CN115477926B - Phase change material and preparation method thereof - Google Patents

Abstract

The invention discloses a phase change material and a preparation method thereof, wherein R=H or F in the structural general formula of the phase change material, namely the molecular formula of the phase change material is C ₁₀H₁₆BF₄ N or C ₁₀H₁₅BF₅ N, and the phase change material is in a crystal structure; the phase change material is prepared by mixing tetrafluoroboric acid solution and BTAB or BTAB derivatives, and self-assembling by naturally volatilizing solvent. The phase change material disclosed by the invention has relatively high thermal decomposition temperature point and uniform crystal particles; meanwhile, the preparation process is simple, easy to operate, sufficient in raw material source, low in production cost, high in yield and good in repeatability.

Description

Phase change material and preparation method thereof

Technical Field

The invention relates to a material and a preparation method thereof, and in particular to a phase change material and a preparation method thereof.

Background technique

Phase change material (PCM) is a type of material that changes its shape by changing the temperature and can also provide latent heat. For crystals, when they are affected by external temperature, pressure, etc., the symmetry of the crystal point group in the same solid phase will change, that is, the crystal structure phase change will occur. For the crystal structure phase change caused by temperature, the symmetry of the crystal generally follows the principle that the symmetry is higher in the high-temperature phase and lower in the low-temperature phase. In general, from the high-temperature phase to the low-temperature phase, the symmetry of the crystal structure becomes lower, and the loss of symmetry operation elements is called symmetry breaking. When a phase change occurs, there are obvious abnormalities in the dielectric properties, thermal entropy change, and phase change of the crystal structure.

Since the beginning of the new century, the excessive use of oil and coal has caused serious pollution to the ecological environment and damaged human health. my country urgently needs to develop industrial new energy and achieve sustainable development. Phase change materials, as an excellent energy storage material, have been widely used in aerospace, construction, military and other fields. According to the classification of material composition, phase change materials mainly include three types: inorganic, organic and organic-inorganic. Among them, organic-inorganic hybrid phase change materials have attracted the attention of many scholars in this field due to their simple synthesis, flexible and diverse structures, and environmental friendliness.

With the advancement of science and technology and the continuous improvement of theory, precise molecular design can synthesize phase change materials with excellent performance. However, only by considering the effective selection of molecular units and the effective selection of intermolecular interactions can the intentional design of phase change be fully realized. In the literature Tang, Y.Y.; Xie, Y.; Zeng, Y.L.; Liu, J.C.; He, W.H.; Huang, X.Q.; Xiong, R.G. Record enhancement of phase transition temperature realized by H/F substitution. Adv. Mater. 2020, 32, e2003530. Xu, Q.; Ye, L.; Liao, R.M.; An, Z.; Wang, C.F.; Miao, L.P.; Shi, C.; Ye, H.Y.; Zhang, Y. H/F substitution induced large increase of Tc in a 3D hybrid rare-earth double perovskite multifunctional compound. Chem. 2022, 28, e202103913., etc., organic-inorganic hybrid materials were obtained by H/F substitution, and F atoms were introduced to increase the rotational potential energy of cations and thus increase the phase transition temperature. However, the phase transition temperature of the target product fluoride is still low and its performance is single, which seriously limits its application scope.

Summary of the invention

Purpose of the invention: The present invention aims to provide a high-temperature phase change material with uniform crystal particles formed by self-assembly; another purpose of the present invention is to provide a method for preparing a phase change material with simple operation, good repeatability and high yield.

Technical solution: The phase change material of the present invention has a general structural formula as shown in formula (1), wherein R=H or F, and the phase change material is a crystalline structure.

Preferably, at a temperature of 296K, the crystal structure belongs to the monoclinic system.

Preferably, at a temperature of 296K, the crystal structure belongs to the P2 ₁ /n space group.

The preparation method of the phase change material comprises the following steps: slowly adding BTAB or a derivative of BTAB into an organic solvent and stirring to dissolve, then adding a tetrafluoroboric acid solution, blending the two solutions, stirring evenly and then standing to obtain the phase change material.

Preferably, the molar ratio of tetrafluoroboric acid to BTAB or a derivative of BTAB is 1:1-1:2. The derivative of BTAB is prepared by reacting p-fluorobenzyl bromide with trimethylamine.

Preferably, the stirring time is 30-60 min, the stirring temperature is 30-40° C., and the standing time is 2-3 weeks.

Preferably, the organic solvent is ethanol or acetonitrile.

The present invention obtains two organic-inorganic hybrid phase change materials by adjusting organic cations, which are non-toxic and low-cost, and meet the requirements of green chemistry. At the same time, high phase transition temperature materials are successfully obtained through the confinement effect induced by the introduction of F atoms, broadening their application market. The discovery of the present invention not only enriches the application content of hybrid materials in the field of green energy, but also provides a feasible way to explore multifunctional high phase transition temperature materials.

Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The phase change material has uniform crystal particles and good stability. The phase change compound of the present invention belongs to the category of molecular ion bases, has a relatively high thermal decomposition temperature point, and has uniform crystal particles. It can be used in synthetic applications in aerospace, building materials, clothing, military, etc., and can construct energy-saving equipment; (2) The preparation method is simple and easy to operate. The preparation method provided by the present invention is self-assembly synthesis by solvent volatilization method under room temperature conditions. The material structure has high stability, and the compound has good structural flexibility, is easy to control, has high yield and good repeatability, and the raw materials used are sufficient and the production cost is low.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a design roadmap of the present invention;

FIG2 is a synthetic route diagram of the phase change compound of the present invention;

FIG3 is a unit cell diagram of the phase change compound in Example 1 at a temperature of 296 K;

FIG4 is a diagram showing the confinement effect of the phase change compound in Example 1 at 296K;

FIG5 is an infrared spectrum of the phase change compound in Example 1;

FIG6 is a powder PXRD diffraction pattern of the phase change compound in Example 1;

FIG7 is a thermogravimetric TGA analysis diagram of the phase change compound in Example 1;

FIG8 is a differential scanning calorimetry diagram of the phase change compound in Example 1.

Detailed ways

The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

Example 1

A phase change material, whose general structural formula is shown in formula (1), wherein R=H or F, and the phase change material is a crystal structure, that is, its molecular formula is C ₁₀ H ₁₆ BF ₄ N or C ₁₀ H ₁₅ BF ₅ N.

The preparation method of the compound C ₁₀ H ₁₆ BF ₄ N is as follows: at room temperature, 1 mol of BTAB (BTAB=benzyltrimethylammonium bromide) is placed in a beaker, and an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetrical tetrafluoroboric acid solution is added to mix the two solutions, and after stirring at 30° C. for 30 minutes, the mixture is allowed to stand at room temperature for 2 weeks to obtain the phase change compound C ₁₀ H ₁₆ BF ₄ N.

The preparation method of the compound C ₁₀ H ₁₅ BF ₅ N is as follows: 20 mmol of p-fluorobenzyl bromide and 20 mmol of trimethylamine are weighed and put into a flask, and then 40 ml of acetonitrile solvent is added. The three are mixed evenly and reacted in an oil bath at 45° C. for 24 hours. Then, the BTAB derivative is obtained by rotary evaporation at 50° C. for 3 hours. At room temperature, 1 mol of the above BTAB derivative is put into a beaker, and an appropriate amount of anhydrous ethanol is slowly added to stir and dissolve, and then 1 mol of a highly symmetrical tetrafluoroboric acid solution is added to merge the two solutions, and after stirring at a temperature of 30° C. for 30 minutes, the solution is allowed to stand at room temperature for 2 weeks to obtain the phase change compound C ₁₀ H ₁₅ BF ₅ N.

Example 2

A phase change material, whose general structural formula is shown in formula (1), wherein R=H or F, and the phase change material is a crystal structure, that is, its molecular formula is C ₁₀ H ₁₆ BF ₄ N or C ₁₀ H ₁₅ BF ₅ N.

The preparation method of the compound C ₁₀ H ₁₆ BF ₄ N is as follows: at room temperature, 1.5 mol BTAB (BTAB = benzyltrimethylammonium bromide) is placed in a beaker, and an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetric tetrafluoroboric acid solution is added to mix the two solutions, and after stirring at a temperature of 35° C. for 40 minutes, the mixture is allowed to stand at room temperature for 3 weeks to obtain the phase change compound C ₁₀ H ₁₆ BF ₄ N.

The preparation method of the compound C ₁₀ H ₁₅ BF ₅ N is as follows: at room temperature, 1.5 mol of the BTAB derivative prepared in Example 1 is placed in a beaker, an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetric tetrafluoroboric acid solution is added to blend the two solutions, and after stirring at 35° C. for 40 minutes, the mixture is allowed to stand at room temperature for 3 weeks to obtain the phase change compound C ₁₀ H ₁₅ BF ₅ N.

Example 3

A phase change material, whose general structural formula is shown in formula (1), wherein R=H or F, and the phase change material is a crystal structure, that is, its molecular formula is C ₁₀ H ₁₆ BF ₄ N or C ₁₀ H ₁₅ BF ₅ N.

The preparation method of the compound C ₁₀ H ₁₆ BF ₄ N is as follows: at room temperature, 2 mol BTAB (BTAB = benzyltrimethylammonium bromide) is placed in a beaker, and an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetric tetrafluoroboric acid solution is added to mix the two solutions, and after stirring at 40° C. for 50 minutes, the mixture is allowed to stand at room temperature for 3 weeks to obtain the phase change compound C ₁₀ H ₁₆ BF ₄ N.

The preparation method of the compound C ₁₀ H ₁₅ BF ₅ N is as follows: at room temperature, 2 mol of the BTAB derivative prepared in Example 1 is placed in a beaker, an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetric tetrafluoroboric acid solution is added to blend the two solutions, and after stirring at 40° C. for 50 minutes, the mixture is allowed to stand at room temperature for 3 weeks to obtain the phase change compound C ₁₀ H ₁₅ BF ₅ N.

Example 4

A phase change material, whose general structural formula is shown in formula (1), wherein R=H or F, and the phase change material is a crystal structure, that is, its molecular formula is C ₁₀ H ₁₆ BF ₄ N or C ₁₀ H ₁₅ BF ₅ N.

The preparation method of the compound C ₁₀ H ₁₆ BF ₄ N is as follows: at room temperature, 1.8 mol BTAB (BTAB = benzyltrimethylammonium bromide) is placed in a beaker, and an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetrical tetrafluoroboric acid solution is added to mix the two solutions, and after stirring at 40° C. for 60 minutes, the mixture is allowed to stand at room temperature for 2 weeks to obtain the phase change compound C ₁₀ H ₁₆ BF ₄ N.

The preparation method of the compound C ₁₀ H ₁₅ BF ₅ N is as follows: at room temperature, 1.8 mol of the BTAB derivative prepared in Example 1 is placed in a beaker, an appropriate amount of anhydrous ethanol is slowly added and stirred to dissolve, and then 1 mol of a highly symmetric tetrafluoroboric acid solution is added to blend the two solutions, and after stirring at 40° C. for 60 minutes, the two solutions are allowed to stand at room temperature for 2 weeks to obtain the phase change compound C ₁₀ H ₁₅ BF ₅ N.

FIG. 1 is a design route diagram of the present invention, and FIG. 2 is a synthesis route diagram of the phase change compound of the present invention.

The phase change compound crystal prepared in Example 1 was analyzed. Single crystals of suitable size were selected under a microscope and Mo Kα rays monochromatized by graphite were used at room temperature. The X-ray diffraction structure of the single crystal was determined on a Bruker Apex II CCD diffractometer, and the crystallographic parameters of the phase change compound are shown in Table 1. Semi-empirical absorption correction was performed using the SADABS method, the unit cell parameters were determined using the least squares method, data reduction and structure analysis were completed using the SAINT and SHELXL program packages, respectively, and all non-hydrogen atoms were anisotropically refined using the full matrix least squares method. The unit cell changes of the compound are shown in Figure 3. As can be seen from the figure, at 296K, the asymmetric unit of the compound consists of a cation and an anion. The B atom in the inorganic anion coordinates with four F atoms to form a slightly distorted tetrahedron BF ₄ ^- . At 296K, both C ₁₀ H ₁₆ BF ₄ N and C ₁₀ H ₁₅ BF ₅ N belong to the monoclinic system, P2 ₁ /n space group.

Table 1 Crystallographic data of compounds

FIG4 is a diagram for analyzing the confinement effect of the compound in Example 1 at 296 K. As shown in FIG4 , after F substitution, the closed plane composed of four inorganic anions has an obvious spatial contraction, which means that the confinement effect on the cation becomes larger and the rotation space of the cation is reduced.

FIG5 is an infrared spectrum characterization of the compound in Example 1. As shown in FIG5 , there is a strong absorption peak at 2947 cm ^-1 , which is the -CH ₃ absorption peak.

FIG6 is a PXRD analysis characterization of the compound in Example 1. From the powder PXRD diffraction pattern, it can be seen that the simulated diffraction peaks are consistent with the diffraction peaks measured in the actual experiment, verifying the purity of the phase.

FIG7 is a thermogravimetric TGA analysis diagram of the compound in Example 1. As shown in FIG7 , the compound has a high stability. At about 600 K, the skeleton of the compound begins to decompose; at 800 ° C, the compound completely collapses.

FIG8 is a differential scanning calorimetry diagram of the compounds in Example 1. As shown in FIG8 , the phase transition temperatures of the two compounds are 410.4 K and 488.4 K, respectively.

Claims (7)

1. A phase change material, characterized in that its general structural formula is as shown in formula (1), wherein R = F, and the phase change material is a crystalline structure 2. The phase change material according to claim 1, characterized in that, at a temperature of 296K, the crystal structure belongs to the monoclinic system. 3 . The phase change material according to claim 1 , wherein at a temperature of 296 K, the crystal structure belongs to a P2 ₁ /n space group. 4. A method for preparing a phase change material according to claim 1, characterized in that it comprises the following steps: slowly adding a derivative of benzyltrimethylammonium bromide to ethanol or acetonitrile and stirring to dissolve, then adding a tetrafluoroboric acid solution, mixing the two solutions, stirring evenly and then standing to obtain a phase change material; the derivative of benzyltrimethylammonium bromide is prepared by reacting p-fluorobenzyl bromide and trimethylamine. 5 . The method for preparing a phase change material according to claim 4 , wherein the molar ratio of the tetrafluoroboric acid to the derivative of benzyltrimethylammonium bromide is 1:1-1:2. 6. The method for preparing a phase change material according to claim 4, characterized in that the stirring time is 30-60 min and the stirring temperature is 30-40°C. 7. The method for preparing a phase change material according to claim 4, characterized in that the standing time is 2-3 weeks.