A method for producing lead iodide

Abstract

The application discloses a preparation method of lead iodide, and comprises the following steps: 1, adding ammonium acetate and glacial acetic acid into a lead acetate solution, adding ammonium hypophosphite into an ammonium iodide solution, and then respectively introducing argon to obtain a lead acetate pretreatment solution and an ammonium iodide pretreatment solution; 2, synchronously and slowly adding the ammonium iodide pretreatment solution and the lead acetate pretreatment solution into a preheated acidic bottom solution in parallel to aging to obtain a suspension; 3, washing the suspension; 4, performing pre-purification; and 5, performing gas phase sublimation purification to obtain the lead iodide. The application introduces the glacial acetic acid, the ammonium acetate and the ammonium hypophosphite, and synchronously adds the raw materials into the preheated acidic bottom solution in parallel to realize in-situ impurity suppression, combines a progressive impurity removal process of subsequent solvothermal pre-purification and gas phase sublimation purification, and isolates air in the whole material transfer process, so that high-purity lead iodide is prepared and is suitable for perovskite photoelectric and X-ray radiation detection fields.

Description

Technical Field

[0001] This invention belongs to the field of metal halide preparation technology, and in particular relates to a method for preparing lead iodide. Background Technology

[0002] Lead iodide is a key precursor material for the preparation of perovskite optoelectronic devices and X-ray radiation detection crystals. The purity, stoichiometry, and impurity content of lead iodide directly determine the film quality, carrier mobility, and signal-noise level of the radiation detection crystal.

[0003] The current mainstream industrial production of lead iodide is synthesis by precipitation from aqueous solution, followed by recrystallization or vacuum sublimation purification. The existing technology has many inherent defects: (1) Lead ions in the aqueous precipitation system are easily hydrolyzed to generate lead hydroxyiodide and lead oxide impurities; dissolved oxygen in the system oxidizes iodide ions to generate free iodine; the above impurities will be wrapped inside the lead iodide grains, and ordinary water washing can only remove surface impurities, while impurities embedded in the grains are difficult to remove; (2) Lead iodide with lead hydroxyiodide impurities is not completely dissolved in DMF (N,N-dimethylformamide) and DMSO (dimethyl sulfoxide) perovskite commonly used solvents, which will cause the leakage current of perovskite devices to increase and the photoelectric conversion efficiency to decrease; (3) Conventional solvent recrystallization has limited ability to remove trace metal impurities of Fe, Na, K and Ca, and the product yield is low; (4) The single vacuum sublimation process consumes a lot of energy, and the single sublimation is not thorough in removing impurities. It must be sublimated repeatedly to meet the purity index. Multiple sublimations bring serious material loss and significantly reduce the overall yield; and the particle size and morphology of the obtained products vary greatly from batch to batch, which is not conducive to large-scale stable production.

[0004] Therefore, there is an urgent need to develop a high-purity lead iodide preparation method that can meet the comprehensive requirements of high purity and batch stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing lead iodide. This method introduces glacial acetic acid, ammonium acetate, and ammonium hypophosphite, and uses a simultaneous and slow addition of preheated acidic base liquid to the raw materials to achieve in-situ impurity suppression. It is combined with a progressive impurity removal process of subsequent solvothermal pre-purification and gas-phase sublimation purification. Furthermore, air is isolated throughout the material transfer process, thus solving the problem that existing lead iodide preparation methods cannot simultaneously achieve high purity and batch stability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing lead iodide, characterized by comprising the following steps: Step 1: Add ammonium acetate to the lead acetate solution and then add glacial acetic acid to adjust the pH value. Add ammonium hypophosphite to the ammonium iodide solution and then pass argon gas through them to obtain lead acetate pretreatment solution and ammonium iodide pretreatment solution. Step 2: In an argon-protected environment, the ammonium iodide pretreatment solution and lead acetate pretreatment solution obtained in Step 1 are slowly added to the preheated acidic bottom solution in parallel and simultaneously, and stirred. Then, the solution is aged to obtain a suspension. Step 3: Wash the suspension obtained in Step 2 sequentially with hot water above 80°C, glacial acetic acid solution, and isopropanol to obtain the crude product; Step 4: Transfer the crude product obtained in Step 3 to a polytetrafluoroethylene-lined autoclave under air-isolated conditions, add a mixed solvent of isopropanol and DMF, repeat the vacuum-argon purging process, and then seal the polytetrafluoroethylene-lined autoclave for solvothermal prepurification to obtain the intermediate; the solvothermal prepurification method is as follows: keep at 110℃~130℃ for 7h~9h, cool down to 75℃~85℃ and then perform hot filtration, and wash the filtrate with isopropanol at 75℃~85℃; Step 5: Transfer the intermediate obtained in Step 4 to a sublimation apparatus under air-isolated conditions for vapor-phase sublimation purification to obtain lead iodide with a purity of not less than 99.997%; the heating temperatures for vapor-phase sublimation purification are successively: 385℃~400℃, 330℃~350℃ and 270℃~290℃.

[0007] This invention employs glacial acetic acid and ammonium acetate to regulate the lead acetate solution and ammonium hypophosphite to regulate the ammonium iodide solution during the synthesis stage, while purging with argon gas to remove dissolved oxygen. This controls the acidity of the solution while inhibiting the hydrolysis of lead ions and the oxidation of iodide ions. Simultaneously, a preheated acidic base solution is added slowly and concurrently, causing lead and iodide ions to mix and precipitate within the large volume of base solution. The ion ratio in the reaction micro-region approaches the stoichiometric ratio. The dilution and buffering effect of the acidic base solution smooths out local concentration peaks and inhibits explosive nucleation. This results in a slower crystal growth rate, allowing impurities adsorbed on the crystal surface sufficient time to desorb and enter the liquid phase. Combined with the preheating of the base solution to increase the ion diffusion rate and the weakly acidic conditions to inhibit the co-precipitation of basic lead salts, the risk of inclusions is further reduced. This inhibits hydroxyl lead iodide and free iodine in the crude product, reduces embedded impurities in the crystals, and alleviates the pressure of subsequent purification. At the same time, ammonium hypophosphite can also guide the directional growth of lead iodide crystals and reduce random agglomeration. The purification process then proceeds in two steps: First, a solvothermal pre-purification is performed using a mixed solvent of DMF (N,N-dimethylformamide) and isopropanol. Under high temperature conditions, lead iodide is dissolved and recrystallized, resulting in grain reconstruction. This releases the lead hydroxyl impurities and some trace metal impurities originally encapsulated within the grains. Temperature-controlled hot filtration retains these impurities in the mother liquor. Second, a gradient temperature vapor-phase sublimation purification process is conducted. The first stage temperature is controlled at 385℃~400℃ to allow the intermediate to sublimate, leaving high-boiling-point metal oxide impurities behind. The second stage temperature is controlled... The first stage temperature is 330℃~350℃, causing alkali metal salts and iron impurities to sublimate. The third stage temperature is controlled at 270℃~290℃, allowing lead iodide to sublimate and be collected. This gas-phase sublimation purification process, by precisely controlling the temperature of each stage and based on the differences in saturated vapor pressure of different substances, separates and collects impurities from lead iodide. This allows for the removal of alkali metals, iron impurities, and free iodine in a single sublimation, reducing energy consumption and minimizing material loss caused by repeated sublimation. Combined with the condition of isolating the entire material transfer process from air, secondary pollution from hydrolysis / oxidation is avoided, ultimately achieving the preparation of high-purity lead iodide.

[0008] The above-mentioned method for preparing lead iodide is characterized in that, in step one, the concentration of the lead acetate solution is 0.8 mol / L to 1.2 mol / L, 50 g to 150 g of ammonium acetate is added to each liter of the lead acetate solution, and the pH value is 1 to 4; the concentration of the ammonium iodide solution is 1.6 mol / L to 2.4 mol / L, the mass ratio of ammonium iodide to ammonium hypophosphite is 1:(0.015 to 0.02), and the molar ratio of lead acetate to ammonium iodide is 1:(2.01 to 2.05).

[0009] This invention controls the molar ratio of lead acetate to ammonium iodide to ensure sufficient iodide ions for the lead acetate to react as completely as possible. This not only improves the utilization rate of raw materials but also avoids unreacted lead ions remaining in the mother liquor, which would burden subsequent processing and cause environmental pollution. A slight excess of iodide ions creates a "common ion effect," reducing the solubility of lead iodide and promoting more complete precipitation. This effectively reduces impurities such as hydroxyl lead iodide generated by lead ion hydrolysis, thus improving product purity from the source. Furthermore, the specific mixing and addition method of this application can reduce the excess of iodide ions, reduce impurity encapsulation, and inhibit iodine complexation side reactions.

[0010] The above-mentioned method for preparing lead iodide is characterized in that, in step two, the temperature of the preheated acidic base solution is 45℃~60℃, the acidic base solution is an acetic acid solution with a pH value of 2~4, the slow addition rate is 4mL / min~7mL / min, the aging process temperature is 65℃~80℃, and the aging time is 4h~8h. The method of simultaneous and slow addition is as follows: the outlets of the ammonium iodide pretreatment solution and the lead acetate pretreatment solution are kept at the same horizontal height and submerged below the surface of the acidic bottom solution, and the horizontal distance between the two outlets is set to 5mm~15mm.

[0011] This invention effectively reduces the formation of hydroxyl lead iodide and impurities encapsulated in the mother liquor by simultaneously and slowly adding ammonium iodide pretreatment solution and lead acetate pretreatment solution to an acidic base solution, while controlling the rate and temperature during the adding and aging processes. By immersing the outlet below the liquid surface, it avoids droplets falling from the air into the liquid, preventing splashing and localized over-concentration. By setting a horizontal spacing of 5mm to 15mm, it ensures that the two outlets are both located in the stirred fluid circulation area and maintain an appropriate distance, preventing direct contact and reaction between lead salt solution and iodine salt solution at the nozzle when the outlets are close together, and preventing localized enrichment of single ions and loss of control over localized supersaturation when the outlets are too far apart. Ultimately, this synergistic and synchronous approach achieves the effects of preventing clogging, reducing localized supersaturation, and reducing the inclusion of precipitated impurities.

[0012] The above-mentioned method for preparing lead iodide is characterized in that the volume ratio of isopropanol to DMF in step four is (3.2~2.8):1, and the solid-liquid ratio of the crude product to the mixed solvent is 1g:(2mL~3mL).

[0013] This invention controls the volume ratio of isopropanol to DMF and the solid-liquid ratio of the crude product to the mixed solvent of isopropanol and DMF. This ensures that sufficient DMF can penetrate and dissolve the crude lead iodide crystals, releasing impurities trapped within the crystal lattice. It also avoids insufficient mixed solvent, which would make the system too viscous and prevent impurities from dissolving and diffusing sufficiently, and excessive mixed solvent, which would cause more lead iodide to dissolve in the mother liquor after hot filtration, thus reducing the yield.

[0014] The above-mentioned method for preparing lead iodide is characterized in that the cooling rate to 75℃~85℃ in step four is 1℃ / h~3℃ / h.

[0015] This invention enables the controlled precipitation of lead iodide by controlling the thermal filtration temperature and cooling rate, thereby improving the efficiency of pre-purification.

[0016] The above-mentioned method for preparing lead iodide is characterized in that the sublimation device in step five includes a sublimation component and a heating device. The sublimation component is a quartz glass tube, and the quartz glass tube is arranged in a horizontal direction with an evaporation zone, a first condensation zone, a second condensation zone, and a third condensation zone connected in sequence. The evaporation zone has an air inlet at the end away from the first condensation zone, and the air inlet is equipped with a pressure gauge. The third condensation zone has an air outlet at the end away from the second condensation zone. The length ratio of the evaporation zone, the first condensation zone, and the second condensation zone is 90:(84~88):(78~89), and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone is 1:(4.9~5.1).

[0017] The above-mentioned method for preparing lead iodide is characterized in that argon gas with a flow rate of 10 sccm to 20 sccm is introduced during the gas-phase sublimation purification process in step five.

[0018] The above-mentioned method for preparing lead iodide is characterized in that, before the gas-phase sublimation purification in step five, the sublimation device is repeatedly subjected to vacuuming and argon purging.

[0019] The above-mentioned method for preparing lead iodide is characterized in that the lead iodide in step five is subjected to vacuum drying, wherein the vacuum drying temperature is 120℃~140℃ and the vacuum drying time is 4h~6h.

[0020] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a synergistic process of "in-situ impurity suppression and synthesis of crude lead iodide - solvothermal pre-purification - temperature gradient gas-phase sublimation purification - air-isolated material transfer" to suppress impurities at the source, advance the impurity removal pressure to the synthesis stage, reduce the difficulty of subsequent purification, and prepare high-purity lead iodide, thereby ensuring the purity and particle size stability of batch products.

[0021] 2. This invention designs a sublimation device with horizontally partitioned sections and sets an inlet and an outlet at each end of the device to introduce argon gas during the gas-phase sublimation purification process, maintain a slight positive pressure in the pipeline to prevent external air from entering, and suppress the decomposition of lead iodide into lead and iodine vapor at high temperatures through the partial pressure effect; at the same time, it can also act as a carrier gas to control the direction of vapor migration, directionally transporting the vapor in the evaporation zone to each temperature zone, and achieve deep purification in a single sublimation by combining flow rate and pressure control.

[0022] 3. The present invention introduces water-soluble small molecule salts into the raw material solution, which can be completely washed away in the subsequent precipitation and washing steps, and will not remain in the lead iodide precipitate, thus not affecting the purity of the finished product.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the sublimation apparatus used in this invention.

[0025] Figure 2 This is a schematic diagram of the sublimation component in the sublimation apparatus used in this invention.

[0026] Figure 3This is a physical image of lead iodide prepared in Example 1 of the present invention.

[0027] Figure 4 The image shows the XRD pattern of lead iodide prepared in Example 1 of this invention.

[0028] Explanation of reference numerals in the attached figures: 1—Sublimation component; 11—Evaporation zone; 12—First condensation zone; 13—Second condensation zone; 131—Thermocouple; 14—Third condensation zone; 141—Circulating liquid cooling pipe; 15—Air inlet; 16—Air outlet; 17—Control valve; 2—Heating equipment. Detailed Implementation

[0029] The sublimation apparatus used in Embodiments 1 to 7 of this invention is as follows: Figure 1 and Figure 2 As shown, the sublimation apparatus includes a sublimation component 1 and a heating device 2. The sublimation component 1 is a quartz glass tube, which is horizontally divided into an evaporation zone 11, a first condensation zone 12, a second condensation zone 13, and a third condensation zone 14. The heating device 2 is a dual-temperature zone independently controlled tubular furnace, with two independent heating chambers respectively fitted outside the evaporation zone 11 and the first condensation zone 12. The second condensation zone 13 and the third condensation zone 14 extend out of the dual-temperature zone independently controlled tubular furnace. A thermocouple 131 for temperature detection is installed in the middle of the axis of the second condensation zone 13. The length ratio of the evaporation zone 11, the first condensation zone 12, and the second condensation zone 13 is 90:(84~88):(78~89), and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone 11 is 1:(4.9~5.1). By controlling the length ratio of the evaporation zone 11, the first condensation zone 12, and the second condensation zone 13, and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone 11, it is possible to ensure that the lead iodide in the intermediate is fully sublimated in the evaporation zone 11, and that the alkali metal salts and iron impurities are fully condensed in the first condensation zone 12, thereby ensuring the impurity removal efficiency while ensuring the yield. The evaporation zone 11 is provided with an air inlet 15 at the end away from the first condensation zone 12. The air inlet 15 is equipped with a pressure gauge and a safety relief valve connected in parallel (opening pressure is 150Pa). The third condensation zone 14 is provided with an air outlet 16 at the end away from the second condensation zone 13. Both the air inlet 15 and the air outlet 16 are equipped with control valves 17 for assisting in adjusting the internal pressure of the quartz glass tube. The evaporation zone 11, the first condensation zone 12, the second condensation zone 13, and the third condensation zone 14 are connected by ground joints. The third condensation zone 14 is provided with a circulating liquid cooling pipe 141, and a coolant, which is an aqueous solution of ethylene glycol or propylene glycol, flows through the circulating liquid cooling pipe 141. The evaporation zone 11 is provided with a sealable inlet for placing intermediates.

[0030] Example 1 The preparation method of this embodiment includes the following steps: Step 1: Add ammonium acetate to a 1.0 mol / L lead acetate solution, then add glacial acetic acid to adjust the pH to 3. Add ammonium hypophosphite to a 2.05 mol / L ammonium iodide solution, and then bubble with argon gas for 30 minutes to obtain lead acetate pretreatment solution and ammonium iodide pretreatment solution. Add 100 g of ammonium acetate to each liter of the lead acetate solution, and the mass ratio of ammonium iodide to ammonium hypophosphite is 1:0.015. Step 2: In an argon-protected environment, the outlets of the ammonium iodide pretreatment solution and lead acetate pretreatment solution obtained in Step 1 are kept at the same horizontal height and submerged 15 mm below the surface of the acetic acid solution with a pH of 3 (the position is higher than the folding blade). The horizontal distance between the two outlets is set to 15 mm, positioned between the outer edge of the folding blade and the container wall, with the outlets maintaining a distance of 20 mm from the outer edge of the folding blade. Then, the ammonium iodide pretreatment solution and lead acetate pretreatment solution are added slowly and synchronously at a rate of 7 mL / min, while stirring at a rate of 500 rpm to form a radial-axial composite circulation flow, ensuring that the liquid can be immediately entrained, diluted, and dispersed by the circulating fluid after flowing out. Then, the solution is aged at 75°C under argon protection for 6 hours to obtain a suspension. The acetic acid solution is preheated to 50°C and maintained at 50°C throughout the addition of the ammonium iodide pretreatment solution and lead acetate pretreatment solution. Step 3: The suspension obtained in Step 2 is washed sequentially with hot water above 80°C, glacial acetic acid solution, and isopropanol to obtain the crude product; the washing is performed twice with hot water above 80°C, three times with glacial acetic acid solution, and twice with isopropanol. Step 4: Transfer the crude product obtained in Step 3 to a polytetrafluoroethylene-lined autoclave under air-isolated conditions, add a mixed solvent of isopropanol and DMF, repeat the vacuum-argon purging process 3 times, then seal the polytetrafluoroethylene-lined autoclave for solvothermal prepurification to obtain an intermediate; the solvothermal prepurification method is as follows: keep at 120℃ for 8 hours, cool down to 75℃ at a rate of 2℃ / h for hot filtration to obtain mother liquor and filtrate, wash the filtrate twice with isopropanol at 75℃, the volume ratio of isopropanol to DMF is 3:1, and the solid-liquid ratio of the crude product to the mixed solvent is 1g:2.5mL; Step 5: Transfer the intermediate obtained in Step 4 to a sublimation apparatus under air-isolated conditions for gas-phase sublimation purification, to obtain the following... Figure 3The lead iodide shown; the specific method for gas-phase sublimation purification is as follows: the intermediate is transferred and spread evenly in evaporation zone 11, and the thickness of the intermediate spread is controlled to ≤4mm to ensure sufficient sublimation of lead iodide. Then, the vacuum-argon purging process is repeated 3 times to make the vacuum degree lower than -0.06MPa. The temperatures of evaporation zone 11, first condensation zone 12, second condensation zone 13 and third condensation zone 14 are set to 390℃, 340℃ and 280℃ respectively (since the second condensation zone 13 extends out of the dual-temperature zone independently controlled tube furnace, the temperature of the second condensation zone 13 is...). The temperature of 280℃ is the temperature at thermocouple 131. In fact, the temperature is gradually reduced along the vapor flow direction, which can buffer the temperature fluctuation of the upstream gas phase and improve the process tolerance. At -25℃, argon gas with a flow rate of 10 sccm is introduced through the gas inlet 15 and the gas outlet 16 is opened. The pressure gauge reading is controlled at 30Pa~100Pa. After the gas phase sublimation and purification is completed, the dual-temperature zone independent temperature-controlled tube furnace and the gas inlet 15 are closed. After natural cooling, the lead iodide condensed in the second condensation zone 13 is collected and discharged through the glove box. Then, it is vacuum dried at 120℃ for 5 hours. In this embodiment, the length ratio of the evaporation zone 11, the first condensation zone 12, and the second condensation zone 13 is 90:85:89, and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone 11 is 1:5.1.

[0031] The XRD pattern of lead iodide prepared in this embodiment is as follows: Figure 4 As shown, the main component of this lead iodide is PbI2; the results of the component analysis of this lead iodide are shown in Table 1.

[0032] Table 1. Element content (ppm) of lead iodide metal impurities in Example 1

[0033] As shown in Table 1, the total metal impurity element content in the lead iodide prepared in this embodiment is <30ppm, and the purity is 99.997%. The test results show that the lead iodide is free of lead hydroxyl iodide, and the yield is 75.3%.

[0034] Comparative Example 1 The preparation method of this comparative example includes the following steps: Step 1: Add 2.1 mol / L ammonium iodide solution dropwise to 1.0 mol / L lead acetate solution at 50℃ at a rate of 7 mL / min, and age at 50℃ for 6 h to obtain a suspension; Step 2: The suspension obtained in Step 1 is washed sequentially with glacial acetic acid solution and isopropanol to obtain the crude product; the glacial acetic acid solution is used for washing 3 times and isopropanol is used for washing 2 times. Step 3: Sublimate the crude product obtained in Step 2 three times at 350℃ to obtain lead iodide.

[0035] Upon testing, the purity of lead iodide prepared in this comparative example was 99.980%, with the presence of hydroxyl lead iodide and a yield of 66.2%. Compared with Example 1, both the purity and yield of lead iodide decreased significantly, and hydroxyl lead iodide was present in the product.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that in step three, the crude product is sublimated three times at 350°C to obtain lead iodide.

[0037] Upon testing, the purity of lead iodide prepared in this comparative example was 99.990%, with the presence of hydroxyl lead iodide and a yield of 66.8%. Compared with Example 1, both the purity and yield of lead iodide decreased significantly.

[0038] Example 2 The preparation method of this embodiment includes the following steps: Step 1: Add ammonium acetate to a 0.8 mol / L lead acetate solution, then add glacial acetic acid to adjust the pH to 4. Add ammonium hypophosphite to a 1.61 mol / L ammonium iodide solution, and then bubble with argon gas for 25 min to obtain lead acetate pretreatment solution and ammonium iodide pretreatment solution. Add 50 g of ammonium acetate to each liter of the lead acetate solution, and the mass ratio of ammonium iodide to ammonium hypophosphite is 1:0.016. Step 2: In an argon-protected environment, keep the outlets of the ammonium iodide pretreatment solution and lead acetate pretreatment solution obtained in Step 1 at the same horizontal height, immersing them 10 mm below the surface of the acetic acid solution with a pH of 2 (the position is higher than the folding blade). The horizontal distance between the two outlets is set to 10 mm, positioned between the outer edge of the folding blade and the container wall, with the outlets maintaining a distance of 15 mm from the outer edge of the folding blade. Then, add the ammonium iodide pretreatment solution and lead acetate pretreatment solution simultaneously and slowly at a rate of 5 mL / min, while stirring at a rate of 300 rpm to form a radial-axial composite circulation flow, ensuring that the liquid can be immediately entrained, diluted, and dispersed by the circulating fluid after flowing out. Then, age the solution at 65°C under argon protection for 4 hours to obtain a suspension. The acetic acid solution is preheated to 45°C and maintained at 45°C throughout the addition of the ammonium iodide pretreatment solution and lead acetate pretreatment solution. Step 3: The suspension obtained in Step 2 is washed sequentially with hot water above 80°C, glacial acetic acid solution, and isopropanol to obtain the crude product; the washing is performed 3 times with hot water above 80°C, 4 times with glacial acetic acid solution, and 3 times with isopropanol. Step 4: Transfer the crude product obtained in Step 3 to a polytetrafluoroethylene-lined autoclave under air-isolated conditions, add a mixed solvent of isopropanol and DMF, repeat the vacuum-argon purging process 4 times, then seal the polytetrafluoroethylene-lined autoclave for solvothermal prepurification to obtain an intermediate; the solvothermal prepurification method is as follows: keep at 110℃ for 7h, cool down to 85℃ at a rate of 3℃ / h for hot filtration to obtain mother liquor and filtrate, wash the filtrate twice with isopropanol at 85℃, the volume ratio of isopropanol to DMF is 3.2:1, and the solid-liquid ratio of the crude product to the mixed solvent is 1g:2mL; Step 5: Transfer the intermediate obtained in Step 4 to a sublimation apparatus under air-isolated conditions for gas-phase sublimation purification to obtain lead iodide. The gas-phase sublimation purification method is as follows: the intermediate is transferred and spread evenly in evaporation zone 11, and the thickness of the intermediate spread is controlled to ≤4mm to ensure sufficient sublimation of lead iodide. Then, the vacuum-argon purging process is repeated 3 times to achieve a vacuum degree below -0.06MPa. Evaporation zone 11, first condensation zone 12, second condensation zone 13, and third condensation zone 14 are set up. The temperatures of condensation zone 14 are 385℃, 330℃, 270℃ (temperature at thermocouple 131) and -10℃ respectively. At the same time, argon gas with a flow rate of 12 sccm is introduced through inlet 15 and outlet 16 is opened, and the pressure gauge reading is controlled at 30Pa~100Pa. After the gas phase sublimation and purification is completed, the dual-temperature zone independent temperature-controlled tube furnace and inlet 15 are closed. After natural cooling, the lead iodide condensed in the second condensation zone 13 is collected, discharged through the glove box, and then vacuum dried at 130℃ for 4 hours. In this embodiment, the length ratio of the evaporation zone 11, the first condensation zone 12, and the second condensation zone 13 is 90:84:82, and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone 11 is 1:5.

[0039] Upon testing, the purity of lead iodide prepared in this example was 99.998%, and no hydroxyl lead iodide was detected, with a yield of 75.6%.

[0040] Example 3 The preparation method of this embodiment includes the following steps: Step 1: Add ammonium acetate to a 1.1 mol / L lead acetate solution, then add glacial acetic acid to adjust the pH to 1. Add ammonium hypophosphite to a 2.24 mol / L ammonium iodide solution, and then bubble with argon gas for 35 minutes to obtain lead acetate pretreatment solution and ammonium iodide pretreatment solution. Add 150 g of ammonium acetate to each liter of the lead acetate solution, and the mass ratio of ammonium iodide to ammonium hypophosphite is 1:0.02. Step 2: In an argon-protected environment, the outlets of the ammonium iodide pretreatment solution and lead acetate pretreatment solution obtained in Step 1 are kept at the same horizontal height and submerged 20 mm below the surface of the acetic acid solution with a pH of 4 (positioned above the folding impeller). The horizontal distance between the two outlets is set to 5 mm, positioned between the outer edge of the folding impeller and the container wall, with the outlets maintaining a distance of 15 mm from the outer edge of the folding impeller. Then, the ammonium iodide pretreatment solution and lead acetate pretreatment solution are added simultaneously and slowly at a rate of 4 mL / min, while stirring at a rate of 450 rpm to form a radial-axial composite circulation flow, ensuring that the liquid can be immediately entrained, diluted, and dispersed by the circulating fluid after flowing out. Then, the solution is aged at 80°C under argon protection for 8 hours to obtain a suspension. The acetic acid solution is preheated to 60°C and maintained at 60°C throughout the addition of the ammonium iodide pretreatment solution and lead acetate pretreatment solution. Step 3: The suspension obtained in Step 2 is washed sequentially with hot water above 80°C, glacial acetic acid solution, and isopropanol to obtain the crude product; wherein the washing is performed once with hot water above 80°C, four times with glacial acetic acid solution, and three times with isopropanol. Step 4: Transfer the crude product obtained in Step 3 to a polytetrafluoroethylene-lined autoclave under air-isolated conditions, add a mixed solvent of isopropanol and DMF, repeat the vacuum-argon purging process 4 times, then seal the polytetrafluoroethylene-lined autoclave for solvothermal prepurification to obtain an intermediate; the solvothermal prepurification method is as follows: keep at 130℃ for 9 hours, cool down to 80℃ at a rate of 2℃ / h for hot filtration to obtain mother liquor and filtrate, wash the filtrate 3 times with isopropanol at 80℃, the volume ratio of isopropanol to DMF is 2.8:1, and the solid-liquid ratio of the crude product to the mixed solvent is 1g:3mL; Step 5: Transfer the intermediate obtained in Step 4 to a sublimation apparatus under air-isolated conditions for gas-phase sublimation purification to obtain lead iodide. The gas-phase sublimation purification method is as follows: the intermediate is transferred and spread evenly in evaporation zone 11, and the thickness of the intermediate spread is controlled to ≤4mm to ensure sufficient sublimation of lead iodide. Then, the vacuum-argon purging process is repeated 3 times to achieve a vacuum degree below -0.06MPa. Evaporation zone 11, first condensation zone 12, second condensation zone 13, and third condensation zone 14 are set up. The temperatures of condensation zone 14 are 400℃, 350℃, 290℃ (temperature at thermocouple 131) and -30℃ respectively. At the same time, argon gas with a flow rate of 20 sccm is introduced through inlet 15 and outlet 16 is opened, and the pressure gauge reading is controlled between 30 Pa and 100 Pa. After the gas phase sublimation and purification are completed, the dual-temperature zone independently temperature-controlled tube furnace and inlet 15 are closed. After natural cooling, the lead iodide condensed in the second condensation zone 13 is collected, discharged through the glove box, and then vacuum dried at 140℃ for 5 hours. In this embodiment, the length ratio of the evaporation zone 11, the first condensation zone 12, and the second condensation zone 13 is 90:88:78, and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone 11 is 1:4.9.

[0041] Upon testing, the lead iodide prepared in this example had a purity of 99.999% and no hydroxyl lead iodide was detected, with a yield of 75.4%.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is that: in step one, the concentration of lead acetate solution is 1.18 mol / L, the concentration of ammonium iodide solution is 2.4 mol / L, 90 g of ammonium acetate is added to each liter of lead acetate solution, and the mass ratio of ammonium iodide to ammonium hypophosphite is 1:0.018.

[0043] Upon testing, the purity of lead iodide prepared in this example was 99.997%, and no hydroxyl lead iodide was detected, with a yield of 75.1%.

[0044] Example 5 The difference between this embodiment and Embodiment 1 is that the cooling rate of the solvothermal prepurification in step four is 1℃ / h.

[0045] Upon testing, the purity of lead iodide prepared in this example was 99.998%, and no hydroxyl lead iodide was detected, with a yield of 75.7%.

[0046] Example 6 The difference between this embodiment and embodiment 2 is that the temperature of the third condensation zone 14 in step five is -40°C, the temperature of vacuum drying is 140°C, and the duration of vacuum drying is 6 hours.

[0047] Upon testing, the purity of lead iodide prepared in this example was 99.998%, and no hydroxyl lead iodide was detected, with a yield of 75.5%.

[0048] Example 7 The difference between this embodiment and Embodiment 2 is that the volume ratio of isopropanol to DMF in step four is 3:1.

[0049] Upon testing, the purity of lead iodide prepared in this example was 99.999%, and no hydroxyl lead iodide was detected, with a yield of 75.7%.

[0050] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing lead iodide, characterized in that, Includes the following steps: Step 1: Add ammonium acetate to the lead acetate solution and then add glacial acetic acid to adjust the pH value. Add ammonium hypophosphite to the ammonium iodide solution and then pass argon gas through them to obtain lead acetate pretreatment solution and ammonium iodide pretreatment solution. Step 2: In an argon-protected environment, the ammonium iodide pretreatment solution and lead acetate pretreatment solution obtained in Step 1 are slowly added to the preheated acidic bottom solution in parallel and simultaneously, and stirred. Then, the solution is aged to obtain a suspension. Step 3: Wash the suspension obtained in Step 2 sequentially with hot water above 80°C, glacial acetic acid solution, and isopropanol to obtain the crude product; Step 4: Transfer the crude product obtained in Step 3 to a polytetrafluoroethylene-lined autoclave under air-isolated conditions, add a mixed solvent of isopropanol and DMF, repeat the vacuum-argon purging process, and then seal the polytetrafluoroethylene-lined autoclave for solvothermal prepurification to obtain the intermediate; the solvothermal prepurification method is as follows: keep at 110℃~130℃ for 7h~9h, cool down to 75℃~85℃ and then perform hot filtration, and wash the filtrate with isopropanol at 75℃~85℃; Step 5: Transfer the intermediate obtained in Step 4 to a sublimation apparatus under air-isolated conditions for vapor-phase sublimation purification to obtain lead iodide with a purity of not less than 99.997%; the vapor-phase sublimation purification temperature includes 385℃~400℃, 330℃~350℃ and 270℃~290℃ set sequentially.

2. The method for preparing lead iodide according to claim 1, characterized in that, In step one, the concentration of the lead acetate solution is 0.8 mol / L to 1.2 mol / L, and 50 g to 150 g of ammonium acetate is added to each liter of the lead acetate solution. The pH value is 1 to 4. The concentration of the ammonium iodide solution is 1.6 mol / L to 2.4 mol / L, the mass ratio of ammonium iodide to ammonium hypophosphite is 1:(0.015 to 0.02), and the molar ratio of lead acetate to ammonium iodide is 1:(2.01 to 2.05).

3. The method for preparing lead iodide according to claim 1, characterized in that, In step two, the temperature of the preheated acidic base solution is 45℃~60℃, the acidic base solution is an acetic acid solution with a pH value of 2~4, and the slow addition rate is 4mL / min~7mL / min; the temperature of the aging process is 65℃~80℃, and the aging time is 4h~8h. The method of simultaneous and slow addition is as follows: the outlets of the ammonium iodide pretreatment solution and the lead acetate pretreatment solution are kept at the same horizontal height and submerged below the surface of the acidic bottom solution, and the horizontal distance between the two outlets is set to 5mm~15mm.

4. The method for preparing lead iodide according to claim 1, characterized in that, In step four, the volume ratio of isopropanol to DMF is (3.2~2.8):1, and the solid-liquid ratio of the crude product to the mixed solvent is 1g:(2mL~3mL).

5. The method for preparing lead iodide according to claim 1, characterized in that, The cooling rate to 75℃~85℃ in step four is 1℃ / h~3℃ / h.

6. The method for preparing lead iodide according to claim 1, characterized in that, The sublimation device mentioned in step five includes a sublimation component (1) and a heating device (2). The sublimation component (1) is a quartz glass tube. The quartz glass tube is connected in the horizontal direction to an evaporation zone (11), a first condensation zone (12), a second condensation zone (13), and a third condensation zone (14). An air inlet (15) is provided at the end of the evaporation zone (11) away from the first condensation zone (12). A pressure gauge is provided at the air inlet (15). An air outlet (16) is provided at the end of the third condensation zone (14) away from the second condensation zone (13). The length ratio of the evaporation zone (11), the first condensation zone (12), and the second condensation zone (13) is 90:(84~88):(78~89), and the ratio of the inner diameter of the quartz glass tube to the length of the evaporation zone (11) is 1:(4.9~5.1).

7. The method for preparing lead iodide according to claim 6, characterized in that, The third condensation zone (14) is provided with a circulating liquid cooling pipe (141), and coolant is circulated in the circulating liquid cooling pipe (141). The temperature of the third condensation zone (14) is -10℃ to -40℃.

8. The method for preparing lead iodide according to claim 1, characterized in that, In step five, argon gas is introduced at a flow rate of 10 sccm to 20 sccm during the gas-phase sublimation purification process.

9. The method for preparing lead iodide according to claim 1, characterized in that, Before the gas-phase sublimation purification described in step five, the sublimation device is repeatedly subjected to vacuuming and argon purging.

10. The method for preparing lead iodide according to claim 1, characterized in that, The lead iodide described in step five is subjected to vacuum drying at a temperature of 120°C to 140°C for a duration of 4 to 6 hours.

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