Supported carbon-doped photocatalyst MnFe-LDH-coated BVC as well as preparation method and application thereof

Abstract

The invention provides a supported carbon-doped photocatalyst MnFe-LDH-coated BVC as well as a preparation method and application thereof, and belongs to the technical field of photocatalytic materials. The method comprises the following steps: mixing straw powder and an acidic LiBr molten salt hydrate, and reacting to obtain biochar; the preparation method comprises the following steps: synthesizing BiVO4 on the surface of biochar in situ to obtain a carbon-based photocatalyst BVC; the preparation method comprises the following steps: mixing BVC and a ferromanganese salt solution to obtain a mixed solution, dropwise adding an alkaline solution into the mixed solution to obtain a turbid liquid, and sequentially carrying out ultrasonic treatment and water bath reaction on the turbid liquid to obtain the supported carbon-doped photocatalyst MnFe-LDH-coated BVC. The composite catalyst provided by the invention is a novel photocatalyst which is non-toxic, environment-friendly and efficient, and can degrade norfloxacin in water under an illumination condition. As a heterogeneous photocatalyst, the photocatalyst is easy to separate, has stable properties, can be repeatedly used, and reduces the treatment cost of polluted water.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and particularly relates to a supported carbon-doped photocatalyst MnFe-LDH@BVC, a preparation method thereof, and an application thereof. Background Art

[0002] Since antibiotics were discovered in the early 20th century, they have become one of the most widely used drugs in the medical field. The emergence of antibiotics has greatly improved humans' ability to combat infectious diseases. Norfloxacin is a fluoroquinolone antibiotic that has been widely used in the respiratory tract and bacterial infections of humans and animals. However, the widespread use and persistence of norfloxacin have led to its retention in the water environment, which may further damage mitochondrial function and cause epigenetic changes in tissues. Moreover, the antibiotic pollution in the water environment induces the emergence of drug-resistant bacteria, significantly increasing the risk of infections in clinical treatment and posing a serious threat to public health. Therefore, to protect the health of humans and the ecological environment, it is urgent to eliminate norfloxacin in wastewater.

[0003] In recent years, a variety of methods have been widely used in the process of treating wastewater contaminated with antibiotics. The microbial treatment method has high requirements for the composition of the influent. Too high a concentration of harmful components or too strong toxicity will affect the growth and reproduction of microorganisms. Moreover, microorganisms are usually repositories of drug-resistant genes, and drug-resistant genes may remain in the biological system and induce the generation of antibiotic-resistant bacteria and drug-resistant genes, posing a greater threat to the environment. The physical method of adsorbing and removing antibiotics can reduce the risk of the generation and spread of drug-resistant genes, but it is difficult for the adsorption method to remove all pollutants. The selection of adsorbent raw materials and the change of preparation procedures significantly affect the adsorption effect of antibiotics. The catalyst preparation cost is high and secondary pollution may occur. Therefore, antibiotic wastewater treatment technologies based on chemical methods have emerged. Among them, the advanced oxidation technology (AOP) is an emerging technology that has received much attention recently, including electrooxidation, ozonation, electro-Fenton, photocatalysis, etc. Among them, the photocatalytic method has significant advantages and is considered an effective means to solve the energy crisis. When the energy of the light source exceeds the bandgap energy of the photocatalyst, electrons transition, and the formed photo-generated electrons and holes can directly participate in the removal of antibiotics. At the same time, photo-generated electrons can activate oxidants to generate free radicals with high oxidation potential and long lifespan for the efficient degradation of antibiotics. It should be noted that the mineralization process of antibiotics is driven by sunlight, so it is very important to select a photocatalyst with an appropriate bandgap.

[0004] Bismuth vanadate is a metal oxide semiconductor material with broad prospects. However, pure bismuth vanadate has a small specific surface area, poor carrier migration efficiency, and severe carrier recombination, which result in unsatisfactory effects in removing antibiotics. Biochar materials have advantages such as rich raw material sources, simple preparation processes, large specific surface areas, and unique pore structures. However, biochar itself has weak catalytic ability and is not the preferred material for treating antibiotic-polluted wastewater. Combining bismuth vanadate with biochar can make full use of the advantages of the two materials and effectively make up for the structural defects of each other. However, the concentration of antibiotics in the real water environment is low. Therefore, the photocatalyst needs to have strong adsorption ability to achieve effective antibiotic enrichment and degradation processes. Layered double hydroxides are two-dimensional clay materials with easily adjustable structures, having high specific surface areas and anion exchange capabilities, and are ideal materials for improving the adsorption performance of catalysts. The composite materials obtained by combining LDH with photocatalysts can rapidly degrade antibiotics from the water environment through the adsorption-photocatalysis process.

[0005] Therefore, it is of great significance to construct a catalyst with both adsorption and photocatalytic functions for the degradation of antibiotics in water. Summary of the Invention

[0006] The purpose of the present invention is to provide a supported carbon-doped photocatalyst MnFe-LDH@BVC, its preparation method and application, to solve the above technical problems.

[0007] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a supported carbon-doped photocatalyst MnFe-LDH@BVC, which comprises the following steps:

[0009] 1) Mix straw powder and acidic LiBr molten salt hydrate and react to obtain biochar;

[0010] 2) Sequentially mix Bi(NO3)3 solution, NH4VO3 solution and urea in biochar, and obtain carbon-doped photocatalyst BVC after heating and reacting;

[0011] 3) Mix the carbon-doped photocatalyst BVC and manganese iron salt solution, add an alkaline solution to obtain a suspension, and sequentially perform ultrasonic treatment and water bath reaction on the suspension to obtain the supported carbon-doped photocatalyst MnFe-LDH@BVC.

[0012] Furthermore, in the step 1), the mass ratio of the straw powder to the acidic LiBr molten salt hydrate is 1:18-22; the acidic LiBr molten salt hydrate is a mixed solution of LiBr and hydrochloric acid. In the mixed solution, the mass fraction of LiBr is 55-65%, and the concentration of hydrochloric acid is 0.4-0.6 mol / L.

[0013] Further, in the step 1), the reaction temperature is 140 - 170 °C, the reaction time is 140 - 160 min, and the mixing time is 1.5 - 2.5 h.

[0014] Further, in the step 2), the Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in a nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in a nitric acid solution; the concentration of the nitric acid solution is independently 1.8 - 2.2 mol / L;

[0015] The concentrations of the Bi(NO3)3 solution and the NH4VO3 solution are independently 0.35 - 0.45 mol / L, the mass - to - volume ratio of the biochar to the Bi(NO3)3 solution is 0.15 - 0.25 g: 18 - 22 mL, and the volume ratio of the Bi(NO3)3 solution to the NH4VO3 solution is 18 - 22: 18 - 22.

[0016] Further, the mass ratio of the urea to the biochar is 2.8 - 3.2: 0.15 - 0.25;

[0017] The temperature of the temperature - rising reaction is 80 - 100 °C, and the time of the temperature - rising reaction is 7 - 9 h.

[0018] Further, in the step 3), the manganese - iron salt solution is a mixed solution of manganese acetate and iron nitrate; in the manganese - iron salt solution, the concentrations of manganese acetate and iron nitrate are independently 0.009 - 0.011 mol / L;

[0019] The alkaline solution is a mixed solution of sodium hydroxide and sodium carbonate. In the alkaline solution, the concentration of sodium hydroxide is 0.3 - 0.4 mol / L, and the concentration of sodium carbonate is 0.12 - 0.18 mol / L.

[0020] Further, in the step 3), the mass - to - volume ratio of the carbon - doped photocatalyst BVC to the manganese - iron salt solution is 0.1 - 0.5 g: 95 - 105 mL; the volume ratio of the manganese - iron salt solution to the alkaline solution is 95 - 105: 95 - 105;

[0021] After the addition of the alkaline solution is completed, the pH value of the suspension is adjusted, and the pH value of the suspension is adjusted to 10.4 - 10.7.

[0022] Further, in the step 3), the mixing time is 28 - 32 min; the ultrasonic treatment time is 28 - 32 min; the temperature of the water - bath reaction is 60 - 70 °C, and the time of the water - bath reaction is 3.5 - 4.5 h.

[0023] The present invention also provides a supported carbon-doped photocatalyst MnFe-LDH@BVC.

[0024] The present invention also provides an application of the supported carbon-doped photocatalyst MnFe-LDH@BVC in degrading norfloxacin, which includes the following steps:

[0025] Mix the supported carbon-doped photocatalyst MnFe-LDH@BVC and the norfloxacin solution, and place the mixture under a light source for reaction; the reaction time is 110 - 130 min;

[0026] In the mixture, the concentration of the photocatalyst MnFe-LDH@BVC is 0.9 - 1.2 g / L; the concentration of the norfloxacin solution is 10 mg / L, and pH = 3; the light source is a 300 W xenon lamp equipped with a 420 nm filter.

[0027] Advantages of the present invention:

[0028] 1) The present invention uses acidic LiBr molten salt hydrate to treat corn straw to prepare biochar spheres at low temperature, in-situ synthesizes BiVO4 on the surface of the carbon spheres, and finally in-situ synthesizes MnFe-LDH on the surface of the carbon-based photocatalyst by hydrothermal method to prepare the composite material MnFe-LDH@BVC. The photocatalytic system constructed with this catalyst can degrade 92.4% of norfloxacin in water within 120 min, and the degradation effect of norfloxacin does not decrease significantly after the catalyst is recycled five times.

[0029] 2) The novel photocatalyst MnFe-LDH@BVC prepared by the present invention is a non-toxic and pollution-free green environmental protection catalyst, which can efficiently degrade norfloxacin in water. As a heterogeneous reaction catalyst, it is easy to separate from the reaction system and can be reused, reducing the use cost of the catalyst. Description of the Drawings

[0030] Figure 1 It is the effect diagram of the photocatalyst MnFe-LDH@BVC obtained with different BVC addition amounts in Examples 1 - 5 of the present invention for degrading norfloxacin. Detailed Embodiments

[0031] The present invention provides a preparation method of a supported carbon-doped photocatalyst MnFe-LDH@BVC, which includes the following steps:

[0032] 1) Mix the straw powder and the acidic LiBr molten salt hydrate and react to obtain biochar;

[0033] 2) Sequentially mix the Bi(NO3)3 solution, the NH4VO3 solution and urea in the biochar, and after heating and reacting, obtain the carbon-doped photocatalyst BVC;

[0034] 3) After mixing the carbon-doped photocatalyst BVC and the manganese-iron salt solution, an alkaline solution is added to obtain a suspension, and the suspension is sequentially subjected to ultrasonic treatment and water bath reaction to obtain the supported carbon-doped photocatalyst MnFe-LDH@BVC.

[0035] In the present invention, the straw powder is preferably corn straw powder.

[0036] In the present invention, in step 1), the mixture obtained from the reaction is filtered, and the separated solid is sequentially washed and dried to obtain biochar;

[0037] In step 2), after the system after the temperature-raising reaction is cooled to room temperature, it is filtered, and the separated solid is sequentially washed and dried to obtain the carbon-doped photocatalyst BVC;

[0038] In step 3), the product after the water bath reaction is filtered, and the separated solid is sequentially washed and dried to obtain the supported carbon-doped photocatalyst MnFe-LDH@BVC; the reagents used for washing in the above steps 1) to 3) are sequentially water and absolute ethanol, and the number of times of washing with water and absolute ethanol is independently 2 to 4 times, further preferably 3 times; the drying temperature is independently 55 to 65 °C, further preferably 58 to 62 °C, more preferably 60 °C; the drying time is independently 10 to 14 h, further preferably 11 to 13 h, more preferably 12 h.

[0039] In the present invention, in step 1), the mass ratio of the straw powder to the acidic LiBr molten salt hydrate is 1:18 to 22, preferably 1:19 to 21, further preferably 1:20; the acidic LiBr molten salt hydrate is a mixed solution of LiBr and hydrochloric acid, and in the mixed solution, the mass fraction of LiBr is 55 to 65%, preferably 58 to 62%, further preferably 60%; the concentration of hydrochloric acid is 0.4 to 0.6 mol / L, preferably 0.5 mol / L.

[0040] In the present invention, in step 1), the reaction temperature is 140 to 170 °C, preferably 150 to 160 °C, further preferably 155 °C; the reaction time is 140 to 160 min, preferably 145 to 155 min, further preferably 150 min; the mixing time is 1.5 to 2.5 h, preferably 2 h.

[0041] In the present invention, in step 2), the Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in a nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in a nitric acid solution; the concentration of the nitric acid solution is independently 1.8 - 2.2 mol / L, preferably 2.0 mol / L;

[0042] The concentrations of the Bi(NO3)3 solution and the NH4VO3 solution are independently 0.35 - 0.45 mol / L, preferably 0.4 mol / L; the mass - to - volume ratio of the biochar to the Bi(NO3)3 solution is 0.15 - 0.25 g:18 - 22 mL, preferably 0.18 - 0.22 g:19 - 21 mL, and more preferably 0.2 g:20 mL; the volume ratio of the Bi(NO3)3 solution to the NH4VO3 solution is 18 - 22:18 - 22, preferably 19 - 21:19 - 21, and more preferably 20:20.

[0043] In the present invention, the mass ratio of urea to biochar is 2.8 - 3.2:0.15 - 0.25, preferably 3:0.2;

[0044] The temperature of the temperature - rising reaction is 80 - 100 °C, preferably 85 - 95 °C, and more preferably 90 °C; the time of the temperature - rising reaction is 7 - 9 h, preferably 8 h.

[0045] In the present invention, in step 3), the manganese - iron salt solution is a mixed solution of manganese acetate and iron nitrate; in the manganese - iron salt solution, the concentrations of manganese acetate and iron nitrate are independently 0.009 - 0.011 mol / L, preferably 0.01 mol / L;

[0046] The alkaline solution is a mixed solution of sodium hydroxide and sodium carbonate. In the alkaline solution, the concentration of sodium hydroxide is 0.3 - 0.4 mol / L, preferably 0.32 - 0.38 mol / L, and more preferably 0.35 - 0.36 mol / L; the concentration of sodium carbonate is 0.12 - 0.18 mol / L, preferably 0.14 - 0.15 mol / L.

[0047] In the present invention, in step 3), the mass - to - volume ratio of the carbon - doped photocatalyst BVC to the manganese - iron salt solution is 0.1 - 0.5 g:95 - 105 mL, preferably 0.2 - 0.4 g:100 mL, and more preferably 0.3 g:100 mL; the volume ratio of the manganese - iron salt solution to the alkaline solution is 95 - 105:95 - 105, preferably 98 - 102:98 - 102, and more preferably 100:100;

[0048] After the addition of the alkaline solution is completed, the pH value of the suspension is adjusted, and the pH value of the suspension is adjusted to 10.4 - 10.7, preferably 10.5 - 10.6.

[0049] In the present invention, in the step 3), the mixing time is 28 - 32 min, preferably 30 min; the ultrasonic treatment time is 28 - 32 min, preferably 30 min; the temperature of the water bath reaction is 60 - 70 °C, preferably 62 - 68 °C, more preferably 65 °C; the time of the water bath reaction is 3.5 - 4.5 h, preferably 4 h.

[0050] The present invention also provides a supported carbon-doped photocatalyst MnFe-LDH@BVC.

[0051] The present invention also provides an application of the supported carbon-doped photocatalyst MnFe-LDH@BVC in the degradation of norfloxacin, including the following steps:

[0052] Mix the supported carbon-doped photocatalyst MnFe-LDH@BVC and the norfloxacin solution, and place the mixed solution under a light source for reaction; the reaction time is 110 - 130 min;

[0053] In the mixed solution, the concentration of the photocatalyst MnFe-LDH@BVC is 0.9 - 1.2 g / L, preferably 1 g / L; the concentration of the norfloxacin solution is 10 mg / L, pH = 3; the light source is a 300 W xenon lamp equipped with a 420 nm filter.

[0054] In the present invention, the reaction time is preferably 120 min.

[0055] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0056] Example 1

[0057] Mix corn straw powder (300 mesh) and acidic LiBr molten salt hydrate (the acidic LiBr molten salt hydrate is a mixed solution of LiBr and hydrochloric acid, the mass fraction of LiBr is 60%, and the concentration of hydrochloric acid is 0.5 mol / L) with a mass ratio of 1:20 in a pressure vessel, stir at a rate of 500 rpm at room temperature for 2 h, then transfer it to an oven and react at 155 °C for 150 min. Filter the reaction mixture for solid-liquid separation, wash the separated solid with deionized water 3 times and then with anhydrous ethanol 3 times, and then dry it at 60 °C for 12 h to obtain biochar.

[0058] Mix 0.2 g of biochar with 20 mL of 0.4 mol / L Bi(NO3)3 solution for 30 min. While stirring at a rate of 500 rpm at room temperature, add 20 mL of 0.4 mol / L NH4VO3 solution dropwise at a rate of 0.5 mL / s, and stir until no bubbles are present. Subsequently, add 3 g of urea to the mixture, and raise the temperature of the reaction system to 90 °C and maintain it for 8 h. The reaction system after the reaction is subjected to solid-liquid separation by filtration. The separated solid is washed three times with deionized water and then three times with absolute ethanol, and then dried at 60 °C for 12 h to obtain the carbon-doped photocatalyst BVC. The Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in nitric acid solution. The concentration of the nitric acid solution is 2.0 mol / L.

[0059] Add 0.1 g of the carbon-doped photocatalyst BVC to 100 mL of a manganese-iron salt solution (the concentrations of manganese acetate and iron nitrate are both 0.01 mol / L) and stir for 30 min. Subsequently, add 100 mL of an alkaline solution (the concentration of sodium hydroxide is 0.35 mol / L and the concentration of sodium carbonate is 0.15 mol / L) at a rate of 1 mL / s to obtain a suspension. Adjust the pH value of the suspension to 10.5 with 5 mol / L hydrochloric acid, and then ultrasonically treat the suspension at a power of 300 W for 30 min and place it in a water bath at 65 °C and stir at a rate of 500 rpm for 4 h. The product after the water bath reaction is separated by filtration to obtain the solid. The solid is washed three times with deionized water and then three times with absolute ethanol, and then dried at 60 °C for 12 h to obtain the supported biochar-based composite catalyst MnFe-LDH@BVC-0.1.

[0060] Example 2

[0061] Same as Example 1, except that the addition amount of the carbon-doped photocatalyst BVC is 0.2 g, and the supported biochar-based composite catalyst MnFe-LDH@BVC-0.2 is obtained.

[0062] Example 3

[0063] Same as Example 1, except that the addition amount of the carbon-doped photocatalyst BVC is 0.3 g, and the supported biochar-based composite catalyst MnFe-LDH@BVC-0.3 is obtained.

[0064] Example 4

[0065] Same as Example 1, except that the addition amount of the carbon-doped photocatalyst BVC is 0.4 g, and the supported biochar-based composite catalyst MnFe-LDH@BVC-0.4 is obtained.

[0066] Example 5

[0067] Same as Example 1, except that the addition amount of carbon-doped photocatalyst BVC is 0.5 g, and the supported biochar-based composite catalyst MnFe-LDH@BVC-0.5 is obtained.

[0068] Example 6

[0069] Mix corn straw powder (300 mesh) and acidic LiBr molten salt hydrate (the acidic LiBr molten salt hydrate is a mixed solution of LiBr and hydrochloric acid, the mass fraction of LiBr is 55%, and the concentration of hydrochloric acid is 0.5 mol / L) with a mass ratio of 1:18 in a pressure vessel, stir at a rate of 500 rpm at room temperature for 2 h, then transfer it to an oven and react at 140 °C for 150 min. Filter the reaction mixture to carry out solid-liquid separation. The separated solid is washed 3 times with deionized water and then 3 times with absolute ethanol, and then dried at 60 °C for 12 h to obtain biochar.

[0070] Mix 0.2 g of biochar with 20 mL of 0.45 mol / L Bi(NO3)3 solution for 30 min. At room temperature and a stirring rate of 500 rpm, add 20 mL of 0.35 mol / L NH4VO3 solution at a rate of 0.5 mL / s, stir until there are no bubbles, and then add 2.9 g of urea to the mixture. The reaction system is heated to 90 °C and maintained for 8 h. The reaction system is subjected to solid-liquid separation by filtration. The separated solid is washed 3 times with deionized water and then 3 times with absolute ethanol, and then dried at 60 °C for 12 h to obtain carbon-doped photocatalyst BVC. The Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in nitric acid solution. The concentration of the nitric acid solution is 2.0 mol / L.

[0071] Add 0.2 g of carbon-doped photocatalyst BVC to 100 mL of manganese-iron salt solution (the concentrations of manganese acetate and iron nitrate are both 0.01 mol / L), stir for 30 min, and then add 100 mL of alkaline solution (the concentration of sodium hydroxide is 0.35 mol / L, and the concentration of sodium carbonate is 0.15 mol / L) at a rate of 1 mL / s to obtain a suspension. Adjust the pH value of the suspension to 10.5 with 5 mol / L hydrochloric acid, then ultrasonically treat the suspension at a power of 300 W for 30 min and place it in a water bath at 65 °C and stir at a rate of 500 rpm for 4 h. The product after the water bath reaction is separated by filtration to obtain the solid. The solid is washed 3 times with deionized water and then 3 times with absolute ethanol, and then dried at 60 °C for 12 h to obtain the supported biochar-based composite catalyst MnFe-LDH@BVC.

[0072] Example 7

[0073] Mix corn straw powder (300 mesh) with an acid LiBr molten salt hydrate (the acid LiBr molten salt hydrate is a mixed solution of LiBr and hydrochloric acid, the mass fraction of LiBr is 65%, and the concentration of hydrochloric acid is 0.5 mol / L) in a mass ratio of 1:22 in a pressure vessel, stir at a rate of 500 rpm at room temperature for 2 h, then transfer to an oven and react at 150 °C for 150 min. Filter the reaction mixture to carry out solid-liquid separation, wash the separated solid with deionized water 3 times and then with absolute ethanol 3 times, and then dry at 60 °C for 12 h to obtain biochar.

[0074] Mix 0.2 g of biochar with 20 mL of 0.35 mol / L Bi(NO3)3 solution for 30 min, and dropwise add 20 mL of 0.45 mol / L NH4VO3 solution at a rate of 0.5 mL / s under stirring at room temperature and a stirring rate of 500 rpm. Stir until no bubbles are present, then add 2.8 g of urea to the mixed solution, and raise the temperature of the reaction system to 90 °C and maintain for 8 h. Carry out solid-liquid separation on the reaction system by filtration, wash the separated solid with deionized water 3 times and then with absolute ethanol 3 times, and then dry at 60 °C for 12 h to obtain carbon-doped photocatalyst BVC. Among them, the Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in a nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in a nitric acid solution, and the concentration of the nitric acid solution is 2.0 mol / L.

[0075] Add 0.1 g of carbon-doped photocatalyst BVC to 100 mL of a manganese-iron salt solution (the concentrations of manganese acetate and iron nitrate are both 0.01 mol / L), stir for 30 min, then add 100 mL of an alkaline solution (the concentration of sodium hydroxide is 0.35 mol / L, and the concentration of sodium carbonate is 0.15 mol / L) at a rate of 1 mL / s to obtain a suspension. Adjust the pH value of the suspension to 10.7 with 5 mol / L hydrochloric acid, then ultrasonically treat the suspension at a power of 300 W for 30 min and place it in a water bath at 65 °C and stir at a rate of 500 rpm for 4 h. Separate the solid from the product after the water bath reaction by filtration, wash the solid with deionized water 3 times and then with absolute ethanol 3 times, and then dry at 60 °C for 12 h to obtain the supported biochar-based composite catalyst MnFe-LDH@BVC.

[0076] Example 8

[0077] Mix corn straw powder (300 mesh) with an acid LiBr molten salt hydrate (the acid LiBr molten salt hydrate is a mixed solution of LiBr and hydrochloric acid, the mass fraction of LiBr is 65%, and the concentration of hydrochloric acid is 0.5 mol / L) at a mass ratio of 1:20 in a pressure vessel, stir at a rate of 500 rpm for 2 h at room temperature, then transfer it to an oven and react at 170 °C for 150 min. Filter the reaction mixture to perform solid-liquid separation. Wash the separated solid three times with deionized water and then three times with absolute ethanol, and then dry it at 60 °C for 12 h to obtain biochar.

[0078] Mix 0.2 g of biochar with 22 mL of 0.35 mol / L Bi(NO3)3 solution for 30 min. At room temperature and a stirring rate of 500 rpm, add 20 mL of 0.35 mol / L NH4VO3 solution dropwise at a rate of 0.5 mL / s, stir until no bubbles are produced, and then add 3.1 g of urea to the mixture. Heat the reaction system to 100 °C and keep it for 8 h. Separate the solid and liquid in the reaction system by filtration. Wash the separated solid three times with deionized water and then three times with absolute ethanol, and then dry it at 60 °C for 12 h to obtain carbon-doped photocatalyst BVC. The Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in nitric acid solution. The concentration of the nitric acid solution is 2.0 mol / L.

[0079] Add 0.3 g of carbon-doped photocatalyst BVC to 100 mL of a manganese-iron salt solution (the concentrations of manganese acetate and iron nitrate are both 0.01 mol / L), stir for 30 min, and then add 100 mL of an alkaline solution (the concentration of sodium hydroxide is 0.35 mol / L and the concentration of sodium carbonate is 0.15 mol / L) at a rate of 1 mL / s to obtain a suspension. Adjust the pH value of the suspension to 10.6 with 5 mol / L hydrochloric acid, then ultrasonically treat the suspension at a power of 300 W for 30 min and place it in a water bath at 65 °C and stir at a rate of 500 rpm for 4 h. Separate the solid in the product after the water bath reaction by filtration. Wash the solid three times with deionized water and then three times with absolute ethanol, and then dry it at 60 °C for 12 h to obtain the supported biochar-based composite catalyst MnFe-LDH@BVC.

[0080] Application Example

[0081] Under dark conditions, the supported carbon-doped photocatalyst MnFe-LDH@BVC prepared in Examples 1 to 5 and the norfloxacin solution were mixed and stirred at a stirring rate of 500 rpm for 30 min. Keeping the stirring rate of 500 rpm unchanged, the mixed solution was placed under a 300 W xenon lamp source with a 420 nm filter for reaction. After 120 min of reaction, the concentration of NOR in the reacted mixed solution was detected by high performance liquid chromatography (HPLC). The concentration of the photocatalyst in the mixed solution was 1 g / L, the concentration of norfloxacin was 10 mg / L, and pH = 3.

[0082] Test results: After adding MnFe-LDH@BVC to the mixed solution, the removal rate of NOR was in the range of 72.0% to 92.4% at 120 min. Among them, for the mixed solution added with the catalyst prepared in Example 3, the removal rate of NOR reached the highest value of 92.4%. Further kinetic analysis of the NOR degradation process found that the first-order reaction kinetic constant was between 10.5×103 min-1 and 20.2×103 min-1. Among them, for the mixed solution added with the catalyst prepared in Example 3, the first-order reaction kinetic constant of NOR degradation was the largest, which was 20.2×103 min-1. In addition, when the concentration of MnFe-LDH@BVC in the mixed solution was adjusted to 0.9 g / L or increased to 1.2 g / L, neither the NOR degradation rate nor the first-order reaction kinetic constant decreased significantly.

[0083] As can be seen from the above examples, the present invention provides a supported carbon-doped photocatalyst MnFe-LDH@BVC and its preparation method and application. The novel photocatalyst MnFe-LDH@BVC prepared in the present invention is a non-toxic and pollution-free green environmental protection catalyst, which can efficiently degrade norfloxacin in water. As a heterogeneous reaction catalyst, it is easy to separate from the reaction system, can be reused, and reduces the use cost of the catalyst.

[0084] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a supported carbon-doped photocatalyst MnFe-LDH@BVC, characterized in that: The following steps are included: 1) mixing straw powder and acidic LiBr molten salt hydrate and reacting them to obtain biochar; 2) Mixing Bi(NO3)3 solution, NH4VO3 solution and urea in biochar in sequence, and heating the mixture to obtain carbon-doped photocatalyst BVC; 3) After mixing the carbon-doped photocatalyst BVC and the manganese iron salt solution, an alkaline solution is added to obtain a suspension, and the suspension is subjected to ultrasonic treatment and water bath reaction in sequence to obtain a supported carbon-doped photocatalyst MnFe-LDH@BVC.

2. The preparation method according to claim 1, characterized in that: In the step 1), the mass ratio of the straw powder to the acidic LiBr molten salt hydrate is 1:18-22; the acidic LiBr molten salt hydrate is a mixture of LiBr and hydrochloric acid, in which the mass fraction of LiBr is 55-65% and the concentration of hydrochloric acid is 0.4-0.6 mol / L.

3. The preparation method according to claim 2, characterized in that: In the step 1), the reaction temperature is 140-170° C., the reaction time is 140-160 min, and the mixing time is 1.5-2.5 h.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In the step 2), the Bi(NO3)3 solution is obtained by dissolving Bi(NO3)3 in a nitric acid solution, and the NH4VO3 solution is obtained by dissolving NH4VO3 in a nitric acid solution; the concentration of the nitric acid solution is independently 1.8 to 2.2 mol / L; The concentrations of the Bi(NO3)3 solution and the NH4VO3 solution are independently 0.35-0.45 mol / L, the mass volume ratio of the biochar and the Bi(NO3)3 solution is 0.15-0.25 g:18-22 mL, and the volume ratio of the Bi(NO3)3 solution and the NH4VO3 solution is 18-22:18-22.

5. The preparation method according to claim 4, characterized in that: The mass ratio of urea to biochar is 2.8-3.2:0.15-0.25; The temperature of the temperature-raising reaction is 80-100° C., and the time of the temperature-raising reaction is 7-9 hours.

6. The preparation method according to claim 1, 2 or 5, characterized in that: In the step 3), the ferromanganese salt solution is a mixture of manganese acetate and ferric nitrate; in the ferromanganese salt solution, the concentrations of manganese acetate and ferric nitrate are independently 0.009 to 0.011 mol / L; The alkaline solution is a mixed solution of sodium hydroxide and sodium carbonate. In the alkaline solution, the concentration of sodium hydroxide is 0.3-0.4 mol / L, and the concentration of sodium carbonate is 0.12-0.18 mol / L.

7. The preparation method according to claim 6, characterized in that: In the step 3), the mass volume ratio of the carbon-doped photocatalyst BVC and the manganese iron salt solution is 0.1-0.5 g: 95-105 mL; the volume ratio of the manganese iron salt solution to the alkaline solution is 95-105: 95-105; After the alkaline solution was added, the pH value of the suspension was adjusted to 10.4-10.

7.

8. The preparation method according to claim 1 or 7, characterized in that: In the step 3), the mixing time is 28 to 32 minutes; the ultrasonic treatment time is 28 to 32 minutes; the water bath reaction temperature is 60 to 70° C., and the water bath reaction time is 3.5 to 4.5 hours.

9. The supported carbon-doped photocatalyst MnFe-LDH@BVC prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the supported carbon-doped photocatalyst MnFe-LDH@BVC according to claim 9 in the degradation of norfloxacin, characterized in that: The following steps are involved: The supported carbon-doped photocatalyst MnFe-LDH@BVC and the norfloxacin solution are mixed, and the mixed solution is placed under a light source for reaction; the reaction time is 110 to 130 minutes; In the mixed solution, the concentration of the photocatalyst MnFe-LDH@BVC is 0.9-1.2 g / L; the concentration of the norfloxacin solution is 10 mg / L, and the pH is 3; and the light source is a 300W xenon lamp equipped with a 420nm filter.

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