Composite phase change material based on shaddock peel carbon aerogel / reduced graphene oxide double frameworks as well as preparation method and application of composite phase change material

Abstract

The invention discloses a carbon aerogel / reduced graphene oxide double-framework composite phase change material based on shaddock peel as well as a preparation method and application of the carbon aerogel / reduced graphene oxide double-framework composite phase change material. According to the method, the carbon aerogel / reduced graphene oxide double-framework material (CPA-rGO) with a hierarchical pore structure is constructed by taking waste shaddock peel as a raw material through freeze drying, a layer-by-layer self-assembly (LbL) technology and a gas-phase reduction and high-temperature carbonization process. And then, loading n-octacosane in the porous skeleton by a vacuum-assisted impregnation method to form the composite phase change material (OCPA-rGO) with a stable shape. The material has excellent leakproof performance (the leakage rate at 70 DEG C is only 4%), high thermal conductivity (0.366 W / (m.K)), remarkable photothermal conversion efficiency (91.6%) and electrothermal response characteristic, has a temperature sensitive resistance function, and can be applied to building energy-saving temperature control and intelligent household high-temperature early warning systems. According to the invention, high-value utilization of agricultural wastes is realized, and a new thought is provided for design of efficient and multifunctional phase change energy storage materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional composite phase change materials, and in particular relates to a grapefruit peel carbon aerogel / reduced graphene oxide dual-skeleton composite phase change material and a preparation method and application thereof. Background Art

[0002] In recent years, with the increasingly severe global energy crisis and the increasing requirements for environmental protection, the development and utilization of renewable energy has become the research focus of scientific researchers in various countries. Solar energy has attracted much attention as a clean and sustainable form of energy. However, the intermittent and unstable nature of solar energy has seriously restricted its large-scale application, so the development of efficient energy storage technology is particularly important.

[0003] Phase change materials (PCMs) have become a hot topic in the field of thermal energy storage because they can absorb or release a large amount of latent heat during the phase change process. Among them, organic PCMs such as n-28alkanes are widely used due to their advantages such as high phase change enthalpy, small supercooling, and good chemical stability. However, traditional organic PCMs still face two key challenges in practical applications: leakage during the phase change process; and insufficient energy conversion efficiency due to low intrinsic thermal conductivity, which seriously affects the efficiency of thermal energy storage and release.

[0004] It is particularly noteworthy that biomass-derived carbon materials have been regarded as ideal carriers for high phase change material loading in recent years due to their natural porous structure and sustainability. However, CN202111639851 discloses a high thermal conductivity phase change microcapsule and its preparation method, which is limited by the shell thickness, resulting in a phase change material loading of ≤70%. In addition, due to the aging of its shell, the mass loss rate after 100 cycles is >5%.

[0005] In terms of material composite strategies, layer-by-layer self-assembly (LbL) technology has attracted attention due to its advantage of being able to precisely control the loading amount of nanomaterials. For example, J. Mater. Chem. A, 2020, 8, 14126 reported that Du et al. assembled black phosphorus / cellulose aerogel composites by LbL, but its photothermal conversion efficiency was only 87.6%.

[0006] Therefore, developing a new type of phase change material based on biomass / graphene composite, which can not only maintain the high load and high energy storage density of the phase change material, but also solve the problems of leakage and poor thermal conductivity, and at the same time achieve lightweight, low cost and large-scale preparation, has become a technical problem to be solved in this field. The present invention successfully solves the above technical problems through innovative material design and preparation process, and provides a new solution for the practical application of phase change energy storage materials. Summary of the invention

[0007] Based on the above-mentioned drawbacks and deficiencies in the prior art, one of the objectives of the present invention is to at least solve one or more of the above problems existing in the prior art. Specifically, the present invention aims to provide a composite phase change material based on a double-skeleton of pomelo peel carbon aerogel / reduced graphene oxide, which can solve the problems of leakage and poor thermal conductivity while maintaining a high load and high energy storage density.

[0008] To achieve the above-mentioned invention objectives, the present invention adopts the following technical solutions:

[0009] A preparation method of a composite phase change material based on a double-skeleton of pomelo peel carbon aerogel / reduced graphene oxide, comprising the following steps:

[0010] (1) Preparation of pomelo peel aerogel: Cut the pomelo peel into pieces, wash it, and freeze-dry it for 30-50 hours to obtain porous pomelo peel aerogel (PA);

[0011] (2) Preparation of pomelo peel-graphene oxide aerogel (PA-GO): Adopt the layer-by-layer self-assembly technology to alternately immerse the polyethyleneimine solution (PEI) and the graphene oxide dispersion on the surface of the pomelo peel aerogel, cycle 3-6 times, and finally remove the excess water to obtain the pomelo peel-graphene oxide aerogel (PA-GO);

[0012] (3) Preparation of graphene oxide aerogel (PA-rGO): After freeze-drying the modified aerogel, reduce it in hydroiodic acid vapor (HI), and then wash it with deionized water to remove the residual hydroiodic acid to obtain reduced graphene oxide aerogel (PA-rGO);

[0013] (4) Preparation of carbonized aerogel (CPA-rGO): The reduced graphene oxide aerogel is subjected to high-temperature carbonization treatment under an inert gas to obtain carbonized aerogel (CPA-rGO);

[0014] (5) Preparation of phase change composite material (OCPA-rGO): Immerse the carbonized aerogel (CPA-rGO) in molten n-octacosane under vacuum conditions, and then use filter paper to remove the excess alkane on the surface to obtain the phase change composite material (OCPA-rGO).

[0015] As a preferred solution, in the step (1), the graphene oxide dispersion is prepared by the following method: Mix graphite powder and concentrated sulfuric acid under an ice bath condition, add potassium permanganate to keep the temperature below 20°C, then transfer it to an oil bath at 40-50°C and stir for 0.5-1 hour, add 100-200 mL of deionized water and then heat it up to 90-100°C and react for 10-30 minutes, dropwise add deionized water and hydrogen peroxide to make the solution turn yellow, and obtain the graphene oxide dispersion (GO) after hydrochloric acid washing, centrifugation, and dialysis purification.

[0016] More preferably, the mass-to-volume ratio of the graphite powder, concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide is 3 g: 70 mL: 9 g: 15 mL, and the concentration of the hydrochloric acid used for washing is 9%.

[0017] As a preferred solution, in the step (2), the concentration of the polyethyleneimine solution is a 30% aqueous solution, the concentration of the graphene oxide dispersion is 1 - 3 mg / mL, and after each impregnation, ultrasonic treatment is performed for 1 - 3 minutes.

[0018] As a preferred solution, in the step (3), the temperature for reduction with hydroiodic acid vapor is 90 - 100 °C, and the time is 1 - 2 hours.

[0019] As a preferred solution, in the step (4), the heating rate for carbonization treatment is 3 - 10 °C / min, the final temperature is 700 - 900 °C, and the heat preservation time is 1 - 3 hours.

[0020] As a preferred solution, in the step (5), the vacuum degree of vacuum impregnation is ≤ -0.08 MPa, the impregnation temperature is 90 - 110 °C, and the time is 20 - 40 minutes.

[0021] The present invention provides a composite phase change material based on a double framework of pomelo peel carbon aerogel / reduced graphene oxide prepared by the above preparation method.

[0022] As a preferred solution, the loading amount of n-octacosane in the composite phase change material is 87 - 93 wt%.

[0023] The present invention provides an application of the above composite phase change material in a building energy-saving temperature control system and a smart home high-temperature early warning system.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) Improvement in anti-leakage performance and increase in loading amount: The natural honeycomb structure of pomelo peel (pore size 10 - 100 μm) and rGO nanosheets form a "micro-nano dual-level water-locking" effect, and the phase change material is fixed synergistically by capillary force and π-π bond. The loading amount of n-octacosane in the present invention is 87 - 93 wt%, and the leakage rate at 70 °C is only 4%.

[0026] (2) Double breakthrough in thermal / electrical conductivity: The natural vascular bundle structure of pomelo peel forms a macroscopic thermal conduction channel, and the rGO nanosheet layer constructs a double-framework synergistic continuous thermal conduction network; in addition, the pomelo peel framework is transformed into a conductive material after high-temperature carbonization, forming a 3D network conductive channel.

[0027] (3) Significantly enhanced structural stability: Due to the establishment of the "soft-hard" synergistic structure of the biomass framework, the structural stability of the material is greatly improved. It can be obtained through testing in the present invention that after high-temperature carbonization, the porosity remains >90%, and the deformation is <5% after 50 compression cycles.

[0028] (4) Multifunctional integrated innovation: The self-supporting conductive network constructed in this invention has a high conductive efficiency of 1.27 mS / cm, a photothermal conversion efficiency of 91.6%, and a resistance-temperature response coefficient of -0.8% / °C in the range of 20 - 80°C. With multifunctional synergy, it combines photothermal / electrothermal conversion and temperature sensing functions, enabling the integration of heat storage - heat conduction - photovoltaic conversion, and expanding the application scenarios in intelligent buildings.

[0029] (5) Environmental protection and sustainable development: This invention uses recycled waste pomelos to replace traditional petroleum-based carriers to prepare lightweight porous carbon aerogels, which are low-cost and environmentally friendly. The environmental protection design of this invention not only meets the requirements of the "dual carbon" strategy, but also redefines the sustainable development standards of phase change materials through the application of waste upgrading recycling and green chemistry principles. Description of the Drawings

[0030] Figure 1 It is a comparison graph of the gray values of the aerogels when PA is immersed in different GO solutions and the Zeta potential of PEI and GO during five cycles of LBL in Examples 1 - 3 of the present invention;

[0031] Figure 2 It is a comparison photo of the anti-leakage performance of Examples 1 - 3 of the present invention, n-octadecane, and Comparative Example 1 at 30°C and 70°C;

[0032] Figure 3 It is a comparison graph of the DSC curves of the 1st, 10th, 20th, 30th, 40th, and 50th thermal cycles of Examples 1 - 3 of the present invention;

[0033] Figure 4 It is a comparison graph of the thermal conductivity and electrical conductivity of Examples 1 - 3 of the present invention and Comparative Examples 1 - 4;

[0034] Figure 5

[0035] Figure 6 It is a comparison graph of the photothermal conversion temperature-time curve and Δt measurement of Examples 1 - 3 of the present invention and Comparative Example 1;

[0036] Figure 7 For Example 3 of the present invention under 300 mW / cm 2 Temperature and voltage change curves under xenon lamp on-off cycle irradiation. Detailed Embodiments

[0037] In order to make the technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0038] Example 1

[0039] The preparation method of the pomelo peel carbon aerogel / reduced graphene oxide (rGO) double-skeleton composite phase change material in this example includes the following steps:

[0040] (1) Preparation of graphene oxide (GO), the specific process is as follows:

[0041] First, put graphite powder (3.0 g) and H2SO4 (70 mL) into a beaker and stir in an ice bath. Then add KMnO4 (9.0 g) and keep the suspension temperature below 20 °C. Secondly, transfer the beaker into an oil bath (40 °C), stir vigorously for 0.5 h, and add 150 mL of deionized water; heat the reaction system to 95 °C and react for 15 min. Thirdly, dropwise add 500 mL of deionized water and 15 mL of H2O2 to make the solution color change from dark brown to yellow. Fourthly, wash with 9% HCl aqueous solution (50 mL each time, repeat 3 times) to remove metal ion impurities and centrifuge. The obtained solid is dried in air and diluted to 600 mL to prepare a graphite oxide aqueous dispersion. Finally, dialyze and purify with a dialysis membrane for one week to remove the remaining metal substances. Then dilute the obtained graphite oxide aqueous dispersion to 1.2 L, stir overnight, and ultrasonicate for 30 minutes to exfoliate it into graphene oxide. Then centrifuge the graphene oxide dispersion at 3000 rpm for 40 minutes to remove the unexfoliated graphite.

[0042] (2) Construction of pomelo peel aerogel matrix (PA), the specific process is as follows:

[0043] Prepare pomelo peel aerogel by removing the outer layer of pomelo peel and retaining the mesocarp. Cut the mesocarp into cylindrical slices, rinse with deionized water to remove impurities, put them in the refrigerator and freeze for 12 h, and then freeze-dry for 48 h to obtain porous pomelo peel aerogel (PA).

[0044] (3) Layer-by-layer (LbL) modification of graphene oxide, the specific process is as follows:

[0045] Immerse PA alternately into PEI aqueous solution (concentration 30%) and graphene oxide dispersion (1 mg / mL), and ultrasonicate (2 minutes per cycle). Gently compress to remove the excess liquid after each immersion. Repeat this alternating process 5 times to obtain graphene oxide-modified aerogel (PA-GO1).

[0046] (4) Gas-phase reduction of graphene oxide-modified aerogel, the specific process is as follows:

[0047] The PA-GO1 sample was freeze-dried and then exposed to HI vapor at 95 °C for 1.5 h to reduce GO to reduced graphene oxide (rGO). It was thoroughly washed with deionized water to remove the residual HI, and the rGO-modified aerogel (PA-rGO1) was obtained.

[0048] (5) High-temperature carbonization to a hierarchical porous structure was carried out as follows:

[0049] The PA-rGO1 aerogel was carbonized in a tubular furnace under an argon atmosphere. A programmed heating scheme was adopted: the heating rate was 5 °C / min to 800 °C, and then it was held for 2.5 h. After cooling to room temperature, the carbonized aerogel (CPA-rGO1) with a multi-scale porous structure was obtained.

[0050] (6) Preparation of the composite phase change composite material (OCPA-rGO1) was carried out as follows:

[0051] The molten n-octacosane was impregnated into the CPA-rGO1 aerogel by vacuum-assisted impregnation. Among them, n-octacosane was melted at 100 °C in a vacuum drying oven, and the aerogel was soaked for 30 min under vacuum conditions to ensure complete infiltration. The excess n-octacosane on the surface was removed with filter paper. The composite phase change material OCPA-rGO1 based on the double-skeleton of pomelo peel carbon aerogel / reduced graphene oxide (rGO) was obtained.

[0052] Among them, the loading rate of n-octacosane was 92.9%

[0053] Example 2

[0054] The preparation method of the composite phase change material based on the double-skeleton of pomelo peel carbon aerogel / reduced graphene oxide (rGO) in this example includes the following steps:

[0055] (1) Preparation of graphene oxide (GO) was carried out as follows:

[0056] First, put graphite powder (3.0 g) and H2SO4 (70 mL) into a beaker and stir in an ice bath. Then add KMnO4 (9.0 g) and keep the suspension temperature below 20 °C. Secondly, transfer the beaker to an oil bath (40 °C), stir vigorously for 0.5 h, and add 150 mL of deionized water; heat the reaction system to 95 °C and react for 15 min. Thirdly, dropwise add 500 mL of deionized water and 15 mL of H2O2 to change the solution color from dark brown to yellow. Fourthly, wash with 9% HCl aqueous solution (50 mL each time, repeat 3 times) to remove metal ion impurities and centrifuge. The obtained solid is dried in air and diluted to 600 mL to prepare a graphene oxide aqueous dispersion. Finally, dialyze and purify with a dialysis membrane for one week to remove the remaining metal substances. Then dilute the obtained graphene oxide aqueous dispersion to 1.2 L, stir overnight, and sonicate for 30 minutes to exfoliate it into graphene oxide. Then centrifuge the graphene oxide dispersion at 3000 rpm for 40 minutes to remove unexfoliated graphite.

[0057] (2) Construction of the naringin peel aerogel matrix, the specific process is as follows:

[0058] Prepare naringin peel aerogel by removing the outer layer of the pomelo peel and retaining the mesocarp. Cut the mesocarp into cylindrical slices, rinse with deionized water to remove impurities, freeze in the refrigerator for 12 h, and freeze-dry for 48 h to obtain porous naringin peel aerogel (PA).

[0059] (3) Layer-by-layer (LbL) modification of graphene oxide, the specific process is as follows:

[0060] Immerse PA alternately in an aqueous PEI solution (concentration 30%) and a graphene oxide dispersion (2 mg / mL), and sonicate (2 minutes per cycle). Gently compress to remove excess liquid after each immersion. Repeat this alternating process 5 times to obtain graphene oxide-modified aerogel (PA-GO2).

[0061] (4) Gas-phase reduction of graphene oxide-modified aerogel, the specific process is as follows:

[0062] Freeze-dry the PA-GO1 sample, then expose it to HI vapor at 95 °C for 1.5 h to reduce GO to reduced graphene oxide (rGO). Thoroughly wash with deionized water to remove residual HI to obtain rGO-modified aerogel (PA-rGO2).

[0063] (5) High-temperature carbonization into a hierarchical porous structure, the specific process is as follows:

[0064] The PA-rGO2 aerogel was carbonized in a tubular furnace under an argon atmosphere. A programmed heating scheme was adopted: the heating rate was 5 °C / min to 800 °C, and then it was held for 2.5 h. After cooling to room temperature, a carbonized aerogel (CPA-rGO2) with a multi-scale porous structure was obtained.

[0065] (6) Preparation of the composite phase change composite material (OCPA-rGO2), the specific process is as follows:

[0066] The molten n-eicosane was impregnated into the CPA-rGO2 aerogel by vacuum-assisted impregnation. Among them, n-eicosane was melted at 100 °C in a vacuum drying oven, and the aerogel was soaked for 30 min under vacuum conditions to ensure complete infiltration. The excess n-eicosane on the surface was removed with filter paper. The OCPA-rGO2, a dual-skeleton composite phase change material based on pomelo peel carbon aerogel / reduced graphene oxide (rGO), was obtained.

[0067] Among them, the loading rate of n-eicosane was 90.1%.

[0068] Example 3

[0069] The preparation method of the dual-skeleton composite phase change material based on pomelo peel carbon aerogel / reduced graphene oxide (rGO) in this example includes the following steps:

[0070] (1) Preparation of graphene oxide (GO), the specific process is as follows:

[0071] First, graphite powder (3.0 g) and H2SO4 (70 mL) were put into a beaker and stirred in an ice bath. Then KMnO4 (9.0 g) was added, and the suspension temperature was kept below 20 °C. Secondly, the beaker was transferred to an oil bath (40 °C) and stirred vigorously for 0.5 h, and 150 mL of deionized water was added; the reaction system was heated to 95 °C and reacted for 15 min. Thirdly, 500 mL of deionized water and 15 mL of H2O2 were added dropwise to change the color of the solution from dark brown to yellow. Fourthly, it was washed with 9% HCl aqueous solution (50 mL each time, repeated 3 times) to remove metal ion impurities and centrifuged. The obtained solid was dried in air and diluted to 600 mL to make a graphite oxide aqueous dispersion. Finally, it was dialyzed and purified with a dialysis membrane for one week to remove the remaining metal substances. Then the obtained graphite oxide aqueous dispersion was diluted to 1.2 L, stirred overnight, and ultrasonicated for 30 minutes to exfoliate it into graphene oxide. Then the graphene oxide dispersion was centrifuged at 3000 rpm for 40 minutes to remove the unexfoliated graphite.

[0072] (2) Construction of the pomelo peel aerogel matrix, the specific process is as follows:

[0073] Pomelo peel aerogel was prepared by removing the outer layer of pomelo peel and retaining the mesocarp. The mesocarp was cut into cylindrical thin slices, rinsed with deionized water to remove impurities, placed in the refrigerator for 12 h of freezing, and freeze-dried for 48 h to obtain porous pomelo peel aerogel (PA).

[0074] (3) Layer-by-layer (LbL) modification with graphene oxide was carried out as follows:

[0075] PA was alternately immersed in an aqueous solution of PEI (concentration 30%) and a graphene oxide dispersion (3 mg / mL), and ultrasonic treatment was performed (2 minutes per cycle). After each immersion, the excess liquid was gently compressed and removed. This alternating process was repeated 5 times to obtain graphene oxide-modified aerogel (PA-GO3).

[0076] (4) Gas-phase reduction of graphene oxide-modified aerogel was carried out as follows:

[0077] The PA-GO3 sample was freeze-dried and then exposed to HI vapor at 95 °C for 1.5 h to reduce GO to reduced graphene oxide (rGO). It was thoroughly washed with deionized water to remove the residual HI, and rGO-modified aerogel (PA-rGO3) was obtained.

[0078] (5) High-temperature carbonization to a hierarchical porous structure was carried out as follows:

[0079] The PA-rGO2 aerogel was carbonized in a tubular furnace under an argon atmosphere. A programmed heating scheme was adopted: the heating rate was 5 °C / min to 800 °C, and then it was held for 2.5 h. After cooling to room temperature, carbonized aerogel (CPA-rGO3) with a multi-scale porous structure was obtained.

[0080] (6) Preparation of composite phase change composite material (OCPA-rGO3) was carried out as follows:

[0081] Molten n-octacosane was impregnated into the CPA-rGO3 aerogel by vacuum-assisted impregnation method. Among them, n-octacosane was melted at 100 °C in a vacuum drying oven, and the aerogel was soaked for 30 min under vacuum conditions to ensure complete infiltration. The excess n-octacosane on the surface was removed with filter paper. Based on pomelo peel carbon aerogel / reduced graphene oxide (rGO) double-skeleton composite phase change material OCPA-rGO3 was obtained.

[0082] Among them, the loading rate of n-octacosane was 89.3%.

[0083] Comparative Example 1

[0084] The difference between the preparation method of the phase change material in this comparative example and that in Example 3 is as follows:

[0085] Without any modification to PA, directly impregnate n-octacosane with PA, that is, only retain the product obtained in steps (2) and (6), denoted as OPA, and other steps are the same as in Example 3.

[0086] Comparative Example 2

[0087] The difference in the preparation method of the phase change material in this comparative example from that in Example 3 lies in:

[0088] After preparing the graphene oxide modified aerogel (PA-GO3), no subsequent reduction, carbonization, and infiltration operations are performed on it.

[0089] Comparative Example 3

[0090] The difference in the preparation method of the phase change material in this comparative example from that in Example 3 lies in:

[0091] After obtaining the rGO modified aerogel (PA-rGO3), no subsequent carbonization and infiltration operations are performed on it.

[0092] Comparative Example 4

[0093] The difference in the preparation method of the phase change material in this comparative example from that in Example 3 lies in:

[0094] After preparing the carbonized aerogel (CPA-rGO3), no operation of infiltrating the phase change material is performed on it.

[0095] Performance detection of Examples 1 - 3 and Comparative Examples 1 - 4:

[0096] Figure 1 This is a comparison graph of the gray values of the aerogels in which PA is immersed in different GO solutions during five cycles of LBL in Examples 1 - 3 of the present invention and the Zeta potentials of PEI and GO. As Figure 1 shown, as the number of cycles increases, the color of the sample becomes darker and more uniform. The darker the color, the greater the GO loading, and as the mass fraction of the GO solution increases, the GO loading increases. However, since the aerogel approaches saturation after 5 cycles, the final colors of the aerogels immersed in the three GO aqueous solutions are close; the driving force for layer-by-layer assembly is the electrostatic interaction between cationic and anionic assembly materials, and the Zeta potentials of PEI and GO in aqueous solution are +13.35 mV and -32.6 mV respectively, indicating that there is an electrostatic attractive interaction between PEI and GO, which can be used for the LbL assembly process of PA-GO.

[0097] Figure 2 This is a comparison graph of the anti-leakage performance photos of Examples 1 - 3 of the present invention, n-octadecane, and Comparative Example 1 at 30 °C and 70 °C. As Figure 2As shown, in contrast, the liquid leakage distribution range of OPA and OCPA-rGOs is very small, showing good shape stability. When heated for 30 minutes, pure octacosane has leaked, while the mass fractions of leaked OPA, OCPA-rGO1, OCPA-rGO2, and OCPA-rGO3 are 10.3%, 7.5%, 6.6%, and 4.0% respectively. The comparison data show that the pomelo peel carbon aerogel has good surface tension and strong capillary force, which can fully encapsulate the molten octacosane and prevent liquid leakage. In addition, with the increase of rGO content, the anti-leakage performance is enhanced because rGO has a higher porosity than the pomelo peel carbon aerogel, which can further enhance the encapsulation effect of octacosane on the basis of improving the thermal conductivity and electrical conductivity of the phase change material.

[0098] Figure 3 Figure for comparing DSC curves of the 1st, 10th, 20th, 30th, 40th, and 50th thermal cycles of Examples 1-3 of the present invention. As Figure 3 shown, after 50 solid-liquid phase change cycles, the positions of the endothermic peak and exothermic peak of OCPA-rGO 1-3 are the same, and the change range of the phase change enthalpy is less than 5%, which can be considered almost unchanged, indicating that OCPA-rGO 1-3 can continuously undergo melting and crystallization phase changes, has good thermal cycle reliability and stability, and can meet the requirements of long-term use.

[0099] Figure 4 Figure for comparing the thermal conductivity and electrical conductivity of Examples 1-3 of the present invention and Comparative Examples 1-4. As Figure 4 shown, by comparing the thermal conductivities of OCPA-rGO 1-3 with three different rGO contents, the thermal conductivity of the composite phase change material increases with the increase of rGO content. The thermal conductivity of OCPA-rGO3 is 0.366 W / (m·K), which is about 1.6 times that of pure octacosane and 6.7 times that of PA, which also proves that the CPA-rGO double skeleton can enhance the thermal conductivity of the composite phase change material; the pomelo peel skeleton is transformed into a conductive material after high-temperature carbonization, forming a 3D network conductive channel. The electrical conductivity of CPA-rGO 1-3 gradually increases with the increase of rGO content. However, organic phase change materials are usually non-conductive, and the electrical conductivity of OCPA-rGO 1-3 will decrease after adding octacosane, but it can be maintained in the range of 0.758 - 1.274 mS / cm, which provides the possibility for the electro-thermal energy conversion of the composite phase change material.

[0100] Figure 5 Figure for comparing the photothermal conversion temperature-time curve and Δt measurement of Examples 1-3 of the present invention and Comparative Example 1. As Figure 5As shown, the Δt values of OCPA-rGO1, OCPA-rGO2, and OCPA-rGO3 are 639 s, 416 s, and 383 s, respectively. Substituting them into Equation 1, the corresponding θ values are 74.4%, 90.6%, and 91.6%, respectively, indicating that rGO can enhance the photothermal conversion efficiency.

[0101]

[0102] Figure 6 This is the electrothermal conversion temperature-time curve and the comparison chart of Δt measurement for Examples 1-3 of the present invention. As Figure 6 shown, according to Joule's law, current passing through a conductor generates heat, and the conductivity of OCPA-rGO 1-3 increases with the increase in the rGO content. This is because the higher the rGO content, the greater the thickness of the rGO film attached to the aerogel skeleton, the stronger the conductive network structure, and the denser the conductive material, resulting in a faster current conduction speed. Therefore, within the same energization time, the heating rates of OCPA-rGO3, OCPA-rGO2, and OCPA-rGO1 decrease in order from high to low. Among them, OCPA-rGO3 and OCPA-rGO2 are close, and both are significantly higher than OCPA-rGO1. The rapid temperature rise during energization and the crystallization plateau region that appears after power-off prove that OCPA-rGO 1-3 can store and release the Joule heat generated by the current, realizing electrothermal conversion and energy storage.

[0103] Figure 7 This is the temperature and voltage change curve of Example 3 of the present invention under the on-off cycle irradiation of a 300 mW / cm 2 xenon lamp. As Figure 7 shown, the temperature and resistance of OCPA-rGO3 change significantly under xenon lamp irradiation and show periodic changes in the cyclic test, indicating that OCPA-rGO3 can accurately detect temperature changes and output signals through voltage changes.

[0104] Given that there are numerous embodiments of the present invention, each embodiment can be determined according to actual application requirements within the limited range of each parameter. The experimental data is huge and numerous, and it is not suitable to list them one by one here. However, the content to be verified and the final conclusions obtained in each embodiment are close.

[0105] The above is only a detailed description of the preferred embodiments and principles of the present invention. For those of ordinary skill in the art, based on the idea provided by the present invention, there will be changes in the specific implementation manners, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a composite phase change material based on a double skeleton of pomelo peel carbon aerogel / reduced graphene oxide, characterized in that, It includes the following steps: (1) Preparation of pomelo peel aerogel: Cut the pomelo peel into pieces, wash it, and freeze-dry for 30 - 50 hours to obtain porous pomelo peel aerogel (PA); (2) Preparation of pomelo peel-graphene oxide aerogel (PA-GO): Alternately impregnate the polyethyleneimine solution (PEI) and graphene oxide dispersion on the surface of the pomelo peel aerogel using the layer-by-layer self-assembly technique for 3 - 6 cycles, and finally remove the excess water to obtain pomelo peel-graphene oxide aerogel (PA-GO); (3) Preparation of reduced graphene oxide aerogel (PA-rGO): Freeze-dry the pomelo peel-graphene oxide aerogel and then reduce it in hydroiodic acid vapor (HI), and subsequently wash it with deionized water to remove the residual hydroiodic acid to obtain reduced graphene oxide aerogel (PA-rGO); (4) Preparation of carbonized aerogel (CPA-rGO): Subject the reduced graphene oxide aerogel to high-temperature carbonization treatment under an inert gas to obtain carbonized aerogel (CPA-rGO); (5) Preparation of phase change composite material (OCPA-rGO): Immerse the carbonized aerogel (CPA-rGO) in molten n-octacosane under vacuum conditions, and then remove the excess alkane on the surface with filter paper to obtain the phase change composite material (OCPA-rGO).

2. The preparation method according to claim 1, wherein In the step (1), the graphene oxide dispersion is prepared by the following method: Mix graphite powder and concentrated sulfuric acid under an ice bath condition, add potassium permanganate to keep the temperature below 20°C, then transfer it to an oil bath at 40 - 50°C and stir for 0.5 - 1 hour, add 100 - 200 mL of deionized water and then raise the temperature to 90 - 100°C and react for 10 - 30 minutes. Dropwise add deionized water and hydrogen peroxide to make the solution turn yellow, and after washing with hydrochloric acid, centrifuging, and dialysis purification, obtain the graphene oxide dispersion (GO).

3. The preparation method according to claim 2, wherein The mass-volume ratio of the graphite powder, concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide is 3 g:70 mL:9 g:15 mL, and the concentration of the hydrochloric acid used for washing is 9%.

4. The preparation method according to claim 1, characterized in that, In the step (2), the concentration of the polyethyleneimine solution is 30%, the concentration of the graphene oxide dispersion is 1 - 3 mg / mL, and after each impregnation, it is ultrasonically treated for 1 - 3 minutes.

5. The preparation method according to claim 1, characterized in that, In the step (3), the temperature for reduction by hydroiodic acid vapor is 90 - 100°C, and the time is 1 - 2 hours.

6. The preparation method according to claim 1, characterized in that, In the step (4), the heating rate for carbonization treatment is 3 - 10°C / min, the final temperature is 700 - 900°C, and the holding time is 1 - 3 hours.

7. The preparation method according to claim 1, characterized in that, In the step (5), the vacuum degree for vacuum impregnation is ≤ -0.08 MPa, the impregnation temperature is 90 - 110°C, and the time is 20 - 40 minutes.

8. A composite phase change material based on a double skeleton of pomelo peel carbon aerogel / reduced graphene oxide prepared by the preparation method according to any one of claims 1 - 7.

9. The composite phase change material according to claim 8, wherein, The loading amount of n-octacosane in the composite phase change material is 87 - 93 wt%.

10. Application of the composite phase change material according to any one of claims 1 - 9 in a building energy-saving temperature control system and a smart home high-temperature warning system.

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