Magnetic carbon aerogel-based phase change material with photo-thermo-electric properties and preparation method thereof

Abstract

The application discloses a magnetic carbon aerogel-based phase change material with photothermal-electric heating performance, which is prepared by interweaving and assembling long-chain segment carboxylated cellulose CNF and graphene oxide GO, and complexing and cross-linking Fe ions of iron nitrate nonahydrate Fe(NO3)3.9H2O, so as to prepare flexible carbon aerogel C-GC with magnetism and elasticity; PCMs can be prepared by adsorbing eicosane through the C-GC; the microstructure of the C-GC is a mutually connected honeycomb porous structure, the GO is a transparent nanosheet, and nanoparticles are uniformly distributed on the nanosheet; the PCMs have magnetism; the C-GC has elasticity, the compression rate is 68.7%, and the C-GC rebounds to the initial height after the pressure is removed, and the recovery rate is 100%. The preparation method comprises the following steps: 1, preparation of a hybrid aerogel; 2, preparation of flexible carbon aerogel; and 3, preparation of carbon aerogel-based composite phase change material. The carbon aerogel-based composite phase change material can be used as a phase change material, a photothermal material and an electric heating material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer materials and photo-thermal-electric conversion phase change energy storage materials, and in particular to a magnetic carbon aerogel-based phase change material with photo-thermal-electric properties and a preparation method thereof. BACKGROUND

[0002] Organic phase change materials have the advantages of high heat energy storage density and constant conversion temperature, and can be applied to the field of energy conversion to enrich heat energy storage methods. For example, in the previous work of the present application group, the prior art 1 (a boron nitride / pigeon powder double-thermal-conductivity-based carbon aerogel and a preparation method and application thereof. Chinese patent: CN113150746A) uses polyethylene glycol as a phase change material and encapsulates it in a boron nitride-doped pigeon powder-based carbon aerogel. The synergistic effect of boron nitride nanosheets and carbon skeleton increases the thermal conductivity of the composite phase change material by 187%, and improves the photo-thermal conversion performance of the composite phase change material. The inventors found new technical problems in subsequent applications:

[0003] 1. After the composite phase change material is mixed with other materials, it is difficult to quickly locate during use, and it is difficult to separate and recover after use;

[0004] 2. When loading phase change materials on the surface of ironware, additional adhesives are needed for assistance.

[0005] According to the research of the inventors, phase change materials with magnetism can simultaneously solve the above problems of positioning, separation and recovery, and do not require the use of phase change materials on the surface of ironware with adhesives.

[0006] After consulting existing literature, it is found that there are a small number of magnetic phase change materials in the prior art. For example, existing literature 2 (Jiang Z, Shu J, Ge Z, et al. Preparation and performance of magnetic phase change microcapsules with organic-inorganic double shell [J]. Solar Energy Materials and Solar Cells, 2022, 240: 111716.) directly adds Fe3O4 magnetic particles to the paraffin emulsion and physically blends them, and synthesizes a melamine formaldehyde resin composite shell to form a primary phase change microcapsule, and then forms a layer of SiO2 on the melamine formaldehyde resin composite shell, finally forming a magnetic phase change microcapsule with a polymer-SiO2 double shell, which encapsulates the magnetic particles well, so that the composite phase change material has the ability of magnetic separation and recovery. Although this scheme realizes the obtaining of a phase change composite material with magnetism, the basic principle of this technical scheme is to directly add a material with magnetism to the phase change material. Based on such a technical principle, such a technical scheme has the same three technical problems:

[0007] 1. The magnetic particles are directly mixed with the phase change material, i.e. the two are physically interacted, resulting in poor dispersibility of the magnetic particles in the high-viscosity phase change material, which leads to a decrease in the magnetism of the composite material;

[0008] 2. The mixing of magnetic particles into the phase change material directly affects the phase change process of the phase change material, thereby leading to a decrease in the phase change performance;

[0009] 3. The composite phase change material formed by mixing the magnetic particles, which do not provide phase change performance, into the phase change material directly leads to a decrease in the adsorption capacity of the phase change material under the premise that the adsorption capacity of the matrix is constant, thereby reducing the unit mass heat storage performance of the final composite phase change material.

[0010] In addition, a magnetic material can also be introduced into the matrix of the phase change material. For example, existing document 3 (Jin L, Han Q, Wang J, et al. Fe3O4-Functionalized κ-Carrageenan / Melanin Hybrid Aerogel-Supported Form-Stable Phase-Change Composites with Excellent Solar / Magnetic-Thermal Conversion Efficiency and Enhanced Thermal Conductivity [J]. ACS Sustainable Chemistry & Engineering, 2023, 11(2): 649-659.) prepared a magnetic form-stable phase change material composite with good solar thermal conversion and thermal storage efficiency by directly physically adding Fe3O4 nanoparticles in κ-carrageenan and melanin, stirring and mixing to form Fe3O4 doped κ-carrageenan / melanin aerogel, and then impregnating n-dodecane into the aerogel. This scheme also achieves the technical effect of obtaining a phase change composite material with magnetism. However, such a technical solution based on the technical principle of introducing a magnetic material into the matrix of the phase change material has the problems of poor dispersion and agglomeration of the magnetic particles in the matrix, as well as a decrease in the unit mass heat storage performance.

[0011] In order to improve the dispersibility of magnetic particles and the heat storage performance per unit mass, the magnetic nanoparticles can be synthesized on the matrix to make them uniformly distributed. For example, the existing document 4 (Tao Z, Yang M, Wu L, et al. Phase change material based on polypyrrole / Fe3O4-functionalized hollow kapok fiber aerogel matrix for solar / magnetic-thermal energy conversion and storage[J]. Chemical Engineering Journal, 2021, 423: 130180.) forms a conductive polymer polypyrrole PPy coating on the natural hollow kapok fiber KF, then in-situ synthesizes Fe3O4 nanoparticles in the residual Fe ion solution, and uses paraffin PW as a phase change material to form a KF@PPy-Fe3O4 / PW composite phase change material, which has good heat conduction capacity and multifunctional heat conversion. The technology uses the method of in-situ preparation of magnetic particles, which solves the problem of agglomeration caused by direct addition of magnetic particles to a certain extent, but the magnetic particles in the aerogel only provide single magnetism, that is, they do not help to improve the heat storage performance per unit mass of the composite material, and they cannot provide additional functions to the aerogel matrix preparation process to enhance the performance of the aerogel matrix. SUMMARY

[0012] The purpose of the present application is to provide a magnetic carbon aerogel-based phase change material with photothermal-electric heating performance and a preparation method thereof.

[0013] The present application solves the technical problems existing in the prior art by the following principles:

[0014] 1. The colloidal properties of Fe ions are utilized to prepare hydrogels, and then aerogels; at the same time, due to the ionic crosslinking and hydrogen bonding between Fe ions and CNF and GO, Fe ions are uniformly distributed during the preparation of hydrogels, and at the same time, through the synergistic effect of Fe ions and CNF and GO, the encapsulation performance and compression resilience of carbon aerogels are enhanced;

[0015] 2. Through carbonization operation, the Fe ions in the aerogel are converted into oxides while realizing the conventional carbon aerogel, so that the composite material obtains magnetism;

[0016] 3. GO is used as a heat-conducting and conductive filler, which provides photothermal performance while building a continuous heat-conducting and conductive path with the carbon skeleton, so that the composite material has high thermal response rate, photothermal conversion efficiency and electric heating conversion efficiency.

[0017] To achieve the above-mentioned purposes of the application, the technical scheme adopted by the application is:

[0018] A magnetic carbon aerogel-based phase change material with photothermal-electrothermal performance is prepared by interweaving long-chain carboxylated cellulose CNF and graphene oxide GO and assembling and cross-linking by Fe ion complexation of iron nitrate nonahydrate Fe(NO3)3·9H2O to prepare a flexible carbon aerogel C-GC with magnetism and elasticity; and then by adsorbing eicosane on the C-GC, a magnetic carbon aerogel-based composite phase change material PCMs with photothermal-electrothermal performance is prepared.

[0019] The microstructure of the C-GC is a honeycomb-like interconnected porous structure, the GO is a transparent nanosheet, and the nanosheet is uniformly distributed with nanoparticles; in the PCMs, the eicosane is uniformly encapsulated in the pore channels of the C-GC.

[0020] The PCMs have magnetism.

[0021] The C-GC has elasticity, the compression rate is 68.7%, and after the pressure is removed, the C-GC rebounds to the initial height, and the recovery rate is 100%.

[0022] A preparation method of a magnetic carbon aerogel-based phase change material with photothermal-electrothermal performance, comprising the following steps:

[0023] Step 1, preparation of a hybrid aerogel, carboxylated cellulose CNF, graphene oxide GO, iron nitrate nonahydrate Fe(NO3)3·9H2O and water meet a certain mass ratio, first, CNF and GO are placed in water, and mechanical stirring is carried out under certain conditions to obtain a CNF suspension, then, Fe(NO3)3·9H2O aqueous solution is added to the suspension, and then, static setting is carried out under certain conditions to obtain a hydrogel, and finally, freeze-drying is carried out under certain conditions to obtain a hybrid aerogel, which is abbreviated as GC;

[0024] In the step 1, the mass ratio of CNF, GO, Fe(NO3)3·9H2O and water is 6:1:2:60; the concentration of the Fe(NO3)3·9H2O aqueous solution is 50 mmol / L;

[0025] In the step 1, the preparation conditions of the CNF suspension are that the stirring time is 10-12 h;

[0026] In the step 1, the static setting conditions are that the static setting time is 48 h;

[0027] In step 1, the freeze-drying conditions are as follows: first, the hydrogel is frozen at a freezing temperature of -30 to -35°C for 4 hours, and then freeze-dried at a freeze-drying temperature of -40 to -45°C for 60 to 72 hours.

[0028] Step 2, preparation of flexible carbon aerogel: under certain conditions, the hybrid aerogel obtained in step 1 is pre-oxidized, and then carbonized under certain conditions to obtain flexible carbon aerogel, abbreviated as C-GC.

[0029] In step 2, the pre-oxidation conditions are as follows: under air conditions, the pre-oxidation temperature is 200℃, the pre-oxidation time is 4h, and the pre-oxidation heating rate is 0.5℃ / min.

[0030] In step 2, the carbonization conditions are as follows: under nitrogen conditions, the carbonization temperature is 800℃, the carbonization time is 2h, and the carbonization heating rate is 5℃ / min.

[0031] Step 3, preparation of carbon aerogel-based composite phase change material: with C-GC obtained in step 2 and eicosane satisfying a certain mass ratio, firstly, under certain conditions, C-GC is placed in liquid eicosane for vacuum impregnation, and magnetic carbon aerogel-based phase change material with photothermal-electrothermal properties can be obtained, abbreviated as PCMs.

[0032] In step 3, the mass ratio of C-GC to eicosane is (2-5):(95-98);

[0033] In step 3, the vacuum impregnation conditions are: impregnation temperature of 60-80℃ and impregnation time of 10-12h.

[0034] A magnetic carbon aerogel-based phase change material with photothermal and electrothermal properties is used as a phase change material. The phase change temperature is 31.47-37.85℃, the latent heat of phase change is 251.56-259.41J / g, and the thermal conductivity is 0.69-0.89W / (m·K).

[0035] The photothermal conversion efficiency is 91-95%, and the electrothermal conversion efficiency is 90-93%.

[0036] This invention has been tested using EDS, SEM, TEM, FT-IR, XRD, DSC, compressive elasticity testing, magnetic testing, planar thermal conductivity testing, leak resistance testing, simulated illumination, and simulated circuit testing, and has the following characteristics:

[0037] EDS testing revealed that the carbon aerogel-based composite phase change material with multi-response thermal energy capture prepared in this invention contains C, N, O, and Fe elements in its C-GC composition.

[0038] The SEM test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has a mutual connection honeycomb porous structure, and eicosane is successfully encapsulated in the carbon aerogel.

[0039] The TEM test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has transparent nanosheet GO, and the nanosheet is uniformly distributed with nanoparticles.

[0040] The FT-IR test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has the same infrared characteristic peak as eicosane, indicating that the process of vacuum adsorbing eicosane by C-GC is a physical action without chemical reaction.

[0041] The XRD test shows that the diffraction peak of the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application does not change obviously, indicating that C-GC has no influence on the crystallization behavior of eicosane, and the composite material is successfully prepared.

[0042] The DSC test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has a melting temperature of 37.33-37.85 DEG C, a melting enthalpy of 251.56-258.48 J / g, a crystallization temperature of 31.47-31.71 DEG C, and a crystallization enthalpy of 251.91-259.41 J / g.

[0043] The DSC cycle test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has high cycle stability and thermal stability, and the enthalpy value of the cycle curve does not change obviously after 200 cycles.

[0044] The compression elasticity test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has good compression and rebound performance, and the recovery rate is 100%.

[0045] The magnetic test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has good magnetism and can be attracted by a magnet.

[0046] The heat conduction test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has good heat conduction performance, and the thermal conductivity coefficient is 0.69-0.89 W / (m·K).

[0047] The leakage test shows that the carbon aerogel-based composite phase change material with multi-response heat energy capture prepared by the application has good leakage prevention performance and does not leak at 80 DEG C for 45 min.

[0048] The encapsulation performance of the prepared multi-response thermal energy capturing carbon aerogel-based composite phase change material has a photo-thermal conversion function, and the photo-thermal conversion efficiency is 91-95% through simulated light irradiation test.

[0049] The encapsulation performance of the prepared multi-response thermal energy capturing carbon aerogel-based composite phase change material has an electro-thermal conversion function, and the electro-thermal conversion efficiency is 90-93% through simulated circuit test.

[0050] Therefore, compared with the prior art, the present application has the following advantages:

[0051] 1. The Fe element nanoparticles are uniformly dispersed in the carbon aerogel matrix, so that the whole composite phase change material has good magnetic properties, and can realize rapid positioning and separation and recovery after use;

[0052] 2. The uniform dispersion of the Fe element magnetic particles makes the melting enthalpy of the composite phase change material 251.56-258.48 J / g, the crystallization enthalpy 251.91-259.41 J / g, and the unit mass heat storage performance is good.

[0053] 3. GO as a heat-conducting and conductive filler, together with the carbon skeleton, constructs a heat-conducting and conductive network structure, and provides photo-thermal performance, enhances the thermal response rate, photo-thermal conversion efficiency and electro-thermal conversion efficiency of the composite material;

[0054] 4. The interconnecting three-dimensional network structure formed by the synergistic effect of hydrogen bonds and ionic crosslinking in CNF, GO and Fe(NO3)3·9H2O enhances the encapsulation performance and compression resilience of the carbon aerogel;

[0055] 5. The magnetic carbon aerogel-based phase change material with photo-thermal-electric properties prepared by the present application has excellent shape stability, thermal stability and cycle stability; BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is the EDS diagram of C-GC;

[0057] Figure 2 is the SEM diagram of C-GC;

[0058] Figure 3 is the TEM diagram of C-GC;

[0059] Figure 4 is the compression elasticity test diagram of C-GC;

[0060] Figure 5 is the photo-thermal conversion test curve diagram of C-GC, eicosane and example 1;

[0061] Figure 6FT-IR graph of eicosane, Comparative Example 1, Example 1, Example 2 and Example 3;

[0062] Figure 7 XRD graph of eicosane, Comparative Example 1, Example 1, Example 2 and Example 3;

[0063] Figure 8 SEM graph of Example 1, Comparative Example 1, Example 2 and Example 3;

[0064] Figure 9 Magnetic test graph of eicosane and Example 1;

[0065] Figure 10 DSC curve graph of eicosane, Comparative Example 1, Example 1, Example 2 and Example 3;

[0066] Figure 11 DSC 200 cycles graph of Example 1;

[0067] Figure 12 Thermal conductivity graph of eicosane, Comparative Example 1, Example 1, Example 2 and Example 3;

[0068] Figure 13 Leakage prevention test graph of eicosane, Comparative Example 1, Example 1, Example 2 and Example 3;

[0069] Figure 14 Electro-thermal conversion test curve graph of Example 1. DETAILED DESCRIPTION

[0070] The present application is further described in detail by the following examples, in conjunction with the accompanying drawings.

[0071] Example 1

[0072] A method for preparing a magnetic carbon aerogel-based phase change material having photo-thermal-electro-thermal properties, comprising the following steps:

[0073] Step 1, preparation of hybrid aerogel, with the mass ratio of carboxylated cellulose CNF, graphene oxide GO, iron nitrate Fe(NO3)3·9H2O and water being 6:1:2:60, first, CNF and GO were placed in water, and mechanical stirring mixing was carried out with a stirring time of 10 h to obtain a suspension with a CNF content of 1 wt.%, then a 50 mmol / L Fe(NO3)3·9H2O aqueous solution was added to the suspension, and then the suspension was allowed to stand for 48 h to obtain a hydrogel, finally, the hydrogel was frozen at a freezing temperature of-30℃ for 4 h, and then freeze-dried at a freeze-drying temperature of-45℃ for 72 h, thereby obtaining the hybrid aerogel, which is referred to as GC for short;

[0074] Step 2, preparation of flexible carbon aerogel, the hybrid aerogel obtained in step 1 was pre-oxidized under air conditions with a pre-oxidation temperature of 200℃, a pre-oxidation time of 4 h and a pre-oxidation heating rate of 0.5℃ / min, and then carbonized under nitrogen conditions with a carbonization temperature of 800℃, a carbonization time of 2 h and a carbonization heating rate of 5℃ / min, thereby obtaining the flexible carbon aerogel, which is referred to as C-GC for short;

[0075] In order to prove the elemental composition of C-GC, EDS test was performed. The test results are shown in Figure 1 As shown in the table, C-GC contains C element, N element, O element and Fe element.

[0076] In order to prove the micro-morphology of C-GC, SEM test and TEM test were performed.

[0077] The SEM test results are shown in Figure 2 As shown in the figure, C-GC presents a mutually connected honeycomb-like porous structure;

[0078] The TEM test results are shown in Figure 3 As shown in the figure, GO in C-GC presents a transparent nanosheet shape, and nanoparticles are uniformly distributed on the nanosheet. In combination with the EDS test, it can be known that the nanoparticles are Fe element particles.

[0079] In order to prove the mechanical properties of C-GC, compression elasticity test was performed. The compression elasticity test results are shown in Figure 4 As shown in the figure, the initial height of C-GC was 20.1 mm, and when a pressure of 1512 Pa, i.e. using a 50 g weight, was applied for compression, the height of the compressed C-GC was 6.3 mm, and the compression rate was 68.7%, after removing the weight, the C-GC quickly rebounded, and the height of the rebounded C-GC was 20.1 mm, i.e. rebounded to the initial height, and the recovery rate was 100%. The test results show that C-GC has good elasticity.

[0080] In order to prove the photo-thermal conversion performance of the C-GC, a simulated light experiment was carried out. The specific method of the simulated light experiment was that the sample was irradiated by a simulated light source and the temperature change was tested. The test results are shown in Figure 5 It can be seen that the C-GC rapidly rises in temperature and no temperature control platform appears. The test results show that the C-GC has good photo-thermal conversion performance.

[0081] Step 3, preparation of the carbon aerogel-based composite phase change material, the mass ratio of the C-GC obtained in step 2 to eicosane was 3:97, first, the C-GC was placed in liquid eicosane at a temperature of 80℃, then vacuum impregnation was carried out under the conditions of an impregnation temperature of 80℃ and an impregnation time of 12h, and a magnetic carbon aerogel-based phase change material with photo-thermal-electric heating performance, referred to as PCMs, was obtained. The carbon aerogel-based composite phase change material obtained in Example 1 is named PCMs-97.

[0082] In order to prove the composition of the PCMs-97, i.e. successful preparation, FT-IR test and XRD test were carried out, and at the same time, in order to make a comparison, eicosane was subjected to FT-IR test and XRD test.

[0083] The FT-IR test results of eicosane are shown in Figure 6 The XRD test is shown in Figure 7 The infrared characteristic peaks and XRD characteristic diffraction peaks of eicosane are the same as the standard peaks;

[0084] The FT-IR test results of the PCMs-97 are shown in Figure 6 The XRD test is shown in Figure 7 The infrared characteristic peaks and XRD characteristic diffraction peaks of the PCMs-97 are the same as those of eicosane, and no obvious change occurs.

[0085] The test results show that the vacuum adsorption of eicosane by the C-GC is a physical action without chemical reaction, i.e. the C-GC has no effect on the crystallization behavior of eicosane, which can ensure the good heat storage capacity of the composite phase change material; at the same time, the above tests prove that the PCMs-97 is successfully prepared.

[0086] In order to prove the micro-morphology of the PCMs-97, the SEM test was carried out on the PCMs-97 obtained in step 3. The test results are shown in Figure 8 It can be seen that the eicosane is uniformly encapsulated in the pores of the C-GC. The test results show that the eicosane is successfully encapsulated in the carbon aerogel.

[0087] In order to prove that the PCMs-97 has magnetic effect, a magnetic test was carried out, and at the same time, in order to make a comparison, a magnetic test was carried out on eicosane.

[0088] The magnetic test results of eicosane are shown inFigure 9 As shown, eicosane is not attracted by the magnet, i.e. has no magnetism;

[0089] The results of the PCM-3 magnetic test are shown in Table 2. Figure 9 As shown, PCM-3 can be attracted by the magnet;

[0090] The test results show that PCM has a magnetic effect; in combination with the EDS test, it can be known that the magnetic effect of PCMs-97 comes from Fe element nanoparticles.

[0091] In order to prove the phase change performance of PCMs-97, differential scanning calorimetry (DSC) test is carried out, and at the same time, eicosane is tested by DSC for comparison.

[0092] The test results of eicosane are shown in Table 1. Figure 10 As shown and shown in Table 1, in the test temperature range of 20-100℃, eicosane has an endothermic peak at 38.22℃ in the melting process, and the latent heat value is 264.59J / g; and has an exothermic peak at 31.38℃ in the crystallization process; and the latent heat value is 265.01J / g.

[0093] The test results of PCMs-97 are shown in Table 2. Figure 10 As shown and shown in Table 1, in the test temperature range of 20-100℃, PCMs-97 has an endothermic peak at 37.82℃ in the melting process, and the latent heat value is 258.48J / g; and has an exothermic peak at 31.47℃ in the crystallization process; and the latent heat value is 259.41J / g.

[0094] Since the eicosane addition amount of PCMs-97 is 97%, compared with the theoretical enthalpy value of eicosane 97%, it can be known that the enthalpy value of PCMs-97 is greater than that of eicosane 97%. The test results show that after adding C-GC, the movement of molecular chain is promoted, so that the latent heat is fully stored and released.

[0095] Table 1 Phase change enthalpy and temperature of composite phase change materials with different eicosane addition amounts

[0096]

[0097] In order to prove the cycle stability of PCMs-97, 200 cycles are tested, and the test results are shown in Table 3. Figure 11 As shown, in 200 cycles, the thermal cycle curve of PCMs-97 is basically unchanged. The test results show that the phase change performance of PCMs-97 does not change before and after the cycle, which shows that the prepared PCMs-97 has good cycle stability.

[0098] In order to prove the thermal conductivity of PCMs-97, thermal conductivity test is carried out, and at the same time, eicosane is tested for comparison.

[0099] The test results of eicosane are shown in Figure 12 As shown in the table 2, the thermal conductivity of eicosane is 0.46 W / (m·K);

[0100] The test results of PCMs-97 are shown in Figure 12 As shown in the table 2, the thermal conductivity of PCMs-97 is 0.69 W / (m·K), which is 50% higher than that of eicosane.

[0101] The test results show that the encapsulation of C-GC is conducive to the construction of the heat conduction path, and improves the heat conduction capacity of PCM-3.

[0102] Table 2 Thermal conductivity of composite phase change materials with different amounts of eicosane

[0103]

[0104] In order to prove the encapsulation performance of PCMs-97 prepared, the leakage prevention test is carried out, and in order to make a comparison, the leakage prevention test is carried out on eicosane. The specific test method is to heat the sample to be tested under the condition of heating temperature of 80℃ and heating time of 45min, and observe the material state.

[0105] The test results of eicosane are shown in Figure 13 Eicosane completely melts and flows around;

[0106] The test results of PCMs-97 are shown in Figure 13 PCMs-97 has no obvious change.

[0107] The test results show that the addition of C-GC makes PCMs-97 have excellent encapsulation performance, which can effectively prevent the leakage of eicosane.

[0108] In order to prove the light-heat conversion performance of PCMs-97, the simulated light experiment is carried out, and in order to make a comparison, the simulated light experiment is carried out on C-GC and eicosane. The specific method of simulated light experiment is to use a simulated light source to irradiate the sample and test the temperature change.

[0109] The test results of eicosane are shown in Figure 5 Eicosane slowly rises in temperature, and has an obvious temperature control platform at 30℃, and the light-heat conversion efficiency reaches 63.55%;

[0110] The test results of PCMs-97 are shown in Figure 5 PCMs-97 rapidly rises in temperature, and has an obvious temperature control platform at 30℃, and the light-heat conversion efficiency reaches 94.26%.

[0111] The test results show that PCMs-97 has good light-heat conversion performance, and it can be proved that the addition of C-GC can significantly enhance the light-heat conversion performance.

[0112] In order to prove the electro-thermal conversion performance of PCMs-97, a simulation circuit experiment is carried out, and at the same time, eicosane is subjected to a simulation circuit experiment for comparison. The specific method of the simulation circuit experiment is to use a direct current power supply to form a path with the sample and test the temperature change.

[0113] The simulation circuit experiment of eicosane cannot measure the data because no conductive path is formed, that is, eicosane does not have electro-thermal conversion performance;

[0114] The test results of the electro-thermal conversion performance of PCMs-97 are shown in Figure 14 Under the simulation circuit, PCMs-97 rapidly heats up, and a temperature control platform appears at 30°C, and the electro-thermal conversion efficiency reaches 92.18%;

[0115] The test results show that the addition of C-GC enables PCMs-97 to have electro-thermal conversion performance.

[0116] In order to prove the influence of the eicosane addition amount on the performance of the phase change material, examples 2, 3, and comparative example 1 are provided, and the eicosane addition amount of the composite phase change material is 95wt.%, 96wt.% and 98wt.% respectively.

[0117] Example 2

[0118] A preparation method of a composite phase change material with an eicosane addition amount of 95wt.%, the steps not specifically explained are the same as those of example 1, and the difference is that in step 3, the eicosane addition amount is 95wt.%, and the obtained material is a composite phase change material with an eicosane addition amount of 95wt.%, which is named PCMs-95.

[0119] In order to prove the composition of PCMs-95, i.e. successful preparation, FT-IR test and XRD test are carried out. The FT-IR test results of PCMs-95 are shown in Figure 6 The XRD test is shown in Figure 7 The infrared characteristic peaks and XRD characteristic diffraction peaks of PCMs-95 are the same as those of PCMs-97, and there is no obvious change. The test results show that the addition amount has no effect on the crystallization behavior of eicosane, and it still has good heat storage capacity; at the same time, the above tests prove that PCMs-95 is successfully prepared.

[0120] In order to prove the micro-morphology of PCMs-95, SEM test is carried out. The test results of PCMs-95 are shown in Figure 8As shown, the eicosane is uniformly encapsulated in the pores of the C-GC. The test results compared with Example 1 show that the eicosane is also successfully encapsulated in the carbon aerogel, but because the amount of eicosane added is less, more network structure is exposed.

[0121] In order to prove the phase change performance of PCMs-95, DSC test was performed. The test results are shown in Table 1 and Figure 1. Figure 10 As shown in Table 1 and Figure 1, PCMs-95 has an endothermic peak at 37.33℃ during the melting process and a latent heat value of 251.56J / g, and an exothermic peak at 31.71℃ during the crystallization process and a latent heat value of 251.91J / g in the temperature range of 20-100℃. The test results compared with Example 1 show that increasing the amount of eicosane added can improve the heat storage capacity.

[0122] In order to prove the thermal conductivity performance of PCMs-95, thermal conductivity test was performed. The test results are shown in Table 2 and Figure 2. Figure 12 As shown in Table 2 and Figure 2, the thermal conductivity of PCMs-95 is 0.89W / (m·K). The test results compared with Example 1 show that increasing the amount of eicosane added will result in a decrease in thermal conductivity.

[0123] According to the DSC test results, increasing the amount of eicosane added can improve the heat storage performance while reducing the thermal conductivity. However, although the thermal conductivity decreases to 0.69W / (m·K) when the amount of eicosane added reaches 97%, it still meets the application requirements, so the more the amount of eicosane added in the range of 95-97% the better.

[0124] In order to prove the encapsulation performance of the prepared PCMs-95, leakage prevention test was performed. The test results are shown in Table 3 and Figure 3. Figure 13 As shown in Table 3 and Figure 3, PCMs-95 has no obvious changes. The test results show that C-GC has excellent encapsulation performance and can effectively prevent the leakage of eicosane.

[0125] Example 3

[0126] A method for preparing a composite phase change material with a eicosane addition amount of 96wt.%, the steps not specifically stated are the same as those of Example 1, the difference is that in step 3, the eicosane addition amount is 96wt.%, and the obtained material is a composite phase change material with a eicosane addition amount of 96wt.%, named PCMs-96.

[0127] The FT-IR test results of PCMs-96 are shown in Figure 4. Figure 6 The XRD test is shown in Figure 5. Figure 7 The SEM test results are shown in Figure 6. Figure 8 The leakage prevention test results are shown in Table 3 and Figure 3. Figure 13 As shown in Table 3 and Figure 3, PCMs-95 has no substantial changes compared with PCMs-96, and the conclusions are consistent.

[0128] The DSC test results of PCMs-96 are shown in Table 1. Figure 10 As shown in Table 1, PCMs-96 has an endothermic peak at 37.85℃ and latent heat value of 254.47 J / g in the melting process, and an exothermic peak at 31.51℃ and latent heat value of 255.22 J / g in the crystallization process in the temperature range of 20-100℃.

[0129] The thermal conductivity test results of PCMs-96 are shown in Table 2. Figure 12 As shown in Table 2, the thermal conductivity of PCMs-96 is 0.81 W / (m·K).

[0130] Comparative Example 1

[0131] A preparation method of a composite phase change material with eicosane addition amount of 98 wt.%, the steps not specifically explained being the same as those in Example 1, and the difference being that in step 3, the eicosane addition amount is 98 wt.%, and the obtained material is a composite phase change material with eicosane addition amount of 98 wt.%, named PCMs-98.

[0132] When PCMs-98 is subjected to vacuum impregnation in step 3, eicosane residues appear, i.e., PCMs-98 is adsorbed to the saturation state, resulting in incomplete adsorption of part of the eicosane. Therefore, the C-GC before adsorption and PCMs-98 after adsorption are weighed and the adsorption amount of eicosane is calculated. The adsorption amount of PCMs-98 is calculated to be 97.83% by weighing.

[0133] The FT-IR test results of PCMs-98 are shown in Table 3. Figure 6 The XRD test results are shown in Table 4. Figure 7 Both the FT-IR test results and the XRD test results of PCMs-98 have no substantial changes compared with PCMs-95, and the obtained conclusions are consistent.

[0134] The DSC test results of PCMs-98 are shown in Table 1. Figure 10 As shown in Table 1, PCMs-98 has an endothermic peak at 37.68℃ and latent heat value of 260.18 J / g in the melting process, and an exothermic peak at 31.40℃ and latent heat value of 260.46 J / g in the crystallization process in the temperature range of 20-100℃.

[0135] The thermal conductivity test results of PCMs-98 are shown in Table 2. Figure 12 As shown in Table 2, the thermal conductivity of PCMs-98 is 0.56 W / (m·K).

[0136] However, the SEM test results of PCMs-98 are shown in Table 5. Figure 8As shown, the eicosane was adsorbed to saturation, filling the pores of the C-GC. The test results compared with Example 1 show that the eicosane was also successfully encapsulated in the carbon aerogel, but, because the eicosane was adsorbed to saturation, the eicosane completely covered the network structure.

[0137] At the same time, the results of the leak-proof test of PCMs-98 are shown in Table 2. Figure 13 As shown, a slight leak occurred at the bottom of PCMs-98.

[0138] In combination with the SEM and leak-proof test results, it can be seen that, after the eicosane was adsorbed to saturation, the C-GC achieved complete encapsulation, resulting in a leak. Therefore, the amount of eicosane added should not reach a saturation state.

[0139] From Example 1, Example 2, Example 3 and Comparative Example 1, the following conclusions can be drawn:

[0140] 1. The ion cross-linking effect of Fe ions is used to enhance the cross-linking degree of CNF, improve the encapsulation performance of the composite phase change material, form a C-GC with a continuous network structure, and make the Fe element magnetic nanoparticles uniformly dispersed in the network structure, with good magnetic properties and compression resilience;

[0141] 2. The high thermal conductivity, high light-heat conversion and high electrical-thermal conversion characteristics of GO and the carbon skeleton in the C-GC are used to improve the thermal conductivity, light-heat conversion and electrical-thermal conversion efficiency, with a thermal conductivity of 0.89 W / (m·K), a light-heat conversion efficiency of 94.26%, and an electrical-thermal conversion efficiency of 92.18%;

[0142] 3. The introduction of the C-GC network skeleton improves the leak resistance of the phase change material, allowing the eicosane in the material to not leak at 80°C for 45 minutes;

[0143] 4. The composite phase change material has a high crystallization enthalpy of 259.41 J / g and a high melting enthalpy of 258.48 J / g, with excellent heat storage performance among the same type of materials.

Claims

1. A method for preparing a magnetic carbon aerogel-based phase change material with photothermal-electrothermal properties, characterized in that It comprises the following steps: Step 1, preparation of hybrid aerogel, carboxylated cellulose CNF, graphene oxide GO, iron nitrate nonahydrate Fe(NO3)3·9H2O and water meet a certain mass ratio, first, CNF and GO are placed in water, and mixed by mechanical stirring under certain conditions to obtain CNF suspension, then Fe(NO3)3·9H2O aqueous solution is added to the suspension, and then it is placed under certain conditions to obtain hydrogel, finally, freeze-drying under certain conditions, that is, GC can be obtained, which is abbreviated as GC; In step 1, the mass ratio of CNF, GO, Fe(NO3)3·9H2O and water is 6:1:2:60; the concentration of Fe(NO3)3·9H2O aqueous solution is 50mmol / L; In step 1, the preparation conditions of CNF suspension are that the stirring time is 10-12h; In step 1, the conditions for standing are that the standing time is 48h; In step 1, the conditions for freeze-drying are that the hydrogel is first frozen under the condition that the freezing temperature is-30--35℃ and the freezing time is 4-6h, and then freeze-dried under the condition that the freeze-drying temperature is-40--45℃ and the freeze-drying time is 60-72h; Step 2, preparation of flexible carbon aerogel, under certain conditions, the hybrid aerogel obtained in step 1 is pre-oxidized, and then carbonized under certain conditions, that is, flexible carbon aerogel C-GC can be obtained; In step 2, the pre-oxidation conditions are that the pre-oxidation temperature is 200℃ under air condition, the pre-oxidation time is 4h, and the pre-oxidation heating rate is 0.5℃ / min; In step 2, the carbonization conditions are that the carbonization temperature is 800℃ under nitrogen condition, the carbonization time is 2h, and the carbonization heating rate is 5℃ / min; Step 3, preparation of carbon aerogel-based composite phase change material, C-GC obtained in step 2 and eicosane meet a certain mass ratio, first, C-GC is placed in liquid eicosane under certain conditions for vacuum impregnation, that is, a magnetic carbon aerogel-based phase change material with photothermal-electric heating performance, which is abbreviated as PCMs, can be obtained; In step 3, the mass ratio of C-GC and eicosane is (2-5):(95-98); In step 3, the vacuum impregnation conditions are that the impregnation temperature is 60-80℃ and the impregnation time is 10-12h.

2. The method of claim 1, wherein: The obtained magnetic carbon aerogel-based phase change material with photothermal-electric heating performance is interwoven and assembled by long-chain carboxylated cellulose CNF and graphene oxide GO, and is cross-linked by Fe ion complexation of iron nitrate nonahydrate Fe(NO3)3·9H2O, to prepare flexible carbon aerogel C-GC with magnetism and elasticity; eicosane is adsorbed by C-GC to obtain a magnetic carbon aerogel-based composite phase change material PCMs with photothermal-electric heating performance; The microstructure of the C-GC is a mutually connected honeycomb-like porous structure, GO is a transparent nanosheet, and nanoparticles are uniformly distributed on the nanosheet; in the PCMs, eicosane is uniformly encapsulated in the pore channels of C-GC; The PCMs have magnetism; The C-GC has elasticity, the compression rate is 68.7%, and the C-GC rebounds to the initial height after the removal of the pressure, and the recovery rate is 100%.

3. The method of claim 2, wherein: The application of the obtained magnetic carbon aerogel-based phase change material with photo-thermal-electric heating performance as a phase change material, the phase change temperature is 31.47-37.85 DEG C, the phase change latent heat is 251.56-259.41 J / g, and the thermal conductivity is 0.69-0.89 W / (m*K).

4. The method of claim 2, wherein: The application of the obtained magnetic carbon aerogel-based phase change material with photo-thermal-electric heating performance as a photo-thermal material, the photo-thermal conversion efficiency is 91-95%.

5. The method of claim 2, wherein: The application of the obtained magnetic carbon aerogel-based phase change material with photo-thermal-electric heating performance as an electric heating material, the electric heating conversion efficiency is 90-93%.

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