Nanometer bismuth telluride and its preparation process

Abstract

The application relates to a preparation process of nanometer bismuth telluride, and belongs to the technical field of nanometer bismuth telluride preparation, which comprises the following steps: preparing a bismuth-based metal organic framework; performing coordination conversion on tellurite; performing calcination and organic conversion; and performing solvent thermal method synthesis on bismuth telluride. The bismuth telluride with the average particle size of 200-300 nm and the reasonable particle size step is synthesized through metal organic framework templating, and the thermoelectric performance of the bismuth telluride is far higher than that of common bismuth telluride materials. The morphology and particle size of the bismuth telluride are accurately controlled through metal organic framework templating, so that the thermoelectric performance of the bismuth telluride is improved.

Description

Technical Field

[0001] This invention belongs to the field of nano-bismuth telluride preparation technology, specifically relating to a nano-bismuth telluride and its preparation process. Background Technology

[0002] Nanoscale bismuth telluride (Bi₂Te₃) is an important semiconductor material widely used in thermoelectric devices, optoelectronic devices, and sensors. Due to its excellent thermoelectric properties and tunability, nanoscale bismuth telluride materials offer significant advantages in improving thermoelectric conversion efficiency. Various methods exist for preparing nanoscale bismuth telluride powder, including solvothermal methods, solution methods, vapor deposition, and mechanical alloying.

[0003] For example, Chinese patent CN115385307A uses a combination of melting and casting ingots and dry ball milling. During the ball milling process, ethyl acetate is added to aid dispersion, which significantly improves the thermoelectric properties of the resulting bismuth telluride bulk and increases the thermoelectric figure of merit ZT.

[0004] For example, Chinese patent CN112723322A describes a method for preparing layered bismuth telluride nanoparticles using a hydrothermal method, in which bismuth telluride nanoparticles are obtained through hydrothermal treatment, washing, and drying.

[0005] However, the methods mentioned above cannot perform template-based control of morphology or stabilize particle size distribution. Summary of the Invention

[0006] The purpose of this invention is to provide a nano-bismuth telluride and its preparation process in order to solve the above-mentioned problems.

[0007] The present invention achieves the above objectives through the following technical solutions:

[0008] This invention provides a process for preparing nano-sized bismuth telluride, comprising the following steps:

[0009] S1. Preparation of bismuth-based metal-organic frameworks:

[0010] (a) Weigh 3-4.5 mmol of 1,3,5-pyromellitic acid and 1-1.5 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 30-60 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h. At this reaction temperature and time, the purity and stability of the bismuth-based metal-organic framework can be ensured, providing support for the subsequent template reaction.

[0011] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven to obtain a white powder, which is the bismuth-based metal-organic framework.

[0012] S2, tellurate coordination transformation:

[0013] (a) Prepare 200-400 mL of sodium tellurate aqueous solution and adjust the pH to 1-2 with hydrochloric acid. Then immerse 0.5-1 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution and soak for 24-48 h.

[0014] (ii) Take out the converted material and place it in a vacuum drying oven. Set the temperature to 60-80℃ and the drying time to 4-8h to obtain the precursor. Store it in a vacuum for later use.

[0015] S3, calcination to remove organic conversion:

[0016] (i) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold the initial room temperature for 20-30 min, then set the heating rate to 5-10℃ / min to 250℃, hold for 2-6 h, and continuously purge oxygen.

[0017] (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for use.

[0018] S4. Solvothermal synthesis of bismuth telluride:

[0019] (a) Take 0.5-1g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.2-0.4g of sodium hydroxide, 0.25-0.5g of polyvinylpyrrolidone and 40-60mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly.

[0020] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 180-200℃, keep it at that temperature for 4-12 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0021] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Then place it in a vacuum drying oven and set the drying temperature to 60-80℃ for 4-8 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0022] As a further optimization of the present invention, the vacuum drying oven in step S1 is set to heat at 60-70°C for 8-12 hours, and the vacuum temperature is controlled at 60-70°C. The drying time is controlled at 8-12 hours. Within this temperature and time range, the solvent and residual moisture in the substance can be effectively evaporated without compromising the thermal stability of the substance.

[0023] As a further optimization of the present invention, the concentration of the sodium tellurate aqueous solution in step S2 is 1-2 mol / L to ensure sufficient coordination. During the conversion process, TeO3... 2- In-situ transformation can occur through coordination with active Bi-O bonds, forming stable BiO-Te bonds. This coordination-based transformation allows the bismuth-based metal-organic framework to irreversibly capture TeO3. 2- Furthermore, bismuth-based metal-organic frameworks for TeO3 2- It exhibits extremely high adsorption capacity and rapid kinetics. However, excessively high concentrations of sodium tellurate in aqueous solution lead to saturation and crystallization, affecting the coordination conversion efficiency of bismuth-based metal-organic frameworks in sodium tellurate aqueous solution; conversely, excessively low concentrations result in coordination conversion to TeO3 within the bismuth-based metal-organic framework. 2- The deficiency affects the further synthesis of bismuth telluride.

[0024] As a further optimization of the present invention, the concentration of sodium hydroxide in step S4 is 75%. Compared with the low-concentration sodium hydroxide system, the high-concentration sodium hydroxide system generates a large number of bismuth telluride nanocrystal seeds within the same time period. Subsequently, the nucleation rate and crystal growth rate of bismuth telluride are slowed down due to the simultaneous growth of a large number of nuclei, resulting in more large-sized nanosheets with uneven particle size distribution. On the other hand, in the later stage of the reaction, sodium hydroxide has a corrosive effect on the incompletely crystallized bismuth telluride nanosheets. This corrosive effect restricts the mutual migration between tellurium and bismuth to form a stable bismuth telluride compound, resulting in an increase in amorphous regions inside the bismuth telluride nanosheets. Therefore, sodium hydroxide needs to be added, and the amount must be moderate.

[0025] A nano-sized bismuth telluride is prepared by the above-described method.

[0026] The beneficial effects of this invention are as follows: through metal-organic framework templated synthesis, hexagonal plate-shaped bismuth telluride with an average particle size between 200 and 300 nm and a reasonable particle size distribution is obtained. Its thermoelectric performance is far superior to that of ordinary bismuth telluride materials. Through metal-organic framework templated precise control, the morphology and particle size of bismuth telluride can be precisely controlled to improve its thermoelectric performance. Attached Figure Description

[0027] Figure 1 A scanning electron microscope image of bismuth telluride, the final product obtained in this invention.

[0028] Figure 2 High-resolution transmission electron microscopy (TEM) image and energy dispersive spectroscopy (EDS) analysis of bismuth telluride, the final product obtained in this invention. Detailed Implementation

[0029] The present application will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0030] I. Materials

[0031] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0032] In this invention, the ethanol used in the ethanol centrifugation washing is a 75% ethanol solution.

[0033] II. Methods

[0034] Example 1

[0035] S1. Preparation of bismuth-based metal-organic frameworks:

[0036] (a) Weigh 3 mmol of 1,3,5-pyromellitic acid and 1 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 30 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h.

[0037] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven at 60℃ for 8 hours to obtain a white powder, which is the bismuth-based metal-organic framework.

[0038] S2, tellurate coordination transformation:

[0039] (a) Prepare 200 mL of sodium tellurate aqueous solution with a concentration of 1 mol / L, and adjust the pH to 2 with hydrochloric acid. Then immerse 0.5 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 24 h.

[0040] (ii) Take out the transformed material and place it in a vacuum drying oven. Set the temperature to 60℃ and the drying time to 4h to obtain the precursor. Store it in a vacuum for later use.

[0041] S3, calcination to remove organic conversion:

[0042] (i) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold at room temperature for 20 min initially, then set the heating rate to 5℃ / min to 250℃, hold for 2 h, and continuously purge oxygen.

[0043] (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for use.

[0044] S4. Solvothermal synthesis of bismuth telluride:

[0045] (a) Take 0.5g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.2g of sodium hydroxide (75% concentration), 0.25g of polyvinylpyrrolidone and 40mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly with magnetic force.

[0046] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 180℃, keep it at that temperature for 4 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0047] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Then place it in a vacuum drying oven and set the drying temperature to 60℃ for 4 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0048] Example 2

[0049] S1. Preparation of bismuth-based metal-organic frameworks:

[0050] (a) Weigh 3.75 mmol of 1,3,5-pyromellitic acid and 1.25 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 45 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h.

[0051] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven at 65°C for 10 hours to obtain a white powder, which is the bismuth-based metal-organic framework.

[0052] S2, tellurate coordination transformation:

[0053] (a) Prepare 300 mL of sodium tellurate aqueous solution with a concentration of 1.5 mol / L, and adjust the pH to 1.5 with hydrochloric acid. Then immerse 0.75 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 36 h.

[0054] (ii) Take out the transformed material and place it in a vacuum drying oven. Set the temperature to 70℃ and the drying time to 6h to obtain the precursor. Store it in a vacuum for later use.

[0055] S3, calcination to remove organic conversion:

[0056] (i) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold at room temperature for 25 min initially, then set the heating rate to 7.5℃ / min to 250℃, hold for 6 h, and continuously purge oxygen.

[0057] (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for use.

[0058] S4. Solvothermal synthesis of bismuth telluride:

[0059] (a) Take 0.75g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.3g of sodium hydroxide (75% concentration), 0.4g of polyvinylpyrrolidone and 50mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly.

[0060] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 190℃, keep it at that temperature for 8 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0061] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Finally, place it in a vacuum drying oven and set the drying temperature to 70℃ for 6 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0062] Example 3

[0063] S1. Preparation of bismuth-based metal-organic frameworks:

[0064] (a) Weigh 4.5 mmol of 1,3,5-pyromellitic acid and 1.5 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 60 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h.

[0065] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven at 70℃ for 12 hours to obtain a white powder, which is the bismuth-based metal-organic framework.

[0066] S2, tellurate coordination transformation:

[0067] (a) Prepare 400 mL of sodium tellurate aqueous solution with a concentration of 2 mol / L, and adjust the pH to 2 with hydrochloric acid. Then immerse 1 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 48 h.

[0068] (ii) Take out the transformed material and place it in a vacuum drying oven. Set the temperature to 80℃ and the drying time to 8h to obtain the precursor. Store it in a vacuum for later use.

[0069] S3, calcination to remove organic conversion:

[0070] (a) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold at room temperature for 30 min initially, then set the heating rate to 10℃ / min to 250℃, hold for 4 h, and continuously purge oxygen.

[0071] (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for use.

[0072] S4. Solvothermal synthesis of bismuth telluride:

[0073] (a) Take 1g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.4g of sodium hydroxide (75% concentration), 0.5g of polyvinylpyrrolidone and 60mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly with magnetic force.

[0074] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 200℃, keep it at that temperature for 12 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0075] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Then place it in a vacuum drying oven and set the drying temperature to 80℃ for 8 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0076] Comparative Example 1

[0077] S1. Preparation of bismuth-based metal-organic frameworks:

[0078] (a) Weigh 3.75 mmol of 1,3,5-pyromellitic acid and 1.25 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 45 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h.

[0079] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven at 65°C for 10 hours to obtain a white powder, which is the bismuth-based metal-organic framework.

[0080] S2, tellurate coordination transformation:

[0081] (a) Prepare 300 mL of sodium tellurate aqueous solution with a concentration of 1.5 mol / L, and adjust the pH to 1.5 with hydrochloric acid. Then immerse 0.75 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 36 h.

[0082] (ii) Take out the transformed material and place it in a vacuum drying oven. Set the temperature to 70℃ and the drying time to 6h to obtain the precursor. Store it in a vacuum for later use.

[0083] S3, calcination to remove organic conversion:

[0084] (i) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold at room temperature for 25 min initially, then set the heating rate to 7.5℃ / min to 250℃, hold for 6 h, and continuously purge oxygen.

[0085] (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for use.

[0086] S4. Solvothermal synthesis of bismuth telluride:

[0087] (a) Take 0.75g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.3g of sodium hydroxide (75% concentration), 0.4g of polyvinylpyrrolidone and 50mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly.

[0088] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 190℃, keep it at that temperature for 8 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0089] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Finally, place it in a vacuum drying oven and set the drying temperature to 70℃ for 6 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0090] Comparative Example 2

[0091] S1. Preparation of bismuth-based metal-organic frameworks:

[0092] (a) Weigh 3.75 mmol of 1,3,5-pyromellitic acid and 1.25 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 45 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h.

[0093] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven at 65°C for 10 hours to obtain a white powder, which is the bismuth-based metal-organic framework.

[0094] S2, tellurate coordination transformation:

[0095] (a) Prepare 300 mL of sodium tellurate aqueous solution with a concentration of 1.5 mol / L, and adjust the pH to 1.5 with hydrochloric acid. Then immerse 0.75 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 36 h.

[0096] (ii) Take out the transformed material and place it in a vacuum drying oven. Set the temperature to 70℃ and the drying time to 6h to obtain the precursor. Store it in a vacuum for later use.

[0097] S3. Solvothermal synthesis of bismuth telluride:

[0098] (a) Take 0.75g of the precursor and place it in a polytetrafluoroethylene reaction vessel, and add 0.3g of sodium hydroxide (75% concentration), 0.4g of polyvinylpyrrolidone and 50mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly.

[0099] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 190℃, keep it at that temperature for 8 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0100] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Finally, place it in a vacuum drying oven and set the drying temperature to 70℃ for 6 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0101] Comparative Example 3

[0102] S1. Preparation of bismuth-based metal-organic frameworks:

[0103] (a) Weigh 3.75 mmol of 1,3,5-pyromellitic acid and 1.25 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After stirring vigorously for 45 min, transfer the solution to a 100 mL polytetrafluoroethylene hydrothermal reactor and heat at 120 °C for 24 h.

[0104] (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven at 65°C for 10 hours to obtain a white powder, which is the bismuth-based metal-organic framework.

[0105] S2, tellurate coordination transformation:

[0106] (a) Prepare 300 mL of sodium tellurate aqueous solution with a concentration of 0.8 mol / L, and adjust the pH to 1.5 with hydrochloric acid. Then immerse 0.75 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 36 h.

[0107] (ii) Take out the transformed material and place it in a vacuum drying oven. Set the temperature to 70℃ and the drying time to 6h to obtain the precursor. Store it in a vacuum for later use.

[0108] S3, calcination to remove organic conversion:

[0109] (i) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold at room temperature for 25 min initially, then set the heating rate to 7.5℃ / min to 250℃, hold for 6 h, and continuously purge oxygen.

[0110] (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for use.

[0111] S4. Solvothermal synthesis of bismuth telluride:

[0112] (a) Take 0.75g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.3g of sodium hydroxide (75% concentration), 0.4g of polyvinylpyrrolidone and 50mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly.

[0113] (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 190℃, keep it at that temperature for 8 hours, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out.

[0114] (III) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Finally, place it in a vacuum drying oven and set the drying temperature to 70℃ for 6 hours. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles.

[0115] Performance testing

[0116] The nano-bismuth telluride powder samples prepared in Examples 1-3 and Comparative Examples 1-3 were tested respectively, and the test data are recorded in the table below:

[0117] project Bismuth telluride average particle size / nm Flake rate / % Hexagonal ratio / % ZT value at 375K Example 1 219 high higher 1.06 Example 2 269 high high 1.13 Example 3 288 high high 1.09 Comparative Example 1 320 high Low 1.36 Comparative Example 2 195 Low Low 1.03 Comparative Example 3 265 Low lower 1.09

[0118] In this invention, hexagonal bismuth telluride with an average particle size of 200-300 nm and reasonable particle size distribution is prepared by templated synthesis of metal-organic frameworks. Its thermoelectric properties far exceed those of ordinary bismuth telluride materials.

[0119] Comparing Comparative Example 1 with Example 2 reveals that, compared to the low-concentration sodium hydroxide system, the high-concentration sodium hydroxide system generates a large number of bismuth telluride nanocrystal seeds within the same timeframe. Subsequently, the nucleation rate and crystal growth rate of bismuth telluride slow down due to the simultaneous growth of a large number of nuclei, resulting in more large-sized nanosheets with uneven particle size distribution. On the other hand, in the later stages of the reaction, sodium hydroxide has a corrosive effect on the incompletely crystallized bismuth telluride nanosheets. This corrosive effect restricts the mutual migration between tellurium and bismuth to form a stable bismuth telluride compound, increasing the amorphous regions inside the bismuth telluride nanosheets. Therefore, sodium hydroxide needs to be added, and the amount must be moderate.

[0120] Comparing Comparative Example 2 with Example 2, it can be seen that the precursor was placed in an alumina crucible, which was then placed in a tube furnace. A heating program was set, initially holding at room temperature for 25 minutes, and then increasing the temperature to 250°C at a rate of 7.5°C / min, holding for 6 hours, and continuously purging oxygen. After the furnace temperature dropped to room temperature, the product was removed and vacuum-packed for use. The purpose was to remove organic matter and improve the thermoelectric properties of the final product while retaining the template.

[0121] Comparing Comparative Example 3 with Example 2 shows that the concentration of sodium tellurate aqueous solution must be moderate. Too low a concentration will lead to coordination conversion to TeO3 in the bismuth-based metal-organic framework. 2- Insufficient concentration will affect the further synthesis of bismuth telluride; excessively high concentration will inevitably affect the coordination conversion efficiency of bismuth-based metal-organic frameworks in sodium tellurate aqueous solution.

[0122] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A preparation process for nano-bismuth telluride, characterized in that, Includes the following steps: S1. Preparation of bismuth-based metal-organic frameworks: (a) Weigh 3-4.5 mmol of 1,3,5-pyromellitic acid and 1-1.5 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. Stir vigorously for 30-60 min and then transfer to a 100 mL polytetrafluoroethylene hydrothermal reactor. Heat at 120 °C for 20-24 h. (ii) After the reaction vessel is cooled to room temperature, the obtained sample is taken out and centrifuged, and washed three times with methanol and N,N-dimethylformamide respectively. Finally, it is dried in a vacuum drying oven to obtain a white powder, which is the bismuth-based metal-organic framework. S2, tellurate coordination transformation: (a) Prepare 200-400 mL of sodium tellurate aqueous solution and adjust the pH to 1-2 with hydrochloric acid. Then immerse 0.5-1 g of bismuth-based metal-organic framework in the above sodium tellurate aqueous solution for 24-48 h. (ii) Take out the converted product and place it in a vacuum drying oven, set the temperature to 60~80℃, and dry for 4~8 h to obtain the precursor, which is then stored under vacuum for later use. The concentration of the sodium tellurate aqueous solution in step S2 is 1~2 mol / L; S3, calcination to remove organic conversion: (a) Place the precursor in a corundum crucible, place the corundum crucible in a tube furnace, set the heating program, hold at room temperature for 20-30 min initially, then set the heating rate to 5-10 ℃ / min to 250 ℃, hold for 2-6 h, and continuously purge oxygen. (ii) After the furnace temperature drops to room temperature, remove the product and vacuum pack it for later use; S4. Solvothermal synthesis of bismuth telluride: (a) Take 0.5-1g of the product and place it in a polytetrafluoroethylene reaction vessel, and add 0.2-0.4g of sodium hydroxide, 0.25-0.5g of polyvinylpyrrolidone and 40-60mL of ethylene glycol. Then place the reaction vessel on a magnetic stirrer and stir it thoroughly with magnetic force. (ii) Seal the reactor in a stainless steel high-temperature jacket, place it in a heating sleeve with heat transfer oil, set the temperature to 180~200℃, keep it at that temperature for 4~12 h, and after the reaction is completed, wait for the temperature to drop to room temperature before taking the reactor out. (iii) After centrifuging the suspension in the reactor, wash it with water three times, then centrifuge and wash it with ethanol three times. Then place it in a vacuum drying oven and set the drying temperature to 60~80℃ for 4~8 h. Take it out to obtain hexagonal sheet-like bismuth telluride nanoparticles. The concentration of sodium hydroxide in step S4 is 75%.

2. The preparation process of nano-bismuth telluride according to claim 1, characterized in that, In step S1, the vacuum drying oven is set to heat at 60~70℃ for 8~12 hours.

3. A nano-bismuth telluride, characterized in that, It is prepared by the preparation process described in any one of claims 1 or 2.

Images