Preparation method of tunable bismuth-based heterojunction photocatalytic materials

Abstract

This invention discloses a method for preparing tunable bismuth-based heterojunction photocatalytic materials, which introduces a low-melting-point molten salt. Bismuth silicate is calcined in the molten salt medium and then reacted with acid to form Bi... 12 ‑X(X=Bi2‑BiOCl,BiOCl)(Bi 12 =Bi 12 SiO 20 Bi2=Bi2SiO5) multi-heterogeneous catalytic materials. By regulating Bi2, Bi 12 The crystal phase ratio can effectively control the band gap position and suppress electron-hole recombination. Simultaneously, the catalyst morphology changes from particulate aggregates to a flower-like structure of stacked nanosheets, which is beneficial for the catalytic reaction. The heterogeneous photocatalyst obtained using the method of this invention has a simple preparation process, requires low temperature, and has low material cost. It also has numerous active sites, can be reused multiple times during degradation, and exhibits good performance, making it a promising candidate for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, and specifically relates to a method for preparing tunable bismuth-based heterojunction photocatalytic materials. Background Technology

[0002] Bismuth silicate is an extremely important photocatalytic composite material, possessing excellent photogenerated carrier mobility and strong photogenerated hole oxidation resistance. Bismuth oxychloride is a semiconductor material with a suitable band structure, and both exhibit photocatalytic properties. In practical applications, the individual sheet structures formed during the preparation of bismuth silicate are too large, and severe layer-by-layer stacking occurs. Bismuth oxychloride suffers from a large band gap and insufficient stability, both of which significantly reduce their photocatalytic efficiency. Therefore, composite structures formed with other materials are one means to improve photocatalytic efficiency.

[0003] Current technologies still cannot effectively control heterostructures, and the resulting heterostructures suffer from instability and uncontrollable performance, which significantly limits the performance of photocatalysis. Furthermore, most existing technologies remain at the laboratory stage, producing materials that are prone to aggregation, have low yields, and require long experimental cycles, preventing their expansion into industrial applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of complex preparation and difficult process in the prior art, and to provide a method for preparing tunable bismuth-based multi-heterojunction photocatalytic materials. The resulting catalyst material has many active sites, which can improve the utilization rate of light, has high catalytic activity, and good dispersibility. It can rapidly degrade organic pollutants in water. At the same time, the raw materials are readily available, the process is simple, and the preparation can be controlled, which is expected to be put into industrial production.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a tunable bismuth-based heterojunction photocatalytic material includes the following steps:

[0007] Step 1: Mix and grind Bi2O3, SiO2, K2CO3, and KCl until homogeneous; wherein the molar ratio of Bi2O3 to SiO2 is 1:1 to 9:1, the molar ratio of K2CO3 to KCl is 0.30:0.65 to 0.35:0.73, and K2CO3 and KCl account for 35wt% to 45wt% of the total mixture.

[0008] Step 2: Calcine the material that was mixed and ground evenly in Step 1 at 620℃~750℃ for 0.5h~3h and then cool it.

[0009] Step 3: Obtain the tunable bismuth-based heterojunction photocatalyst material using one of the following methods:

[0010] Method 1: Add water to the material obtained in step 2 and adjust the pH to 0.5-1.5, stir in a water bath, centrifuge and dry to obtain the final product;

[0011] Method 2: Wash the material obtained in step 2 with water and alcohol alternately several times, then dry it; add water and adjust the pH to 1-3, add salt, stir in a water bath, centrifuge and dry to obtain the final product.

[0012] In one embodiment, step one involves mixing and ball milling for 3 to 8 hours.

[0013] In one embodiment, in step one, K2CO3 combines with KCl to form a complex salt, denoted as K2CO3-KCl.

[0014] In one embodiment, in step two, the heating rate is set to 5°C / min during calcination, and the temperature is maintained for 0.5h to 3h after reaching the calcination temperature.

[0015] In one embodiment, in method one, 0.5g to 3g of the material obtained in step two is weighed, 80mL to 150mL of water is added, then acid is added to adjust the pH to 0.5 to 1.5, the mixture is stirred for 10min to 30min, centrifuged 3 to 5 times, and the water bath conditions are: stirring at 30℃ for 10min to 30min.

[0016] In one embodiment, in method two, 0.1g to 0.35g of the material obtained in step two is weighed, washed repeatedly with alternating water and alcohol, and then dried; then 30mL to 50mL of water is added, stirred for 1h to 2h, acid is added to adjust the pH to 1 to 3, 5mL to 60mL of salt solution with a concentration of 1g / L to 3g / L is added, stirred for 10min to 40min, and then centrifuged 3 to 5 times.

[0017] In one embodiment, the salt added in method two is one or more of NaCl, NaBr, LiCl, and ZnCl2.

[0018] In one embodiment, the water bath conditions for Method 2 are: stirring at 30°C for 30 to 40 minutes.

[0019] The method for preparing tunable bismuth-based heterojunction photocatalysts of this invention yields tunable bismuth-based heterojunction photocatalysts that can be used as catalysts for wastewater treatment. These materials purify water by decomposing organic matter and pollutants in the water.

[0020] Industrial production processes may generate a lot of industrial wastewater, including many organic dyes. By directly adding the photocatalyst prepared in this invention into the industrial wastewater, organic matter and pollutants in the water can be decomposed through surface adsorption and oxidation, thereby reducing its pollution to the environment.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. In this invention, Bi is formed during the reaction by adding molten salt (e.g., K2CO3-KCl). 12 The type II heterojunction structure of -X (X = Bi2-BiOCl, BiOCl) enables effective separation of photogenerated carriers. Furthermore, the introduction of X to form the heterojunction generates oxygen vacancies, leading to adsorbed oxygen. Simultaneously, by adding molten salt to induce a displacement reaction, the crystallization process can be controlled, precisely regulating the proportion of the generated crystalline phases. This, in turn, controls the chemical reaction process, activates the catalyst surface, and generates more active functional groups, making it easier to generate oxygen vacancies and adsorb oxygen.

[0023] 2. The molten salt introduced in this invention can form bismuth oxyhalide with the generated bismuth groups during the reaction. Adjusting the formation of the heterojunction during this process affects the positions of the valence and conduction bands of the catalyst, thereby controlling the band gap and altering its position. The prepared bismuth silicate exhibits a significantly narrower band gap. By introducing bismuth oxychloride, the band gap of the catalyst can be altered as needed, reducing the recombination rate of photogenerated carriers. Simultaneously, defect energy levels are generated during the reaction through the introduction of defects, facilitating the transition and separation of photogenerated carriers.

[0024] 3. The method used in this invention is simple. By adding molten salt, the reaction temperature can be effectively reduced, the particle size of the material can be decreased, the reaction can be easily controlled, and the Bi2 and Bi2 ratios can be effectively regulated. 12 The crystal phase ratio is optimized to better react with halogens in molten salt, thereby improving the performance of the prepared material. The operation process is simple, reduces energy consumption during the reaction, and can be used in actual production.

[0025] 4. In this invention, a heterogeneous catalytic material is generated by introducing molten salt. The reaction temperature is low, the operation process is simple, the preparation cycle is moderate, and the material cost is not high. The prepared catalytic material can improve its performance while ensuring the yield and is not prone to agglomeration, providing a new approach to realizing the transition from laboratory to industrialization. Attached Figure Description

[0026] Figure 1 The image shows a flower-like SEM image formed by the stacking of modified nanosheets.

[0027] Figure 2The diagram shows the photocatalytic degradation of Rhodamine B by photocatalysts prepared in one-step and two-step methods. Detailed Implementation

[0028] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples. The technical solutions of the present invention are not limited to the specific embodiments listed below, but also include any combination of the specific methods.

[0029] A method for preparing tunable bismuth-based heterojunction photocatalytic materials specifically includes the following steps:

[0030] Step 1: Weigh the raw materials Bi2O3 and SiO2 according to a molar ratio of 1:1 to 9:1. Select K2CO3 and KCl as the salts used in this invention, weigh them at 35wt% to 45wt%, mix them, and grind them evenly by ball milling for 3h to 5h to obtain powder material A.

[0031] In this step, Bi2O3 and SiO2 are weighed out according to the appropriate mass and then simply mixed with 35wt% to 45wt% K2CO3 and KCl and ball-milled. Before firing, the molten salt and raw materials can be mixed evenly.

[0032] Step 2: Weigh 3g to 5g of the uniformly ground powder material A above, and calcine it in a muffle furnace at 620℃ to 750℃ with a heating rate of 5℃ / min to 15℃ / min, and finally hold it at that temperature for 0.5h to 3h. After the reaction is complete, remove the sample and cool it to obtain powder material B.

[0033] This step modifies the catalyst, causing the molten salt added in step one to react with the raw materials, which alters the positions of the catalyst's valence band and conduction band, facilitating subsequent modification to adjust the powder's band gap.

[0034] Step 3: Prepare the final product using one of the following methods.

[0035] Method 1: Weigh 0.5g to 3g of powder material B, add 80mL to 100mL of water, adjust the pH to the range of 0.5 to 1.5, and stir in a water bath. After 10min to 30min, a solution is obtained. Centrifuge this solution 3 to 5 times, wash and dry the resulting precipitate to obtain the desired product C.

[0036] In this step, the modified powder is added, and the pH value is adjusted in one step. The microstructure is then regulated under a 30°C water bath to form a type II heterojunction structure. On one hand, controlling the addition of molten salt in step two allows for precise control of the generated crystalline phase ratio. On the other hand, the one-step formation reduces reaction steps, simplifying the preparation process.

[0037] Method 2: Wash powder material B alternately with water and alcohol 3 to 5 times. Dry the resulting sample to obtain the product. Take 0.1 g to 0.35 g of the product and add 30 mL to 50 mL of water, then stir for 1 to 2 hours. Add nitric acid to adjust the pH to 1 to 3 and stir for 10 to 40 minutes. Finally, add 5 mL to 60 mL of NaCl, NaBr, LiCl, and ZnCl2 salt solutions with concentrations of 1 g / L to 3 g / L respectively, and stir in a water bath for 10 to 40 minutes. Centrifuge the stirred sample 3 to 5 times to obtain the desired sample D.

[0038] In this step, the molten salt from step two is washed away, and new molten salt is added to regulate the microstructure of the catalyst, causing it to form a type II heterojunction structure. This method allows the prepared catalyst to generate more defects during the process, making photogenerated carrier transitions and separation easier. Furthermore, the addition of molten salt allows for precise control of the crystal phase ratio, generating more oxygen vacancies and adsorbed oxygen, making the prepared product more conducive to industrialization.

[0039] Of the two methods of this invention, Method 1 is simpler, while Method 2 produces Product D which degrades water pollutants more efficiently and effectively, making it more conducive to industrialization.

[0040] Based on the above technical solutions and principles, the following are some specific embodiments of the present invention.

[0041] Example 1

[0042] (1) The raw materials Bi2O3 and SiO2 are weighed in a molar ratio of 1:1. 35wt% K2CO3-KCl is used as the salt in this invention. After mixing and ball milling for 3h, a uniform powder material A is obtained; wherein the molar ratio of K2CO3 to KCl is 0.30:0.65.

[0043] (2) Weigh 3g of the uniformly ground powder material A and calcine it in a muffle furnace at 620℃ with a heating rate of 5℃ / min, and finally hold it at that temperature for 0.5h. After the reaction is complete, take out the sample and cool it to obtain powder material B;

[0044] (3) Weigh 0.5g of powder material B, add 80mL of water to adjust the pH to 0.5, stir in a water bath for 10min to obtain a solution, centrifuge the solution 3 times, wash and dry it to obtain the desired product C;

[0045] (4) After washing the powder material B three times in the order of water-alcohol, the obtained sample was dried, 0.2g was added to 30mL of water and stirred for 1h, nitric acid was added to adjust the pH, and when the pH value was adjusted to about 1, stirring was continued for 60min. Finally, 5mL of NaCl salt solution with a concentration of 1.8g / L was added and stirred in a water bath for 10min. The stirred sample was centrifuged three times to obtain the required sample D.

[0046] Example 2

[0047] (1) Weigh the raw materials Bi2O3 and SiO2 in a molar ratio of 3:1, and add 40wt% K2CO 3、 KCl, the salt used in this invention, is mixed and ball-milled for 3 hours to obtain a uniform powder material A; wherein the molar ratio of K2CO3 to KCl is 0.33:0.66.

[0048] (2) Weigh 3.5g of the uniformly ground powder material A and calcine it in a muffle furnace at 690℃ with a heating rate of 10℃ / min, and finally hold it at that temperature for 0.8h. After the reaction is complete, take out the sample and cool it to obtain powder material B;

[0049] (3) Weigh 1g of powder material B, add 100mL of water, adjust the pH to 1, stir in a water bath for 30min to obtain a solution, centrifuge the solution for 4 minutes, then wash and dry to obtain the desired product C.

[0050] (4) After washing the powder material B three times in the order of water-alcohol, the obtained sample was dried, 0.30g was added to 35mL of water and stirred for 1.5h. Nitric acid was added to adjust the pH. When the pH value was adjusted to about 1.5, stirring was continued for 40min. Finally, 10mL of NaBr salt solution with a concentration of 1.6g / L was added and stirred in a water bath for 30min. The stirred sample was centrifuged three times to obtain the required sample D.

[0051] The SEM image of product D obtained in this embodiment is as follows: Figure 1 As shown, the powder particles are stacked together in a thin sheet structure with a thickness of about 0.05 μm. The surface of the nanosheets is relatively smooth and the sheets overlap with each other. This inorganic material exhibits a heterojunction morphology structure grown on nanosheets, exposing a large number of sites on the surface and forming a three-dimensional structure that is intertwined in space.

[0052] Figure 2The photocatalytic degradation curves are obtained by adding catalyst products C and D obtained in this embodiment into a solution containing Rhodamine B organic dye and degrading them. In the experiment, 10 mg / L of Rhodamine B was used, and after adding the photocatalyst, the photocatalytic reaction was carried out for 90 min, including 60 min of dark reaction and 30 min of light reaction. As can be seen from the photocatalytic degradation graph, the degradation rate is close to 100% under 30 min of light irradiation. This is due to the heterojunction splitting electron-holes, inhibiting recombination, and at the same time increasing the surface area and the formation of defects, providing more active sites for the prepared catalyst, allowing more organic pollutants to react at the active sites, thereby effectively improving the photocatalytic effect.

[0053] Example 3

[0054] (1) The raw materials Bi2O3 and SiO2 are weighed in a molar ratio of 6:1. 42wt% K2CO3-KCl is used as the salt in this invention. After mixing and ball milling for 3 hours, a uniform powder material A is obtained; wherein the molar ratio of K2CO3 to KCl is 0.35:0.73.

[0055] (2) Weigh 4g of the uniformly ground powder material A and calcine it in a muffle furnace at 720℃ with a heating rate of 10℃ / min, and hold it at that temperature for 1h. After the reaction is complete, remove the sample and cool it to obtain powder material B;

[0056] (3) Weigh 3g of powder material B, add 100mL of water to adjust the pH to 1.5, stir in a water bath for 30min to obtain a solution, centrifuge the solution 5 times, wash and dry it to obtain the desired product C;

[0057] (4) After washing the powder material B in the order of water-alcohol five times, the obtained sample was dried, 0.35g was added to 50mL of water and stirred for 1h. Nitric acid was added to adjust the pH. When the pH value was adjusted to about 1, stirring was continued for 30min. Finally, 45mL of LiCl salt solution with a concentration of 2g / L was added and stirred in a water bath for 40min. The stirred sample was centrifuged three times to obtain the required sample D.

[0058] The present invention features a simple operation method, producing powder materials with uniform particle size that are not prone to agglomeration. Utilizing a heterojunction structure with excellent activity increases the overall catalytic sites, thereby increasing the number of active sites during the reaction process and helping to regulate the activity of the catalytic sites to exhibit higher photocatalytic performance. Furthermore, this photocatalyst has broad applicability and recyclability for antibiotics, and is capable of degrading rhodamine B, tetracycline (TC), and ciprofloxacin (CIP), greatly expanding its application scope and prospects.

[0059] In more embodiments of the present invention, different combinations of the aforementioned parameters were used. For example, in step 1), the mixing ratio of Bi2O3 to SiO2 was selected as 1:1, 3:1, 4:1, 6:1, and 9:1, respectively. K2CO3-KCl was selected as the salt for the development experiment in this invention, with proportions of 35wt%, 40wt%, and 45wt%, respectively. The ball milling time was selected as 3h, 3.5h, 4h, 4.5h, and 5h, respectively. The results showed that powder A could be prepared in all of these cases.

[0060] Similarly, in step 2), powder A is weighed in amounts of 3.0g, 3.3g, 3.5g, 3.7g, 3.9g, 4.3g, 4.6g, and 5.0g, respectively, and calcined in a muffle furnace at 620℃, 634℃, 730℃, and 745℃, with heating rates of 5℃ / min, 10℃ / min, and 15℃ / min, and holding times of 0.5h, 0.8h, 1h, 2h, and 3h, respectively. After cooling, powder B can be prepared from the initial sample.

[0061] Similarly, in step 3), the amount of powder B obtained in the above experiment can be 0.5g, 1g, 1.5g, 2g, or 3g. After reaction, the pH is adjusted to 0.1, 0.5, 1, or 1.5 by adding different amounts of water (80mL, 85mL, 90mL, 95mL, or 100mL). Then, the mixture is stirred in a water bath for 10min, 15min, 20min, or 30min. After cooling to room temperature, the mixture is centrifuged 3, 4, or 5 times, washed, and dried in a drying oven. The results show that powder product C can be obtained in all cases.

[0062] For example, in step 4), the obtained fraction B is washed with water and alcohol alternately 3, 4, and 5 times. After drying, the resulting samples are used to obtain the product. 0.1g, 0.15g, 0.25g, and 0.35g of the sample are added with water in amounts of 30mL, 40mL, and 50mL, respectively, and stirred for 1h, 1.3h, 1.4h, and 1.5h. Nitric acid is added to adjust the pH to 1, 2, and 3. After adding salts of different concentrations, the mixture is stirred and centrifuged. The washed samples are then dried to obtain product D.

[0063] In summary, this invention introduces the low-melting-point molten salt K₂CO₃-KCl. Bismuth silicate is calcined in the molten salt medium and then reacted with acid to form Bi. 12 -X(X=Bi2-BiOCl、BiOCl)(Bi 12 =Bi 12 SiO 20 Bi2=Bi2SiO5) multi-heterogeneous catalytic materials. By regulating Bi2, Bi 12The crystal phase ratio can effectively control the band gap position and suppress electron-hole recombination. Simultaneously, the catalyst morphology changes from particulate aggregates to a flower-like structure of stacked nanosheets, which is beneficial for the catalytic reaction. The heterogeneous photocatalyst obtained using the method of this invention has a simple preparation process, requires low temperature, and has low material cost. It also has numerous active sites, can be reused multiple times during degradation, and exhibits good performance, making it a promising candidate for industrial production.

[0064] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, substitutions, combinations, simplifications, etc. made based on the principles or spirit of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for preparing a controllable bismuth-based multi-heterojunction photocatalytic material, characterized in that, Includes the following steps: Step 1: Mix and grind Bi2O3, SiO2, K2CO3, and KCl until homogeneous. K2CO3 and KCl combine to form a composite salt. The molar ratio of Bi2O3 to SiO2 is 1:1 to 9:1, and the molar ratio of K2CO3 to KCl is 0.30:0.65 to 0.35:0.

73. K2CO3 and KCl account for 35 wt% to 45 wt% of the total mixture. The mixing and grinding process is as follows: ball milling for 3 to 8 hours. Step 2: Calcine the material that was mixed and ground uniformly in Step 1 at 620 ℃~750 ℃ ​​for 0.5 h~3 h and then cool it. Step 3: Obtain the tunable bismuth-based heterojunction photocatalyst material using one of the following methods: Method 1: Weigh 0.5 g to 3 g of the material obtained in step 2, add 80 mL to 150 mL of water, then add acid to adjust the pH to 0.5 to 1.5, stir in a water bath, centrifuge and dry to obtain the product. The water bath conditions are: 30 ℃ stirring for 10 min to 30 min. Method 2: Weigh 0.1 g to 0.35 g of the material obtained in step 2, wash it repeatedly with water and alcohol, and then dry it; then add 30 mL to 50 mL of water, stir for 1 h to 2 h, add acid to adjust the pH to 1 to 3, add 5 mL to 60 mL of salt solution with a concentration of 1 g / L to 3 g / L, stir in a water bath, centrifuge and dry to obtain the product. The added salt is one or more of NaCl, NaBr, LiCl and ZnCl2. The water bath conditions are: stirring at 30 ℃ for 30 min to 40 min.

2. The method of claim 1, wherein the preparation of the controllable Bi-based multi-heterojunction photocatalytic material is characterized by, In step two, the heating rate is set to 5 ℃ / min during calcination, and the temperature is maintained for 0.5 h to 3 h after reaching the calcination temperature.

3. The method for preparing the tunable bismuth-based multi-heterojunction photocatalytic material according to claim 1, characterized in that, Method 1 involves stirring for 10 to 30 minutes and centrifuging 3 to 5 times.

4. The tunable bismuth-based heterojunction photocatalytic material obtained by the preparation method according to any one of claims 1 to 3 is used for wastewater treatment, which achieves the purpose of purifying water quality by decomposing organic matter and pollutants in water.

5. The application according to claim 4, characterized in that, The tunable bismuth-based heterojunction photocatalyst material is directly added to industrial wastewater.

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