the concentration of nickel nitrate in the mixed solution was controlled to be 100mg / mL, then the mixed solution was subjected to ultrasonic dispersion for 30min, and reacted under stirring conditions for 3h, and the product was centrifugally separated and dried at 80°C under vacuum conditions for 24h, finally obtaining a MOF(Zn, Ni) precursor containing two metal components; the MOF(Zn, Ni) precursor containing two metal components was placed in an Ar gas atmosphere protection, and was programmed to heat to 1000°C at a heating rate of 2°C / min, and was carbonized at the temperature for 3h, and the carbonized product was immersed in a 12M hydrochloric acid solution, and was subjected to chemical etching at room temperature for 12h to remove free nickel nanoparticles not covered by the carbon layer, and the etched product was repeatedly washed with deionized water until the filtrate was neutral to completely remove residual acid and nickel ions, and the purified product was dried at 80°C under vacuum conditions for 24h, finally obtaining a gradient heterostructure nickel-coupled high-graphitized carbon hybrid carrier.

[0038] (2) Preparation of a photothermal synergistic phase change composite film:

[0039] The gradient heterostructure nickel-coupled high-graphitized carbon hybrid carrier prepared above and stearyl alcohol were added to an ethanol solution in a mass ratio of 3:7, ultrasonic treatment was performed for 30min to ensure complete contact and sufficient mixing, and then drying was performed in a vacuum oven at 80°C for 24h to obtain a composite phase change material; the composite phase change material and polytetrafluoroethylene were added to an agate mortar in a mass ratio of 8:1, mixed thoroughly, and pressed into a photothermal synergistic phase change composite film.

[0040] We successfully constructed the gradient heterostructure nickel coupling high graphitized carbon hybrid carrier by in-situ confined growth technology, through the coordination regulation and pyrolysis strategy of molecular level carbon precursor, Figure 1 The TEM images clearly show the nickel coupling high graphitized plasma enhanced sites, from Figure 2 The XRD results show that the carrier has peaks at 44.2°, 51.5° and 76.1°, corresponding to the (111), (200) and (220) crystal planes of nickel nanoparticles, respectively. In addition, a broad peak is observed at 26.6°, corresponding to the graphite carbon layer around the nickel nanoparticles. This carrier can effectively adsorb stearyl alcohol and quickly realize photothermal conversion, from Figure 3 The XRD results of the composite phase change material show the characteristic peaks of stearyl alcohol, confirming that the composite phase change material with excellent crystalline properties is successfully obtained by the experimental scheme. The DSC test results of the composite phase change material prepared in this implementation example are shown in Figure 4 The results show that the melting temperature of the composite phase change material is 59.6℃, the melting enthalpy is 156.3J / g, the freezing temperature is 53.7℃, and the freezing enthalpy is 152.5J / g, Figure 5 The DSC test results of the composite phase change material after 200 cycles show that the phase change temperature and phase change enthalpy of the composite phase change material before and after the cycle only have a slight change, confirming that the composite phase change material obtained by the scheme has good cycle stability. The photothermal data curve of the phase change composite film is shown in Figure 6 Under the light intensity of 1 standard sun, the lower surface temperature of the phase change composite film rises to 44.5℃ within 60s, and the photothermal energy storage efficiency is as high as 90.7%, confirming that the prepared phase change composite film has excellent photothermal conversion performance.

[0041] Implementation Example 2

[0042] (1) Preparation of gradient heterostructure cobalt coupling high graphitized carbon hybrid carrier material:

[0043] The zinc nitrate hexahydrate and 2-amino terephthalic acid are dispersed in a DMF solvent in a molar ratio of 2:1 to form a homogeneous mixed solution, then a triethylamine solution is added to adjust the pH value of the system to 7, and a colloidal suspension is obtained after stirring. The colloidal suspension is subjected to centrifugal separation, DMF solvent washing 3 times and methanol solvent washing 3 times in sequence, and then dried at 80°C under vacuum for 24h to obtain MOF(Zn) powder; the MOF(Zn) powder and cobalt nitrate are dispersed in a DMF solvent, and the concentration of cobalt nitrate in the mixed solution is controlled to be 100mg / mL, then the mixed solution is subjected to ultrasonic dispersion for 30min, and the product is dried at 80°C under vacuum for 24h after centrifugal separation. Finally, the MOF(Zn, Co) precursor containing two metal components is obtained; the MOF(Zn, Co) precursor containing two metal components is placed in an Ar gas atmosphere, and the temperature is programmed to rise to 1000°C at a rate of 2°C / min, and then carbonized at this temperature for 3h. The carbonized product is immersed in a 12M hydrochloric acid solution and chemically etched at room temperature for 12h to remove free cobalt nanoparticles not covered by the carbon layer. The etched product is repeatedly washed with deionized water until the filtrate is neutral to completely remove residual acid and cobalt ions. The purified product is dried at 80°C under vacuum for 24h to obtain a gradient heterostructure cobalt-coupled high-graphitized carbon hybrid carrier.

[0044] (2) Preparation of the photothermal synergistic phase change composite film:

[0045] The gradient heterostructure cobalt-coupled high-graphitized carbon hybrid carrier prepared above and stearyl alcohol are added to an ethanol solution in a mass ratio of 3:7, ultrasonic treated for 30min to ensure complete contact and thorough mixing, and then dried in a vacuum oven at 80°C for 24h to obtain a composite phase change material; the composite phase change material and polytetrafluoroethylene are added to an agate mortar in a mass ratio of 8:1, mixed thoroughly and pressed into a photothermal synergistic phase change composite film.

[0046] The test results show that the melting temperature of the composite phase change material is 59.3°C, the melting enthalpy is 156.7J / g, the freezing temperature is 53.1°C, and the freezing enthalpy is 151.8J / g. After 200 cycles, the phase change temperature and phase change enthalpy value do not change significantly, and the thermal cycle stability is excellent. The photothermal conversion efficiency of the phase change composite film is as high as 91.2%, which confirms that the prepared phase change composite film has excellent photothermal conversion performance.

[0047] Case 3

[0048] (1) Preparation of the gradient heterostructure iron-coupled high-graphitized carbon hybrid carrier material:

[0049] Zinc nitrate hexahydrate and 2-amino terephthalic acid were dispersed in DMF solvent in a molar ratio of 2:1 to form a homogeneous mixed solution, then triethylamine solution was added to adjust the pH value of the system to 7, and a colloidal suspension was obtained after stirring. The colloidal suspension was subjected to centrifugal separation, DMF solvent washing 3 times and methanol solvent washing 3 times in sequence, and then dried at 80°C under vacuum for 24h to obtain MOF(Zn) powder; the MOF(Zn) powder and ferric nitrate were dispersed in DMF solvent, and the concentration of ferric nitrate in the mixed solution was controlled at 100mg / mL, then the mixed solution was subjected to ultrasonic dispersion for 30min and reacted under stirring for 3h, and the product was centrifugally separated and dried at 80°C under vacuum for 24h, finally obtaining MOF(Zn,Fe) precursor containing two metal components; the MOF(Zn,Fe) precursor containing two metal components was subjected to programmed temperature rising at a temperature rising rate of 2°C / min to 1000°C under Ar atmosphere protection, and carbonized at the temperature for 3h, the carbonized product was immersed in 12M hydrochloric acid solution and subjected to chemical etching at room temperature for 12h to remove free iron nanoparticles not covered by carbon layer, the etched product was repeatedly washed with deionized water until the filtrate was neutral to completely remove residual acid and iron ions, and the purified product was dried at 80°C under vacuum for 24h, finally obtaining gradient heterogeneous structure iron-coupled high-graphitized carbon hybrid carrier.

[0050] (2) Preparation of photo-thermal synergistic phase change composite film:

[0051] The above-prepared gradient heterogeneous structure iron-coupled high-graphitized carbon hybrid carrier and stearyl alcohol were added to ethanol solution in a mass ratio of 3:7, ultrasonically treated for 30min to ensure complete contact and sufficient mixing, and then dried in a vacuum oven at 80°C for 24h to obtain a composite phase change material; the composite phase change material and polytetrafluoroethylene were added to an agate mortar in a mass ratio of 8:1, mixed thoroughly and pressed into a photo-thermal synergistic phase change composite film.

[0052] The test results show that the melting temperature of the composite phase change material is 58.8°C, the melting enthalpy is 157.0J / g, the freezing temperature is 53.6°C, the freezing enthalpy is 150.9J / g, and after 200 cycles, the phase change temperature and phase change enthalpy value do not change significantly, and the composite phase change material has excellent thermal cycle stability. The photo-thermal conversion efficiency of the phase change composite film is as high as 90.4%, which confirms that the prepared phase change composite film has excellent photo-thermal conversion property.

Claims

1. A photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure, characterized in that: It includes a gradient heterostructure metal-coupled highly graphitized carbon hybrid carrier, a hydroxyl-containing organic phase change material adsorbed in the pores of the gradient heterostructure metal-coupled highly graphitized carbon hybrid carrier, and a polymer binder that forms an interpenetrating network structure composite membrane with the gradient heterostructure metal-coupled highly graphitized carbon hybrid carrier and the hydroxyl-containing organic phase change material; The method for preparing the photothermal synergistic phase change composite film based on the gradient carbon-based heterostructure comprises the following steps: (1) In a metal-organic framework material MOF (A), an exogenous metal ion B is adsorbed to obtain a MOF (A, B) precursor containing two metal components; (2) carbonizing the MOF (A, B) precursor containing two metal components prepared in step (1) at high temperature under an inert atmosphere, and etching the metal nanoparticles not coated with carbon with an acid solution to obtain a gradient heterostructure metal-coupled highly graphitized carbon hybrid support; (3) adding the gradient heterostructure metal-coupled highly graphitized carbon hybrid support prepared in step (2) and the hydroxyl-containing organic phase change material to an ethanol solution in a mass ratio of 4:1 to 1:4, ultrasonically treating for 20 to 60 minutes to ensure complete contact and sufficient mixing, and drying in a vacuum oven at 30 to 100° C. for 12 to 24 hours to obtain a composite phase change material; (4) Add the composite phase change material prepared in step (3) and the polymer binder into an agate mortar at a mass ratio of 10:1 to 5:1, mix thoroughly, and press into a phase change composite film.

2. The photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure according to claim 1, characterized in that: The gradient heterostructure metal coupled highly graphitized carbon hybrid carrier has graphite sp 2 The hybrid orbital and the metal d orbital form an electron tunneling effect to excite localized plasmon resonance; the graded carbon-based topological skeleton phonon confinement effect of the gradient heterostructure metal coupled with the highly graphitized carbon hybrid carrier suppresses thermal relaxation energy loss; an electrostatic effect is formed with the hydroxyl-containing organic phase change material to regulate its phase change dynamics; and a flexible functional film is formed through interpenetrating network composite calendering with the polymer binder.

3. The photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure according to claim 1, characterized in that: The hydroxyl-containing organic phase change material is selected from one or more of n-octanol, n-decanol, octanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, cetearyl alcohol, behenyl alcohol, and polyethylene glycol in any combination; the polymer binder is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, polyacrylic acid, polyimide, epoxy resin, polyurethane, and polyacrylonitrile.

4. The photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure according to claim 1, characterized in that: The preparation method of the MOF (A, B) precursor containing two metal components in step (1) is specifically as follows: (a) dispersing a zinc-containing metal salt and an amino-containing organic ligand in a DMF solvent at a molar ratio of 1:2 to 2:1 to form a homogeneous mixed solution; (b) adding triethylamine to the homogeneous mixed solution of step (a) to adjust the pH value of the system to 7-8, and obtaining a colloidal suspension after stirring; (c) centrifuging the colloidal suspension, washing it with DMF solvent 3 to 5 times, and washing it with methanol solvent 3 to 5 times, and then drying it at 60 to 80° C. under vacuum conditions for 12 to 24 hours to obtain MOF (A) powder; (d) dispersing the MOF (A) powder and a metal salt containing catalytic properties in a DMF solvent to obtain a mixed solution, wherein the concentration of the metal salt containing catalytic properties in the mixed solution is controlled to be 25 to 125 mg / mL; (e) ultrasonically dispersing the mixed solution of step (d) for 20 to 60 minutes, then reacting under stirring for 2 to 5 hours, centrifuging the reaction product, and drying it under vacuum at 60 to 80° C. for 12 to 24 hours to finally obtain a MOF (A, B) precursor containing two metal components.

5. The photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure according to claim 4, characterized in that: The zinc-containing metal salt includes: one or more of zinc nitrate, zinc sulfate, zinc acetate, and zinc chloride; the amino-containing organic ligand includes: one or more of 2-aminoterephthalic acid, 3-amino-1,2,4-triazole, and 2-aminobiphenyl-4,4'-dicarboxylic acid; the metal salt with catalytic properties includes: one or more of nickel nitrate, nickel sulfate, nickel acetate, nickel chloride, cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, ferric nitrate, ferric chloride, ferric sulfate, and ferric acetate.

6. The photothermal synergistic phase change composite film based on a gradient carbon-based heterostructure according to claim 1, characterized in that: The preparation method of the gradient heterostructure metal-coupled highly graphitized carbon hybrid carrier in step (2) is specifically as follows: (a) placing a MOF (A, B) precursor containing two metal components under inert atmosphere, heating the temperature to 900-1200°C at a heating rate of 1-5°C / min, and carbonizing at this temperature for 2-6 h; (b) immersing the carbonized product of step (a) in a 6-12 M hydrochloric acid solution and chemically etching at room temperature for 6-24 hours to remove free metal nanoparticles not coated by the carbon layer; (c) repeatedly washing the product after etching in step (b) with deionized water until the filtrate is neutral to completely remove residual acid and metal ions to obtain a purified product; (d) drying the purified product of step (c) under vacuum conditions at 60-80° C. for 12-24 h to obtain a gradient heterostructured metal-coupled highly graphitized carbon hybrid support.

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