Preparation method of bismuth-based composite photocatalyst for regulating polyphase oxides

Abstract

The application discloses a preparation method of a bismuth-based composite photocatalyst for regulating multiphase oxides, and is characterized by the following steps: on the basis of preparing bismuth silicate and bismuth tungstate by a solid-phase method, calcining the two respectively, and then mixing them, and preparing a composite photocatalyst with a nanosheet stacking morphology through one-step modification halogenation by water bath heating. The method uses halogen salt molten salt as a reaction medium, effectively reduces the calcination temperature, increases the active sites of bismuth silicate and bismuth tungstate, and has no side reaction in the one-step modification process of the composite photocatalyst, thereby avoiding the problems of impurities and interfaces existing in the multi-step modification process. The bismuth-based composite photocatalyst is easy to form a nanosheet stacking morphology, can more efficiently form a heterojunction, reduces the recombination rate of photo-generated electrons and holes, improves the utilization rate of sunlight, further improves the photocatalytic performance, and the obtained catalyst has good degradation ability for organic dyes and part of antibiotics.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, and specifically relates to a method for preparing a bismuth-based composite photocatalyst that regulates multiphase oxides. Background Technology

[0002] In the field of pollution treatment, photocatalysis technology can utilize solar energy to degrade pollutants in dye wastewater into inorganic small molecules, which is a means of pollution control. By separately calcining various oxides Bi2O3, SiO2, and WO3, and obtaining the desired crystal phase through one-step modification, oxygen vacancies are generated on the surface of the final bismuth silicate-bismuth tungstate heterostructure, which can produce more active groups. This method can also control the halogen concentration to regulate the band gap position and obtain a smaller band gap.

[0003] Currently, whether it is a single-component photocatalyst or a composite heterogeneous catalytic material, most of them exhibit a thick, sheet-like accumulation in morphology, which cannot limit the surface area and effectively expose the active sites, further limiting the degradation efficiency of pollutants. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing bismuth-based composite photocatalysts with regulated multiphase oxides. This method has simple process, simple equipment requirements, and controllable reaction conditions. The resulting material has high purity and good crystallinity. The obtained composite photocatalyst has a uniform particle size distribution, a nanosheet stacked structure, and more active sites. This structure can effectively improve the utilization rate of light and enhance photocatalytic activity.

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

[0006] A method for preparing a bismuth-based composite photocatalyst for regulating multiphase oxides includes the following steps:

[0007] Step 1: Mix bismuth silicate (Bi2SiO5) powder, bismuth tungstate powder and the first part of molten halide salt, and ball mill to obtain bismuth silicate-bismuth tungstate composite powder;

[0008] Step 2, execute one of the following methods:

[0009] Method 1 involves washing the bismuth silicate-bismuth tungstate composite powder several times with deionized water and ethanol respectively to remove residual salts from the product. After drying the washed powder, it is reacted in a water bath, and the pH value is adjusted to 1-2. The second part of the molten halide salt is added to continue the reaction. After drying and washing, the modified powder is obtained, which is the composite photocatalyst prepared by the two-step method of bismuth tungstate-bismuth silicate-bismuth oxyhalide.

[0010] Method 2 involves leaving the bismuth silicate-bismuth tungstate composite powder obtained in step 1 unwashed, retaining the residual salt in the product, performing a water bath reaction, adjusting the pH value to 1-2, and then drying and washing to obtain the modified powder, which is the composite photocatalyst prepared by one-step modification of bismuth tungstate-bismuth silicate-bismuth oxyhalide.

[0011] In one embodiment, the bismuth silicate powder is prepared by the following method:

[0012] Bi₂O₃ and SiO₂ were used as reactants, and NaCl and KCl were used as the third part of the molten halide salt. The reactants and the third part of the molten halide salt were loaded into a nylon can and ball-milled with zirconium oxide as the grinding ball. The mixture was heated to 500℃ to 700℃ in air at a heating rate of 10℃ / min to 20℃ / min and then calcined for 4h to 7h to obtain bismuth silicate powder.

[0013] In one embodiment, the molar ratio of Bi2O3 to SiO2 is 1:1 to 1:9, the molar ratio of NaCl to KCl in the third part of the molten halide salt is 1:1, the mass percentage of the third part of the molten halide salt is 30% to 40%, and the ball milling time is controlled at 3 to 6 hours.

[0014] In one embodiment, the bismuth tungstate powder is prepared by the following method:

[0015] Using Bi2O3 and WO3 as reactants, and NaCl and KCl as the fourth part of the molten halide salt, Bi2O3 was first ground, and then WO3 was added to Bi2O3 and mixed and ground evenly. The reactants and the fourth part of the molten halide salt were loaded into a nylon can and ball-milled with zirconium oxide as the grinding ball. The mixture was heated to 630-660℃ at a heating rate of 5℃ / min in air atmosphere and then calcined for 1-3 hours to obtain bismuth tungstate powder.

[0016] In one embodiment, the molar ratio of Bi2O3 to WO3 is 1:3, the molar ratio of NaCl to KCl in the fourth part of the molten halide salt is 1:1, the mass percentage of the fourth part of the molten halide salt is 30%, and the ball milling time is controlled at 3 to 6 hours.

[0017] In one embodiment, in Method 1, the water bath reaction temperature is 30°C, the time is 30-60 min, the pH is adjusted and the reaction continues for another 30-60 min, and then the first part of the molten brine salt is added and the reaction continues for another 2-3 h.

[0018] In one embodiment, the first portion of the molten halide salt is NaCl and / or KCl, accounting for 30% by mass.

[0019] In one embodiment, in method two, the water bath reaction temperature is 30°C to 50°C, the time is 30 to 60 minutes, and the reaction continues for another 30 to 60 minutes after adjusting the pH.

[0020] In one embodiment, in Method 1 and Method 2, the drying and washing method is as follows: wash several times alternately with deionized water and ethanol, and then dry in an oven at 60°C.

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

[0022] 1. This method uses molten halide salt as the reaction medium, which effectively reduces the calcination temperature. The molten halide salt medium also helps to improve the reaction rate and product formation. In this method, Bi₂O₃, SiO₂, WO₃, and the subsequently generated bismuth tungstate and bismuth silicate can all be uniformly dispersed in the molten halide salt for reaction. Then, a one-step modification is performed directly through a water bath process, solving the problem of potential impurity crystalline phases in the product when heterojunctions are formed during the two-step modification process. Uniform mixing helps to improve reaction efficiency and product purity.

[0023] 2. This scheme involves calcining different oxides of Bi₂O. 3、 SiO 2、 The reaction of WO3 followed by the mixing of products promotes the breaking of bismuth-oxygen bonds, thereby increasing the oxygen vacancy concentration and promoting the generation of catalytically active groups. By controlling the concentration of different halogens, the generation of the desired crystal phase can be controlled. After one-step modification, it is easier to obtain adsorbed oxygen and break bonds, which is beneficial to improving the catalytic performance of the photocatalyst. Through one-step modification and control of molten salt concentration, the band gap position can be better regulated. The composite bismuth silicate-bismuth tungstate heterogeneous photocatalyst produced by this method has a smaller band gap.

[0024] 3. Solid-state methods for preparing bismuth silicate and bismuth tungstate tend to result in large, sheet-like stacked morphologies with small specific surface areas and few active sites, which is detrimental to the photocatalytic process. This method improves the morphology of the composite photocatalyst by combining a molten halide salt method with a one-step liquid-phase halogen modification. The bismuth silicate-modified bismuth tungstate photocatalyst readily forms a nanosheet stacked structure, which further promotes the recombination between bismuth silicate and bismuth tungstate, thereby forming heterojunctions more efficiently. This avoids the ineffective heterostructures caused by thick sheet-like stacking, reduces the recombination rate of photogenerated electrons and holes, and improves the utilization rate of sunlight, thus further enhancing the photocatalytic performance of the composite material.

[0025] 4. This method simplifies the washing step and directly obtains bismuth silicate-bismuth tungstate composite photocatalyst material through water bath reaction modification, simplifying the modification steps. The desired product structure and performance can be adjusted by controlling the reaction temperature and time. The reaction steps are simple and the reaction conditions are suitable, which is conducive to expanding the production scale and industrialization. At the same time, the product obtained by one-step modification has good ability to degrade organic dyes and some antibiotics, and the degradation effect is improved. Attached Figure Description

[0026] Figure 1 This is a photocatalytic degradation curve of Rhodamine B using a bismuth-based composite photocatalyst. Detailed Implementation

[0027] 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.

[0028] A method for preparing a bismuth-based composite photocatalyst that regulates multiphase oxides involves using bismuth silicate and bismuth tungstate as raw materials to prepare a modified bismuth silicate heterogeneous photocatalyst material in one step. Based on the solid-state preparation of bismuth silicate and bismuth tungstate, the two materials are calcined separately and then mixed, followed by one-step halogenation modification via water bath heating to prepare a composite photocatalyst with a nanosheet stacked morphology. The specific steps include:

[0029] Step 1: Weigh Bi2O3 and SiO2 according to a certain molar ratio. Select NaCl and KCl as the third part of the halide molten salt for the experiment. Put the reactants and the third part of the halide molten salt into nylon cans, mix and ball mill them with zirconium oxide as grinding balls, and calcine them at a certain temperature to obtain bismuth silicate (Bi2SiO5) powder.

[0030] Specifically, in this step, Bi₂O₃ and SiO₂ are mixed in a molar ratio of 1:1, 1:3, or 1:9, and NaCl and KCl are added in a molar ratio of 1:1 to 1:3. The mixture is then ball-milled for 3–5 hours. The resulting powder is calcined at 600–690°C for 4–7 hours to obtain bismuth silicate (Bi₂SiO₅) powder. This step achieves the solid-state preparation of bismuth silicate.

[0031] Step 2: Weigh Bi₂O₃ and WO₃ separately according to their molar ratio. Select NaCl and KCl as the fourth part of the molten halide salt for the experiment. First, grind the weighed Bi₂O₃, then add the weighed WO₃ to the Bi₂O₃ and mix and grind evenly. Place the reactants and the fourth part of the molten halide salt into nylon containers, mix and ball-mill using zirconium oxide as grinding balls, and then calcine at a certain temperature to obtain bismuth tungstate powder.

[0032] Specifically, in this step, Bi₂O₃ and WO₃ are weighed separately at molar ratios of 1:2 and 1:3. The weighed Bi₂O₃ is first ground, and then the weighed WO₃ is added to the Bi₂O₃ in 3 to 5 portions and mixed and ground evenly. The reactants and the molten halide salt from the fourth part are separately placed in nylon containers, mixed and ball-milled for 3 to 5 hours using zirconium oxide as a grinding ball, and then calcined at 600 to 690°C to obtain bismuth tungstate powder. This step realizes the solid-phase preparation of bismuth tungstate.

[0033] Step 3: Mix the product obtained from the above experiment with the first part of the molten halide salt in different ratios of bismuth silicate and bismuth tungstate, and ball mill for about 1 to 3 hours to mix the above mixed powder evenly for subsequent reactions.

[0034] Step 4: Wash the powder obtained in Step 3 alternately with deionized water and ethanol 3-6 times to remove residual salts from the product. After drying the washed powder, react and stir in a water bath at 30°C for 30 minutes. Adjust the pH to 1 with nitric acid and continue stirring for 30-60 minutes. Add molten halide salts of different concentrations and types from the second part and stir for 2-3 hours. After drying and washing, the modified powder is obtained, which is the composite photocatalyst prepared by the two-step method of bismuth tungstate-bismuth silicate-bismuth halooxygenate.

[0035] Step 5: Without washing, react and stir the powder obtained in Step 3 at 30°C in a water bath for 30 minutes. Add nitric acid to adjust the pH to 1, and continue stirring for 30–60 minutes. Stir for 2–3 hours without adding the molten halide salt. After drying and washing, the modified powder is obtained, which is the composite photocatalyst prepared by one-step modification of bismuth tungstate-bismuth silicate-bismuth oxyhalide.

[0036] This catalyst has a nanosheet stacked structure and can be used to degrade organic dyes, antibiotics, etc.

[0037] This invention uses molten halide salt as the reaction medium, effectively reducing the calcination temperature while increasing the active sites of bismuth silicate and bismuth tungstate. The one-step modification of the composite photocatalyst is free of side reactions, avoiding the problems of impurities and interfaces inherent in multi-step modification methods. The bismuth-based composite photocatalyst readily forms a nanosheet stacked morphology, enabling more efficient formation of heterojunctions. This reduces the recombination rate of photogenerated electrons and holes while increasing the utilization rate of sunlight, further enhancing photocatalytic performance. This method is simple, has a short cycle time, requires simple equipment, and is low in cost, making it suitable for industrialization. The resulting composite material, due to its numerous active sites in the powder, exhibits high photocatalytic performance and demonstrates good ability to degrade organic dyes and some antibiotics.

[0038] The following are some embodiments of the present invention.

[0039] Example 1

[0040] (1) Bi2O3 and SiO2 were weighed at a molar ratio of 1:3. NaCl and KCl were selected as the third part of the molten halide salt for the experiment. The molar ratio of NaCl to KCl was 1:1. The reactants and the third part of the molten halide salt were respectively placed in nylon cans, mixed and ball-milled for 3 hours with zirconium oxide as the grinding ball, and calcined at 630℃ to obtain bismuth silicate powder.

[0041] (2) Bi₂O₃ and WO₃ were weighed separately at a molar ratio of 1:3. NaCl and KCl were selected as the molten salts for the fourth part of the experiment, with a molar ratio of 1:1. The weighed Bi₂O₃ was first ground, and then the weighed WO₃ was added to Bi₂O₃ in three portions and mixed and ground evenly. The reactants and the molten salts for the fourth part of the halide were placed separately into nylon containers, mixed and ball-milled for 5 hours using zirconium oxide as grinding balls, and then calcined at 630℃ to obtain bismuth tungstate powder.

[0042] (3) The product obtained from the above experiment is mixed with the first part of the molten halide salt in different ratios of bismuth silicate and bismuth tungstate. The mixture is ball-milled for 2 hours to obtain the above mixed powder evenly, thus obtaining the bismuth silicate-bismuth tungstate heterogeneous photocatalyst, namely the nanosheet stacked structure morphology photocatalyst.

[0043] (4) The bismuth silicate-bismuth tungstate powder obtained in (3) was washed four times alternately with deionized water and ethanol to remove residual salts from the product. After drying the washed powder, it was reacted and stirred in a water bath at 30°C for 30 minutes. Nitric acid was added to adjust the pH to 1, and stirring was continued for 30 minutes. Different concentrations of the second part of the halide molten salt were added and stirred for 2 hours. After drying and washing, the modified powder was obtained.

[0044] (5) The bismuth silicate-bismuth tungstate powder obtained in (3) was reacted in a water bath at 30°C with stirring for 30 minutes without washing. Nitric acid was added to adjust the pH to 1, and stirring was continued for 30 minutes. Molten salt without adding halide was stirred for 2 hours. After drying and washing, the modified powder was obtained.

[0045] Example 2

[0046] (1) Bi2O3 and SiO2 were weighed at a molar ratio of 1:9. NaCl and KCl were selected as the third part of the molten halide salt for the experiment. The molar ratio of NaCl to KCl was 1:1. The reactants and the third part of the molten halide salt were respectively placed in nylon cans, mixed and ball-milled for 3 hours with zirconium oxide as the grinding ball, and calcined at 660℃ to obtain bismuth silicate powder.

[0047] (2) Bi₂O₃ and WO₃ were weighed separately at a molar ratio of 1:3. NaCl and KCl were selected as the fourth part of the molten halide salt for the experiment, with a molar ratio of 1:1. The weighed Bi₂O₃ was first ground, and then the weighed WO₃ was added to Bi₂O₃ in 4 portions and mixed and ground evenly. The reactants and the molten halide salts selected as the fourth part of the experiment, with a molar ratio of 1:1, were placed in nylon cans, mixed and ball-milled for 5 hours using zirconium oxide as grinding balls, and then calcined at 660℃ to obtain bismuth tungstate powder.

[0048] (3) The product obtained from the above experiment is mixed with the first part of the molten halide salt in different ratios of bismuth silicate and bismuth tungstate. The mixture is ball-milled for 2 hours to obtain the above mixed powder evenly, thus obtaining the bismuth silicate-bismuth tungstate heterogeneous photocatalyst, i.e. the structured morphology photocatalyst.

[0049] (4) The bismuth silicate-bismuth tungstate powder obtained in (3) was washed four times alternately with deionized water and ethanol to remove residual salts from the product. After drying the washed powder, it was reacted and stirred in a water bath at 30°C for 40 minutes. Nitric acid was added to adjust the pH to 1, and stirring was continued for 30 minutes. Different concentrations of the second part of the halide molten salt were added and stirred for 3 hours. After drying and washing, the modified powder was obtained.

[0050] (5) The bismuth silicate-bismuth tungstate powder obtained in (3) was reacted and stirred in a water bath at 30°C for 40 minutes without washing. Nitric acid was added to adjust the pH value to 1, and stirring was continued for 30 minutes. Molten salt without adding halide was stirred for 3 hours. After drying and washing, the modified powder was obtained.

[0051] Figure 1 The catalyst obtained in this embodiment was added to a solution containing Rhodamine B organic dye and its photocatalytic degradation curve was obtained. In the experiment, a total of 30 mL of Rhodamine B was taken, with a concentration of 10 mg / L. The amount of catalyst added was 3 mg. After addition, the photocatalytic reaction was carried out for 180 min, including 60 min of dark reaction and 120 min of light reaction. It can be seen that under the condition of 120 min of light irradiation, the degradation rate is close to 100%.

[0052] In more embodiments of the present invention, the aforementioned parameters were combined in different ways. For example, in step 1), the molar ratio of Bi2O3 to SiO2 was selected as 1:1, 1:3, 1:9, and 1:12, respectively, and the calcination temperature was selected as 600℃, 630℃, 660℃, and 690℃, respectively. The results showed that bismuth silicate powder could be prepared in all of these ways.

[0053] Similarly, in step 2), the heating rate was selected as 10℃ / min, 15℃ / min, and 20℃ / min, and the calcination temperature was selected as 600℃, 630℃, 660℃, and 690℃. The results showed that bismuth tungstate powder could be prepared in all of these cases.

[0054] Similarly, in step 3), when ball milling and mixing, the ball milling time can be selected as 1 hour, 2 hours, or 3 hours. The results show that bismuth silicate-bismuth tungstate heterogeneous photocatalysts can be prepared in all of these cases.

[0055] 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 bismuth-based composite photocatalyst that regulates multiphase oxides, characterized in that, Includes the following steps: Step 1: Mix bismuth silicate powder, bismuth tungstate powder and the first part of molten halide salt, and ball mill to obtain bismuth silicate-bismuth tungstate composite powder; the first part of molten halide salt is NaCl and KCl; Step 2, execute one of the following methods: Method 1: The bismuth silicate-bismuth tungstate composite powder is washed several times alternately with deionized water and ethanol to remove residual salts from the product. After drying the washed powder, it is reacted in a water bath at 30°C for 30-60 minutes, and the pH value is adjusted to 1-2. The reaction is continued for another 30-60 minutes, and then the second part of the molten halide salt is added and the reaction is continued for 2-3 hours. After drying and washing, the modified powder is obtained, which is the composite photocatalyst prepared by the two-step method of bismuth tungstate-bismuth silicate-bismuth oxyhalide. Method 2: The bismuth silicate-bismuth tungstate composite powder obtained in step 1 is not washed, and the residual salt in the product is retained. The product is reacted in a water bath at 30℃~50℃ for 30~60 min, and the pH value is adjusted to 1~2. The reaction is continued for 30~60 min. After drying and washing, the modified powder is obtained, which is the composite photocatalyst prepared by one-step modification of bismuth tungstate-bismuth silicate-bismuth oxyhalide. The bismuth silicate powder is prepared by the following method: Using Bi₂O₃ and SiO₂ as reactants, the reactants and the third part of the molten halide salt were loaded into a nylon can, and ball-milled using zirconium oxide as a grinding ball. The mixture was then heated to 500℃~700℃ at a heating rate of 10℃ / min~20℃ / min under air atmosphere and calcined for 4 h~7 h to obtain bismuth silicate powder; the third part of the molten halide salt was NaCl and KCl. The bismuth tungstate powder is prepared by the following method: Using Bi2O3 and WO3 as reactants, Bi2O3 is first ground, and then WO3 is added to Bi2O3 and mixed and ground evenly. The reactants and the fourth part of the molten halide salt are loaded into a nylon can and ball-milled with zirconium oxide as the grinding ball. The mixture is heated to 630~660℃ at a heating rate of 5℃ / min in air atmosphere and then calcined for 1~3h to obtain bismuth tungstate powder. The fourth part of the molten halide salt is NaCl and KCl.

2. The method for preparing bismuth-based composite photocatalysts with regulated multiphase oxides according to claim 1, characterized in that, The molar ratio of Bi2O3 to SiO2 is 1:1 to 1:9, the molar ratio of NaCl to KCl in the third part of the molten halide salt is 1:1, the mass percentage of the third part of the molten halide salt is 30% to 40%, and the ball milling time is controlled at 3 to 6 hours.

3. The method for preparing bismuth-based composite photocatalysts for regulating multiphase oxides according to claim 1, characterized in that, The molar ratio of Bi2O3 to WO3 is 1:3, and the molar ratio of NaCl to KCl in the fourth part of the molten halide salt is 1:1; the mass percentage of the fourth part of the molten halide salt is 30%, and the ball milling time is controlled at 3 to 6 hours.

4. The method for preparing a bismuth-based composite photocatalyst for regulating multiphase oxides according to claim 1, characterized in that, In both methods one and two, the drying and washing method is as follows: wash several times alternately with deionized water and ethanol, and then dry in an oven at 60°C.

5. The catalyst obtained by the preparation method of the bismuth-based composite photocatalyst for regulating multiphase oxides according to any one of claims 1 to 4 is used for the degradation of organic dyes and antibiotics.

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