CN110339843B - Preparation method of magnetic bismuth oxide/bismuth vanadate composite photocatalyst - Google Patents

Abstract

Magnetic composite photocatalyst Mn_xZn_1‑xFe₂O₄/β‑Bi₂O₃/BiVO₄Belonging to the field of inorganic catalytic materials. The invention firstly prepares Mn by a hydrothermal method_xZn_1‑xFe₂O₄Then preparing Mn by coprecipitation-roasting method_xZn_1‑xFe₂O₄/BiVO₄The magnetic composite photocatalyst Mn is prepared by adopting a precipitation-roasting method_xZn_1‑xFe₂O₄/β‑Bi₂O₃/BiVO₄. The method has the advantages of simple preparation process, less used equipment cost and less energy consumption. Prepared Mn_xZn_1‑xFe₂O₄/β‑Bi₂O₃/BiVO₄The composite photocatalytic material prepared by 0.1g is large in specific surface area, strong in stability and high in photocatalytic activity, 50mL of 10mg/L rhodamine B solution is degraded under the irradiation of a simulated sunlight xenon lamp, the degradation rate reaches 92.8% after 3 hours of illumination, the recovery rate after 3 times of repeated use is more than 89.7%, and the degradation rate of 3 times of repeated use on rhodamine B is still more than 84.9%. The product prepared by the invention can be widely used in the field of photocatalytic degradation of organic pollutants.

Description

Preparation method of magnetic bismuth oxide/bismuth vanadate composite photocatalyst

Technical Field

The invention relates to a magnetic bismuth oxide/bismuth vanadate composite photocatalyst Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Belonging to the technical field of inorganic catalytic materials.

Background

Semiconductor photocatalytic technology is a new technology to deal with environmental issues because of traditional photocatalysts (e.g. alumina, silica, etc.)TiO₂And ZnO) has a large energy gap, and can only utilize 3% -5% of the ultraviolet light in solar energy, and people are making efforts to research and develop novel semiconductor photocatalysts at the present stage. Found that Bi₂O₃BiOBr, BiOI and BiVO₄The bismuth-based visible light catalyst has the advantages of low cost, high efficiency and the like, and is widely applied to the degradation of organic pollutants in wastewater and the preparation of H₂And CO₂And (4) reduction. Besides, many scholars prove that the bismuth-based semiconductor photocatalyst has certain photocatalytic activity under the irradiation of visible light, so that the research of bismuth-based visible light materials becomes a hotspot. In the development of novel bismuth-based photocatalysts, beta-Bi₂O₃The band gap of the material is 2.58eV, the material can absorb visible light with the wavelength of more than 400nm, and the preparation method mainly comprises a chemical precipitation method, a sol-gel method, a microemulsion method, a hydrothermal synthesis method, a solid phase room temperature method and the like. BiVO₄The bismuth vanadate has various structures, wherein monoclinic scheelite type, tetragonal zirconium silicate type and tetragonal scheelite (high-temperature phase) type are common, the forbidden band width is 2.3-2.4 eV, the bismuth vanadate can respond to a visible light region, and the photocatalysis effect is good. BiVO₄The preparation method mainly comprises a chemical precipitation method, a roasting method, a hydrothermal method and the like. The photocatalyst is mostly in a suspension state in a photocatalytic reaction system, is in a slurry state after the photocatalytic reaction, and is difficult to separate, recycle and reuse, which is a main factor for restricting the application process of the photocatalyst. The magnetic composite photocatalyst is recycled through an external magnetic field, and the defect that the suspended photocatalyst is not easy to recycle is overcome. Mn_xZn_1-xFe₂O₄(manganese-zinc-ferrite) with conventional metallic soft magnetic materials such as Fe₃O₄Compared with ferroferric oxide, the ferroferric oxide has the characteristics of high saturation magnetization, high magnetic conductivity and the like, and has the advantages of high production efficiency, low cost, stable product performance and the like. Therefore, with Mn_xZn_1-xFe₂O₄The composite photocatalyst prepared from the magnetic matrix has strong magnetism and is convenient to separate and recycle.

At the present stage, research on the magnetic composite catalyst mainly focuses on improving the catalytic activity of the magnetic composite catalyst, and reports on how to prepare the magnetic composite catalyst with high catalytic activity and high recovery rate are relatively highLess. For example, in the invention patent "a method for preparing a manganese-zinc-ferrite-bismuth oxide magnetic photocatalyst" (publication No. CN104437536A) (reference 1), the disclosed method is: firstly, Mn is prepared by a roasting method_xZn_1-xFe₂O₄And then preparing Mn by using a dipping roasting method_xZn_1-xFe₂O₄/β-Bi₂O₃A magnetic composite photocatalyst. The main disadvantages of this method are: (1) preparation of manganese zinc ferrite (Mn) by roasting method_xZn_1-xFe₂O₄) The temperature of the reaction is 1200 ℃, the energy consumption is high, and the prepared sample has larger particle size and smaller specific surface area, which is not beneficial to Mn_xZn_1-xFe₂O₄And beta-Bi₂O₃The stability of the compound cannot be ensured due to the sufficient combination of the components; (2) composite beta-Bi prepared by roasting method₂O₃/Mn_xZn_1-xFe₂O₄The specific surface area is small, which is not beneficial to the full contact and reaction between the catalyst and organic pollutants in the photocatalytic degradation process; (3) mn prepared by roasting method_xZn_1-xFe₂O₄Small coercive force, limited magnetic retention capacity and no contribution to Mn_xZn_1-xFe₂O₄/β-Bi₂O₃And (4) recycling. Also for example, "chemical research and application" 2010 05 th stage "magnetic photocatalyst BiVO₄/Fe₃O₄Study on the degradation of methylene blue "(reference 2), the magnetic matrix Fe was sonicated₃O₄And BiVO₄Compounding to prepare the magnetic visible-light-driven photocatalyst BiVO easy for solid-liquid separation₄/Fe₃O₄. The method has the following defects: (1) the magnetic composite photocatalyst has low efficiency and BiVO (BiVO) under simulated sunlight₄/Fe₃O₄The degradation rate of the magnetic composite photocatalyst to methylene blue within 5h is 96.2%, and the recycled BiVO₄/Fe₃O₄The degradation rate of methyl orange is more than 80 percent, and the effect on dye which is difficult to degrade, such as rhodamine B, is not investigated; (2) the recovery rate of the magnetic composite photocatalyst is not high and is only 84%; (3) the preparation process has more impurities and is difficult to ensureThe organic silicon and the organic silicon are uniformly and firmly combined, the production cost is higher, and a large amount of volatile organic compounds are discharged in the subsequent drying and heat treatment processes, so that the pollution to the atmospheric environment is caused.

Mn prepared by hydrothermal method_xZn_1-xFe₂O₄The composite photocatalyst has better magnetic stability, is more beneficial to magnetic recovery and has no secondary pollution to the environment; compared with a product prepared by a roasting method, the hydrothermal method has smaller particle size and larger specific surface area, and can better ensure firm combination between the catalytic matrix and the magnetic matrix, so that the combination has better stability. Thus, the hydrothermal method is used for preparing Mn_xZn_1-xFe₂O₄Then with beta-Bi₂O₃、BiVO₄Composite improvement of beta-Bi₂O₃And BiVO₄The catalytic effect, recovery rate and magnetic stability of the catalyst are necessary.

Disclosure of Invention

The invention aims at the beta-Bi prepared by the roasting method₂O₃、Mn_xZn_1-xFe₂O₄The problems of high energy consumption, unstable photocatalytic activity of the compound, limited magnetic retention capacity and the like exist, and the hydrothermal method is adopted to prepare Mn_xZn_1-xFe₂O₄And hydrothermal-coprecipitation-roasting method for preparing Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄A new method of a magnetic composite photocatalyst, which not only solves the problem of beta-Bi₂O₃/BiVO₄The preparation method is simple, the production cost is low, the period is short, the catalytic activity is high, the magnetic composite photocatalyst is convenient to separate and recover from a liquid phase suspension system through an external magnetic field, the recovered catalyst still has high catalytic activity, the resource recycling is simply and efficiently realized, and the possible secondary pollution caused by the catalyst is avoided.

The magnetic composite photocatalyst Mn of the invention_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The preparation method comprises the following steps:

(1)Mn_xZn_1-xFe₂O₄preparation of

ZnO according to a molar ratio: MnO: fe₂O₃13.3: 32.8: 53.9, respectively weighing a proper amount of zinc sulfate, ferric sulfate and manganese sulfate, adding 25mL of deionized water, and dissolving by ultrasonic oscillation to obtain a mixed solution; under the action of magnetic stirring, dropwise adding a NaOH solution with a certain concentration into the mixed solution, adjusting the pH of the solution to 13, and continuously stirring for 15 min; transferring the stirred solution into a 100mL reaction kettle, and reacting for 5h at 200 ℃; after the reaction is finished, cooling and suction filtering are carried out, filter cakes are respectively washed for 5 times by distilled water and ethanol, the filter cakes are dried for 12 hours at the temperature of 80 ℃, and Mn is obtained by grinding_xZn_1-xFe₂O₄。

(2)Mn_xZn_1-xFe₂O₄/BiVO₄Preparation of

Weighing a certain amount of bismuth nitrate pentahydrate, and adding HNO with the concentration of 2mol/L₃In the solution, ultrasonic oscillation is carried out to dissolve the solution to obtain a solution A; according to Bi (NO)₃)₃·5H₂Weighing tartaric acid according to different proportions, and dissolving the tartaric acid in hot water at the temperature of 80 ℃ to obtain a solution B; in a molar ratio of Bi (NO)₃)₃·5H₂O:NH₄VO₃Weighing ammonium metavanadate at the ratio of 1:1, and dissolving the ammonium metavanadate in hot water at the temperature of 80 ℃ to obtain a solution C; dripping the solution B into the solution C to obtain a mixed solution D; then adding the solution A into the mixed solution D, cooling the solution, and adjusting the pH of the solution to 7.5 by using ammonia water to obtain BiVO₄A precursor of (a); according to Mn_1-xZn_xFe₂O₄:BiVO₄The mass ratio is 10:100 weighing the Mn obtained above_1-xZn_xFe₂O₄Adding into BiVO₄Performing water bath reaction on the precursor at 80 ℃ for 30min, filtering, drying, grinding, placing in a muffle furnace at 450 ℃ for reaction for 3h, taking out, and cooling to room temperature to obtain Mn_xZn_1-xFe₂O₄/BiVO₄。

(3)Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Preparation of

Weighing a proper amount of bismuth nitrate, adding the bismuth nitrate into 10mL of 2mol/L HNO₃Dissolving with ultrasound to obtain clear solution, and adding into 40mL of 0.6mol/L Na₂CO₃In the solution, mechanically stirring for 2h to obtain beta-Bi₂O₃Precursor solution; in the form of beta-Bi₂O₃:Mn_xZn_1-xFe₂O₄/BiVO₄Weighing Mn according to the mass ratio of 5-15: 100_xZn_1-xFe₂O₄/BiVO₄To beta-Bi₂O₃Mechanically stirring the precursor solution for 2 hours, filtering, washing a filter cake with distilled water, then placing the filter cake in a drying oven at 60 ℃ for drying for 12 hours, and grinding to obtain composite precursor powder; putting the precursor powder into a muffle furnace, roasting at 380 ℃ for 10min, then quickly taking out the precursor powder from the muffle furnace, and naturally cooling to obtain Mn with different mass ratios_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄. By adopting the technical scheme, the invention mainly has the following effects:

(1) the magnetic composite photocatalyst Mn prepared by the method_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Has high photocatalytic activity, and 0.1g of Mn is prepared under the irradiation of a xenon lamp simulating sunlight_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The magnetic composite photocatalyst is dispersed in 50mL of rhodamine B solution with the concentration of 10mg/L, and the degradation rate reaches 92.8 percent after illumination for 3 hours.

(2) The magnetic composite photocatalyst Mn prepared by the method_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Under the action of an external magnetic field, the recovery rate after 3 times of repeated use is more than 89.7%, and the degradation rate of 3 times of repeated use on rhodamine B still reaches more than 84.9%.

(3) The invention is prepared by a hydrothermal-coprecipitation-roasting method, and the specific surface area of the magnetic composite photocatalyst reaches 17.8m²Perg, strong stability and simple preparation operationThe required equipment is less and the energy consumption is low.

Drawings

FIG. 1 is BiVO₄、β-Bi₂O₃/Mn_xZn_1-xFe₂O₄And beta-Bi₂O₃/BiVO₄/Mn_xZn_1-xFe₂O₄X-ray diffraction pattern of (a).

FIG. 2 shows beta-Bi₂O₃/BiVO₄And beta-Bi₂O₃/BiVO₄/Mn_xZn_1-xFe₂O₄An infrared spectrum of (1).

Fig. 3 is a hysteresis chart of a magnetic sample.

Detailed Description

The present invention will be further described with reference to the following specific embodiments.

Example 1

Preparation of magnetic composite photocatalyst Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The method comprises the following specific steps:

(1)Mn_xZn_1-xFe₂O₄preparation of

ZnO according to a molar ratio: MnO: fe₂O₃13.3: 32.8: 53.9, respectively weighing a proper amount of zinc sulfate, ferric sulfate and manganese sulfate, adding 25mL of deionized water, and dissolving by ultrasonic oscillation to obtain a mixed solution; under the action of magnetic stirring, dropwise adding a NaOH solution with a certain concentration into the mixed solution, adjusting the pH of the solution to 13, and continuously stirring for 15 min; transferring the stirred solution into a 100mL reaction kettle, and reacting for 5h at 200 ℃; after the reaction is finished, cooling and suction filtering are carried out, filter cakes are respectively washed for 5 times by distilled water and ethanol, the filter cakes are dried for 12 hours at the temperature of 80 ℃, and Mn is obtained by grinding_xZn_1-xFe₂O₄。

(2)Mn_xZn_1-xFe₂O₄/BiVO₄Preparation of

Weighing a certain amount of bismuth nitrate pentahydrate, and adding HNO with the concentration of 2mol/L₃Dissolving in solution by ultrasonic oscillationSolution A; according to Bi (NO)₃)₃·5H₂Weighing tartaric acid according to different proportions, and dissolving the tartaric acid in hot water at the temperature of 80 ℃ to obtain a solution B; in a molar ratio of Bi (NO)₃)₃·5H₂O:NH₄VO₃Weighing ammonium metavanadate at the ratio of 1:1, and dissolving the ammonium metavanadate in hot water at the temperature of 80 ℃ to obtain a solution C; dripping the solution B into the solution C to obtain a mixed solution D; then adding the solution A into the mixed solution D, cooling the solution, and adjusting the pH of the solution to 7.5 by using ammonia water to obtain BiVO₄A precursor of (a); according to Mn_1-xZn_xFe₂O₄:BiVO₄The mass ratio is 10:100 weighing the Mn obtained above_1-xZn_xFe₂O₄Adding into BiVO₄Performing water bath reaction on the precursor at 80 ℃ for 30min, filtering, drying, grinding, placing in a muffle furnace at 450 ℃ for reaction for 3h, taking out, and cooling to room temperature to obtain BiVO₄/Mn_1-xZn_xFe₂O₄。

(3)Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Preparation of

Weighing a proper amount of bismuth nitrate, adding the bismuth nitrate into 10mL of 2mol/L HNO₃Dissolving in solution with ultrasound to obtain clear solution, and adding into 40mL of 0.6mol/L Na at a certain speed₂CO₃In the solution, mechanically stirring for 2h to obtain beta-Bi₂O₃Precursor solution; in the form of beta-Bi₂O₃:BiVO₄/Mn_xZn_1-xFe₂O₄Weighing Mn according to the mass ratio of 5:100_xZn_1-xFe₂O₄/BiVO₄To beta-Bi₂O₃Mechanically stirring the precursor solution for 2 hours, filtering, washing a filter cake with distilled water, then placing the filter cake in a drying oven at 60 ℃ for drying for 12 hours, and grinding to obtain composite precursor powder; putting the precursor powder into a muffle furnace, roasting at 380 ℃ for 10min, then quickly taking out the precursor powder from the muffle furnace, and naturally cooling to obtain Mn with different mass ratios_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄。

Example 2

Preparation of magnetic composite photocatalyst Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The method comprises the following specific steps:

(1) the same as in (1) in example 1.

(2) Same as example 1 (2)

(3)β-Bi₂O₃/BiVO₄/Mn_xZn_1-xFe₂O₄Preparation of

Weighing a proper amount of bismuth nitrate, adding the bismuth nitrate into 10mL of 2mol/L HNO₃Dissolving in solution with ultrasound to obtain clear solution, and adding into 40mL of 0.6mol/L Na at a certain speed₂CO₃In the solution, mechanically stirring for 2h to obtain beta-Bi₂O₃Precursor solution; in the form of beta-Bi₂O₃:BiVO₄/Mn_xZn_1-xFe₂O₄Weighing Mn according to the mass ratio of 10:100_xZn_1-xFe₂O₄/BiVO₄To beta-Bi₂O₃Mechanically stirring the precursor solution for 2 hours, filtering, washing a filter cake with distilled water, then placing the filter cake in a drying oven at 60 ℃ for drying for 12 hours, and grinding to obtain composite precursor powder; putting the precursor powder into a muffle furnace, roasting at 380 ℃ for 10min, then quickly taking out the precursor powder from the muffle furnace, and naturally cooling to obtain Mn with different mass ratios_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄。

Example 3

Preparation of magnetic composite photocatalyst Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The method comprises the following specific steps:

(1) the same as in (1) in example 1.

(2) Same as example 1 (2)

(3)Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Preparation of

Weighing a proper amount of bismuth nitrate, adding the bismuth nitrate into 10mL of bismuth nitrate with the volume of 2mol/L HNO₃Dissolving in solution with ultrasound to obtain clear solution, and adding into 40mL of 0.6mol/L Na at a certain speed₂CO₃In the solution, mechanically stirring for 2h to obtain beta-Bi₂O₃Precursor solution; in the form of beta-Bi₂O₃:BiVO₄/Mn_xZn_1-xFe₂O₄Weighing Mn according to the mass ratio of 15:100_xZn_1-xFe₂O₄/BiVO₄To beta-Bi₂O₃Mechanically stirring the precursor solution for 2 hours, filtering, washing a filter cake with distilled water, then placing the filter cake in a drying oven at 60 ℃ for drying for 12 hours, and grinding to obtain composite precursor powder; putting the precursor powder into a muffle furnace, roasting at 380 ℃ for 10min, then quickly taking out the precursor powder from the muffle furnace, and naturally cooling to obtain Mn with different mass ratios_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄。

Results of the experiment

Magnetic composite photocatalyst Mn prepared in example 2_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The catalytic degradation activity is optimal. For easy comparison, beta-Bi was prepared₂O₃Sample and BiVO₄。β-Bi₂O₃The preparation method is that BiVO is not added in the step (3) of the example 2₄/Mn_xZn_1-xFe₂O₄；BiVO₄The preparation method is that no Mn is added in the step (2) of the example 1_xZn_1-xFe₂O₄。

β-Bi₂O₃The XRD pattern of (A) is shown in FIG. 1(b), and each diffraction peak corresponds to pure β -Bi₂O₃The characteristic peak (JCPDS #27-0050) with characteristic reflection peaks including (210), (201), (220), (222), (200) and (400) etc. proves that the sample is the pure square crystal structure of beta-Bi₂O₃。β-Bi₂O₃The infrared absorption spectrum of (2) is as shown in FIG. 2(c), and it is 1383cm^-1、846.3cm^-1、585.6cm^-1Has a peak of beta-Bi₂O₃Typical Bi-O bond absorption peak。

BiVO₄The XRD pattern of (A) is shown in FIG. 1(c), and BiVO is prepared₄According to the JCPDS PDF document No.14-0688, strong diffraction peaks exist in the crystal faces (110), (011), (121), (040), (200), (002), (211), (150), (240), (042), (220), (161), (321) and (123), and the prepared sample is m-BiVO₄。BiVO₄The infrared absorption spectrum of (c) is as shown in FIG. 2(b), at 615cm^-1Is attributed to VO₄At 430cm^-1The peak of (A) is VO₄Caused by inconsistent contraction movement of V1^[9]The presence of BiVO in the sample is also proved₄The complete crystal form of (a).

Magnetic composite photocatalyst Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄XRD diffraction of (B) is shown in FIG. 1(a), Mn_xZn_{1- x}Fe₂O₄For modifying beta-Bi₂O₃In which Mn is not observed_xZn_1-xFe₂O₄Characteristic diffraction peaks, which may be due to Mn in the sample per unit mass_xZn_1-xFe₂O₄Is low in content of (2), and Mn_xZn_1-xFe₂O₄Peak of (2) is represented by beta-Bi₂O₃The strong diffraction peak is covered. Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄Has an infrared absorption spectrum of 585.6cm as shown in FIG. 2(a)^-1And 472cm^-1Mn of (C)_xZn_1-xFe₂O₄Characteristic absorption peak, further shows that the whole process of preparing the catalyst by loading does not change Mn_xZn_1-xFe₂O₄The self structure of (B) shows Mn_xZn_1-xFe₂O₄Is present, which complements the XRD result well; at 1383cm^-1、846.3cm^-1、585.6cm^-1The absorption peak of Bi-O bond shows that the sample contains the beta-Bi with complete crystal form₂O₃(ii) a At 635cm^-1、480cm^-1Peak pair ofThe inconsistent contraction oscillation peak of V2 p of V-O indicates that the sample contains BiVO₄。Mn_xZn_1-xFe₂O₄The magnetic parameters of (A) were measured as shown in FIG. 3(a), and the saturation magnetization was 75.13 emu/g. Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The magnetic parameters of (a) were measured as in FIG. 3(b), and the saturation magnetization was 2.67 emu/g.

The photocatalysis experiment shows that 0.1g of magnetic composite photocatalyst Mn is used for preparing under the irradiation of a xenon lamp simulating sunlight_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄50mL of 10mg/L rhodamine B solution is degraded, the degradation rate of the rhodamine B after 3 hours of illumination reaches 92.8%, and the degradation rate after 3 times of recycling still reaches 84.9%; the test showed that the average recovery of the three recoveries was 89.7%, indicating that Mn was prepared using the present invention_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The magnetic composite photocatalyst has higher photocatalytic activity and stability.

Claims (2)

1. Magnetic bismuth oxide/bismuth vanadate composite photocatalyst Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The preparation method comprises the following steps:

(1)Mn_xZn_1-xFe₂O₄the preparation of (1): ZnO according to a molar ratio: MnO: fe₂O₃13.3: 32.8: 53.9, respectively weighing a proper amount of zinc sulfate, ferric sulfate and manganese sulfate, adding 25mL of deionized water, and dissolving by ultrasonic oscillation to obtain a mixed solution; under the action of magnetic stirring, dropwise adding a NaOH solution with a certain concentration into the mixed solution, adjusting the pH of the solution to 13, and continuously stirring for 15 min; transferring the stirred solution into a 100mL reaction kettle, and reacting for 5h at 200 ℃; after the reaction is finished, cooling and suction filtering are carried out, filter cakes are respectively washed for 5 times by distilled water and ethanol, the filter cakes are dried for 12 hours at the temperature of 80 ℃, and Mn is obtained by grinding_xZn_1-xFe₂O₄；

(2)Mn_xZn_1-xFe₂O₄/BiVO₄The preparation of (1): weighing a certain amount of bismuth nitrate pentahydrate, and adding HNO with the concentration of 2mol/L₃In the solution, ultrasonic oscillation is carried out to dissolve the solution to obtain a solution A; according to Bi (NO)₃)₃·5H₂Weighing tartaric acid according to different proportions, and dissolving the tartaric acid in hot water at the temperature of 80 ℃ to obtain a solution B; in a molar ratio of Bi (NO)₃)₃·5H₂O:NH₄VO₃Weighing ammonium metavanadate at the ratio of 1:1, and dissolving the ammonium metavanadate in hot water at the temperature of 80 ℃ to obtain a solution C; dripping the solution B into the solution C to obtain a mixed solution D; then adding the solution A into the mixed solution D, cooling the solution, and adjusting the pH of the solution to 7.5 by using ammonia water to obtain BiVO₄A precursor of (a); according to Mn_1-xZn_xFe₂O₄:BiVO₄The mass ratio is 10:100 weighing the Mn obtained above_1-xZn_xFe₂O₄Adding into BiVO₄Performing water bath reaction on the precursor at 80 ℃ for 30min, filtering, drying, grinding, placing in a muffle furnace at 450 ℃ for reaction for 3h, taking out, and cooling to room temperature to obtain Mn_xZn_1-xFe₂O₄/BiVO₄；

(3)Mn_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The preparation of (1): weighing a proper amount of bismuth nitrate, adding the bismuth nitrate into 10mL of 2mol/L HNO₃Dissolving with ultrasound to obtain clear solution, and adding into 40mL of 0.6mol/L Na₂CO₃In the solution, mechanically stirring for 2h to obtain beta-Bi₂O₃Precursor solution; in the form of beta-Bi₂O₃:Mn_xZn_1-xFe₂O₄/BiVO₄Weighing Mn according to the mass ratio of 5-15: 100_xZn_1-xFe₂O₄/BiVO₄To beta-Bi₂O₃Mechanically stirring the precursor solution for 2 hours, filtering, washing a filter cake with distilled water, then placing the filter cake in a drying oven at 60 ℃ for drying for 12 hours, and grinding to obtain composite precursor powder; putting the precursor powder into a muffle furnace, roasting at 380 ℃ for 10min, then quickly taking out the precursor powder from the muffle furnace, and naturally cooling the precursor powderThereby obtaining Mn with different mass ratios_xZn_{1- x}Fe₂O₄/β-Bi₂O₃/BiVO₄。

2. The magnetic bismuth oxide/bismuth vanadate composite photocatalyst Mn according to claim 1_xZn_1-xFe₂O₄/β-Bi₂O₃/BiVO₄The preparation method is characterized in that the preparation method is prepared by a hydrothermal-coprecipitation-roasting method, and the catalytic active component beta-Bi is realized₂O₃、BiVO₄The magnetic material is firmly combined with the magnetic material and the matrix.

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