Phase change microcapsule composite heat storage material with photocatalytic property and preparation method thereof

Abstract

The application discloses a phase change microcapsule composite heat storage material with photocatalytic characteristics and a preparation method thereof. The phase change microcapsule composite heat storage material has a whole core-shell structure, paraffin as a core, crystalline TiO2 with photocatalytic characteristics as a shell wall coated on the surface of the paraffin, and nano-titanium nitride and carbon nanotube composite blended photothermal conversion particles as core-shell modification materials uniformly attached to the surface of the TiO2. The phase change microcapsule composite heat storage material has a stable core-shell structure, full-spectrum solar photothermal conversion capacity, and effectively improves the coating rate, the thermal conductivity and the photocatalytic efficiency, retains the thermal properties of paraffin and inhibits leakage and corrosion.

Description

Technical Field

[0001] This invention relates to a phase change microcapsule composite thermal storage material with photocatalytic properties and its preparation method. This material belongs to the energy field and is applied in the fields of solar photocatalysis and thermal energy storage. Background Technology

[0002] With the growth of energy and the development of industry, global energy demand has increased dramatically. Improving energy efficiency and developing renewable energy sources are important issues facing humanity. Renewable solar energy has significant advantages, making its efficient utilization a promising option for future global development. Solar thermal energy conversion is an important utilization method, largely relying on capture, conversion, and storage processes. The efficiency of solar thermal energy utilization depends on the thermophysical and optical properties of heat storage and photon capture materials. Phase change materials (PCMs) can utilize thermal energy through phase change processes (such as solid-solid, solid-liquid, and liquid-gas processes) and are considered energy-saving materials for solar energy storage. Phase change energy storage is a method of thermal energy storage that utilizes the latent heat of phase change of phase change storage materials to achieve energy storage and utilization. This helps improve energy efficiency and develop renewable energy sources, and has become a very active and cutting-edge research direction in the fields of energy science and materials science in recent years.

[0003] Organic phase change materials (PCMs) are widely considered promising energy storage materials due to their large latent heat, wide melting temperature range, physical and chemical stability, suitable phase change temperature range, and high energy storage density. Furthermore, these materials rarely or never experience supercooling during phase change, and they are non-toxic and have good thermal reliability. However, most pure PCMs suffer from unstable solid-liquid phase change processes, are prone to leakage and loss, leading to decreased reversibility after multiple phase change cycles and eventual failure. Their low thermal conductivity also hinders their practical application performance. Moreover, most current research on MPCMs focuses primarily on improving thermal properties, with limited research into multifunctional applications. Summary of the Invention

[0004] The purpose of this invention is to provide a phase change microcapsule composite thermal storage material with photocatalytic properties and its preparation method. This invention uses paraffin as the core material, crystalline TiO2 as the microcapsule wall material, and uniformly attaches photothermal conversion particles (TiN-CNTs)—a composite blend of nano-titanium nitride (TiN) and carbon nanotubes (CNTs)—to the TiO2 surface as a core-shell modification material, resulting in a material with high light absorption, high thermal conductivity, high coating efficiency, and high photocatalytic efficiency.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned objectives is as follows:

[0006] A phase change microcapsule composite thermal storage material with photocatalytic properties is presented as a core-shell structure. Crystalline TiO2 with photocatalytic properties coats the surface of a paraffin, while TiN-CNTs composite photothermal conversion particles are uniformly attached to the TiO2 surface as a core-shell modifier. The mass ratio of the core paraffin, the TiO2 shell, the TiN in the core-shell modifier, and the CNTs in the core-shell modifier is 100:(20-25):(1-2):(1-2).

[0007] As a preferred embodiment of the above technical solution, the microcapsule composite thermal storage material has an average particle size of 1-5 μm, a wall material of crystalline TiO2 with a brookite crystal form, a core-shell structure coverage of 73.1%-75%, and a shell wall thickness of 100-300 nm.

[0008] A method for preparing the above-mentioned phase change microcapsule composite thermal storage material with photocatalytic properties, the main steps of which are as follows:

[0009] S1: Prepare raw materials according to the mass ratio of paraffin: tetrabutyl titanate (TBT): CNTs: TiN of 100:100:(1-2):(1-2);

[0010] S2: In the solvent formamide, sodium dodecyl sulfate (SDS) is used as a surface modifier to modify the paraffin, so that it is fully mixed with the melted paraffin to obtain a transparent paraffin mixed emulsion;

[0011] S3: Add tetrabutyl titanate (TBT) solution dropwise to the paraffin mixed emulsion and stir thoroughly to fully mix the paraffin emulsion system and obtain the precursor solution;

[0012] S4: Add a trace amount of acetic acid to the precursor solution prepared in S3 and stir thoroughly. Then, add a mixture of deionized water and formamide dropwise to the reaction mixture using a constant pressure dropping funnel. After the reaction, amorphous TiO2@paraffin microcapsules are obtained.

[0013] S5: Add an appropriate amount of crystallization inducing agent to the amorphous TiO2@paraffin microcapsule system prepared in S4, and after the reaction, brookite-type TiO2@paraffin microcapsules are obtained;

[0014] S6: Weigh CNTs and TiN according to step S1, disperse them fully in formamide solvent, and then gradually add them to the brookite-type TiO2@paraffin microcapsule system prepared in S5 to react fully and obtain crude microcapsules.

[0015] S7: The crude microcapsule product obtained in S6 was washed with ethanol and then centrifuged and filtered. The resulting dark gray solid substance was TiN-CNTs composite blended photothermal conversion particle modified TiO2@paraffin microcapsule composite thermal storage material, that is, phase change microcapsule composite thermal storage material with photocatalytic properties.

[0016] As a preferred embodiment of the above technical solution, the purity of paraffin, TBT, CNTs, and TiN in S1 is not less than 99.0%. Specifically, the CNTs have a length of 10-30 μm, a tube diameter of 20-30 nm, and a carboxyl content greater than 1.2 wt%; the TiN has a size of 10-40 nm; and the CNTs are preferably carboxylated multi-walled carbon nanotubes (C-MWCNTs).

[0017] As a preferred embodiment of the above technical solution, the specific operation of S2 is as follows: The paraffin is placed in a three-necked flask and then heated to 70-75°C in a magnetically stirred water bath. The rotation speed of the magnetically stirred water bath is set to 500-600 rpm / min. After the paraffin is completely melted, SDS is weighed and added to the three-necked flask as a surface modifier, allowing it to mix thoroughly with the melted paraffin. Then, formamide is added as a reaction solvent, and the rotation speed of the magnetically stirred water bath is further increased to 800-900 rpm / min. After heating and stirring for 2.5-3 hours, a uniform and stable oil-in-water emulsion (O / W) is formed. The mass ratio of paraffin to SDS is 100:(25-50), preferably 100:(30-35); the mass ratio of paraffin to formamide is 2:(10-20), preferably 2:(15-20).

[0018] As a preferred embodiment of the above technical solution, in S3, the mass ratio of paraffin to TBT is 1:(0.8-1.2), and the stirring time is 20-60 minutes.

[0019] As a preferred embodiment of the above technical solution, in S4, the mass ratio of paraffin to acetic acid is 50:(0.5-1.5), preferably 50:(1-1.5), and the stirring time is 10-15 minutes; the mass ratio of water to formamide is (0.5-1.5):10, the mass ratio of paraffin to water is 2:(0.5-1.5), the stirring time is 2-4 hours, and the stirring speed is generally 500-800 rpm / min.

[0020] As a preferred embodiment of the above technical solution, in S5, the crystallization induction agent is NaF, the mass ratio of paraffin to NaF is 10:(1.5-2.5), the stirring time is 10-25 hours, and the stirring speed is generally 200-500 rpm / min.

[0021] As a preferred embodiment of the above technical solution, in S6: CNTs are dispersed in 20-30 ml of formamide and ultrasonically dispersed at 20-30°C for 30 minutes. Then, TiN is added to the dispersion and ultrasonically dispersed for another 1-2 hours. The reaction time between the mixed dispersion of TiN and CNTs with formamide and TiO2@paraffin microcapsules is 5-6 hours.

[0022] Compared with existing paraffin phase change thermal storage materials and their modification methods, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material prepared in this invention has the following advantages: high light absorption rate, high thermal conductivity, high coating rate, and high photocatalytic efficiency.

[0023] 1. This invention uses the sol-gel method to construct a stable O / W system, utilizes the SDS modification to make TiO2 nanoparticles tightly adsorbed on the paraffin surface, and utilizes the amphiphilicity of the formamide reaction system to overcome the disadvantage of oil-soluble paraffins being difficult to encapsulate, forming a stable core-shell structure. The high coating rate effectively improves the thermal conductivity and thermal stability of the material, and inhibits leakage and corrosion while retaining the thermal properties of the paraffin.

[0024] 2. This invention introduces TiN-CNTs composite material as a modified loading material for microcapsules. Since TiN has a wide light absorption range due to surface plasmon resonance effect, it forms a spectral complement with TiO2. Furthermore, the carboxylated multi-walled carbon nanotubes with high thermal conductivity and excellent optical properties have abundant oxygen-containing functional groups, providing reactive sites. This allows metal nanoparticles such as TiO2 and TiN to be anchored on them, synthesizing a very uniform nano-carbon-based composite material. This further improves the thermal and light absorption properties of the phase change material and realizes full-spectrum photothermal conversion.

[0025] 3. This invention introduces TiN-CNTs composite materials. Unlike Au and Ag, which form Schottky interfaces with TiO2, TiN forms an ohmic interface with TiO2, which is beneficial for the transfer of hot electrons to the conduction band of TiO2. In addition, carboxylated multi-walled carbon nanotubes (C-MWCNTs) can serve as channels for electron transfer and inhibit the binding of electron-hole pairs, thereby promoting the rapid transfer of photogenerated electrons in TiO2 and improving catalytic efficiency.

[0026] 4. The wall material of the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material prepared in this invention is crystalline TiO2, which has good photocatalytic activity, can effectively degrade organic pollutants, sterilize, etc., and is non-toxic and has high chemical stability. Attached Figure Description

[0027] Figure 1 The image shows a SEM image of the phase change microcapsule composite thermal storage material with photocatalytic properties of the present invention; where (a) represents TiN-CNTs nanocomposite material, (b) and (c) represent TiO2@paraffin microcapsules, and (d) represents the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material prepared in Example 1.

[0028] Figure 2 This is a TEM image of the phase change microcapsule composite thermal storage material with photocatalytic properties obtained in Example 1.

[0029] Figure 3 The images show the DSC diagrams of the phase change microcapsule composite thermal storage materials with photocatalytic properties obtained in Examples 1-3.

[0030] Figure 4 The images show the XRD patterns of the phase change microcapsule composite thermal storage material with photocatalytic properties obtained in Example 1, as well as the XRD patterns of paraffin, TiO2@paraffin, TiN-CNTs, TiN, and CNTs.

[0031] Figure 5 The images show the Raman spectra of the phase change microcapsule composite thermal storage materials with photocatalytic properties obtained in Examples 1-3.

[0032] Figure 6 The images show the ultraviolet-visible-near-infrared absorption spectra of the phase change microcapsule composite thermal storage materials with photocatalytic properties obtained in Examples 1-3.

[0033] Figure 7 The curves show the time-dependent photodegradation rate of methylene blue solution for the phase change microcapsule composite thermal storage materials with photocatalytic properties obtained in Examples 1-3. Detailed Implementation

[0034] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0035] In the following examples, the purity of the paraffin, C-MWCNTs, TiN, TBT, NaF, SDS and acetic acid is not less than 99.0%; the length of C-MWCNTs is 10-30 μm, the tube diameter is 20-30 nm, and the carboxyl content is greater than 1.2 wt%; the size of TiN is 10-30 nm.

[0036] In the following embodiments, the photothermal conversion efficiency is calculated by measuring the ratio of the heat change of the material under a certain light intensity over time. The photocatalytic efficiency was measured using methylene blue as the target pollutant under simulated light source irradiation at room temperature. The absorbance value of the characteristic absorption peak of methylene blue at 664 nm was selected as the parameter for measuring the photocatalytic effect.

[0037] Example 1

[0038] A phase change microcapsule composite thermal storage material with photocatalytic properties is specifically a TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material. The material exhibits a core-shell structure, with the paraffin as the core and crystalline TiO2 with photocatalytic properties coating the surface. TiN-CNTs composite photothermal conversion particles are uniformly attached to the TiO2 surface as the core-shell modification material. The mass ratio of paraffin, TiO2, TiN, and CNTs is 100:(23-24):2:1. Figure 1 and Figure 2 As shown, the microcapsules have a particle size of 2.5-3.5 μm, a shell wall thickness in the range of 150-200 nm, and a core-shell structure coverage rate of 73.1%.

[0039] The above-mentioned TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material is prepared by the following steps:

[0040] (1) Pretreatment: Weigh 4g of sliced ​​paraffin and 1.3g of SDS and disperse them in 30ml of formamide. Place the mixture in a magnetic stirring water bath and stir at 75℃ and 800rpm / min for 2.5h to form a uniform and stable oil-in-water emulsion (O / W).

[0041] (2) Sol-gel method: 4g of TBT as a TiO2 precursor was slowly added dropwise to the above (O / W) emulsion and stirred for 40 minutes to ensure thorough mixing of the reaction system. Then, 0.08ml of acetic acid was added to the reaction system and stirred for 10 minutes. Next, the stirring speed was adjusted to 600-700rpm / min, and a mixed solution of 2ml of deionized water and 20ml of formamide was slowly added dropwise to the reaction system to promote the hydrolysis of TBT. After 3 hours of reaction, an amorphous TiO2@paraffin microcapsule solution system was obtained.

[0042] (3) Add 0.8 g NaF to the microcapsule system obtained in step (2), stir for 18 hours at a stirring speed of 300-400 rpm / min to induce TiO2 crystal transformation, and obtain crystalline TiO2@paraffin microcapsule system. Its scanning electron microscope image is shown below. Figure 1 As shown in b and c.

[0043] (4) Weigh 40 mg of C-MWCNTs and 80 mg of TiN and ultrasonically disperse them in 20 ml of formamide to obtain a TiN-CNTs mixed solution (its scanning electron microscope image is shown below). Figure 1 As shown in a); the TiN-CNTs mixed solution was added dropwise to the microcapsule system obtained in step (3), and the reaction was continued for 6 hours. The microcapsules were combined with the oxygen-containing functional groups of C-MWCNTs through self-assembly. After the reaction was completed, the obtained microcapsule sample was washed three times with anhydrous ethanol and filtered to obtain a dark gray solid substance, which is the TiN-CNTs modified TiO2@paraffin microcapsule composite heat storage material (TiN-CNTs / TiO2@paraffin(1)).

[0044] like Figure 1 (a) As shown in the scanning electron microscope image, TiN nanoparticles are uniformly dispersed on the surface of CNTs, further enhancing the dispersion among the CNTs. Figure 1 BD scanning electron microscope image and Figure 2 Transmission electron microscopy (TEM) images show that the TiN-CNTs-modified TiO2@paraffin microcapsule composite thermal storage material exhibits a typical core-shell structure modified with TiN-CNTs. The microcapsule particle size is 2.5-3.5 μm, and the TiO2 shell thickness is around 177 nm.

[0045] like Figure 3 , 4 As shown, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material in Example 1 has characteristic absorption peaks of paraffin, TiO2, TiN and C-MWCNTs, confirming that the composite material contains four substances: paraffin, TiO2, TiN and C-MWCNTs.

[0046] like Figure 5 As shown, the results obtained by DSC testing are as follows: The latent heat of phase change of the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in this embodiment is 140.5 J / g, and the coating rate reaches 73% compared with pure paraffin (191.7 J / g).

[0047] like Figure 6As shown, compared with TiO2@paraffin, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in the examples retains the ultraviolet absorption capacity, expands the absorption band from the ultraviolet light range to the near-infrared spectral region, and achieves full-band absorption, while also increasing the absorption intensity.

[0048] like Figure 7 As shown, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in this embodiment exhibits a methylene blue degradation rate of 91.4% after 120 min of ultraviolet irradiation, which is 25.5% higher than that of TiO2@paraffin microcapsules (65.9%).

[0049] Example 2

[0050] A phase change microcapsule composite thermal storage material with photocatalytic properties is specifically a TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material. The material exhibits a core-shell structure, with the paraffin as the core and photocatalytically active crystalline TiO2 forming the shell. Photothermal conversion particles, a composite blend of TiN-CNTs, are uniformly attached to the TiO2 surface as the core-shell modifier. The mass ratio of paraffin, TiO2, TiN, and CNTs is 100:(23-24):1.5:1.5. The microcapsules have a particle size in the range of 2-5 μm, a shell wall thickness in the range of 100-200 nm, and a core-shell structure coverage rate of 74.1%.

[0051] The specific preparation method includes the following steps:

[0052] (1) Pretreatment: Weigh 4g of sliced ​​paraffin and 1.3g of SDS and disperse them in 30ml of formamide. Place the mixture in a magnetic stirring water bath and stir at 75℃ and 800rpm / min for 2.5h to form a uniform and stable oil-in-water emulsion (O / W).

[0053] (2) Sol-gel method: 4g of TBT as a TiO2 precursor was slowly added dropwise to the above (O / W) emulsion and stirred for 40 minutes to ensure thorough mixing of the reaction system. Then, 0.08ml of acetic acid was added to the reaction system and stirred for 10 minutes. Next, the stirring speed was adjusted to 600-700rpm / min, and a mixed solution of 2ml of deionized water and 20ml of formamide was slowly added dropwise to the reaction system to promote the hydrolysis of TBT. After 3 hours of reaction, an amorphous TiO2@paraffin microcapsule solution system was obtained.

[0054] (3) Add 0.8g NaF to the microcapsule system obtained in step (2), stir for 18 hours at a stirring speed of 300-400rpm / min to induce TiO2 crystal transformation and obtain crystalline TiO2@paraffin microcapsule system.

[0055] (4) Weigh 60 mg of C-MWCNTs and 60 mg of TiN and ultrasonically disperse them in 20 ml of formamide. Add the mixture dropwise to the microcapsule system obtained in step (3) and continue the reaction for 6 hours. The C-MWCNTs bind to the microcapsules through the self-assembly of the oxygen-containing functional groups. After the reaction is complete, wash the obtained microcapsule sample three times with anhydrous ethanol and filter it to obtain a dark gray solid substance, which is the TiN-CNTs modified TiO2@paraffin microcapsule composite heat storage material (TiN-CNTs / TiO2@paraffin(2)).

[0056] like Figure 3 , 4 As shown, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material in Example 2 has characteristic absorption peaks of paraffin, TiO2, TiN and C-MWCNTs, confirming that the composite material contains four substances: paraffin, TiO2, TiN and C-MWCNTs.

[0057] like Figure 5 As shown, the results obtained by DSC testing are as follows: The latent heat of phase change of the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in this embodiment is 142.1 J / g, and the coating rate reaches 74.1% compared with pure paraffin (191.7 J / g).

[0058] like Figure 6 As shown, compared with TiO2@paraffin, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in the examples retains the ultraviolet absorption capacity, expands the absorption band from the ultraviolet light range to the near-infrared spectral region, and achieves full-band absorption, while also increasing the absorption intensity.

[0059] like Figure 7 As shown, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in this embodiment exhibits a methylene blue degradation rate of 94.2% after 120 min of ultraviolet irradiation, which is 28.3% higher than that of TiO2@paraffin microcapsules (65.9%).

[0060] Example 3

[0061] A phase change microcapsule composite thermal storage material with photocatalytic properties is specifically a TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material. The material exhibits a core-shell structure, with paraffin as the core and crystalline TiO2 with photocatalytic properties as the shell wall covering the surface of paraffin. Photothermal conversion particles of TiN-CNTs composite blend are uniformly attached to the surface of TiO2 as the core-shell modification material. The mass ratio of paraffin, TiO2, TiN, and CNTs is 100:(23-24):1:2.

[0062] The specific preparation method includes the following steps:

[0063] (1) Pretreatment: Weigh 4g of sliced ​​paraffin and 1.3g of SDS and disperse them in 30ml of formamide. Place the mixture in a magnetic stirring water bath and stir at 75℃ and 800rpm / min for 2.5h to form a uniform and stable oil-in-water emulsion (O / W).

[0064] (2) Sol-gel method: 4g of TBT as a TiO2 precursor was slowly added dropwise to the above (O / W) emulsion and stirred for 40 minutes to ensure thorough mixing of the reaction system. Then, 0.08ml of acetic acid was added to the reaction system and stirred for 10 minutes. Next, the stirring speed was adjusted to 600-700rpm / min, and a mixed solution of 2ml of deionized water and 20ml of formamide was slowly added dropwise to the reaction system to promote the hydrolysis of TBT. After 3 hours of reaction, an amorphous TiO2@paraffin microcapsule solution system was obtained.

[0065] (3) Add 0.8g NaF to the microcapsule system obtained in step (2), stir for 18 hours at a stirring speed of 300-400rpm / min to induce TiO2 crystal transformation and obtain crystalline TiO2@paraffin microcapsule system.

[0066] (4) Weigh 80 mg of C-MWCNTs and 40 mg of TiN and ultrasonically disperse them in 20 ml of formamide. Add the mixture dropwise to the microcapsule system obtained in step (3) and continue the reaction for 6 hours. The C-MWCNTs bind to the microcapsules through the self-assembly of the oxygen-containing functional groups. After the reaction is complete, wash the obtained microcapsule sample three times with anhydrous ethanol and filter it to obtain a dark gray solid substance, which is the TiN-CNTs modified TiO2@paraffin microcapsule composite heat storage material (TiN-CNTs / TiO2@paraffin(3)).

[0067] like Figure 3 , 4As shown, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material in Example 3 has characteristic absorption peaks of paraffin, TiO2, TiN and C-MWCNTs, confirming that the composite material contains four substances: paraffin, TiO2, TiN and C-MWCNTs.

[0068] like Figure 5 As shown, the results obtained by DSC testing are as follows: The latent heat of phase change of the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in this embodiment is 143.8 J / g, and the coating rate reaches 75% compared with pure paraffin (191.7 J / g).

[0069] like Figure 6 As shown, compared with TiO2@paraffin, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in the examples retains the ultraviolet absorption capacity, expands the absorption band from the ultraviolet light range to the near-infrared spectral region, and achieves full-band absorption, while also increasing the absorption intensity.

[0070] like Figure 7 As shown, the TiN-CNTs modified TiO2@paraffin microcapsule composite thermal storage material obtained in this embodiment exhibits a methylene blue degradation rate of 97.5% after 120 min of ultraviolet irradiation, which is 31.6% higher than that of TiO2@paraffin microcapsules (65.9%).

[0071] The above description is only a preferred embodiment and specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any local adjustments that can be conceived by those skilled in the art within the technical scope of the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention is determined by the claims and is not limited to the above preferred embodiments. All solutions within its scope should be bound by the present invention.

Claims

1. A phase change microcapsule composite thermal storage material with photocatalytic properties, characterized in that: The microcapsule composite thermal storage material has a core-shell structure, with paraffin as the core and crystalline TiO2 with photocatalytic properties as the shell wall coating the paraffin surface. Photothermal conversion particles composed of nano-titanium nitride and carbon nanotubes are uniformly attached to the TiO2 surface as core-shell modification materials. The mass ratio of the core paraffin, shell TiO2, nano-titanium nitride, and carbon nanotubes is 100:(20-25):(1-2):(1-2). The microcapsules have an average particle size of 1-5 µm, a core-shell structure with a shell wall thickness of 100-300 nm, and a shell wall coverage of not less than 70%; the carbon nanotubes have a length of 10-30 µm, a tube diameter of 20-30 nm, and a carboxyl content greater than 1.2 wt%; and the nano-titanium nitride has a size of 10-40 nm.

2. The preparation method of the phase change microcapsule composite thermal storage material according to claim 1, characterized in that: The specific preparation steps are as follows: S1: Prepare raw materials according to the mass ratio of paraffin wax: tetrabutyl titanate: carbon nanotubes: nano-titanium nitride of 100: 100: (1-2): (1-2); S2: In the solvent formamide, sodium dodecyl sulfate is used as a surface modifier to modify paraffin wax, so that it is fully mixed with the melted paraffin wax to obtain a transparent paraffin wax emulsion. S3: Add tetrabutyl titanate dropwise to the paraffin mixed emulsion and stir thoroughly to fully mix the paraffin mixed emulsion and obtain the precursor solution; S4: Add a trace amount of acetic acid to the precursor solution prepared in S3 and stir thoroughly. Then, add a mixed solution of water and formamide dropwise using a constant pressure dropping funnel while stirring. After the reaction, an amorphous TiO2@paraffin microcapsule system is obtained. S5: Add an appropriate amount of crystallization inducing agent to the amorphous TiO2@paraffin microcapsule system prepared in S4, and after the reaction, obtain a crystalline TiO2@paraffin microcapsule system; S6: Carbon nanotubes and nano-titanium nitride are ultrasonically dispersed in formamide and reacted fully. Then, they are gradually added to the crystalline TiO2@paraffin microcapsule system prepared in S5 and reacted fully. The resulting solid product is a phase change microcapsule composite thermal storage material with photocatalytic properties.

3. The preparation method according to claim 2, characterized in that: In S2, the transparent paraffin mixed emulsion is an oil-in-water emulsion, with a mass ratio of paraffin to sodium dodecyl sulfate of 100:(25-50) and a mass ratio of paraffin to formamide of 2:(10-20).

4. The preparation method according to claim 2, characterized in that: In S3, the mass ratio of paraffin to tetrabutyl titanate is 1:(0.8-1.2), and the stirring time is 20-60 minutes.

5. The preparation method according to claim 2, characterized in that: In S4, the amount of acetic acid added is based on the mass ratio of paraffin to acetic acid in the precursor solution being 50:(0.5-1.5); the mass ratio of water to formamide in the mixed solution of water and formamide is (0.5-1.5):10, and the mass ratio of paraffin to water in the precursor solution is 2:(0.5-1.5).

6. The preparation method according to claim 2, characterized in that: In S5, the crystallization induction agent is NaF, and the mass ratio of paraffin to NaF in the amorphous TiO2@paraffin microcapsule system is 10:(1.5-2.5). After addition, the stirring time is 10-25 hours.

7. The preparation method according to claim 2, characterized in that: In S6: carbon nanotubes are dispersed in formamide and ultrasonically dispersed at 20-30℃. Then, nano-titanium nitride is added and ultrasonically dispersed for 1-2 hours. The dispersion concentration of carbon nanotubes and nano-titanium nitride in formamide is 1-10 mg / ml. After being added to the crystalline TiO2@paraffin microcapsule system, the reaction time is 3-8 hours.

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