Nano bismuth telluride and preparation process thereof

Abstract

The invention relates to a preparation process of nano bismuth telluride, and belongs to the technical field of preparation of nano bismuth telluride, and the preparation process comprises the following steps: preparing a bismuth-based metal organic framework; carrying out coordination conversion on tellurate; calcining to remove organic conversion; and synthesizing bismuth telluride by a solvothermal method. The hexagonal flaky bismuth telluride with the average particle size of 200-300nm and reasonable particle size step-by-step is prepared through metal organic framework templating synthesis, the thermoelectric performance of the hexagonal flaky bismuth telluride is far better than that of a common bismuth telluride material, and the morphology and the particle size of the bismuth telluride are accurately controlled through metal organic framework templating accurate control so as to improve the thermoelectric performance of the bismuth telluride.

Description

Technical Field

[0001] The invention belongs to the technical field of nano-bismuth telluride preparation, and specifically relates to nano-bismuth telluride and a preparation process thereof. Background Art

[0002] Nano-bismuth telluride (Bi2Te3) is an important semiconductor material, widely used in thermoelectric devices, optoelectronic devices and sensors. Due to its excellent thermoelectric properties and adjustability, nano-scale bismuth telluride materials have significant advantages in improving thermoelectric conversion efficiency. There are many methods for preparing nano-bismuth telluride powders, and common preparation methods include: solvothermal method, solution method, vapor deposition method, mechanical alloying method, etc.

[0003] For example, Chinese patent CN115385307A adopts a method of combining smelting ingots and dry ball milling, and adds ethyl acetate to assist dispersion during the ball milling process. The thermoelectric performance of the resulting bismuth telluride block is significantly improved, and the thermoelectric figure of merit ZT is improved;

[0004] Another example is Chinese patent CN112723322A, which discloses a method for preparing layered bismuth telluride nanoparticles by hydrothermal method, wherein bismuth telluride nanoparticles are obtained by hydrothermal method, washing and drying.

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

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

[0007] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0008] The present invention provides a preparation process of nano-bismuth telluride, comprising the following steps:

[0009] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

[0010] (i) Weigh 3-4.5 mmol of 1,3,5-trimethylbenzene trimesic acid and 1-1.5 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After vigorously stirring for 30-60 min, transfer them to a 100 ml polytetrafluoroethylene hydrothermal autoclave and heat them at 120 ° C for 24 h. At this reaction temperature and reaction 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 reactor is cooled to room temperature, the obtained sample is taken out, centrifuged and washed three times with methanol and N,N-dimethylformamide respectively, and finally dried in a vacuum drying oven to obtain a white powder, which is a bismuth-based metal organic framework.

[0012] S2, tellurite coordination transformation:

[0013] (i) preparing 200-400 mL of sodium tellurite aqueous solution, adjusting the pH to 1-2 with hydrochloric acid, and then immersing 0.5-1 g of bismuth-based metal-organic framework in the sodium tellurite aqueous solution for 24-48 hours;

[0014] (ii) taking out the transformed product and placing it in a vacuum drying oven, setting the temperature to 60-80°C and drying time to 4-8 hours to obtain the precursor, which is then stored in a vacuum until use.

[0015] S3, calcination to remove organic conversion:

[0016] (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 20 to 30 minutes, then setting the temperature to 250° C. at 5 to 10° C. / min, keeping the temperature for 2 to 6 hours, and continuously passing oxygen;

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

[0018] S4. Solvothermal synthesis of bismuth telluride:

[0019] (i) taking 0.5-1 g of the product and placing it in a polytetrafluoroethylene reaction kettle, and adding 0.2-0.4 g of sodium hydroxide, 0.25-0.5 g of polyvinyl pyrrolidone and 40-60 mL of ethylene glycol, and then placing the reaction kettle on a magnetic stirrer device for sufficient magnetic stirring;

[0020] (ii) the reactor is sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, the temperature is set to 180-200° C., and the temperature is kept for 4-12 hours. After the reaction is completed, the temperature is lowered to room temperature, and the reactor is taken out;

[0021] (iii) The suspension in the reactor is centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times, and then placed in a vacuum drying oven with a drying temperature of 60 to 80° C. and a drying time of 4 to 8 hours, and hexagonal flake nano-bismuth telluride is obtained.

[0022] As a further optimization scheme 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 water in the substance can be effectively evaporated without destroying the thermal stability of the substance.

[0023] As a further optimization scheme of the present invention, the concentration of the sodium tellurate aqueous solution in step S2 is 1-2 mol / L, in order to fully carry out the coordination. During the conversion process, TeO3 2- The bismuth-based metal-organic framework can be transformed in situ by coordinating with the active Bi-O bonds to form stable BiO-Te bonds. This coordination-bond-based transformation enables the irreversible capture of TeO3 in bismuth-based metal-organic frameworks. 2- In addition, the bismuth-based metal-organic framework has a great influence on the 2- It has ultra-high adsorption capacity and fast kinetics. If the concentration of sodium tellurite aqueous solution is too high, sodium tellurite is easy to saturate and crystallize, which affects the coordination conversion efficiency of bismuth-based metal organic framework in sodium tellurite aqueous solution; if the concentration is too low, it will cause the coordination conversion to TeO3 of bismuth-based metal organic framework. 2- Insufficient, which affects the further synthesis of bismuth telluride.

[0024] As a further optimization scheme of the present invention, the concentration of sodium hydroxide in step S4 is 75%. Compared with the low-concentration sodium hydroxide system, a large amount of bismuth telluride nanocrystal seeds will be generated in the same time with a high-concentration sodium hydroxide system. Subsequently, the nucleation rate and crystal growth rate of bismuth telluride will be slowed down due to the simultaneous growth of a large number of nuclei, thereby producing more large-sized nanosheets and 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. These corrosive effects restrict the mutual migration between tellurium and bismuth to form a stable bismuth telluride compound, which increases the amorphous area inside the bismuth telluride nanosheet, so sodium hydroxide needs to be added and the amount needs to be moderate.

[0025] A nano bismuth telluride is prepared by the preparation method.

[0026] The beneficial effect of the present invention is that: through metal organic framework template synthesis, hexagonal flake bismuth telluride with an average particle size between 200 and 300 nm and a reasonable particle size distribution is obtained, and its thermoelectric performance far exceeds that of ordinary bismuth telluride materials. Through metal organic framework template precise control, the morphology and particle size of bismuth telluride are precisely controlled to improve its thermoelectric performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope photo of the final product bismuth telluride obtained by the present invention;

[0028] Figure 2 The high-resolution transmission microscope photo and energy spectrum analysis of the final product bismuth telluride prepared by the present invention. DETAILED DESCRIPTION

[0029] The present application is described in further detail below. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technicians in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0030] 1. Materials

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

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

[0033] 2. Methods

[0034] Example 1

[0035] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

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

[0037] (ii) After the reactor is cooled to room temperature, the obtained sample is taken out, centrifuged and washed three times with methanol and N,N-dimethylformamide respectively, and finally heated in a vacuum drying oven at 60° C. for 8 h to obtain a white powder, which is a bismuth-based metal organic framework.

[0038] S2, tellurite coordination transformation:

[0039] (i) preparing 200 mL of a 1 mol / L sodium telluride aqueous solution, adjusting the pH to 2 with hydrochloric acid, and then immersing 0.5 g of a bismuth-based metal-organic framework in the sodium telluride aqueous solution for 24 hours;

[0040] (ii) Take out the transformed product and place it in a vacuum drying oven, set the temperature to 60°C, and dry it for 4 hours to obtain the precursor, which is then stored in a vacuum until use.

[0041] S3, calcination to remove organic conversion:

[0042] (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 20 minutes, then heating to 250°C at 5°C / min, keeping the temperature for 2 hours, and continuously passing oxygen;

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

[0044] S4. Solvothermal synthesis of bismuth telluride:

[0045] (i) 0.5 g of the product was placed in a polytetrafluoroethylene reactor, and 0.2 g of 75% sodium hydroxide, 0.25 g of polyvinyl pyrrolidone and 40 mL of ethylene glycol were added, and then the reactor was placed on a magnetic stirrer device for sufficient magnetic stirring;

[0046] (ii) The reactor was sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, set the temperature to 180°C, and kept warm for 4 hours. After the reaction was completed, the temperature dropped to room temperature and the reactor was taken out;

[0047] (iii) The suspension in the reactor was centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times. The suspension was then placed in a vacuum drying oven and dried at 60° C. for 4 hours to obtain hexagonal nano-bismuth telluride.

[0048] Example 2

[0049] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

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

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

[0052] S2, tellurite coordination transformation:

[0053] (i) preparing 300 mL of a 1.5 mol / L sodium telluride aqueous solution, adjusting the pH to 1.5 with hydrochloric acid, and then immersing 0.75 g of a bismuth-based metal-organic framework in the sodium telluride aqueous solution for 36 hours;

[0054] (ii) Take out the transformed product and place it in a vacuum drying oven, set the temperature to 70°C, and dry it for 6 hours to obtain the precursor, which is then stored in a vacuum until use.

[0055] S3, calcination to remove organic conversion:

[0056] (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 25 minutes, then heating to 250°C at 7.5°C / min, keeping the temperature for 6 hours, and continuously passing oxygen;

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

[0058] S4. Solvothermal synthesis of bismuth telluride:

[0059] (i) 0.75 g of the product was placed in a polytetrafluoroethylene reactor, and 0.3 g of 75% sodium hydroxide, 0.4 g of polyvinyl pyrrolidone and 50 mL of ethylene glycol were added, and then the reactor was placed on a magnetic stirrer device for sufficient magnetic stirring;

[0060] (ii) The reactor was sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, set at 190°C, and kept warm for 8 hours. After the reaction was completed, the temperature dropped to room temperature and the reactor was taken out;

[0061] (iii) The suspension in the reactor was centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times. The suspension was then placed in a vacuum drying oven and dried at 70° C. for 6 hours to obtain hexagonal nano-bismuth telluride.

[0062] Example 3

[0063] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

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

[0065] (ii) After the reactor is cooled to room temperature, the obtained sample is taken out, centrifuged and washed three times with methanol and N,N-dimethylformamide respectively, and finally heated in a vacuum drying oven at 70° C. for 12 h to obtain a white powder, which is a bismuth-based metal organic framework.

[0066] S2, tellurite coordination transformation:

[0067] (i) preparing 400 mL of a 2 mol / L sodium telluride aqueous solution, adjusting the pH to 2 with hydrochloric acid, and then immersing 1 g of a bismuth-based metal-organic framework in the sodium telluride aqueous solution for 48 hours;

[0068] (ii) The transformed product was taken out and placed in a vacuum drying oven, the temperature was set to 80°C, the drying time was 8 hours, and the precursor was obtained, which was stored in a vacuum until use.

[0069] S3, calcination to remove organic conversion:

[0070] (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 30 minutes, then heating to 250°C at 10°C / min, keeping the temperature for 4 hours, and continuously passing oxygen;

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

[0072] S4. Solvothermal synthesis of bismuth telluride:

[0073] (i) taking 1 g of the product and placing it in a polytetrafluoroethylene reaction kettle, and adding 0.4 g of 75% sodium hydroxide, 0.5 g of polyvinyl pyrrolidone and 60 mL of ethylene glycol, and then placing the reaction kettle on a magnetic stirrer device for sufficient magnetic stirring;

[0074] (ii) The reactor was sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, set the temperature to 200°C, and kept warm for 12 hours. After the reaction was completed, the temperature dropped to room temperature and the reactor was taken out;

[0075] (iii) The suspension in the reactor was centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times. The suspension was then placed in a vacuum drying oven and dried at 80° C. for 8 h. Hexagonal nano-bismuth telluride was obtained.

[0076] Comparative Example 1

[0077] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

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

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

[0080] S2, tellurite coordination transformation:

[0081] (i) preparing 300 mL of a 1.5 mol / L sodium telluride aqueous solution, adjusting the pH to 1.5 with hydrochloric acid, and then immersing 0.75 g of a bismuth-based metal-organic framework in the sodium telluride aqueous solution for 36 hours;

[0082] (ii) Take out the transformed product and place it in a vacuum drying oven, set the temperature to 70°C, and dry it for 6 hours to obtain the precursor, which is then stored in a vacuum until use.

[0083] S3, calcination to remove organic conversion:

[0084] (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 25 minutes, then heating to 250°C at 7.5°C / min, keeping the temperature for 6 hours, and continuously passing oxygen;

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

[0086] S4. Solvothermal synthesis of bismuth telluride:

[0087] (i) 0.75 g of the product was placed in a polytetrafluoroethylene reactor, and 0.3 g of 75% sodium hydroxide, 0.4 g of polyvinyl pyrrolidone and 50 mL of ethylene glycol were added, and then the reactor was placed on a magnetic stirrer device for sufficient magnetic stirring;

[0088] (ii) The reactor was sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, set at 190°C, and kept warm for 8 hours. After the reaction was completed, the temperature dropped to room temperature and the reactor was taken out;

[0089] (iii) The suspension in the reactor was centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times. The suspension was then placed in a vacuum drying oven and dried at 70° C. for 6 hours to obtain hexagonal nano-bismuth telluride.

[0090] Comparative Example 2

[0091] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

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

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

[0094] S2, tellurite coordination transformation:

[0095] (i) preparing 300 mL of a 1.5 mol / L sodium telluride aqueous solution, adjusting the pH to 1.5 with hydrochloric acid, and then immersing 0.75 g of a bismuth-based metal-organic framework in the sodium telluride aqueous solution for 36 hours;

[0096] (ii) Take out the transformed product and place it in a vacuum drying oven, set the temperature to 70°C, and dry it for 6 hours to obtain the precursor, which is then stored in a vacuum until use.

[0097] S3. Solvothermal synthesis of bismuth telluride:

[0098] (i) 0.75 g of the precursor was placed in a polytetrafluoroethylene reactor, and 0.3 g of 75% sodium hydroxide, 0.4 g of polyvinyl pyrrolidone and 50 mL of ethylene glycol were added, and then the reactor was placed on a magnetic stirrer device for sufficient magnetic stirring;

[0099] (ii) The reactor was sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, set at 190°C, and kept warm for 8 hours. After the reaction was completed, the temperature dropped to room temperature and the reactor was taken out;

[0100] (iii) The suspension in the reactor was centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times. The suspension was then placed in a vacuum drying oven and dried at 70° C. for 6 hours to obtain hexagonal nano-bismuth telluride.

[0101] Comparative Example 3

[0102] S1. Preparation of Bismuth-based Metal-Organic Frameworks:

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

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

[0105] S2, tellurite coordination transformation:

[0106] (i) preparing 300 mL of a sodium telluride aqueous solution with a concentration of 0.8 mol / L, adjusting the pH to 1.5 with hydrochloric acid, and then immersing 0.75 g of a bismuth-based metal-organic framework in the sodium telluride aqueous solution for 36 hours;

[0107] (ii) Take out the transformed product and place it in a vacuum drying oven, set the temperature to 70°C, and dry it for 6 hours to obtain the precursor, which is then stored in a vacuum until use.

[0108] S3, calcination to remove organic conversion:

[0109] (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 25 minutes, then heating to 250°C at 7.5°C / min, keeping the temperature for 6 hours, and continuously passing oxygen;

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

[0111] S4. Solvothermal synthesis of bismuth telluride:

[0112] (i) 0.75 g of the product was placed in a polytetrafluoroethylene reactor, and 0.3 g of 75% sodium hydroxide, 0.4 g of polyvinyl pyrrolidone and 50 mL of ethylene glycol were added, and then the reactor was placed on a magnetic stirrer device for sufficient magnetic stirring;

[0113] (ii) The reactor was sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, set at 190°C, and kept warm for 8 hours. After the reaction was completed, the temperature dropped to room temperature and the reactor was taken out;

[0114] (iii) The suspension in the reactor was centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times. The suspension was then placed in a vacuum drying oven and dried at 70° C. for 6 hours to obtain hexagonal nano-bismuth telluride.

[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 obtained were recorded in the following table:

[0117] project Average particle size of bismuth telluride / nm Flaky rate / % Hexagon rate / % 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 the present invention, hexagonal flake bismuth telluride with an average particle size of 200 to 300 nm and a reasonable particle size distribution is obtained through metal organic framework template synthesis, and its thermoelectric performance far exceeds that of ordinary bismuth telluride materials;

[0119] Comparing Comparative Example 1 with Example 2, it can be seen that a large number of bismuth telluride nanocrystal seeds are generated in the same time compared with the low-concentration sodium hydroxide system in the high-concentration sodium hydroxide system, and then the nucleation rate and crystal growth rate of bismuth telluride are slowed down due to the simultaneous growth of a large number of nuclei, thereby producing more large-sized nanosheets and 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. These corrosive effects restrict the mutual migration between tellurium and bismuth to form a stable bismuth telluride compound, which increases the amorphous area inside the bismuth telluride nanosheet, so sodium hydroxide needs to be added and the amount needs to be moderate;

[0120] By comparing Comparative Example 2 with Example 2, it can be seen that the precursor is placed in a corundum crucible, the corundum crucible is placed in a tubular furnace, and a heating program is set. The initial room temperature is kept for 25 minutes, and then the temperature is set to 250°C at 7.5°C / min, and kept for 6 hours, and oxygen is continuously passed. After the furnace temperature drops to room temperature, the product is taken out and vacuum-packed for use. The purpose is to remove the organic matter therein and improve the thermoelectric performance of the final product while retaining the template.

[0121] By comparing Comparative Example 3 with Example 2, it can be seen that the concentration of the sodium tellurite aqueous solution should be selected appropriately. Too low a concentration will result in the coordination conversion to TeO3 of the bismuth-based metal organic framework. 2- If the concentration is insufficient, it will affect the subsequent synthesis of bismuth telluride; if the concentration is too high, it will inevitably affect the coordination conversion efficiency of the bismuth-based metal-organic framework in the sodium telluride aqueous solution.

[0122] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A process for preparing nano-bismuth telluride, characterized in that: The following steps are involved: S1. Preparation of Bismuth-based Metal-Organic Frameworks: (i) Weigh 3-4.5 mmol of 1,3,5-trimethylbenzene carboxylic acid and 1-1.5 mmol of bismuth nitrate pentahydrate and dissolve them in 80 mL of methanol solution. After vigorous stirring for 30-60 min, transfer them to a 100 ml polytetrafluoroethylene hydrothermal autoclave and heat them at 120° C. for 20-24 h. (ii) After the reactor is cooled to room temperature, the obtained sample is taken out, centrifuged and washed three times with methanol and N,N-dimethylformamide respectively, and finally dried in a vacuum drying oven to obtain a white powder, which is a bismuth-based metal organic framework. S2, tellurite coordination transformation: (i) preparing 200-400 mL of sodium tellurite aqueous solution, adjusting the pH to 1-2 with hydrochloric acid, and then immersing 0.5-1 g of bismuth-based metal-organic framework in the sodium tellurite aqueous solution for 24-48 hours; (ii) Take out the converted product and place it in a vacuum drying oven, set the temperature to 60-80°C, and dry it for 4-8 hours to obtain the precursor, which is then stored in a vacuum until use. S3, calcination to remove organic conversion: (i) placing the precursor in a corundum crucible, placing the corundum crucible in a tube furnace, setting a heating program, initially keeping the temperature at room temperature for 20 to 30 minutes, then setting the temperature to 250° C. at 5 to 10° C. / min, keeping the temperature for 2 to 6 hours, and continuously passing oxygen; (ii) After the furnace temperature drops to room temperature, take out the product and vacuum pack it for use. S4. Solvothermal synthesis of bismuth telluride: (i) taking 0.5-1 g of the product and placing it in a polytetrafluoroethylene reaction kettle, and adding 0.2-0.4 g of sodium hydroxide, 0.25-0.5 g of polyvinyl pyrrolidone and 40-60 mL of ethylene glycol, and then placing the reaction kettle on a magnetic stirrer device for sufficient magnetic stirring; (ii) the reactor is sealed in a stainless steel high-temperature jacket, placed in a heating sleeve with heat-conducting oil, the temperature is set to 180-200° C., and the temperature is kept for 4-12 hours. After the reaction is completed, the temperature is lowered to room temperature, and the reactor is taken out; (iii) The suspension in the reactor is centrifuged and then washed with water for three times, and then centrifuged and washed with ethanol for three times, and then placed in a vacuum drying oven with a drying temperature of 60 to 80° C. and a drying time of 4 to 8 hours, and hexagonal flake nano-bismuth telluride is obtained.

2. The process for preparing nano-bismuth telluride according to claim 1, characterized in that: In step S1, the vacuum drying oven is set at 60-70° C. and heated for 8-12 hours.

3. The process for preparing nano-bismuth telluride according to claim 1, characterized in that: The concentration of the sodium tellurite aqueous solution in step S2 is 1-2 mol / L.

4. The process for preparing nano-bismuth telluride according to claim 1, characterized in that: The concentration of sodium hydroxide in step S4 is 75%.

5. A nano-bismuth telluride, characterized in that: The invention is prepared by the preparation process described in any one of claims 1 to 4.

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