Photocatalyst for open pit coal mine drainage water treatment and preparation method thereof

Abstract

The invention relates to the technical field of coal mine wastewater treatment, in particular to a photocatalyst for open pit coal mine drainage water treatment and a preparation method thereof.The preparation method comprises the steps that bivalent iron salt and trivalent iron salt are dissolved in deoxidized deionized water, a mixed salt solution is obtained, under inert gas and mechanical stirring, the mixed salt solution is dropwise added into an excessive ammonia water solution, stirring is conducted, and the photocatalyst is obtained; carrying out precipitation reaction to obtain superparamagnetic Fe3O4 nano powder; the preparation method comprises the following steps: dispersing superparamagnetic Fe3O4 nano powder into a mixed solvent of absolute ethyl alcohol and water to obtain a magnetic fluid, slowly dropwise adding tetraethoxysilane and ammonia water into the magnetic fluid under mechanical stirring and ultrasonic treatment, and carrying out catalytic hydrolysis reaction to obtain Fe3O4 coated SiO2 microspheres; slowly dropwise adding a suspension of a titanium source into the suspension of the Fe3O4 (at) SiO2 microspheres under vigorous stirring to obtain a mixed suspension, and performing hydrothermal crystallization on the mixed suspension to obtain Fe3O4 (at) SiO2 (at) N-TiO2 microspheres; and under stirring, sequentially dropwise adding a dilute nitric acid solution of bismuth salt and an aqueous solution of a bromine source into the suspension of the Fe3O4 (at) SiO2 (at) N-TiO2 microspheres, and carrying out an in-situ reaction to obtain the Fe3O4 (at) SiO2 (at) N-TiO2 / BiOBr photocatalyst.

Description

Technical Field

[0001] This invention relates to the field of coal mine wastewater treatment and resource recycling technology, and in particular to a photocatalyst for open-pit coal mine drainage water treatment and its preparation method. Background Technology

[0002] my country has abundant coal resources, and open-pit mining generates a large amount of mine water, also known as coal mine drainage water. This water has a complex composition, containing high concentrations of suspended solids (such as coal dust and rock fragments), dissolved salts, oils, and various heavy metal ions. It is also characterized by high turbidity and high hardness, classifying it as recalcitrant industrial wastewater. Direct discharge without proper treatment will not only cause serious water pollution and ecological damage but also represent a huge waste of water resources.

[0003] Currently, the treatment of coal mine drainage water still largely relies on traditional processes, such as natural sedimentation, coagulation and flocculation, and filtration—physicochemical methods. However, these methods have significant limitations: simple sedimentation treatment has limited effectiveness, and the effluent often fails to meet standards; conventional advanced treatment processes such as chemical oxidation and membrane separation can improve water quality, but they suffer from high treatment costs, high energy consumption, and the potential for secondary pollution from chemical sludge or concentrated brine. Traditional technologies are particularly inefficient in the deep removal of low-concentration organic pollutants and ionic heavy metals.

[0004] Photocatalytic oxidation, as an advanced oxidation process, can utilize light energy to generate highly oxidizing free radicals, thoroughly degrading organic pollutants and reducing heavy metal ions. It boasts advantages such as thorough reaction and no secondary pollution, showing great promise in the field of water treatment. However, applying this technology to actual coal mine drainage water treatment still faces several technical bottlenecks: First, conventional photocatalysts (such as TiO2) only respond to ultraviolet light, resulting in low solar energy utilization efficiency and high energy consumption; second, nanoparticle catalysts are difficult to effectively separate and recover from the water body after use, leading not only to catalyst loss and increased operating costs but also potential secondary pollution caused by nanoparticle residues; third, the high turbidity of coal mine drainage water severely hinders light transmission, greatly reducing photocatalytic reaction efficiency; and fourth, complex water composition may cause poisoning or shielding of catalyst active sites, leading to a rapid decline in catalytic performance.

[0005] To address these issues, researchers have undertaken numerous improvements, such as broadening the photoresponse range of catalysts through elemental doping or avoiding catalyst separation problems through immobilization techniques. However, existing technologies have yet to achieve an effective balance between high-efficiency catalysis, easy recovery, interference resistance, and visible light utilization. For instance, some studies have used supported catalysts to solve the separation problem but at the expense of catalytic activity; some visible light catalysts, while improving light energy utilization, face challenges such as complex preparation, poor stability, or difficulty in recovery.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a photocatalyst for treating drainage water in open-pit coal mines and its preparation method, which significantly improves the treatment efficiency of drainage water in open-pit coal mines.

[0008] In a first aspect, the present invention provides a method for preparing a photocatalyst for treating drainage water in open-pit coal mines, comprising the following steps: S1. Dissolve ferrous salts and ferric salts in deoxygenated and deionized water to obtain a mixed salt solution. Under inert gas protection and mechanical stirring, add the mixed salt solution dropwise into an excess ammonia solution to carry out a precipitation reaction. After the reaction is completed, perform magnetic field separation, washing and drying treatment in sequence to obtain superparamagnetic Fe3O4 nanopowder. S2. Superparamagnetic Fe3O4 nanopowder was dispersed in a mixed solvent of anhydrous ethanol and water to obtain a magnetic fluid. Under the combined action of mechanical stirring and ultrasound, tetraethyl orthosilicate and ammonia were slowly added dropwise to the magnetic fluid to carry out a catalytic hydrolysis reaction. After the reaction was completed, magnetic separation, washing and drying were carried out in sequence to obtain Fe3O4@SiO2 core-shell structured microspheres. S3. Under vigorous stirring, the suspension of titanium source is slowly added dropwise to the suspension of Fe3O4@SiO2 core-shell structured microspheres to obtain a mixed suspension. The mixed suspension is then transferred to a hydrothermal reactor for hydrothermal crystallization. After the reaction is completed, magnetic field separation, washing, drying and calcination are performed in sequence to obtain Fe3O4@SiO2@N-TiO2 microspheres. S4. Under stirring, a dilute nitric acid solution of bismuth salt and an aqueous solution of bromine source are added dropwise to the suspension of Fe3O4@SiO2@N-TiO2 microspheres to carry out in-situ reaction. After the reaction is completed, magnetic separation, washing and drying are carried out in sequence to obtain Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst.

[0009] As a preferred embodiment of this technical solution, in step S1, the molar ratio of divalent ferric salt to trivalent ferric salt is 1:1.5 to 1:2; Preferably, the divalent iron salt includes at least one of FeCl2·4H2O and FeSO4·7H2O; Preferably, the trivalent iron salt includes at least one of FeCl3·6H2O and Fe(NO3)3·9H2O.

[0010] In a preferred embodiment of this technical solution, during step S1, the precipitation reaction is controlled at a temperature of 50-70°C, a pH value of 10-12, and a time of 2-4 hours.

[0011] As a preferred embodiment of this technical solution, in step S2, the volume ratio of anhydrous ethanol to water in the mixed solvent of anhydrous ethanol and water is 4:1. The amount of tetraethyl orthosilicate added is 5% to 15% of the mass of the photocatalyst.

[0012] As a preferred embodiment of this technical solution, in step S2, the catalytic hydrolysis reaction is continuously stirred at room temperature for 6-12 hours.

[0013] As a preferred embodiment of this technical solution, in step S3, the hydrothermal crystallization is performed at a temperature of 120~160℃ for a time of 12~24h.

[0014] As a preferred embodiment of this technical solution, in step S3, during the calcination, the temperature is controlled at 350~450℃ and the time is 2~4h under an ammonia atmosphere. During this process, nitrogen atoms produced by the decomposition of NH3 will be incorporated into the TiO2 lattice, replacing some oxygen atoms to form N-TiO2, thereby extending its light response range to the visible light region.

[0015] In a preferred embodiment of this technical solution, in step S4, a dilute nitric acid solution of bismuth salt is added dropwise to the suspension of Fe3O4@SiO2@N-TiO2 microspheres under stirring. After stirring for 0.5 to 1.5 hours, an aqueous solution of bromine source is added dropwise. After the addition is complete, the reaction continues for 4 to 6 hours.

[0016] Using dilute nitric acid to prepare bismuth salt can effectively prevent the hydrolysis of bismuth salt to produce a white precipitate, which would lead to loading failure; while the slow addition of bromine source can also effectively ensure that BiOBr can nucleate and grow on the N-TiO2 surface in a controllable manner, forming a uniform heterojunction.

[0017] As a preferred embodiment of this technical solution, in step S4, the bismuth salt includes at least one of Bi(NO3)3·5H2O, BiCl3 and Bi2(SO4)3, and is preferably Bi(NO3)3·5H2O. Bi(NO3)3·5H2O has good reaction kinetics and is easy to form a regular nanosheet structure. The bromine source includes C 16 H 33 At least one of N(CH3)3Br, NaBr, KBr and NH4Br, preferably C 16 H 33 N(CH3)3Br,C 16 H 33 N(CH3)3Br is Br - The source is a surfactant, which can effectively regulate the microstructure of BiOBr and increase its specific surface area; Preferably, the molar ratio of bismuth salt to bromine source is expressed as Bi 3+ With Br -The molar ratio is 1:1.

[0018] This invention employs a "stepwise method" of first synthesizing N-TiO2 and then growing BiOBr in situ on its surface, which can form a denser and more efficient heterojunction interface, greatly promoting the separation and migration of photogenerated carriers and improving quantum efficiency.

[0019] The doping of nitrogen element enables TiO2 to utilize visible light, while the narrow bandgap of BiOBr further broadens the spectral utilization range. Together, they can achieve efficient utilization of solar energy.

[0020] Secondly, the present invention also discloses a photocatalyst for open-pit coal mine drainage water treatment prepared by the above preparation method, wherein the molar ratio of N-TiO2 to BiOBr in the Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst is 1:0.1 to 1:0.5. Preferably, the molar ratio of Fe3O4 to TiO2 is 1:2 to 1:6; Preferably, in N-TiO2, the molar ratio of Ti to N is 1:0.01 to 1:0.05; Preferably, the weight of the SiO2 shell is 10% to 20% of the total weight of the Fe3O4@SiO2 core-shell structure.

[0021] The method for preparing a photocatalyst for open-pit coal mine drainage water treatment according to the present invention has at least the following beneficial effects: In the preparation method of this invention, superparamagnetic Fe3O4 nanoparticles are first prepared by co-precipitation and used as a carrier for the photocatalyst. The huge specific surface area of ​​the superparamagnetic Fe3O4 nanoparticles can efficiently adsorb and enrich pollutants, transforming "photocatalysis" into "local high-concentration enrichment catalysis," thereby significantly improving the rate and efficiency of surface catalytic reactions and overcoming the problem of slow reaction rates at low concentrations. Furthermore, the photocatalyst is endowed with superparamagnetism, allowing for rapid recovery within seconds using an external magnetic field after the photocatalytic reaction, solving the recovery problem. Then, a SiO2 intermediate layer is wrapped around the magnetic core using a hydrothermal / sol-gel method to prevent oxidation, dissolution, or photocorrosion of the magnetic core during photocatalysis, ensuring the long-term magnetic and chemical stability of the catalyst. Finally, a stepwise loading method was used to first synthesize N-TiO2 on the surface of Fe3O4@SiO2 core-shell microspheres, and then BiOBr was grown in situ on its surface to construct a heterojunction interface. This not only promoted the separation and migration of photogenerated carriers and achieved spatial separation of photogenerated electrons and holes, but also preserved the catalyst's strong redox ability, enabling the catalyst to generate more highly active free radicals (such as ·OH, ·O2) under light irradiation. -This catalyst exhibits a synergistic and efficient degradation and removal capability for various organic pollutants (phenols, aromatics, oils) and heavy metal ions (such as Cr(VI)) in coal mine drainage water. Furthermore, it successfully extends the light response range from the ultraviolet region to the visible light region and even part of the near-infrared light, achieving efficient utilization of the entire solar spectrum and significantly reducing dependence on artificial ultraviolet light sources, thereby substantially reducing catalytic energy consumption. In addition, the Fe3O4 magnetic core endows the catalyst with strong magnetism. Under the action of an external magnetic field, the catalyst can achieve rapid and thorough solid-liquid separation from the treated water within tens of seconds, with a recovery rate of over 99.9%. This perfectly solves the core industrialization problem of the difficulty in recovering nanoparticle catalysts and their tendency to cause secondary pollution, fundamentally reducing operating costs. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating the preparation process of the photocatalyst for open-pit coal mine drainage water treatment according to the present invention. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 Preparation of S1 superparamagnetic Fe3O4 nanopowder The divalent ferric salt FeCl2·4H2O and the trivalent ferric salt FeCl3·6H2O were dissolved in deoxygenated and deionized water to obtain a mixed salt solution, wherein the molar ratio of the divalent ferric salt to the trivalent ferric salt was 1:1.3. Under the protection of nitrogen inert gas and vigorous mechanical stirring at 500-800 rpm, the above mixed salt solution was added dropwise to an excess of ammonia solution with a concentration of 2.0-4.0 mol / L. The reaction temperature was controlled at 50-70℃ and the pH of the reaction solution was between 10 and 12. After the addition was completed, the reaction was continued at a constant temperature for 2-4 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field. The black precipitate was collected and washed several times with deionized water and anhydrous ethanol until the supernatant was neutral and free of chloride ions. Finally, the product was dried in a vacuum drying oven at 60-80℃ for 12 hours to obtain superparamagnetic Fe3O4 nanoparticles.

[0028] Preparation of S2, Fe3O4@SiO2 core-shell structured microspheres The superparamagnetic Fe3O4 nanopowder prepared in step S1 was dispersed in a mixed solvent of anhydrous ethanol and deionized water (the volume ratio of anhydrous ethanol to water was 4:1), and ultrasonically treated for 30 minutes to form a uniform magnetofluid suspension. Ethyl orthosilicate (TEOS) was slowly added dropwise to the above-mentioned magnetofluid suspension under the combined action of mechanical stirring and ultrasound, wherein the amount of TEOS added was 20% of the total mass of the target catalyst; Add an appropriate amount of ammonia water dropwise as a catalyst and stir continuously at room temperature for 6 to 12 hours to carry out the catalytic hydrolysis reaction; After the reaction was completed, the Fe3O4@SiO2 core-shell structured microspheres were separated by an external magnetic field, washed thoroughly with ethanol, and finally dried at 60°C for 6 hours to obtain Fe3O4@SiO2 core-shell structured microspheres.

[0029] Preparation of S3, Fe3O4@SiO2@N-TiO2 microspheres Tetrabutyl titanate was dissolved in anhydrous ethanol to form a suspension of titanium source; Fe3O4@SiO2 core-shell structured microspheres obtained in step S2 were dispersed in another part of anhydrous ethanol and ultrasonically formed a uniform suspension of Fe3O4@SiO2 core-shell structured microspheres, wherein the amount of tetrabutyl titanate added was based on a molar ratio of Fe3O4 to TiO2 of 1:4. Under vigorous stirring, the suspension of titanium source was slowly added dropwise to the suspension of Fe3O4@SiO2 core-shell structured microspheres to ensure that the titanium source precursor was fully and uniformly adsorbed on the surface of the support. After the addition was completed, the mixture was transferred to a hydrothermal reactor and reacted at 120~160℃ for 12~24 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field, and the precipitate was washed several times with deionized water and anhydrous ethanol alternately. It was then dried under vacuum at 60°C to obtain the Fe3O4@SiO2@TiO2 precursor. Fe3O4@SiO2@TiO2 precursor was placed in a tube furnace, and high-purity (99.99%) ammonia gas was introduced at a flow rate of 100 sccm. After the air was removed, the temperature was raised to 400℃ at a rate of 5℃ / min and calcined at this temperature for 3 hours. After cooling to room temperature, Fe3O4@SiO2@N-TiO2 microspheres were obtained.

[0030] Preparation of S4, Fe3O4@SiO2@N-TiO2 / BiOBr photocatalysts The Fe3O4@SiO2@N-TiO2 microspheres obtained in step S3 were dispersed in deionized water; a 0.1 mol / L Bi(NO3)3·5H2O dilute nitric acid solution was prepared using 0.5~1.0 mol / L nitric acid solution, and a 0.1 mol / L L Bi(NO3)3·5H2O solution was prepared simultaneously. 16 H 33 An aqueous solution of N(CH3)3Br; Under stirring, a dilute nitric acid solution of bismuth salt was added dropwise to a suspension of Fe3O4@SiO2@N-TiO2 microspheres. After stirring for 0.5 to 1.5 hours, an aqueous solution of bromine source was added dropwise. After the addition was complete, the reaction continued for 4 to 6 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field, and the precipitate was washed several times with deionized water and anhydrous ethanol alternately. The precipitate was then dried under vacuum at 60°C to obtain the Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst.

[0031] Figure 1 This is a flowchart illustrating the preparation process of the catalyst of this invention.

[0032] Example 2 Preparation of S1 superparamagnetic Fe3O4 nanopowder The divalent ferric salt FeSO4·7H2O and the trivalent ferric salt Fe(NO3)3·9H2O were dissolved in deoxygenated and deionized water to obtain a mixed salt solution, wherein the molar ratio of the divalent ferric salt to the trivalent ferric salt was 1:1.5. Under the protection of nitrogen inert gas and vigorous mechanical stirring at 500-800 rpm, the above mixed salt solution was added dropwise to an excess of ammonia solution with a concentration of 2.0-4.0 mol / L. The reaction temperature was controlled at 50-70℃ and the pH of the reaction solution was between 10 and 12. After the addition was completed, the reaction was continued at a constant temperature for 2-4 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field. The black precipitate was collected and washed several times with deionized water and anhydrous ethanol until the supernatant was neutral and free of chloride ions. Finally, the product was dried in a vacuum drying oven at 60-80℃ for 12 hours to obtain superparamagnetic Fe3O4 nanoparticles.

[0033] Preparation of S2, Fe3O4@SiO2 core-shell structured microspheres The superparamagnetic Fe3O4 nanopowder prepared in step S1 was dispersed in a mixed solvent of anhydrous ethanol and deionized water (the volume ratio of anhydrous ethanol to water was 4:1), and ultrasonically treated for 30 minutes to form a uniform magnetofluid suspension. Ethyl orthosilicate (TEOS) was slowly added dropwise to the above-mentioned magnetofluid suspension under the combined action of mechanical stirring and ultrasound, wherein the amount of TEOS added was 15% of the total mass of the target catalyst; Add an appropriate amount of ammonia water dropwise as a catalyst and stir continuously at room temperature for 6 to 12 hours to carry out the catalytic hydrolysis reaction; After the reaction was completed, the Fe3O4@SiO2 core-shell structured microspheres were separated by an external magnetic field, washed thoroughly with ethanol, and finally dried at 60°C for 6 hours to obtain Fe3O4@SiO2 core-shell structured microspheres.

[0034] Preparation of S3, Fe3O4@SiO2@N-TiO2 microspheres Tetrabutyl titanate was dissolved in anhydrous ethanol to form a suspension of titanium source; Fe3O4@SiO2 core-shell structured microspheres obtained in step S2 were dispersed in another part of anhydrous ethanol and ultrasonically formed a uniform suspension of Fe3O4@SiO2 core-shell structured microspheres, wherein the amount of tetrabutyl titanate added was based on a molar ratio of Fe3O4 to TiO2 of 1:6. Under vigorous stirring, the suspension of titanium source was slowly added dropwise to the suspension of Fe3O4@SiO2 core-shell structured microspheres to ensure that the titanium source precursor was fully and uniformly adsorbed on the surface of the support. After the addition was completed, the mixture was transferred to a hydrothermal reactor and reacted at 120~160℃ for 12~24 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field, and the precipitate was washed several times with deionized water and anhydrous ethanol alternately. It was then dried under vacuum at 60°C to obtain the Fe3O4@SiO2@TiO2 precursor. Fe3O4@SiO2@TiO2 precursors were placed in a tube furnace, and high-purity (99.99%) ammonia gas was introduced at a flow rate of 100 sccm. After the air was removed, the temperature was raised to 350℃ at a rate of 5℃ / min and calcined at this temperature for 4 hours. After cooling to room temperature, Fe3O4@SiO2@N-TiO2 microspheres were obtained.

[0035] Preparation of S4, Fe3O4@SiO2@N-TiO2 / BiOBr photocatalysts The Fe3O4@SiO2@N-TiO2 microspheres obtained in step S3 were dispersed in deionized water; a 0.2 mol / L BiCl3 dilute nitric acid solution was prepared using 0.5~1.0 mol / L nitric acid solution, and a 0.2 mol / L KBr aqueous solution was prepared at the same time; Under stirring, a dilute nitric acid solution of bismuth salt was added dropwise to a suspension of Fe3O4@SiO2@N-TiO2 microspheres. After stirring for 0.5 to 1.5 hours, an aqueous solution of bromine source was added dropwise. After the addition was complete, the reaction continued for 4 to 6 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field, and the precipitate was washed several times with deionized water and anhydrous ethanol alternately. The precipitate was then dried under vacuum at 60°C to obtain the Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst.

[0036] Example 3 Preparation of S1 superparamagnetic Fe3O4 nanopowder The ferrous salt FeCl2·4H2O and the ferric salt FeCl3·6H2O were dissolved in deoxygenated and deionized water to obtain a mixed salt solution, wherein the molar ratio of the ferrous salt to the ferric salt was 1:1:2. Under the protection of nitrogen inert gas and vigorous mechanical stirring at 500-800 rpm, the above mixed salt solution was added dropwise to an excess of ammonia solution with a concentration of 2.0-4.0 mol / L. The reaction temperature was controlled at 50-70℃ and the pH of the reaction solution was between 10 and 12. After the addition was completed, the reaction was continued at a constant temperature for 2-4 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field. The black precipitate was collected and washed several times with deionized water and anhydrous ethanol until the supernatant was neutral and free of chloride ions. Finally, the product was dried in a vacuum drying oven at 60-80℃ for 12 hours to obtain superparamagnetic Fe3O4 nanoparticles.

[0037] Preparation of S2, Fe3O4@SiO2 core-shell structured microspheres The superparamagnetic Fe3O4 nanopowder prepared in step S1 was dispersed in a mixed solvent of anhydrous ethanol and deionized water (the volume ratio of anhydrous ethanol to water was 4:1), and ultrasonically treated for 30 minutes to form a uniform magnetofluid suspension. Ethyl orthosilicate (TEOS) was slowly added dropwise to the above-mentioned magnetofluid suspension under the combined action of mechanical stirring and ultrasound, wherein the amount of TEOS added was 5% of the total mass of the target catalyst; Add an appropriate amount of ammonia water dropwise as a catalyst and stir continuously at room temperature for 6 to 12 hours to carry out the catalytic hydrolysis reaction; After the reaction was completed, the Fe3O4@SiO2 core-shell structured microspheres were separated by an external magnetic field, washed thoroughly with ethanol, and finally dried at 60°C for 6 hours to obtain Fe3O4@SiO2 core-shell structured microspheres.

[0038] Preparation of S3, Fe3O4@SiO2@N-TiO2 microspheres Tetrabutyl titanate was dissolved in anhydrous ethanol to form a suspension of titanium source; Fe3O4@SiO2 core-shell structured microspheres obtained in step S2 were dispersed in another part of anhydrous ethanol and ultrasonically formed a uniform suspension of Fe3O4@SiO2 core-shell structured microspheres, wherein the amount of tetrabutyl titanate added was based on a molar ratio of Fe3O4 to TiO2 of 1:2. Under vigorous stirring, the suspension of titanium source was slowly added dropwise to the suspension of Fe3O4@SiO2 core-shell structured microspheres to ensure that the titanium source precursor was fully and uniformly adsorbed on the surface of the support. After the addition was completed, the mixture was transferred to a hydrothermal reactor and reacted at 120~160℃ for 12~24 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field, and the precipitate was washed several times with deionized water and anhydrous ethanol alternately. It was then dried under vacuum at 60°C to obtain the Fe3O4@SiO2@TiO2 precursor. Fe3O4@SiO2@TiO2 precursor was placed in a tube furnace, and high-purity (99.99%) ammonia gas was introduced at a flow rate of 100 sccm. After the air was removed, the temperature was raised to 450℃ at a rate of 5℃ / min and calcined at this temperature for 2 hours. After cooling to room temperature, Fe3O4@SiO2@N-TiO2 microspheres were obtained.

[0039] Preparation of S4, Fe3O4@SiO2@N-TiO2 / BiOBr photocatalysts The Fe3O4@SiO2@N-TiO2 microspheres obtained in step S3 were dispersed in deionized water; a dilute nitric acid solution of 0.05 mol / L BiCl3 was prepared using 0.5~1.0 mol / L nitric acid solution, and a 0.05 mol / L NaBr aqueous solution was prepared at the same time; Under stirring, a dilute nitric acid solution of bismuth salt was added dropwise to a suspension of Fe3O4@SiO2@N-TiO2 microspheres. After stirring for 0.5 to 1.5 hours, an aqueous solution of bromine source was added dropwise. After the addition was complete, the reaction continued for 4 to 6 hours. After the reaction was completed, solid-liquid separation was performed using an external magnetic field, and the precipitate was washed several times with deionized water and anhydrous ethanol alternately. The precipitate was then dried under vacuum at 60°C to obtain the Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst.

[0040] Compare with Example 1 This comparative example is basically the same as Example 1, except that: superparamagnetic Fe3O4 nanopowder was not introduced, and SiO2 was used as the catalyst support to prepare SiO2@N-TiO2 / BiOBr photocatalyst.

[0041] Compare with Example 2 This comparative example is basically the same as Example 1, except that: no SiO2 intermediate protective layer was set, and the Fe3O4@N-TiO2 / BiOBr photocatalyst was prepared. Compare with Example 3 This comparative example is basically the same as Example 1, except that Fe3O4@SiO2@N-TiO2 microspheres are mixed with purchased BiOBr powder to prepare Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst.

[0042] Experimental Example 1 This experimental example tested the degradation rate of pollutants by the photocatalysts obtained in Example 1 and Control Examples 1-3 using simulated coal mine drainage water. The specific implementation steps are as follows: To simulate the water quality of coal mine drainage water, a solution of 20 mg / L pyridine characteristic pollutant was prepared.

[0043] Add 100 mL of pollutant solution and 50 mg of catalyst to the reactor. Under dark conditions, continuously stir magnetically for 30 minutes to allow the catalyst and pollutant to reach adsorption-desorption equilibrium, eliminating the interference of dark adsorption on subsequent photocatalytic degradation data.

[0044] Turn on the xenon lamp and start timing. At regular intervals (e.g., 0, 10, 20, 30, 60, 90, 120 min), take 4 mL of the reaction solution and immediately filter it through a 0.22 μm filter membrane or separate it using an external magnet to completely remove the catalyst particles and obtain a clear supernatant.

[0045] The absorbance of pyridine was measured using a UV spectrophotometer at the maximum characteristic absorption wavelength of 255 nm. The remaining concentration was calculated using the following formula and a pre-plotted standard curve. Table 1 shows the test results.

[0046] η (%) = (1 - C t / C0) × 100% Where η is the degradation rate, C0 is the initial concentration, and C t The concentration at time t Table 1 Degradation rate after 120 minutes of visible light irradiation.

[0047] As shown in Table 1, the catalyst of the present invention achieves a pyridine removal rate of up to 98.5% within 120 minutes, exhibiting excellent visible light photocatalytic activity. After five cycles, the catalyst retains an activity rate of over 94%, and nearly 100% recovery can be achieved through magnetic separation each time, demonstrating excellent stability and reusability, thus solving the problem of catalyst recovery.

[0048] Experimental Example 2 This experimental example tested the photogenerated charge separation efficiency and transport capability of the photocatalysts obtained in Example 1 and Control Examples 1-3 by measuring current and impedance electrochemical signals. The specific implementation steps are as follows: Take 5 mg of catalyst sample, disperse it in 1 mL of Nafion / ethanol solution (0.5 wt%), and sonicate for 30 minutes to form a uniform ink.

[0049] The above ink was uniformly coated onto a pre-cleaned fluorine-doped tin oxide (FTO) conductive glass using a drop-coating method, air-dried at room temperature, and then dried overnight at 60°C to obtain the working electrode to be tested.

[0050] The transient photocurrent response and transient photocurrent response were tested using an electrochemical workstation, and the test results are shown in Table 2.

[0051] Table 2 Photoelectrochemical performance data

[0052] As shown in Table 2, the catalyst obtained in Example 1 of this invention produced the strongest and most stable photocurrent response, indicating that its N-TiO2 / BiOBr heterojunction structure effectively promoted the separation of electron-hole pairs and rapidly transported electrons to the external circuit. Furthermore, the catalyst in Example 1 had the smallest impedance arc radius, indicating that it had the lowest charge transfer resistance and the smoothest interfacial charge transport process. The arc radius of Comparative Example 1 was similar to that of Example 1, demonstrating the non-participation of the magnetic nucleus. The photocurrent of Comparative Example 2 was significantly lower and more unstable because, without the protection of the SiO2 layer, the Fe3O4 magnetic nucleus directly contacted the active layer, becoming the recombination center of photogenerated electron-hole pairs, greatly reducing the charge separation efficiency and leading to extremely high charge transport resistance. Comparative Example 3, due to the inability to form an effective heterojunction interface through physical mixing, had a lower photocurrent, and electrons needed to overcome a very high energy barrier to transport between different components.

[0053] Experimental Example 3 The present invention also verified the purification ability of the catalysts obtained in Example 1 and Comparative Examples 1-3 on actual open-pit coal mine drainage water. The specific implementation steps are as follows: The water sample was allowed to stand for 2 hours to settle, and the supernatant was taken to remove large suspended particles.

[0054] Take 200 mL of pretreated water sample and put it into a 250 mL quartz reactor, then add 100 mg of catalyst.

[0055] Magnetic stirring was performed in the dark for 30 minutes to reach adsorption-desorption equilibrium.

[0056] Turn on a 300 W xenon lamp (with a 420 nm cutoff filter) to simulate visible light irradiation and continue the reaction for 4 hours.

[0057] After the reaction was completed, the catalyst was rapidly separated using an external magnetic field, and the supernatant was collected for testing. The test results are shown in Table 3.

[0058] Table 3 Test Results

[0059] As shown in Table 3, the catalyst obtained in Example 1 of this invention exhibits the best overall purification effect, with removal rates of 87.1% for CODcr, 97.7% for turbidity, and 98.0% for total iron. The effluent quality meets the standard of "Water Quality Standard for Landscape and Environmental Water Use in Urban Wastewater Reuse" (GB / T 18921-2019). Although Control Example 1 showed comparable initial results, it could not achieve magnetic recovery and therefore could not be recycled. Control Example 2 suffered from severe performance degradation due to structural damage. Control Example 3 had the worst treatment effect due to insufficient activity.

[0060] In summary, this invention, through the synergistic design of a magnetic core, an insulating layer, and a heterojunction, enables efficient, stable, and recyclable treatment of coal mine drainage water.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a photocatalyst for treating drainage water in open-pit coal mines, characterized in that, Includes the following steps: S1. Dissolve ferrous salts and ferric salts in deoxygenated and deionized water to obtain a mixed salt solution. Under the protection of an inert gas and mechanical stirring, add the mixed salt solution dropwise into an excess of ammonia solution to carry out a precipitation reaction and obtain superparamagnetic Fe3O4 nanopowder. S2. Superparamagnetic Fe3O4 nanopowder was dispersed in a mixed solvent of anhydrous ethanol and water to obtain a magnetic fluid. Under the combined action of mechanical stirring and ultrasound, tetraethyl orthosilicate and ammonia were slowly added dropwise to the magnetic fluid to carry out a catalytic hydrolysis reaction, and Fe3O4@SiO2 core-shell structured microspheres were obtained. S3. Under vigorous stirring, the suspension of titanium source is slowly added dropwise to the suspension of Fe3O4@SiO2 core-shell structured microspheres to obtain a mixed suspension. The mixed suspension is then transferred to a hydrothermal reactor for hydrothermal crystallization to obtain Fe3O4@SiO2@N-TiO2 microspheres. S4. Under stirring, a dilute nitric acid solution of bismuth salt and an aqueous solution of bromine source are added dropwise to the suspension of Fe3O4@SiO2@N-TiO2 microspheres to carry out an in-situ reaction, thereby obtaining the Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of ferrous salt to ferric salt is 1:1.5 to 1:2; Preferably, the divalent iron salt includes at least one of FeCl2·4H2O and FeSO4·7H2O; Preferably, the trivalent iron salt includes at least one of FeCl3·6H2O and Fe(NO3)3·9H2O.

3. The preparation method according to claim 1, characterized in that, In step S1, the precipitation reaction is carried out at a temperature of 50-70°C, a pH of 10-12, and a time of 2-4 hours.

4. The preparation method according to claim 1, characterized in that, In step S2, the volume ratio of anhydrous ethanol to water in the mixed solvent of anhydrous ethanol and water is 4:

1. The amount of tetraethyl orthosilicate added is 5% to 15% of the mass of the photocatalyst.

5. The preparation method according to claim 1, characterized in that, In step S2, the catalytic hydrolysis reaction is carried out by continuous stirring at room temperature for 6 to 12 hours.

6. The preparation method according to claim 1, characterized in that, In step S3, during the hydrothermal crystallization, the temperature is controlled at 120~160℃ and the time is 12~24h.

7. The preparation method according to claim 1, characterized in that, In step S3, the calcination temperature is controlled at 350~450℃ and the time is 2~4h.

8. The preparation method according to claim 1, characterized in that, In step S4, a dilute nitric acid solution of bismuth salt is added dropwise to the suspension of Fe3O4@SiO2@N-TiO2 microspheres under stirring. After stirring for 0.5~1.5h, an aqueous solution of bromine source is added dropwise. After the addition is complete, the reaction continues for 4~6h.

9. The preparation method according to claim 1, characterized in that, In step S4, the bismuth salt includes at least one of Bi(NO3)3·5H2O, BiCl3, and Bi2(SO4)3; The bromine source includes C 16 H 33 At least one of N(CH3)3Br, NaBr, KBr and NH4Br.

10. A photocatalyst for treating drainage water in open-pit coal mines, characterized in that, Prepared by the preparation method according to any one of claims 1-9, In the Fe3O4@SiO2@N-TiO2 / BiOBr photocatalyst, the molar ratio of N-TiO2 to BiOBr is 1:0.1 to 1:0.

5. Preferably, the molar ratio of Fe3O4 to TiO2 is 1:2 to 1:6; Preferably, in N-TiO2, the molar ratio of Ti to N is 1:0.01 to 1:0.05; Preferably, the weight of the SiO2 shell is 10% to 20% of the total weight of the Fe3O4@SiO2 core-shell structure.

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