Composite phase change material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of energy storage, and relates to a composite phase change material and a preparation method and application thereof. The composite phase-change material comprises a paraffin base body and a heat-conducting phase-change material dispersed in the paraffin base body. The heat-conducting phase-change material comprises at least one of biomass-based graphene, copper nanowire foam and Fe3O4 modified biomass-based graphene. Bamboo powder is converted into few-layer graphene through an interlayer type microwave plasma technology, the few-layer graphene is modified by Fe3O4 nanoparticles and then compounded with paraffin, and finally, a two-dimensional heat conduction network-three-dimensional metal framework-nanometer light absorber synergistic structure is constructed through copper nanowire foam packaging. The photothermal conversion efficiency of the prepared composite phase change material reaches 73.47%, the thermal conductivity is improved to 3.157 W.m <-1 >. K <-1 >, the phase change enthalpy retention rate is larger than 98%, and leakage is avoided. The method is suitable for solar heat storage, intelligent building and electronic device heat management, and green and low-cost production is achieved through biomass waste recycling.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and in particular relates to a composite phase change material and a preparation method and application thereof. Background Art

[0002] Paraffin wax (PW), as a typical organic solid-liquid phase change material, has become a research hotspot in the field of thermal energy storage due to its high phase change latent heat (180-230 J / g, about 5 times that of water), suitable phase change temperature (25-80 ℃, highly compatible with solar thermal utilization, building heating, etc.) and excellent chemical stability (phase change enthalpy decay rate <5% after 500 thermal cycles and no supercooling phenomenon). However, paraffin wax faces three technical bottlenecks in its practical application: (1) The intrinsic thermal conductivity of paraffin wax is only 0.2-0.4 W·m -1 ·K -1 , resulting in slow heat transfer during charging and a significant temperature gradient during heat release, increasing the risk of local overheating; (2) The absorbance of pure paraffin in the UV-visible-near infrared band (200-2500 nm) is <0.1, and it cannot directly absorb solar energy; (3) The volume change rate of paraffin phase change is 15-30%, and liquid leakage leads to a decrease in heat storage capacity (the phase change enthalpy decreases by 12% after 50 cycles) and equipment corrosion.

[0003] In existing technologies, thermal conductivity is often improved by adding carbon-based additives, metal-based additives, traditional photothermal materials, microencapsulation, and metal foam encapsulation. However, carbon-based additives such as carbon nanotubes (CNTs) cause severe agglomeration due to their high specific surface area. 1 wt% CNT addition only increases the thermal conductivity of paraffin by 30.3%. Graphene oxide (GO) has limited thermal conductivity improvement due to its oxygen-containing groups (1 wt% GO only reaches 0.32 W·m -1 ·K -1 Metal-based additives such as copper nanoparticles (Cu NPs) have significant phonon scattering at the paraffin interface. 10 wt% addition only increases thermal conductivity by 46.3% and easily catalyzes paraffin oxidation. Traditional photothermal materials such as carbon black have an absorbance of <0.5 in the near-infrared band. 10 wt% addition has a photothermal conversion efficiency of only 60.1%. Fe3O4 nanoparticles have poor thermal conductivity (5.9 W·m -1 ·K -1 ) leads to local overheating; the thermal conductivity of the microcapsule polymer shell in the encapsulation technology is only 0.15 W·m -1 ·K -1 , the thermal conductivity of the 50% filling rate system only increased by 12%, the leakage rate of expanded graphite (EG) packaging reached 3.2% at 70°C, and there were problems with complex preparation process and poor interface compatibility. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite phase change material and its preparation method and application, to solve the problems of low thermal conductivity, low photothermal conversion efficiency and phase change leakage of paraffin wax, and to develop a paraffin-based composite phase change material with high-efficiency photothermal-thermal conductivity, low-cost preparation and reliable packaging, which becomes the key to breaking through the large-scale utilization of solar energy.

[0005] In order to achieve the above object, the technical solution of the present invention is: In a first aspect, the present invention provides a composite phase change material, comprising a paraffin matrix and a thermally conductive phase change material dispersed within the paraffin matrix; the thermally conductive phase change material is selected from at least one of biomass-based graphene, copper nanowire foam, and Fe3O4-modified biomass-based graphene.

[0006] The present invention adopts paraffin wax (PW) as the phase change material of the matrix, making full use of its advantages such as high phase change latent heat, chemical stability, low cost, environmental protection and adjustable phase change temperature. The thermal conductive phase change materials added to the paraffin matrix, such as biomass-based graphene (BMPG), copper nanowire foam (CNF) and Fe3O4-modified biomass-based graphene (BMPG-Fe3O4), can significantly improve the thermal conductivity and photothermal conversion efficiency. This is because biomass-based graphene (BMPG) has a two-dimensional network structure formed by stacking a few layers of single-atom carbon layers, low defects and high graphitization properties; copper nanowire foam (CNF) has a three-dimensional copper nanowire skeleton structure and capillary adsorption effect of its pores; in Fe3O4-modified biomass-based graphene (BMPG-Fe3O4), the "nano thermal bridge" formed by Fe3O4, biomass-based graphene and copper nanowire foam optimizes the phonon transmission path, solves the three major contradictions of low-cost graphene preparation and high crystallinity, improved photothermal conversion efficiency and maintenance of phase change latent heat, and enhanced thermal conductivity and packaging reliability, and develops a paraffin-based composite phase change material with high-efficiency photothermal-thermal conductivity, low-cost preparation and reliable packaging.

[0007] In some other embodiments, the composite phase change material is selected from one of paraffin wax / biomass-based graphene composite phase change material, paraffin wax / copper nanowire foam composite phase change material, paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material.

[0008] The thermal conductivity of the paraffin / biomass-based graphene composite phase change material is at least 2.25 times higher than that of pure paraffin, and the light-to-heat conversion efficiency can reach up to 61.97%. The thermal conductivity of the paraffin / biomass-based graphene / copper nanowire foam composite phase change material is at least 11 times higher than that of pure paraffin, reaching 2.772 W·m -1 ·K -1, and maintained good thermal and morphological stability after 50 heating and cooling cycles. The paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material has a photothermal conversion efficiency of up to 73.47% and a thermal conductivity of up to 3.157 W·m -1 ·K -1 , 12.6 times that of pure paraffin. The paraffin / Fe₃O₄-modified biomass-based graphene / copper nanowire foam composite achieves optimal performance due to its phase transition, creating a synergistic thermal conductivity mechanism of "two-dimensional network + three-dimensional skeleton + nano-thermal bridges." In practical applications, one or more of these composite materials can be selected based on the application scenario to meet specific requirements.

[0009] In some other embodiments, the content of biomass-based graphene in the paraffin wax / biomass-based graphene composite phase change material is 0.1 wt%-0.5 wt%; for example, the content of biomass-based graphene is 0.1 wt%, 0.3 wt%, and 0.5 wt%. Biomass-based graphene within this ratio range has optimal dispersion performance, thermal conductivity, and light-to-heat conversion efficiency in paraffin wax.

[0010] Alternatively, in the paraffin wax / copper nanowire foam composite phase change material, the content of the copper nanowire foam is 30 wt%-35 wt%; the copper nanowire foam within this ratio range has the best dispersion performance, thermal conductivity and light-to-heat conversion efficiency in paraffin wax.

[0011] Alternatively, in the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, the biomass-based graphene content is 0.1 wt%-0.5 wt%, and the copper nanowire foam content is 30 wt%-35 wt%. Alternatively, the copper nanowire foam content is 30 wt%, 32 wt%, 34 wt%, and 35 wt%. Biomass-based graphene / copper nanowire foam within this ratio range exhibits optimal dispersion, thermal conductivity, and light-to-heat conversion efficiency in paraffin wax.

[0012] Alternatively, in the paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material, the Fe3O4-modified biomass-based graphene content is 0.1 wt%-0.5 wt%, and the copper nanowire foam content is 30 wt%-35 wt%; alternatively, the copper nanowire foam content is 30 wt%, 32 wt%, 34 wt%, and 35 wt%. The Fe3O4-modified biomass-based graphene / copper nanowire foam within this ratio range exhibits optimal dispersion in paraffin wax, thermal conductivity, and light-to-heat conversion efficiency.

[0013] The mass ratio of biomass-based graphene to Fe3O4 in Fe3O4-modified biomass-based graphene is 1: (1-3). In the Fe3O4-modified biomass-based graphene, the surface plasmon resonance effect of Fe3O4 in situ grown on the biomass-based graphene enhances light harvesting, reversing the efficiency loss caused by the introduction of CNF.

[0014] In some other embodiments, biomass-based graphene is a two-dimensional network composed of 2-8 single-atom carbon layers stacked together, and Raman spectroscopy is 2D / I G 0.70-0.82, I D / I G <0.58; the structure has the characteristics of few layers, low defects and high graphitization. The highly crystalline biomass-based graphene has an absorption rate of 92.7% in the 800-2500 nm light band, achieving efficient photothermal conversion.

[0015] Alternatively, the copper nanowire foam has a three-dimensional copper nanowire skeleton structure with a particle size of 50-100 nm; the CNF with this structure can enhance the composite interface with PW / BMPG, and at the same time, due to the capillary adsorption effect of the CNF pores, the composite phase change material after compounding is leak-free and the thermal conductivity is improved.

[0016] Alternatively, Fe₃O₄-modified biomass-based graphene, with uniform and well-crystalline Fe₃O₄ nanoparticles loaded onto the biomass-based graphene surface, can enhance the composite phase-change material's efficiency in capturing and converting light energy by increasing light absorption (broad-spectrum light capture) and heat conduction (reducing interfacial thermal resistance).

[0017] In a second aspect, the present invention provides a method for preparing the composite phase-change material described in the first aspect, comprising the steps of heating and melting a paraffin matrix, adding a thermally conductive phase-change material, mixing the mixture uniformly, and cooling to form the composite phase-change material; the thermally conductive phase-change material comprises at least one of biomass-based graphene, copper nanowire foam, and Fe₃O₄-modified biomass-based graphene. This preparation method is simple to operate, low-cost, and has promising application prospects.

[0018] In some other embodiments, the temperature at which the paraffin matrix is ​​heated and melted is 65-85°C, and the mixing method is selected from one of ultrasonic dispersion and vacuum impregnation; for example, the temperature at which the paraffin matrix is ​​heated and melted is 70 or 80°C.

[0019] The thermally conductive phase change material content in the composite phase change material is 0.1 wt%-0.5 wt%. This ratio range provides good dispersion of the thermally conductive phase change material content, significantly improving light-to-heat conversion efficiency and thermal conductivity while reducing production costs.

[0020] In some other embodiments, the preparation method of biomass-based graphene is as follows: carbonizing a nitrogen source under inert protection to obtain a carbonized nitrogen source; mixing the carbonized nitrogen source with biochar, and then performing microwave plasma conversion treatment under inert protection to obtain biomass-based graphene; Alternatively, the copper nanowire foam is prepared as follows: the copper foam is sequentially cleaned with anhydrous ethanol, water, and hydrochloric acid, then rinsed with water, dried with nitrogen, and dried to obtain a clean copper foam; the cleaned copper foam is immersed in an alkaline solution for reaction to obtain a modified copper foam; polytetrafluoroethylene, natural graphite, and anhydrous ethanol are mixed to obtain a suspension; the suspension is dropwise applied to the surface of the modified copper foam, and the copper nanowire foam is obtained after drying, heat treatment under inert gas protection, and cooling. Alternatively, the preparation method of the Fe3O4-modified biomass-based graphene is as follows: after mixing the biomass-based graphene with a solvent, adding a soluble iron salt and mixing, then adding sodium acetate and stirring, and performing a hydrothermal reaction to obtain the Fe3O4-modified biomass-based graphene.

[0021] In some other embodiments, in the method for preparing biomass-based graphene, the nitrogen source is selected from at least one of urea, dicyandiamide, melamine foam, and aniline; the temperature of the carbonization treatment is 800-1000°C, and the carbonization treatment time is 1-2 hours; the mixing ratio of the carbonized nitrogen source to the biochar is (2-3):1; the biochar is at least one of bamboo powder, straw powder, and fruit shell; the particle size of the biochar is 50-500 μm; the power of the microwave plasma conversion treatment is 700-900 W, the frequency is 2-3 GHz, and the time is 5-15 seconds; Preferably, the nitrogen source is melamine foam; the carbonization treatment temperature is 900°C, and the carbonization treatment time is 1 hour; the mixing ratio of the carbonized nitrogen source to the biochar is 2.4:1; the biochar is bamboo powder; the microwave plasma conversion treatment power is 800 W, the frequency is 2.45 GHz, and the time is 10 seconds; Alternatively, in the preparation method of copper nanowire foam, the concentration of hydrochloric acid is 15-25 wt%, the drying temperature is 75-85°C, the alkaline solution includes sodium hydroxide and ammonium persulfate, the concentration of sodium hydroxide is 2-3 M, the concentration of ammonium persulfate is 0.1-0.2 M, and the reaction time in the alkaline solution is 20-30 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite, and anhydrous ethanol is 1 mg: (450-550) mg: (250-350) mL; the drying temperature is 45-55°C, and the drying time is 3-5 hours; the heat treatment atmosphere is nitrogen, the temperature is increased to 350-450°C at 3-5°C / min, and the temperature is maintained for 1.5-2.5 hours; Preferably, in the preparation method of the copper nanowire foam, the concentration of hydrochloric acid is 20 wt%, the drying temperature is 80 ° C, the concentration of sodium hydroxide in the alkaline solution is 2.5 M, the concentration of ammonium persulfate is 0.15 M, and the reaction time in the alkaline solution is 25 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite and anhydrous ethanol is 1 mg: 500 mg: 300 mL; the drying temperature is 50 ° C, and the drying time is 4 hours; the heat treatment atmosphere is nitrogen, the temperature is increased to 400 ° C at 5 ° C / min, and the temperature is kept for 2 hours; Alternatively, in the method for preparing the Fe3O4-modified biomass-based graphene, the biomass-based graphene is added to a solvent, a soluble iron salt is added and mixed, and then sodium acetate is added, followed by a hydrothermal reaction to obtain the Fe3O4-modified biomass-based graphene; The solvent is a mixed solvent composed of diethylene glycol and ethylene glycol, and the volume ratio of diethylene glycol to ethylene glycol is (30-40): 10; The ratio of biomass-based graphene to solvent is 10 mg : (40-50) mL; The soluble iron salt is one of FeCl3, ferric nitrate and ferric sulfate; The mass ratio of biomass-based graphene to soluble iron salt is 1: (1-3); illustratively, the mass ratio of biomass-based graphene to soluble iron salt is 1: 1, 1: 2, 1: 3.

[0022] The mass ratio of biomass-based graphene to sodium acetate is 10:(75-85); The temperature of the hydrothermal reaction is 180-220°C, and the time of the hydrothermal reaction is 10-15 hours; Preferably, the volume ratio of diethylene glycol to ethylene glycol in the solvent is 35:10; The ratio of biomass-based graphene to solvent was 10 mg:45 mL; The soluble iron salt is FeCl3; The mass ratio of biomass-based graphene to FeCl3 is 1:3; The mass ratio of biomass-based graphene to sodium acetate is 10:80; The hydrothermal reaction temperature was 200 °C and the hydrothermal reaction time was 12 h.

[0023] In some other embodiments, the composite phase change material is selected from one of paraffin wax / biomass-based graphene composite phase change material, paraffin wax / copper nanowire foam composite phase change material, paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material; The preparation method of the paraffin wax / biomass-based graphene composite phase change material is as follows: The paraffin matrix is ​​heated and melted, and then vacuum-dried biomass-based graphene is added, ultrasonic dispersion and heating and stirring are performed, and the paraffin / biomass-based graphene composite phase change material is obtained by cooling and molding. Preferably, the temperature for heating and melting the paraffin matrix is ​​60-80°C, the temperature for ultrasonic dispersion is 60-80°C, and the time for ultrasonic dispersion is 0.5-1.5 h; the temperature for heating and stirring is 90-110°C, and the time for heating and stirring is 1-3 h; The composite phase change material has a heavy thermal conductive phase change material content of 0.1 wt%-0.5 wt%; Alternatively, the preparation method of the paraffin wax / copper nanowire foam composite phase change material is as follows: The paraffin matrix is ​​heated and melted, and then copper nanowire foam is added, mixed by vacuum impregnation method, and cooled and formed to obtain the paraffin / copper nanowire foam composite phase change material; In the paraffin wax / copper nanowire foam composite phase change material, the content of the copper nanowire foam is 30 wt%-35 wt%; Preferably, the vacuum impregnation method is performed at a mixing temperature of 75-85°C and a mixing time of 1-2 h; Alternatively, the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material is prepared as follows: heating and melting the paraffin wax / biomass-based graphene, then adding the copper nanowire foam, mixing by vacuum impregnation, and cooling and molding to obtain the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material; Alternatively, in the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; Preferably, the temperature of the vacuum impregnation mixing method is 75-85°C and the time is 1-2 h; Alternatively, the preparation method of the paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is as follows: The paraffin wax is heated and melted, and then biomass-based graphene modified with Fe3O4 and copper nanowire foam are added, mixed by vacuum impregnation, and cooled and formed to obtain a paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material; In the paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material, the content of Fe3O4-modified biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; Preferably, the mixing temperature of the vacuum impregnation method is 75-85° C. and the mixing time is 1-2 h.

[0024] In a third aspect, the present invention provides applications of the composite phase change material described in the first aspect in heat storage of solar water heaters, intelligent temperature-controlled building walls, and thermal management of electronic devices.

[0025] Beneficial effects of the present invention: (1) The present invention adopts paraffin wax (PW) as a phase change material based on the matrix, making full use of its advantages of high phase change latent heat, chemical stability, low cost, environmental protection and adjustable phase change temperature. The thermal conductive phase change material added to the paraffin matrix can significantly improve the thermal conductivity and photothermal conversion efficiency. This is because biomass-based graphene (BMPG) has a two-dimensional network structure composed of a few layers of single atomic carbon layers, low defects and high graphitization characteristics, and copper nanowire foam (CNF) has a three-dimensional copper nanowire skeleton structure and capillary adsorption effect of its pores; in Fe3O4-modified biomass-based graphene (BMPG-Fe3O4), Fe3O4 forms a "nano thermal bridge" with biomass-based graphene and copper nanowire foam, which optimizes the phonon transmission path, solves the three major contradictions of low-cost graphene preparation and high crystallinity, photothermal conversion efficiency improvement and phase change latent heat maintenance, and thermal conductivity enhancement and packaging reliability, and develops a paraffin-based composite phase change material with high-efficiency photothermal-thermal performance, low-cost preparation, and reliable packaging.

[0026] (2) The preparation method of the present invention is simple in operation and low in cost, and has good application prospects. The sandwich carbon foam induced microwave plasma conversion technology is adopted, bamboo powder is used as raw material, melamine foam (CMF) is used as the induction medium, and microwave plasma treatment is carried out under a nitrogen atmosphere. The prepared BMPG has excellent crystallinity and conductivity, and its Raman spectrum I 2D / I D Up to 0.82; The PW / BMPG composite phase change material was prepared by melt blending BMPG and paraffin wax, ultrasonically dispersing the mixture, heating and stirring, and cooling to form the mixture. The addition of BMPG significantly improved the thermal conductivity and photothermal conversion efficiency of paraffin wax. When the BMPG content was 0.5 wt%, the thermal conductivity of paraffin wax reached 0.841 W·m -1 ·K -1 , the photothermal conversion efficiency reaches 61.97%; Copper nanowire foam (CNF) was prepared by in-situ growth of copper nanoparticles on the surface of copper foam. Using this as the encapsulation medium, CNF was introduced into the PW / BMPG system by vacuum impregnation. The addition of CNF effectively solved the leakage problem during the paraffin phase transition and further increased the thermal conductivity of the composite material to 2.772 W·m -1 ·K-1 , but the photothermal conversion efficiency was reduced by 19.57%; Using BMPG as a carrier, Fe₃O₄ nanoparticles were in situ grown on its surface via a solvothermal method. The modified BMPG-Fe₃O₄ was then introduced into a paraffin wax and CNF system to prepare PW / BMPG-Fe₃O₄ / CNF. The introduction of Fe₃O₄ nanoparticles significantly improved the photothermal conversion efficiency of the composite phase-change material, reaching a maximum of 73.47%, while maintaining excellent cyclic thermal stability.

[0027] In summary, the present invention utilizes biomass waste to prepare BMPG, then in situ grows copper nanoparticles on the surface of copper foam to produce copper nanowire foam (CNF). Using BMPG as a carrier, Fe₃O₄ nanoparticles are in situ grown on its surface via a solvothermal method. The modified BMPG-Fe₃O₄ is then introduced into a paraffin wax and CNF system to construct a synergistic "two-dimensional thermal conductive network-three-dimensional metal skeleton-nanolight absorber" structure. The resulting composite phase-change material achieves a photothermal conversion efficiency of 73.47% (a 217% increase over pure paraffin wax) and a thermal conductivity of 3.157 W·m⁻¹. -1 ·K -1 (12.6 times that of pure paraffin), with a phase change enthalpy retention rate of >98% and no leakage. This achieves efficient resource utilization and green transformation. The prepared composite phase change material significantly improves photothermal conversion efficiency and thermal conductivity while maintaining high heat storage capacity, solving the problem of paraffin phase change leakage. The simple and low-cost preparation process has promising application prospects in a wide range of fields, including solar thermal conversion and storage, and human thermal management. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 Schematic diagram of the preparation process of biomass-based graphene (BMPG) in Example 1, wherein a is a schematic diagram of the sandwich carbon foam induced microwave plasma conversion process, b is a quartz reactor, c is a schematic diagram of the induction period of the microwave plasma conversion process, and d is a schematic diagram of the plasma generation process; Figure 2 TEM and HRTEM images of BMPG prepared in Example 1; Figure 3 is the XRD pattern of BMPG prepared in Example 1; Figure 4 The Raman spectra of BMPG obtained in Example 1 and 2D / I G and I D / I G The fluctuation range diagram, where a is the Raman spectrum of BMPG obtained by ten parallel experiments, and b is the I corresponding to different experimental times. 2D / I G and I D / I G The ratio of Figure 5 This is the XRD pattern of PW / BMPG-Fe3O4 / CNF prepared in Example 9; Figure 6 TEM and Mapping images of BMPG-Fe3O4 prepared in Example 8; Figure 7 The SEM images of CNF prepared in Example 4 and PW / BMPG / CNF prepared in Example 5, wherein a is the SEM image of CNF prepared in Example 4, and b is the SEM image of PW / BMPG / CNF prepared in Example 5; Figure 8 This is a diagram showing the flexibility of PW / BMPG-Fe3O4 / CNF prepared in Example 9; Figure 9 Graph showing the thermal energy release curves of the upper and lower surfaces of pure PW and PW / BMPG-Fe3O4 / CNF prepared in Example 9. DETAILED DESCRIPTION

[0030] Those skilled in the art will appreciate that the following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the invention. Unless otherwise specified, the examples were performed under conventional conditions or manufacturer's recommended conditions. Components used without manufacturer's indication are commercially available conventional products.

[0031] Solar energy is a renewable energy with abundant reserves (annual radiation totaling 5.6×10 24 J, which is more than 10,000 times the global annual energy consumption. It has great potential in building heating, industrial heating and other fields, but its intermittent nature (radiation intensity fluctuates more than 20 times during the day and night) and low density (average surface radiation of 1 kW / m 2 ) leads to a spatial and temporal mismatch between heat supply and demand. Conventional sensible heat storage (energy storage density 0.2-0.5 MJ / m 3 ) cannot meet the continuous energy supply, and phase change materials (PCMs) have high energy storage density (100-300 MJ / m 3 ) becomes the key.

[0032] Although paraffin-based phase change materials have been applied in fields such as solar thermal storage, they face three technical bottlenecks: ① Low intrinsic thermal conductivity (0.2-0.4 W / m·K), resulting in a solar heating system with a charging time of 4.5 hours (2.1 hours longer than the metal foam system) and a large temperature difference in heat release; ② Absorbance in the ultraviolet-near infrared band is <0.1, requiring external black chrome coating (costing $200 / m 2 , energy loss>30%)); ③ Phase change volume change of 15-30% leads to leakage (phase change enthalpy drops by 12% after 50 cycles). Existing microcapsule / metal foam packaging has problems such as limited improvement in thermal conductivity or complex process.

[0033] The specific scheme adopted in the present invention is as follows: Embodiments of the present invention provide a composite phase change material comprising a paraffin wax matrix and a thermally conductive phase change material dispersed within the paraffin wax matrix; the thermally conductive phase change material comprising at least one of biomass-based graphene, copper nanowire foam, and Fe3O4-modified biomass-based graphene. Optionally, the composite phase change material is selected from a paraffin wax / biomass-based graphene composite phase change material, a paraffin wax / copper nanowire foam composite phase change material, a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, or a paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material.

[0034] Some other embodiments of the present invention provide methods for preparing composite phase change materials, wherein the method for preparing a paraffin wax / biomass-based graphene composite phase change material is as follows: a nitrogen source is carbonized under inert protection to obtain a carbonized nitrogen source; the carbonized nitrogen source is mixed with biomass charcoal, and then subjected to microwave plasma conversion treatment under inert protection to obtain biomass-based graphene; the paraffin wax matrix is ​​heated and melted, and then vacuum-dried biomass-based graphene is added, ultrasonic dispersion and heated and stirred are performed, and cooling and molding are performed to obtain a paraffin wax / biomass-based graphene composite phase change material.

[0035] The preparation method of the paraffin wax / copper nanowire foam composite phase change material is as follows: the copper foam is cleaned with anhydrous ethanol, water, and hydrochloric acid in sequence, then rinsed with water, blown dry with nitrogen, and dried to obtain a clean copper foam; the cleaned copper foam is immersed in an alkaline solution for reaction to obtain a modified copper foam; polytetrafluoroethylene, natural graphite, and anhydrous ethanol are mixed to obtain a suspension; the suspension is dropwise applied to the surface of the modified copper foam, and the copper nanowire foam is obtained after drying, heat treatment under inert gas protection, and cooling. The paraffin matrix is ​​heated and melted, and then copper nanowire foam is added, mixed by a vacuum impregnation method, and cooled and formed to obtain a paraffin / copper nanowire foam composite phase change material.

[0036] The preparation method of the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material is as follows: heating and melting the paraffin wax / biomass-based graphene, then adding the copper nanowire foam, mixing by vacuum impregnation, and cooling and forming to obtain the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material; The preparation method of the paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is as follows: biomass-based graphene is added to a solvent, a soluble iron salt is added and mixed, and sodium acetate is added, followed by a hydrothermal reaction to obtain Fe3O4 modified biomass-based graphene; The paraffin wax is heated and melted, and then Fe3O4-modified biomass-based graphene and copper nanowire foam are added, mixed by a vacuum impregnation method, and cooled and formed to obtain a paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material.

[0037] To address the challenges of paraffin wax's low thermal conductivity, low photothermal conversion efficiency, and phase change leakage, this invention utilizes biomass waste to produce BMPG. This composite system, BMPG-Fe₃O₄-copper nanowire foam, achieves a synergistic improvement in photothermal conversion efficiency to 73.47% and thermal conductivity to 3.157 W / m·K while maintaining high thermal storage capacity. Furthermore, the three-dimensional metal framework eliminates leakage. This green and low-cost process has broad applications in solar thermal storage, human thermal management, and other fields.

[0038] The preparation method and characteristics of the composite phase change material of the present invention are further described below in conjunction with specific embodiments: Example 1 A method for preparing a paraffin wax / biomass-based graphene composite phase change material (PW / BMPG) comprises the following steps: Preparation of biomass-based graphene (BMPG): Melamine foam (Henan Zhongyuan Dahua Group Co., Ltd.) was placed in a tube furnace and heated to 900°C under nitrogen for 1 hour to produce carbonized melamine foam (CMF). This was then cut and used. Carbonized melamine foam (CMF) and bamboo powder (100 mesh) were placed in a quartz reactor at a mass ratio of 2.4:1. Two pieces of CMF were placed parallel to each other with a spacing of 3 mm. After nitrogen was introduced to the reactor to expel air, microwave plasma treatment (microwave oven power 800 W, frequency 2.45 GHz) was performed for 10 seconds. After the reaction, the biomass-based graphene was washed with ethanol, dried with concentrated sulfuric acid, and the surface acid residue was removed with sodium hydroxide to produce the biomass-based graphene, labeled BMPG.

[0039] An appropriate amount of BMPG was vacuum-dried at 80°C for 2 hours. Paraffin wax (PW) was heated to 70°C to melt, and a certain amount of petroleum ether was added to form a dispersion (approximately three times the mass of the paraffin). BMPG was added at a PW:BMPG mass ratio of 999:1. After ultrasonic dispersion at 70°C for 1 hour, the mixture was heated and stirred at 100°C for 2 hours to evaporate the petroleum ether. After cooling and forming, the paraffin wax / biomass-based graphene composite phase change material was obtained. The resulting product is labeled PW / BMPG (BMPG content 0.1wt%).

[0040] Example 2 A method for preparing a paraffin wax / biomass-based graphene composite phase change material (PW / BMPG) is disclosed. Unlike Example 1, BMPG is added at a PW:BMPG mass ratio of 997:3. The other preparation steps are the same as those in Example 1. The resulting product is labeled PW / BMPG (BMPG content 0.3 wt%).

[0041] Example 3 A method for preparing a paraffin wax / biomass-based graphene composite phase change material (PW / BMPG) is disclosed. Unlike Example 2, BMPG is added at a PW:BMPG mass ratio of 995:5. The other preparation steps are the same as those in Example 1. The resulting product is labeled PW / BMPG (BMPG content 0.5 wt%).

[0042] Example 4 A method for preparing a paraffin wax / copper nanowire foam composite phase change material (PW / CNF) comprises the following steps: First, cut the foam copper (Suzhou Keshenghe Metal Material, specification: 130 ppi) into 20×20×2 mm 3 The cube was ultrasonically cleaned with anhydrous ethanol for 1 hour, rinsed with deionized water, and ultrasonically cleaned with 20 wt% hydrochloric acid for 5 minutes. After rinsing with deionized water, it was blown dry with nitrogen and dried at 80°C. It was then immersed in an alkaline solution containing 2.5 M sodium hydroxide and 0.15 M ammonium persulfate and reacted for 25 minutes to obtain modified copper foam. Polytetrafluoroethylene and natural graphite were then dissolved in anhydrous ethanol (300 mL) at a mass ratio of 1:500, stirred for 30 minutes, and then drop-coated on the surface of the modified copper foam and dried at 50°C for 4 hours. Subsequently, the temperature was increased to 400°C at 5°C / min under nitrogen protection, kept at this temperature for 2 hours, and cooled to obtain copper nanowire foam (CNF).

[0043] Using the vacuum impregnation method, paraffin wax (PW) was vacuum melted at 80°C, and CNF was immersed in the melted paraffin for 1 hour (the mass ratio of PW: CNF was 2:1). After cooling and forming, the resulting product was labeled PW / CNF.

[0044] Example 5 A method for preparing a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG / CNF) comprises the following steps: The PW / BMPG (BMPG content 0.1 wt%) prepared in Example 1 was vacuum melted at 80°C and impregnated with CNF prepared in Example 4 for 1 hour (the mass ratio of PW / BMPG to CNF was 2:1). After cooling and molding, a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material was obtained, and the obtained product was labeled PW / BMPG / CNF.

[0045] Example 6 A method for preparing a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG / CNF) comprises the following steps: The PW / BMPG (BMPG content 0.3 wt%) prepared in Example 2 was vacuum melted at 80°C and impregnated with the CNF prepared in Example 4 for 1 hour (the mass ratio of PW / BMPG to CNF was 2:1). After cooling and molding, a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material was obtained, and the obtained product was labeled PW / BMPG / CNF.

[0046] Example 7 A method for preparing a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG / CNF) comprises the following steps: The PW / BMPG (BMPG content 0.5 wt%) prepared in Example 3 was vacuum melted at 80°C and impregnated with the CNF prepared in Example 4 for 1 hour (the mass ratio of PW / BMPG to CNF was 2:1). After cooling and molding, a paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material was obtained, and the obtained product was labeled PW / BMPG / CNF.

[0047] Example 8 A method for preparing a paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG-Fe3O4 / CNF) comprises the following steps: Preparation of BMPG-Fe3O4: 10 mg of BMPG prepared in Example 1 was added to a mixed solvent (a mixed solvent consisting of 35 mL of diethylene glycol and 10 mL of ethylene glycol) and ultrasonically dispersed. Anhydrous FeCl3 was added and ultrasonication continued (the mass ratio of BMPG to anhydrous FeCl3 was 1:1). After that, the mixture was transferred to an oil bath and heated (heating temperature 120°C). 80 mg of sodium acetate was added and stirred for 1 hour. The mixture was transferred to an autoclave and reacted at 200°C for 12 hours to obtain BMPG-Fe3O4. BMPG-Fe3O4 was introduced into the PW / CNF system prepared in Example 4, where the mass ratio of PW / CNF:BMPG-Fe3O4 was 997:3. After cooling and molding, a paraffin / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material was obtained. The resulting product was labeled PW / BMPG-Fe3O4 / CNF-1.

[0048] Example 9 A method for preparing a paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG-Fe3O4 / CNF) comprises the following steps: The difference from Example 8 is that in the preparation of BMPG-Fe3O4, the mass ratio of BMPG to anhydrous FeCl3 is 1:2; the other preparation steps are the same as those in Example 8, and the obtained product is marked as PW / BMPG-Fe3O4 / CNF-2.

[0049] Example 10 A method for preparing a paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material (PW / BMPG-Fe3O4 / CNF) comprises the following steps: The difference from Example 8 is that in the preparation of BMPG-Fe3O4, the mass ratio of BMPG to anhydrous FeCl3 is 1:3; the other preparation steps are the same as those in Example 8, and the obtained product is marked as PW / BMPG-Fe3O4 / CNF-3.

[0050] Comparative Example 1 A method for preparing a paraffin wax / biomass-based graphene composite phase change material (PW / BMPG) differs from Example 1 in that melamine foam and bamboo powder are directly mixed, nitrogen is introduced, and the air is expelled, followed by microwave plasma treatment (microwave oven power 800W, frequency 2.45GHz) for 10 seconds. The specific preparation steps are as follows: Preparation of biomass-based graphene (BMPG): Melamine foam (Henan Zhongyuan Dahua Group Co., Ltd.) and bamboo powder (100 mesh) were placed in a quartz reactor at a specific spacing and mass ratio (two pieces of CMF were placed parallel to each other in a quartz dish with a spacing of 3 mm, with a mass ratio of 2.4:1). After nitrogen was introduced and air was expelled, the mixture was subjected to microwave plasma treatment (microwave oven power 800W, frequency 2.45GHz) for 10 seconds. After the reaction, the mixture was washed and dried to produce biomass-based graphene, labeled BMPG.

[0051] An appropriate amount of BMPG was vacuum-dried at 80°C for 2 hours. Paraffin wax (PW) was heated to 70°C to melt, and a certain amount of petroleum ether was added to form a dispersion (approximately three times the mass of the paraffin). BMPG was added at a mass ratio of 999:1. After ultrasonic dispersion at 70°C for 1 hour, the mixture was heated and stirred at 100°C for 2 hours to evaporate the petroleum ether. After cooling and forming, the paraffin wax / biomass-based graphene composite phase change material was obtained. The resulting product is labeled PW / BMPG (BMPG content 0.1 wt%).

[0052] Comparative Example 2 A method for preparing a paraffin wax / copper nanowire foam composite phase change material (PW / CNF) differs from Example 4 in that the addition of polytetrafluoroethylene and natural graphite is omitted. Instead, the modified copper foam is directly heated to 400°C at 5°C / min under nitrogen protection, held at this temperature for 2 hours, and cooled to obtain copper nanowire foam (CNF). The specific preparation steps are as follows: First, cut the foam copper (Suzhou Keshenghe Metal Material, specification: 130 ppi) into 20×20×2mm 3 The cube was ultrasonically cleaned with anhydrous ethanol for 1 hour, rinsed with deionized water, and ultrasonically cleaned with 20 wt% hydrochloric acid for 5 minutes. After rinsing with deionized water, it was blown dry with nitrogen and dried at 80°C. It was then immersed in an alkaline solution containing 2.5M sodium hydroxide and 0.15M ammonium persulfate and reacted for 25 minutes to obtain modified foam copper. Subsequently, the temperature was raised to 400°C at 5°C / min under nitrogen protection, kept warm for 2 hours, and cooled to obtain copper nanowire foam (CNF).

[0053] Using the vacuum impregnation method, paraffin wax (PW) was vacuum melted at 80°C, and CNF was immersed in the melted paraffin wax (the mass ratio of PW:CNF was 2:1) for 1 hour. After cooling and forming, the resulting product was labeled PW / CNF.

[0054] Performance Testing The samples prepared in the examples of the present invention and the comparative examples were subjected to Raman spectrum, thermal conductivity, TEM, mapping, and X-ray powder diffraction tests, and the results are as follows: Figures 1-9 As shown, BMPG is the sample prepared in Example 1, PW / BMPG is the sample with different mass ratios of biomass-based graphene to paraffin prepared in Examples 1-3, PW / CNF is the sample with different mass ratios of biomass-based graphene to paraffin prepared in Example 4, PW / BMPG / CNF is the sample with different mass ratios of biomass-based graphene to paraffin prepared in Examples 5-7, and PW / BMPG-Fe3O4 / CNF is the sample with different mass ratios of BMPG to anhydrous FeCl3 prepared in Examples 8-10 introduced into the PW / CNF system.

[0055] Figure 1 The figure is a schematic diagram of the preparation process of biomass-based graphene (BMPG) in Example 1, wherein a is a schematic diagram of the sandwich carbon foam induced microwave plasma conversion process, b is a quartz reactor, c is a microwave plasma conversion process, and d is a schematic diagram of the plasma generation process. Figure 1 As shown in a and b, two pieces of carbonized melamine foam (CMF) were placed in parallel in a quartz dish with a distance of 3 mm, and the bamboo powder was placed in a quartz reactor with a mass ratio of 2.4:1. Figure 1 In step b), nitrogen is introduced to expel air, followed by microwave plasma treatment, ethanol washing, concentrated sulfuric acid drying, and sodium hydroxide to remove residual surface acid. The quartz reactor's lid and base are airtightly connected via a rubber seal and elastic band. A quartz wool insulation layer is pre-placed at the bottom. A small quartz reaction vessel is built in to accommodate the reactants in a sandwich-like manner. A three-stage scrubber is used to treat exhaust gases. Precise control of parameters such as nitrogen flow and reaction position ensures concentrated plasma generation and a stable reaction atmosphere under the microwave field, making it suitable for efficient thermal conversion of biomass. Depend on Figure 1 As shown in Figure c, CMF starts the initial thermal effect through microwave absorption, providing an energy basis for subsequent plasma generation. However, the temperature at this stage is not enough to directly generate graphene, and further energy accumulation is required. Figure 1 As shown in Figure d, the plasma formation period is the core stage of graphene synthesis. The ultra-high temperature environment achieves rapid reconstruction of the carbon source, which verifies that the sandwich CMF structure can efficiently induce plasma and confirms that the microwave plasma method can directly prepare few-layer graphene from biomass (Raman spectroscopy shows I 2D / I G The process does not require catalysts and substrates, and has the advantages of being green and low-cost.

[0056] Figure 2 TEM and HRTEM images of BMPG obtained in Example 1. Figure 2 The middle image shows that BMPG is in the form of 2-8 thin flakes, with a wrinkled structure at the edges. The interlamellar spacing is 0.345 nm, consistent with the calculated (002) diffraction peak in the subsequent XRD spectrum. The wrinkled edge structure provides abundant defect sites. This few-layer structure reduces phonon scattering, while the wrinkled defects provide anchoring points for subsequent Fe3O4 loading, laying the foundation for subsequent interface modification.

[0057] Figure 3 is the XRD pattern of BMPG obtained in Example 1. Figure 3 It can be seen that the graphite (002) peak at 26.0° (interlayer spacing 3.45 Å) indicates that the turbo-layered structure of BMPG has a larger interlayer spacing than that of conventional graphite (3.35 Å), which is caused by the interlayer distortion introduced by microwave plasma treatment. This structural feature enhances the thermal conductivity of BMPG.

[0058] Figure 4 The Raman spectra of BMPG obtained in Example 1 and 2D / I G and I D / I G The fluctuation range diagram, where a is the Raman spectrum of BMPG obtained by ten parallel experiments, and b is the I corresponding to different experimental times. 2D / I G and I D / I G The ratio of . Figure 4 From the a in the graphene graphene, we can see that the characteristic peaks of graphene include: D peak (~1350 cm -1 , derived from sp 3 hybrid carbon and lattice defects), G peak (~1580 cm -1 , arising from C-C bond and C=C double bond stretching vibration) and 2D peak (~2700 cm -1 , the second-order characteristic peak of two-phonon resonance Raman scattering, which is related to the stacking mode and number of carbon atoms). 2D / I G The ratio determines the number of layers (the larger the ratio, the fewer the layers), I D / I G Reflects the defect density (the larger the ratio, the more defects and the lower the degree of graphitization) (Chem Soc Rev, 2018,47 (5): 1822-1873). Figure 4 As can be seen from b in the figure, the BMPG spectrum shows a high-intensity sharp 2D peak and a low-intensity D peak. 2D / I G Up to 0.82, I D / I GThe average value is as low as 0.58, confirming its few-layer, low-defect, and highly graphitized properties, indicating that BMPG is a high-quality graphene material. This property is directly related to the photothermal efficiency, achieving efficient photothermal conversion.

[0059] Figure 5 The XRD pattern of PW / BMPG-Fe3O4 / CNF prepared in Example 9 is shown in FIG. Figure 5 It can be seen that in addition to the graphite peak (002) of BMPG, the (220) and (311) crystal plane peaks of Fe3O4 (2θ=30.1° and 35.4°) are newly added, proving that Fe3O4 is successfully loaded. The introduction of Fe3O4 increases the thermal conductivity by 3.157 W·m -1 ·K -1 , attributed to the “nano thermal bridge” formed between Fe3O4, BMPG and CNF, which optimizes the phonon transmission path.

[0060] Figure 6 TEM and Mapping diagram of BMPG-Fe3O4 prepared in Example 8. Figure 6 It can be seen that 5-10 nm Fe3O4 particles are uniformly distributed on the BMPG surface. The nanoparticles exhibit clear lattice fringes with a lattice spacing of 0.253 nm, corresponding to the (311) crystal plane of Fe3O4 (PDF#89-0691), confirming the crystallinity and phase purity of the Fe3O4 nanoparticles. Fe and O element mapping shows good interfacial compatibility. This structure improves the photothermal efficiency of PW / BMPG-Fe3O4 / CNF. The surface plasmon resonance effect of Fe3O4 enhances light capture, reversing the efficiency decrease caused by the introduction of CNF.

[0061] Figure 7 The SEM images of CNF prepared in Example 4 and PW / BMPG / CNF prepared in Example 5 are shown in FIG. a, a SEM image of CNF prepared in Example 4, and b SEM image of PW / BMPG / CNF prepared in Example 5. Figure 7 As shown in Figure a, the diameter of the three-dimensional copper nanowire skeleton of CNF is 50-100 nm. Figure 7 As shown in Figure b, the three-dimensional copper nanowire skeleton of the CNF is tightly integrated with the PW / BMPG composite interface. This structure is directly related to the leak-free property, which is attributed to the capillary adsorption effect of the CNF pores. Furthermore, the three-dimensional skeleton enhances thermal conductivity.

[0062] Figure 8This image demonstrates the flexibility of the PW / BMPG-Fe3O4 / CNF composite prepared in Example 9. This image demonstrates the flexible properties of the composite phase-change material cut into 4×6×2 cm dimensions. The material's ability to bend and deform without breaking is attributed to the synergistic effect of the three-dimensional copper nanowire foam (CNF) framework and biomass-based graphene (BMPG): the CNF metal network provides structural support, while the two-dimensional BMPG sheets impart flexibility. Furthermore, the paraffin wax (PW) fills the pores, forming a flexible matrix. This property makes it suitable for the conformable wearability requirements of wearable thermal management devices.

[0063] Figure 9 The thermal energy release curves of the upper and lower surfaces of pure PW and PW / BMPG-Fe3O4 / CNF prepared in Example 9 are shown in Figure 1. Pure PW has a low thermal conductivity (0.251 W·m -1 ·K -1 ), after the bottom contacted the simulated skin interface at 35℃, the temperature dropped sharply from 67℃ to below 40℃ within 400s, while the top still maintained above 55℃. The axial temperature difference exceeded 15℃, and the heat release was uneven. PW / BMPG-Fe3O4 / CNF formed an efficient thermal conductive network (thermal conductivity 3.157 W·m -1 ·K -1 ), the curve trend verifies the synergistic heat conduction mechanism of "two-dimensional network + three-dimensional skeleton + nano thermal bridge", the temperature difference between the upper and lower surfaces is ≤ 2.5 ℃, and the effective thermal therapy temperature range of 40~70 ℃ is maintained for about 800 s, which is 95% longer than that of pure PW. This reflects the optimization of temperature uniformity and continuous heat release capacity of the composite thermal conductive network, meeting the needs of wearable thermal therapy.

[0064] In order to further verify the photothermal conversion performance of a series of composite phase change materials prepared using bamboo powder as raw material through sandwich carbon foam induced microwave plasma conversion technology, its application effect was tested as follows: Thermal conductivity test Test method: Using a hot wire thermal conductivity tester (model TA612C), the sample was processed into a disc with a diameter of 20 mm and a thickness of 2 mm. A constant heat flow was applied between the hot plate and the cold plate. The thermal conductivity was calculated by measuring the temperature difference between the upper and lower surfaces. The formula is: The results are shown in Tables 1 and 2.

[0065] in, λ is the thermal conductivity (W·m -1 ·K -1 ), Q h and Q c is the heat flow output of the upper and lower heat sensors (W·m -2 ),L is the sample thickness (m), Δ t is the temperature difference (K).

[0066] Table 1 Thermal conductivity of paraffin composite phase change materials of BMPG and other graphene-based materials

[0067] Among them, the graphite nanosheets (Applied Energy, 2013, 110: 163-172), multi-walled carbon nanotubes (Applied Energy, 2013, 110: 163-172), graphene (The Journal of Physical Chemistry C, 2011, 115(17): 8753-8758.), randomly arranged graphite nanosheets (Composites Part A: Applied Science and Manufacturing, 2013, 44: 40-46), and aligned graphite nanosheets (Composites Part A: Applied Science and Manufacturing, 2013, 44: 40-46) in Table 1.

[0068] As can be seen from Table 1, compared with other graphene materials, the thermal conductivity of BMPG in Example 3 at 0.5 wt% addition (0.913 W·m -1 ·K -1 ) is significantly higher than that of graphene nanosheets (0.322 W·m -1 ·K -1 ), multi-walled carbon nanotubes (0.257 W·m -1 ·K -1 ), which verifies that the BMPG prepared by sandwich microwave plasma in Example 3 has a better thermal conductivity enhancement effect.

[0069] Table 2 Comparison of thermal conductivity and photothermal conversion efficiency

[0070] In Table 2, the photothermal conversion efficiency improvement rate is the photothermal conversion efficiency of PW / BMPG-Fe3O4 / CNF in Examples 8-10 compared with that of PW / BMPG / CNF in Example 6. As can be seen from Table 2, the thermal conductivity of pure paraffin (PW) is 0.251 W·m -1 ·K -1, which is consistent with the properties of conventional organic phase change materials. PW / BMPG system: With the increase of BMPG content (Examples 1-3), the thermal conductivity is significantly improved. When the BMPG content is 0.5 wt% (Example 3), the thermal conductivity reaches 0.913 W·m -1 ·K -1 , which is 3.64 times higher than pure PW. This is attributed to the two-dimensional layer structure of BMPG forming a continuous heat conduction network, which reduces the interfacial thermal resistance. The thermal conductivity of PW / CNF reaches 2.220 W·m -1 ·K -1 (8.84 times higher than pure PW), originating from a metal thermal network constructed from a 50-100 nm three-dimensional copper nanowire skeleton. However, the photothermal efficiency was only 32.21% due to the metal reflection effect and the absence of a photothermal component (Example 4). The PW / BMPG / CNF system: After the introduction of copper nanowire foam (CNF) (Examples 5-7), the thermal conductivity was further increased to 2.772 W·m -1 ·K -1 (Increased by 11 times, Example 6). The three-dimensional metal skeleton of CNF forms a synergistic thermal conduction path with BMPG. PW / BMPG-Fe3O4 / CNF system: After Fe3O4 nanoparticle modification (Examples 8-10), the thermal conductivity reaches up to 3.157 W·m -1 ·K -1 , which is 12.58 times higher than pure PW (Example 9). The high thermal conductivity of Fe3O4 (5.9 W·m -1 ·K -1 ) form “nano-thermal bridges” with BMPG and CNF networks to optimize phonon transport.

[0071] The thermal conductivity of Comparative Example 1 is 0.315 W·m -1 ·K -1 The thermal conductivity of comparative example 2 is 1.523 W·m -1 ·K -1 This is because the melamine foam was not carbonized in Comparative Example 1, resulting in a significant increase in the defect density of biomass-based graphene induced by microwave plasma, disordered stacking of the sheets and inability to form a continuous thermal conductive network, and a 35.2% decrease in thermal conductivity compared with Example 1; while polytetrafluoroethylene and natural graphite were not added in Comparative Example 2, resulting in uneven growth of copper nanowires on the surface of the foam copper and fracture of the skeleton structure, increased interfacial thermal resistance, and a 31.4% decrease in thermal conductivity compared with Example 4.

[0072] Photothermal conversion efficiency test Test method: Use 300 W xenon lamp to simulate sunlight (intensity 1500 W·m -2 ), the sample was placed in an insulated box and the center temperature change was recorded by a thermocouple. The test results are shown in Table 2. Photothermal conversion efficiency η The calculation formula is:

[0073] in, m is the sample mass (g), Δ H m is the phase change enthalpy (J·g -1 ), P is the light intensity (m W·cm -2 ), S is the illumination area (cm 2 ), Δ t is the phase transition time (s).

[0074] As shown in Table 2, for the PW / BMPG system, increasing BMPG content (Examples 1-3) significantly improves the photothermal efficiency due to its broad-spectrum absorption properties, reaching 61.97% at 0.5 wt% (Example 3), achieving a breakthrough compared to pure PW (which cannot directly absorb light energy). For the PW / BMPG / CNF system, introducing copper nanowire foam (CNF) (Examples 5-7) reduces the photothermal efficiency to 49.84% due to the metallic reflection effect of CNF (Example 6). However, this trend can be reversed by Fe₃O₄ modification.

[0075] PW / BMPG-Fe3O4 / CNF system: The surface plasmon resonance effect of Fe3O4 nanoparticles enhances light capture capability (Examples 8-10). When BMPG:FeCl3=1:3, the photothermal efficiency reaches 73.47%, which is 47.4% higher than that of PW / BMPG / CNF (specifically, compared with Example 6) (Example 9), and is superior to the single modification effects of carbon black (60.1%) and Fe3O4 nanoparticles (47.9%) reported in the literature.

[0076] Thermal stability and phase change latent heat test Test method: Differential scanning calorimetry (DSC) was used in N2 atmosphere at 10℃·min -1 The melting enthalpy (ΔH m) was measured by heating and cooling rate, and the thermal stability was evaluated by thermogravimetric analysis (TGA) in the range of 30–600 °C. The test results are shown in Table 3.

[0077] Table 3 Comparison of phase change latent heat and thermal stability test

[0078] From the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests in Table 3, it can be seen that the melting enthalpy of pure paraffin wax (PW) is 199.86 J·g -1The thermal decomposition starting temperature is 200 °C. As the biomass-based graphene (BMPG) doping amount increases from 0.1 wt% to 0.5 wt% (Examples 1-3), the melting enthalpy of the PW / BMPG system decreases to 168.69 J·g -1 The thermal decomposition starting temperature was increased to 210 °C, and the melting enthalpy retention rate exceeded 97.9% after 50 cycles (Example 3). After the introduction of copper nanowire foam (CNF) encapsulation (Examples 4-7), the melting enthalpy of PW / CNF (Example 4) was 165.72 J·g -1 , solidification enthalpy 155.23 J·g -1 The thermal decomposition starting temperature reached 210°C, the complete pyrolysis temperature was 345°C, the residual mass at 600°C was 29.63%, and the melting enthalpy retention rate after 50 cycles was 97.5%. This confirms that the three-dimensional skeleton structure of CNF not only increases the thermal decomposition temperature but also maintains the heat storage capacity of paraffin through physical encapsulation. The melting enthalpy of the PW / BMPG / CNF system (Examples 5-7) further decreased to 115.48 J·g -1 The thermal decomposition starting temperature reached 215 ℃, which was attributed to the synergistic effect of BMPG and CNF, which not only reduced the proportion of paraffin but also improved the thermal stability through the metal network of CNF.

[0079] When BMPG was surface-modified with Fe3O4 nanoparticles (BMPG:FeCl3=1:3), the melting enthalpy of PW / BMPG-Fe3O4 / CNF was maintained at 116.57 J·g -1 , meeting the energy storage requirements (Example 10), the thermal decomposition starting temperature rose to 220 ° C, and the melting enthalpy retention rate reached 98.3% after 50 cycles, achieving the synergistic optimization of phase change latent heat and thermal stability.

[0080] Application Examples To evaluate the applicability of composite phase change materials in human thermal management, a heat energy release test was conducted with an effective hyperthermia temperature range of 40 to 70°C: PW / BMPG-Fe3O4 / CNF was cut into 4×6×2 cm wearable units, heated to 67°C by light, and then placed on a 35°C silicone plate (simulating the skin interface), with the upper and lower surface temperatures monitored simultaneously; pure PW of the same mass electrically heated to 67°C was used as a control. Figure 9 As shown, pure PW has low thermal conductivity (0.251 W·m -1 ·K -1) exhibits significant temperature hysteresis—the bottom temperature plummets to below 40°C within 400 seconds after contact with the platform, while the top temperature remains above 55°C due to low internal heat conduction, indicating that heat transfer occurs primarily through air convection, with axial heat conduction failing. In contrast, the PW / BMPG-Fe₃O₄ / CNF (Example 9) achieves an axial temperature difference of ΔT ≤ 2.5°C between the upper and lower surfaces, thanks to the BMPG-Fe₃O₄-CNF composite thermal network. The material maintains the effective thermotherapy temperature range for nearly 800 seconds, extending the effective heat release time at the contact surface by 95% compared to pure PW. This material achieves efficient, uniform, and continuous thermal energy management, providing key material support for wearable solar thermotherapy devices.

[0081] In summary, this invention utilizes biomass waste to prepare BMPG, creates copper nanowire foam (CNF) by in situ growing copper nanoparticles on the surface of copper foam, uses BMPG as a carrier, and in situ grows Fe₃O₄ nanoparticles on its surface via a solvothermal method. The modified BMPG-Fe₃O₄ is then introduced into a paraffin wax and CNF system, achieving efficient resource utilization and green conversion. The resulting composite phase-change material not only possesses high heat storage capacity, but also significantly improves photothermal conversion efficiency and thermal conductivity, solving the problem of paraffin wax phase change leakage. The simple and low-cost preparation process offers promising application prospects, with potential applications in a wide range of fields, including solar thermal conversion and storage, and human thermal management.

[0082] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A composite phase change material, characterized in that: It comprises a paraffin matrix and a thermal conductive phase change material dispersed in the paraffin matrix; the thermal conductive phase change material is selected from at least one of biomass-based graphene, copper nanowire foam and Fe3O4-modified biomass-based graphene.

2. The composite phase change material according to claim 1, characterized in that: The composite phase change material is selected from one of paraffin wax / biomass-based graphene composite phase change material, paraffin wax / copper nanowire foam composite phase change material, paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material.

3. The composite phase change material according to claim 2, characterized in that: In the paraffin wax / biomass-based graphene composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%; Or, in the paraffin wax / copper nanowire foam composite phase change material, the content of copper nanowire foam is 30 wt% - 35 wt%; Alternatively, in the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; Or, in the paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material, the content of Fe3O4-modified biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; The mass ratio of biomass-based graphene to Fe3O4 in the Fe3O4-modified biomass-based graphene is 1: (1-3).

4. The composite phase change material according to claim 1, characterized in that: The biomass-based graphene is a two-dimensional network formed by stacking 2-8 single-atom carbon layers. 2D / I G 0.70-0.82, I D / I G <0.58; Or, the copper nanowire foam has a three-dimensional copper nanowire skeleton structure and a particle size of 50-100 nm; Alternatively, the Fe3O4 particles in the Fe3O4-modified biomass-based graphene are distributed on the surface of the biomass-based graphene; and the particle size of the Fe3O4 particles is 5-10 nm.

5. A method for preparing the composite phase change material according to any one of claims 1 to 4, characterized in that: The steps include: The paraffin matrix is ​​heated and melted, and then the heat-conductive phase change material is added, mixed evenly, and then cooled and formed to obtain a composite phase change material; The thermally conductive phase change material includes at least one of biomass-based graphene, copper nanowire foam, and Fe3O4-modified biomass-based graphene.

6. The method for preparing a composite phase change material according to claim 5, characterized in that: The temperature at which the paraffin matrix is ​​heated and melted is 65-85° C., and the mixing method is selected from one of ultrasonic dispersion and vacuum impregnation; The content of the thermal conductive phase change material in the composite phase change material is 0.1 wt%-0.5 wt%.

7. The method for preparing a composite phase change material according to claim 5, characterized in that: The preparation method of the biomass-based graphene is as follows: a nitrogen source is carbonized under inert protection to obtain a carbonized nitrogen source; the carbonized nitrogen source is mixed with biochar, and then subjected to microwave plasma conversion under inert protection to obtain the biomass-based graphene; Alternatively, the copper nanowire foam is prepared as follows: the copper foam is sequentially cleaned with anhydrous ethanol, water, and hydrochloric acid, then rinsed with water, dried with nitrogen, and dried to obtain a clean copper foam; the cleaned copper foam is immersed in an alkaline solution for reaction to obtain a modified copper foam; polytetrafluoroethylene, natural graphite, and anhydrous ethanol are mixed to obtain a suspension; the suspension is dropwise applied to the surface of the modified copper foam, and the copper nanowire foam is obtained after drying, heat treatment under inert gas protection, and cooling. Alternatively, the preparation method of the Fe3O4-modified biomass-based graphene is as follows: after mixing the biomass-based graphene with a solvent, adding a soluble iron salt and mixing, then adding sodium acetate and stirring, and performing a hydrothermal reaction to obtain the Fe3O4-modified biomass-based graphene.

8. The method for preparing a composite phase change material according to claim 7, characterized in that: In the method for preparing biomass-based graphene, the nitrogen source is selected from at least one of urea, dicyandiamide, melamine foam, and aniline; the temperature of the carbonization treatment is 800-1000°C, and the carbonization treatment time is 1-2 hours; The mixing mass ratio of the carbonized nitrogen source to the biochar is (2-3):1; the biochar is at least one of bamboo powder, straw powder and fruit shell; the particle size of the biochar is 50-500 μm; The microwave plasma conversion treatment has a power of 700-900 W, a frequency of 2-3 GHz, and a time of 5-15 seconds; Preferably, the nitrogen source is melamine foam; the temperature of the carbonization treatment is 900° C., and the carbonization treatment time is 1 hour; the mixing mass ratio of the carbonized nitrogen source to the biochar is 2.4:1; the biochar is bamboo powder; the microwave plasma conversion treatment power is 800 W, the frequency is 2.45 GHz, and the time is 10 seconds; Alternatively, in the method for preparing the copper nanowire foam, the concentration of hydrochloric acid is 15-25 wt%, the drying temperature is 75-85°C, the alkaline solution includes sodium hydroxide and ammonium persulfate, the concentration of sodium hydroxide is 2-3 M, the concentration of ammonium persulfate is 0.1-0.2 M, and the reaction time in the alkaline solution is 20-30 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite, and anhydrous ethanol is 1 mg: (450-550) mg: (250-350) mL; the drying temperature is 45-55°C, and the drying time is 3-5 hours; the heat treatment atmosphere is nitrogen, the temperature is increased to 350-450°C at 3-5°C / min, and the temperature is maintained for 1.5-2.5 hours; Preferably, in the preparation method of the copper nanowire foam, the concentration of hydrochloric acid is 20 wt%, the drying temperature is 80 ° C, the concentration of sodium hydroxide in the alkaline solution is 2.5 M, the concentration of ammonium persulfate is 0.15 M, and the reaction time in the alkaline solution is 25 minutes; the mixing ratio of polytetrafluoroethylene, natural graphite and anhydrous ethanol is 1 mg: 500 mg: 300 mL; the drying temperature is 50 ° C, and the drying time is 4 hours; the heat treatment atmosphere is nitrogen, the temperature is increased to 400 ° C at 5 ° C / min, and the temperature is kept for 2 hours; Alternatively, in the method for preparing the Fe3O4-modified biomass-based graphene, the biomass-based graphene is added to a solvent, a soluble iron salt is added and mixed, and then sodium acetate is added, followed by a hydrothermal reaction to obtain the Fe3O4-modified biomass-based graphene; The solvent is a mixed solvent consisting of diethylene glycol and ethylene glycol, and the volume ratio of diethylene glycol to ethylene glycol is (30-40):10; The ratio of biomass-based graphene to solvent is 10 mg : (40-50) mL; The soluble iron salt is one of FeCl3, ferric nitrate and ferric sulfate; The mass ratio of biomass-based graphene to soluble iron salt is 1:(1-3); The mass ratio of biomass-based graphene to sodium acetate is 10:(75-85); The temperature of the hydrothermal reaction is 180-220 °C, and the time of the hydrothermal reaction is 10-15 h; Preferably, the volume ratio of diethylene glycol to ethylene glycol in the solvent is 35:10; The ratio of biomass-based graphene to solvent was 10 mg:45 mL; The soluble iron salt is FeCl3; The mass ratio of biomass-based graphene to FeCl3 is 1:3; The mass ratio of biomass-based graphene to sodium acetate is 10:80; The hydrothermal reaction temperature was 200 °C and the hydrothermal reaction time was 12 h.

9. The method for preparing a composite phase change material according to claim 5, characterized in that: The composite phase change material is selected from one of paraffin wax / biomass-based graphene composite phase change material, paraffin wax / copper nanowire foam composite phase change material, paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, and paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material; The preparation method of the paraffin wax / biomass-based graphene composite phase change material is as follows: The paraffin matrix is ​​heated and melted, and then vacuum-dried biomass-based graphene is added, ultrasonic dispersion and heating and stirring are performed, and the paraffin / biomass-based graphene composite phase change material is obtained by cooling and molding. Preferably, the temperature for heating and melting the paraffin matrix is ​​60-80°C, the temperature for ultrasonic dispersion is 60-80°C, and the time for ultrasonic dispersion is 0.5-1.5 h; the temperature for heating and stirring is 90-110°C, and the time for heating and stirring is 1-3 h; The composite phase change material has a heavy thermal conductive phase change material content of 0.1 wt%-0.5 wt%; Alternatively, the preparation method of the paraffin wax / copper nanowire foam composite phase change material is as follows: The paraffin matrix is ​​heated and melted, and then copper nanowire foam is added, mixed by vacuum impregnation method, and cooled and formed to obtain the paraffin / copper nanowire foam composite phase change material; In the paraffin wax / copper nanowire foam composite phase change material, the content of the copper nanowire foam is 30 wt% - 35 wt%; Preferably, the temperature of the vacuum impregnation mixing method is 75-85°C and the time is 1-2 h; Alternatively, the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material is prepared as follows: heating and melting the paraffin wax / biomass-based graphene, then adding the copper nanowire foam, mixing by vacuum impregnation, and cooling and molding to obtain the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material; Alternatively, in the paraffin wax / biomass-based graphene / copper nanowire foam composite phase change material, the content of biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; Preferably, the temperature of the vacuum impregnation mixing method is 75-85°C and the time is 1-2 h; Alternatively, the preparation method of the paraffin wax / Fe3O4 modified biomass-based graphene / copper nanowire foam composite phase change material is as follows: The paraffin wax is heated and melted, and then biomass-based graphene modified with Fe3O4 and copper nanowire foam are added, mixed by vacuum impregnation, and cooled and formed to obtain a paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material; In the paraffin wax / Fe3O4-modified biomass-based graphene / copper nanowire foam composite phase change material, the content of Fe3O4-modified biomass-based graphene is 0.1 wt%-0.5 wt%, and the content of copper nanowire foam is 30 wt%-35 wt%; Preferably, the mixing temperature of the vacuum impregnation method is 75-85° C. and the mixing time is 1-2 h.

10. Use of the composite phase change material according to any one of claims 1 to 4 in heat storage of solar water heaters, intelligent temperature-controlled building walls, and thermal management of electronic devices.

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