A mxene / mwcnt enhanced biochar-based composite phase change material and a preparation method thereof

Abstract

The application relates to the technical field of phase change materials, and discloses a MXene / MWCNT enhanced biochar-based composite phase change material and a preparation method thereof, which comprises the following steps: S1, MWCNT and a metal salt are used to prepare a suspension; biomass is added into the suspension, and a precursor is obtained through drying; S2, the precursor is subjected to heat treatment to obtain biochar; the biochar and a perfluorooctanoic acid ethanol solution are subjected to blending and drying to obtain a support material; S3, the support material and a MXene solution are subjected to blending and drying to obtain an enhanced support material; and S4, the enhanced support material is subjected to a vacuum impregnation method to obtain a bio-based composite phase change material. The composite PCM prepared by the application has a thermal conductivity which is increased by 313.77% and 26.3% respectively compared with paraffin and a non-enhanced composite PCM. The biochar-based support material is used, and the encapsulation efficiency of paraffin is increased again to 85.18%.

Description

Technical Field

[0001] This invention relates to the field of phase change materials technology, and more specifically, to an MXene / MWCNT-enhanced biochar-based composite phase change material and its preparation method. Background Technology

[0002] Currently, rapid global economic development has fueled a fossil fuel crisis and increased greenhouse gas emissions, with the worsening environmental problems ultimately threatening global sustainable development. Statistics (Biomass-derived porouscarbons support in phase change materials for building energy efficiency: a review) show that global energy demand reached 556.63 trillion kilojoules in 2020, and this figure is projected to grow to 820 trillion kilojoules by 2040. Although the utilization rate of clean energy has improved in recent years with the development of renewable energy, traditional energy sources (such as natural gas) will still account for more than 76% of energy demand by 2040. The severe energy problem is undoubtedly driving the development of renewable and clean energy. However, the stability of renewable energy sources such as solar and wind power is a key factor limiting their widespread application. Therefore, more and more researchers are exploring the conversion and storage of clean energy to improve energy stability and address the problem of energy supply and demand asynchrony. This approach can utilize renewable energy more effectively, reduce dependence on fossil fuels, promote the transformation of the energy system, and accelerate the achievement of carbon neutrality goals.

[0003] Current thermal energy storage technologies mainly include sensible thermal energy storage, chemical thermal energy storage, phase change thermal energy storage, and electrochemical thermal energy storage. Among them, phase change thermal energy storage technology occupies an important position in the field of thermal energy storage due to its safety, stability, and large storage capacity. Phase change thermal energy storage mainly relies on the solid-liquid phase change process of phase change materials (PCMs) to achieve energy conversion by absorbing or releasing a large amount of latent heat, thereby alleviating the problem of the imbalance between supply and demand of clean energy. However, in its liquid state, PCMs have a serious risk of leakage, which can not only lead to the failure of the thermal energy storage system, but may even cause major industrial safety problems. In addition, most PCMs have poor thermal conductivity, making it difficult to quickly transfer and absorb heat, resulting in significant heat loss. These problems, to some extent, limit the engineering application of solid-liquid phase change PCMs. To solve these problems, composite PCMs have emerged. Composite PCMs encapsulate PCMs with encapsulating materials, effectively solving their leakage problems. At the same time, by rationally utilizing the properties of encapsulating materials or adding appropriate reinforcing agents, the thermal conductivity and photothermal conversion capacity of composite PCMs can be improved.

[0004] Porous materials, including biochar, graphene, and carbon nanotubes, are ideal for storing PCMs due to their excellent pore structure and large specific surface area. These materials have been widely used in composite PCM research, solving the problems of PCM leakage and insufficient thermal performance. In the treatment of waste biomass, many industries still use traditional methods such as incineration or landfill. However, these methods not only waste biomass energy but also cause serious environmental pollution. With the introduction of environmental goals such as carbon neutrality, the recycling of waste biomass has become an issue that cannot be ignored. Waste biomass can be pyrolyzed at high temperatures under specific conditions to produce biochar, which has a good pore structure and a large specific surface area—an environmentally friendly carbon material. As a carbon material, biochar typically has good adsorption capacity and high thermal conductivity. Furthermore, due to its black appearance, biochar has strong light absorption and photothermal conversion capabilities. Therefore, biochar has been widely used as an encapsulation material in composite PCM research. Studies have shown that using biochar prepared from biomass to store solid-liquid phase change PCMs not only achieves waste utilization but also effectively solves the PCM leakage problem.

[0005] The development of biochar-based composite PCM provides an effective approach for the utilization of biomass and solid-liquid PCM. Although biochar, as a product of high-value utilization of biomass, possesses good thermal conductivity and adsorption properties, its thermal conductivity and porosity still lag behind industrial carbon materials such as expanded graphite and multi-walled carbon nanotubes (MWCNTs), limiting its widespread application in various fields. However, the large-scale use of industrial carbon materials inevitably leads to environmental pollution, which contradicts the principles of energy conservation, environmental protection, and carbon neutrality.

[0006] For example, the patent with publication number CN116410530A discloses a high thermal conductivity carbon nanotube composite masterbatch and its preparation method. It only synthesizes a leak-free composite PCM, ignoring the photothermal conversion capability and thermal conductivity.

[0007] For example, the patent with publication number CN107603571A discloses the preparation of a shaped expanded graphite-based erythritol medium-temperature composite phase change thermal storage material. Its use of industrial carbon materials brings certain pollution, and the composite PCM prepared by biochar has been continuously narrowing the gap with it under reasonable treatment.

[0008] For example, the journal *Enhancing the light-thermal absorption and conversion capacity of diatom-based biomass / polyethylene glycol composites phase change material by introducing MXene* utilizes MXene as an "enhancer" for photothermal absorption and conversion to prepare novel shape-stable phase change materials. However, it does not focus on optimizing thermal conductivity, thus having certain limitations.

[0009] For example, patent CN109777368A discloses a porous carbon composite phase change material and its preparation method, which uses a graphene-based coating to enhance the thermal conductivity of the porous carbon skeleton. The graphene-based coating in this patent is applied by soaking and drying. The coating obtained by this method only covers the surface of the carbon skeleton, and problems such as coating failure inevitably occur during application, failing to form a stable reinforcing effect.

[0010] For example, the patent with publication number CN116536032A discloses a composition for preparing high thermal conductivity composite phase change materials, the high thermal conductivity composite phase change materials and their preparation methods and applications. The gas preparation steps in this patent are complex, and a large number of chemical reagents are used in the process, which causes serious environmental pollution. Moreover, the high temperature graphitization and precise chemical modification processes may be difficult to maintain in large-scale production, thus making it difficult to achieve large-scale application. Summary of the Invention

[0011] Technical problem solved by the present invention

[0012] This invention addresses the problems of poor thermal conductivity and poor photothermal conversion capability of biochar-based composite PCM. Based on this, while ensuring the utilization of waste biomass, this invention successfully enhances the thermal properties (photothermal conversion capability and thermal conductivity) of biochar-based composite PCM, expanding its application scenarios and improving the competitiveness of clean support materials in the field of composite PCM.

[0013] The technical solution adopted in this invention

[0014] This invention uses oleophobic biochar as the basic supporting framework and adds a small amount of reinforcing materials (thermal conductivity reinforcing material MWCNT and photothermal conversion reinforcing material MXene) to improve the thermal properties of biochar-based composite PCM, including thermal conductivity and photothermal conversion capabilities.

[0015] To elaborate, that is to say:

[0016] First, the present invention provides a method for preparing an MXene / MWCNT-enhanced biochar-based composite phase change material, comprising the following steps:

[0017] S1 MWCNT and metal salt were used to prepare a suspension; biomass was added to the suspension and dried to obtain the precursor.

[0018] S2 heat-treats the precursor to obtain biochar; the biochar is then blended with a perfluorooctanoic acid ethanol solution and dried to obtain a support material.

[0019] S3 involves blending the support material with an MXene solution and then drying it to obtain an enhanced support material;

[0020] Bio-based composite phase change materials were obtained from S4 reinforced support material by vacuum impregnation.

[0021] According to some preferred embodiments, in S1, the ratio of MWCNT to metal salt is 1g:30-100ml, and the concentration of metal salt is 1-3M.

[0022] According to some preferred embodiments, in S1, the mass ratio of MWCNT to biomass is 1:0.05 to 0.2.

[0023] According to some preferred embodiments, in S1, biomass includes at least one of wood materials, kitchen waste, and organic waste.

[0024] According to some preferred embodiments, in S1, the metal salt includes at least one of ZnCl2, CaCl2, FeCl3, FeCl2, Zn(NO3)2, Ca(NO3)2, and Fe(NO3)3.

[0025] According to some preferred embodiments, in S2, the heat treatment is carried out in a high-temperature tube furnace at a rate of 3-6°C / min, increasing the temperature from 25°C to 500-700°C and holding it for 1-4 hours under a nitrogen atmosphere.

[0026] According to some preferred embodiments, in S2, the ratio of biochar to perfluorooctanoic acid ethanol solution is 1g:10-20ml, and the concentration of perfluorooctanoic acid ethanol solution is 0.01-0.05mol / L.

[0027] According to some preferred embodiments, in S2, biochar and perfluorooctanoic acid ethanol solution are shaken and mixed at room temperature for 36-60 hours, then rinsed with anhydrous ethanol, and then subjected to 60-90°C for 20-30 hours.

[0028] According to some preferred embodiments, in S3, the ratio of the support material to the MXene solution is 1g:2-10mg / ml, and the concentration of the MXene solution is 3-8mg / ml.

[0029] According to some preferred embodiments, in S3, the blending is performed by ultrasonic blending, and the drying is carried out at 85°C until completely dry.

[0030] According to some preferred embodiments, in S3, the MXene is prepared by using Ti3AlC2 as a precursor and selectively etching the Al layer with a mixture of LiF and hydrochloric acid to prepare MXene nanosheets.

[0031] Specifically, 3.12 g of LiF was mixed with 40 ml of 9 M hydrochloric acid solution and reacted at 40 °C for 30 min. 2.00 g of Ti3AlC2 powder was slowly added, and the mixture was reacted thoroughly at 500 rpm and 40 °C for 48 h. A small amount of 1 M hydrochloric acid solution was added to the resulting suspension, and the mixture was centrifuged at 5000 rpm for 5 min, repeated 5 times. The sample was then washed with 1 M hydrochloric acid and LiCl solution. After washing, the sample was centrifuged at 3000 rpm for 30 min to obtain MXene precipitate, which was then washed with deionized water until neutral. 0.5 g of MXene powder was dissolved in 30 ml of deionized water, sonicated for 30 min, and then centrifuged at 3000 rpm for 15 min. The supernatant was collected, filtered through a 0.22 μm aqueous filter membrane, dried, and the monolayer MXene material was obtained.

[0032] In addition to the aforementioned methods for preparing MXene, those skilled in the art may also choose other methods for preparing MXene.

[0033] According to some preferred embodiments, in S4, the vacuum impregnation method is used: the reinforcing support material is immersed in an excess of paraffin wax and the vacuum environment is maintained at 50-70°C for 2-5 hours. After impregnation, the composite is placed in a constant temperature chamber and rotated every once in a while to ensure gravity-free deposition until no molten paraffin wax seeps out, thus obtaining a bio-based composite phase change material.

[0034] Second, the present invention provides an MXene / MWCNT-enhanced biochar-based composite phase change material obtained by the aforementioned preparation method.

[0035] Beneficial effects achieved by the present invention

[0036] (1) This invention uses biological waste as the source of biochar, thereby enabling the high-value utilization of biomass and improving energy utilization efficiency; at the same time, it is more environmentally friendly and energy-saving than industrial products.

[0037] (2) This invention achieves the incorporation and activation of MWCNTs in a one-step process and loads MXenes through an immersion process. Incorporating MWCNTs during biomass activation simplifies the processing steps and reduces application requirements. During the immersion activation process, MWCNTs can fully contact the biomass and effectively adhere to it. In the subsequent slow carbonization process, as the temperature rises and organic matter decomposes, the biochar gradually forms a good connection with the MWCNTs, and some MWCNTs enter the pores of the biochar. When heat is transferred to the composite material, these MWCNTs can form an effective thermally conductive network, improving the thermal conductivity of the material. If MWCNTs are directly incorporated into the molded biochar, the connection may be unstable, and the MWCNTs will be distributed on the surface of the biochar, failing to form a thermally conductive network efficiently, greatly reducing its thermal conductivity enhancement effect.

[0038] (3) This invention optimizes the preparation process of the support material by incorporating MWCNTs, thereby increasing the storage space of biochar. Based on this, one improvement method is to use whole wood instead of pulverized biomass, preserving the original water-carrying channels of the wood biomass to create a larger storage space. However, to achieve a stable connection between biochar and MWCNTs, the activation and incorporation of MWCNTs are combined into one step. This is because, under normal circumstances, the application of biochar involves pulverized biomass, burning it into carbon, adding some additives, loading it with PCM, and then molding it. This method mainly reduces the number of steps, but the pressing process can also cause certain difficulties in application.

[0039] (4) The composite PCM prepared by this invention exhibits thermal conductivity improvements of 313.77% and 26.3% compared to paraffin and unreinforced composite PCM, respectively. The enhanced photothermal conversion capability is manifested in two aspects: firstly, in the illumination experiment, the temperature change before and after enhancement differed by 20.7℃; secondly, in the absorbance test, in the main concentrated areas of radiation energy (visible light and near-infrared), the absorbance of the reinforced support material was 21.16% and 30.67% higher than that of the ordinary oleophobic material, respectively. Both thermal conductivity and photothermal conversion capability (radiation absorption capability) are significantly enhanced.

[0040] (5) The composite PCM provided by the present invention uses biochar-based support material, which further improves the encapsulation efficiency of paraffin to 85.18%, which is already at the leading level in the industry. Attached Figure Description

[0041] Figure 1 This is a diagram of the apparatus used to test samples on a photothermal conversion test bench.

[0042] Figure 2 The image shows a DSC image of the composite PCM and paraffin prepared in Example 1.

[0043] Figure 3 The temperature change curves of the composite PCM prepared in Example 1 and Comparative Example 1 during the photothermal conversion capability test are shown.

[0044] Figure 4 Infrared photographs taken at different time points during the photothermal conversion capability test of the composite PCM prepared in Example 1 and Comparative Example 1.

[0045] Figure 5 The graph shows the absorbance test results of the carbon material of Example 1 and Comparative Example 1 at different wavelengths.

[0046] Figure 6 SEM image of the reinforced support material of Example 1 (scale bar: 50 μm);

[0047] Figure 7 SEM image of the reinforced support material of Example 1 (scale bar: 5 μm). Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0049] Preparation of MXene:

[0050] MXene nanosheets were prepared by selectively etching the Al layer using Ti3AlC2 as a precursor and a mixture of LiF and hydrochloric acid. 3.12 g of LiF was mixed with 40 ml of 9M hydrochloric acid solution and reacted at 40 °C for 30 min. 2.00 g of Ti3AlC2 powder was slowly added, and the mixture was reacted thoroughly at 500 rpm and 40 °C for 48 h. A small amount of 1M hydrochloric acid solution was added to the resulting suspension, and the mixture was centrifuged at 5000 rpm for 5 min, repeated 5 times. The sample was then washed with 1M hydrochloric acid and LiCl solution, and centrifuged at 3000 rpm for 30 min to obtain MXene precipitate, which was washed with deionized water until neutral. 0.5 g of MXene powder was dissolved in 30 ml of deionized water, sonicated for 30 min, and then centrifuged at 3000 rpm for 15 min. The supernatant was collected, filtered through a 0.22 μm aqueous filter membrane, dried, and the monolayer MXene material was obtained.

[0051] Example 1

[0052] MWCNTs were mixed with 2M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried white pine waste at a ratio of MWCNT to white pine waste of 1:10 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. It was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously introduced at a rate of 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0053] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 5 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g:5 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0054] The composite PCM was prepared using a vacuum impregnation method. First, a beaker containing excess liquid paraffin was placed in a vacuum drying oven at 60°C to maintain a stable temperature. Then, a reinforcing support material was added to the beaker, and the vacuum environment was maintained at 60°C for 3 hours. After impregnation, the composite PCMs were removed, placed on filter paper, and placed in a 70°C constant temperature oven. The filter paper was replaced every 15 minutes, and the composite PCMs were rotated to prevent uneven PCM distribution due to gravity deposition. This process continued until no molten paraffin seeped out onto the filter paper, resulting in a reinforced and leak-free composite PCM.

[0055] Example 2

[0056] MWCNTs were mixed with 3M ZnCl2 solution at a ratio of 1g:60ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried white pine waste at a ratio of MWCNT to white pine waste of 1:12 (wt%). After sonication for 3h, the mixture was placed in a shaker and shaken for 24h. It was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously purging at 200mL / min. After the sample was removed, the biochar was mixed with a 0.03 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0057] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 5 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g:5 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0058] The preparation of composite PCM is the same as in Example 1.

[0059] Example 3

[0060] MWCNTs were mixed with 2M ZnCl2 solution at a ratio of 1g:40ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated 3 times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried white pine waste at a ratio of MWCNT to white pine waste of 1:10 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. It was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously purging at 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0061] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 6 mg / ml MXene solution. Then, biochar and MXene dispersion were mixed at a ratio of 1 g:5 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0062] The preparation of composite PCM is the same as in Example 1.

[0063] Example 4

[0064] MWCNTs were mixed with 1.5M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This process was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried coffee grounds at a ratio of MWCNT to coffee grounds waste of 1:20 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. It was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously purging at 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0065] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 5 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g:5 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0066] The preparation of composite PCM is the same as in Example 1.

[0067] Example 5

[0068] MWCNT was mixed with 2M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated 3 times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried corn stalks at a ratio of MWCNT to corn stalks of 1:7 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. The mixture was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously introduced at a rate of 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0069] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 3 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g: 12 ml, sonicated for 4 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0070] The composite PCM was prepared in the same manner as in Example 1. After obtaining the composite PCM powder, it was subjected to molding treatment.

[0071] Example 6

[0072] MWCNTs were mixed with 2M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried corn stalks at a ratio of MWCNTs to corn stalks of 1:5 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. The mixture was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously introduced at a rate of 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0073] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 3 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g: 15 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0074] The composite PCM was prepared in the same manner as in Example 1. After obtaining the composite PCM powder, it was subjected to molding treatment.

[0075] Example 7

[0076] MWCNTs were mixed with 2M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with cleaned and dried kitchen waste at a ratio of MWCNTs to kitchen waste of 1:15 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. The mixture was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously purging at 200mL / min. After sample extraction, biochar was mixed with a 0.02 mol / L perfluorooctanoic acid (PFOA) ethanol solution at a ratio of 1 g: 15 ml, and mixed at room temperature for 48 h in a shaker at 150 rpm. The mixture was then rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to obtain a support material with oleophobic properties and containing MWCNTs. The MXene incorporation method was as follows: a monolayer of MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 5 mg / ml MXene solution. Subsequently, the biochar and MXene dispersion were mixed at a ratio of 1 g: 8 ml, sonicated for 5 h, and then completely dried in an 85 °C oven to obtain the reinforced support material.

[0077] The composite PCM was prepared in the same manner as in Example 1. After obtaining the composite PCM powder, it was subjected to molding treatment.

[0078] Example 8

[0079] MWCNTs were mixed with 1.5M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with cleaned and dried kitchen waste at a ratio of MWCNTs to kitchen waste of 1:20 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. The mixture was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously purging at 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0080] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 6 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g:10 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0081] The composite PCM was prepared in the same manner as in Example 1. After obtaining the composite PCM powder, it was subjected to molding treatment.

[0082] Example 9

[0083] MWCNTs were mixed with 2M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried white pine waste at a ratio of MWCNT to white pine waste of 1:10 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. It was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously introduced at a rate of 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0084] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 3 mg / ml MXene solution. Then, biochar and MXene dispersion were mixed at a ratio of 1 g: 6 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0085] The preparation of composite PCM is the same as in Example 1.

[0086] Example 10

[0087] MWCNTs were mixed with 2M ZnCl2 solution at a ratio of 1g:50ml, sonicated for 30min, and allowed to stand for 5min. This mixture was repeated three times to obtain a MWCNT / ZnCl2 suspension. The suspension was then mixed with washed and dried waste coffee grounds at a ratio of MWCNTs to waste coffee grounds of 1:15 (wt%). After sonication for 2h, the mixture was placed in a shaker and shaken for 24h. It was then filtered and completely dried in an oven at 80℃. The dried MWCNT / ZnCl2 / biomass mixture was heated from 25℃ to 600℃ at a rate of 5℃ / min in a high-temperature tube furnace and held for 2h, followed by natural cooling with nitrogen gas continuously purging at 200mL / min. After the sample was removed, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 ml and mixed at room temperature in a shaker at 150 r / min for 48 h. Then, it was rinsed twice with anhydrous ethanol and dried at 75 °C for 24 h to finally obtain a support material with oleophobic properties and containing MWCNTs.

[0088] The MXene incorporation method is as follows: Monolayer MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 6 mg / ml MXene solution. Subsequently, biochar and MXene dispersion were mixed at a ratio of 1 g:3 ml, sonicated for 5 h, and then completely dried in an 85℃ drying oven to obtain the reinforced support material.

[0089] The composite PCM was prepared in the same manner as in Example 1. After obtaining the composite PCM powder, it was subjected to molding treatment.

[0090] Comparative Example 1

[0091] Cleaned and dried white pine waste was soaked in a 2 mol / L ZnCl2 solution for 24 h, filtered, and then placed in a 65℃ drying oven for 24 h to dehydrate completely. The dried ZnCl2 / biomass mixture was then heated in a high-temperature tube furnace from 25℃ to 600℃ at a rate of 5℃ / min and held for 2 h, followed by natural cooling with nitrogen gas flowing through at 200 mL / min. After sample removal, the biochar was mixed with a 0.02 mol / L perfluorooctanoic acid ethanol solution at a ratio of 1 g: 15 mL and mixed at room temperature in a shaker at 150 rpm for 48 h. The mixture was then rinsed twice with anhydrous ethanol and dried at 75℃ for 24 h to obtain biochar with oleophobic properties.

[0092] The composite PCM was prepared using a vacuum impregnation method. First, a beaker containing excess liquid paraffin was placed in a vacuum drying oven at 60°C to maintain a stable temperature. Then, oleophobic biochar was added to the beaker, and the vacuum environment was maintained at 60°C for 3 hours. After impregnation, the composite PCMs were removed, placed on filter paper, and placed in a constant temperature oven at 70°C. The filter paper was replaced and the composite PCMs were rotated every 15 minutes to prevent uneven PCM distribution due to gravity deposition, until no molten paraffin seeped out onto the filter paper, resulting in a leak-free composite PCM.

[0093] Comparative Example 2

[0094] The process for preparing oleophobic biochar is the same as in Comparative Example 1.

[0095] MWCNT was mixed with deionized water at a ratio of 1 g:50 ml, sonicated for 30 min, and allowed to stand for 5 min. This process was repeated three times to obtain a MWCNT suspension. The suspension was then mixed with oleophobic biochar at a ratio of 1:10 (wt%), sonicated for 2 h, and then placed in a shaker for 24 h. The mixture was then filtered and completely dried in an oven at 80 °C. A monolayer of MXene was mixed with deionized water and sonicated for 5 min to obtain a well-dispersed 5 mg / ml MXene solution. This solution was then mixed with the oleophobic biochar / MWCNT mixture at a ratio of 1 g:5 ml, sonicated for 5 h, and then completely dried in an oven at 85 °C to obtain a simple-to-use, surface-loaded enhanced biochar.

[0096] Test case

[0097] Through such Figure 1 The temperature change of the sample under a simulated light source during the photothermal conversion test bench, as shown, reflects the sample's photothermal conversion capability. The thermal conductivity of the sample was characterized using a HotDisk thermal conductivity meter. The results are shown in Table 1.

[0098] Table 1

[0099]

[0100] Figure 2 The image shows a DSC image of the composite PCM and paraffin prepared in Example 1.

[0101] Figure 3 The temperature change curves of the composite PCM prepared in Example 1 and Comparative Example 1 during the photothermal conversion capability test are shown.

[0102] Figure 4 Infrared photographs taken at different time points during the photothermal conversion capability test of the composite PCM prepared in Example 1 and Comparative Example 1.

[0103] Figure 5 The graph shows the absorbance test results of the carbon material of Example 1 and Comparative Example 1 at different wavelengths.

[0104] Table 2 shows the thermal parameters of the composite PCM prepared by paraffin and Example 1.

[0105] Table 2

[0106]

[0107] The formula for calculating the encapsulation ratio is:

[0108]

[0109] Among them, H M，PW and H F，PW For the enthalpy of melting and the enthalpy of crystallization of paraffin, H M，PW / BC-MM With H F，PW / BC-MM The melting enthalpy and crystallization enthalpy are those of Example 1.

[0110] The encapsulation efficiency calculation formula is referenced from: The preparation of a green shape-stabilized composite phase change material of polyethylene glycol / SiO2 with enhanced thermal performance based on oil shale ash via temperature-assisted sol-gel method.

[0111] Meanwhile, the encapsulation efficiencies of other types of phase change materials are listed here, as detailed in Table 3.

[0112] Table 3

[0113]

[0114] A: A novel form-stable phase change material of palmitic acid-carbonized pepper straw for thermal energy storage.

[0115] B:Porous biochar / heptadecane composite phase change material withleak-proof,high thermal energy storage capacity and enhanced thermalconductivity.

[0116] C: Water evaporation inspired biomass-based PCM from daisy stem and paraffin for building temperature regulation.

[0117] D:Capric-stearic acid mixture impregnated carbonized waste sugar beetpulp as leak-resistive composite phase change material with effective thermalconductivity and thermal energy storage performance.

[0118] The surface morphology of the reinforced support material prepared in Example 1 was observed, and the results are as follows: Figure 6 and Figure 7 As shown.

[0119] Depend on Figures 6-7 It can be seen that, in addition to the MXene that extensively covers the surface, Figure 7 The image shows MWCNTs in the pores. Biochar contains a large number of MWCNTs in its pore channels, which is unattainable with surface blending.

Claims

1. A method for the preparation of MXene / MWCNT reinforced biochar-based composite phase change material, characterized by, The method comprises the following steps: S1: mixing MWCNT and ZnCl2 solution to prepare a suspension; adding biomass into the suspension, and drying to obtain a precursor; S2: heat-treating the precursor to obtain biochar; S3: mixing the support material and MXene solution, and drying to obtain an enhanced support material; S4: vacuum impregnating the enhanced support material in paraffin to obtain a bio-based composite phase change material. S2 comprises at least one of features (S2-1) to (S2-3):

2. The method of claim 1, wherein the MXene / MWCNT-enhanced biochar-based composite phase change material is prepared by the steps of: (S2-1) heat treatment: in a high-temperature tube furnace, the temperature is raised from 25℃ to 500-700℃ at a rate of 3-6℃ / min and kept for 1-4h under a nitrogen atmosphere. S2 comprises at least one of features (S2-2) to (S2-3):

3. The method of claim 1, wherein the MXene / MWCNT-enhanced biochar-based composite phase change material is prepared by the steps of: (S2-2) the ratio of biochar to perfluorooctanoic acid ethanol solution is 1g:10-20ml, and the concentration of perfluorooctanoic acid ethanol solution is 0.01-0.05mol / L; (S2-3) biochar and perfluorooctanoic acid ethanol solution are shaken and blended at room temperature for 36-60h, then rinsed with anhydrous ethanol, and dried at 60-90℃ for 20-30h. S3 comprises at least one of features (S3-1) to (S3-2):

4. The method of claim 1, wherein the MXene / MWCNT-enhanced biochar-based composite phase change material is prepared by the steps of: (S3-1) the ratio of support material to MXene solution is 1g:2-10mg / ml, and the concentration of MXene solution is 3-8mg / ml; (S3-2) the blending is ultrasonic blending, and the drying is carried out at 85℃ until completely dry. S3 comprises feature (S3-3):

5. The method of claim 1, wherein the MXene / MWCNT-enhanced biochar-based composite phase change material is prepared by the steps of: (S3-3) the preparation method of MXene is as follows: taking Ti3AlC2 as a precursor, using a mixed solution of LiF and hydrochloric acid, and selectively etching the Al layer to prepare MXene nanosheets. In S4, the vacuum impregnation method is as follows: the enhanced support material is immersed in excess paraffin, and maintained in a vacuum environment at 50-70℃ for 2-5h; after the impregnation is completed, the composite is placed in a constant temperature box, and turned over every certain period of time to ensure no gravity deposition until no molten paraffin seeps out, thereby obtaining a bio-based composite phase change material.

6. The method of claim 1, wherein the MXene / MWCNT-enhanced biochar-based composite phase change material is prepared by the steps of: S1 comprises at least one of features (S1-1) to (S1-2):

7. The method of producing MXene / MWCNT-enhanced biochar-based composite phase change material according to any one of claims 1 to 6, characterized in that, (S1-1) the ratio of MWCNT to ZnCl2 is 1g:30-100ml, and the concentration of ZnCl2 is 1-3M; (S1-2) the mass ratio of MWCNT to biomass is 1:0.05-0.

2. S1 comprises feature (S1-3):

8. The method of claim 7, wherein the MXene / MWCNT-enhanced biochar-based composite phase change material is prepared by the steps of: (S1-3) the biomass comprises at least one of wood material, kitchen waste, and organic waste.

9. A MXene / MWCNT-enhanced biochar-based composite phase change material prepared by the method according to any one of claims 1 to 8. ​

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