BiOI-based composite photocatalyst and method for photocatalytic degradation of methylene blue

Abstract

The invention discloses a BiOI-based composite photocatalyst and a method for photocatalytic degradation of methylene blue, and relates to the technical field of methylene blue degradation. The method comprises the following steps: firstly, adjusting the pH value of methylene blue wastewater to be less than or equal to 7.0, then adding a BiOI-based composite photocatalyst and H2O2 into the methylene blue wastewater, and carrying out light treatment for not less than 40 minutes to finish photocatalytic degradation of methylene blue. The research of the invention finds for the first time that the BiOI-based composite photocatalyst not only has certain activity of photocatalysis of methylene blue, but also can be combined with hydrogen peroxide to improve the catalytic activity of hydrogen peroxide; compared with single application, the combined use of the two has obviously higher degradation efficiency on methylene blue in wastewater, and the highest degradation efficiency is up to 98.0%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of methylene blue degradation, and particularly relates to a composite photocatalyst based on BiOI and a method for photocatalytic degradation of methylene blue. BACKGROUND

[0002] Water pollution is one of the major environmental challenges faced by mankind, which directly affects the sustainable development of the ecosystem and human civilization. In dye wastewater, organic dyes are difficult to degrade due to their complex chemical structure, forming persistent pollution in the environment, not only dyeing rivers into eerie fluorescent colors, but also causing mass death of animals and plants. More seriously, the synergistic toxicity of dye molecules and heavy metals is amplified step by step through the food chain enrichment effect, ultimately damaging human beings. Human contact or drinking of these contaminated water will cause acute poisoning, organ damage, cancer treatment, etc. Although adsorption and biological degradation technologies provide possibilities for treatment, various problems are still difficult to face.

[0003] Methylene blue is a common cationic salt-based dye, which is dark green crystalline or powdery, soluble in water and ethanol, and insoluble in ethers. Methylene blue shows good stability in air, and its aqueous solution is strongly alkaline with high toxicity, and its chemical formula is C 16 H 18 N3ClS. Methylene blue has a wide range of uses in chemical indicators, dyes, biologically active substances, and medicines. Methylene blue wastewater is very dark in color, which will reduce the transparency and light transmittance of water when discharged into water, and will seriously affect living organisms, and also has serious harm to human body such as carcinogenesis.

[0004] The existing methods for treating methylene blue wastewater are physical method, chemical method, biological method and photocatalytic method. The physical method is to use adsorption (porous solid adsorbent such as activated carbon) and membrane separation (semi-permeable membrane technology such as nanofiltration, ultrafiltration and reverse osmosis) and other technologies to effectively separate methylene blue from water molecules. The physical method is simple in operation, high in treatment efficiency, but high in cost, and easy to cause secondary pollution and other problems. The chemical method is to use electricity, light and other ways to excite active substances, and effectively oxidize and decompose methylene blue molecules by generating high oxidation-reduction potential. The chemical method can effectively remove suspended solids and colloidal substances in wastewater, but the removal effect of dissolved methylene blue is limited. The biological method is to use microorganisms to absorb, transform and degrade organic pollutants such as methylene blue in the process of growth and reproduction. The advantage of the biological method is that microorganisms are rich in species, can adapt to different wastewater components, and have strong impact load capacity. However, the treatment efficiency of the biological method is greatly affected by factors such as temperature, pH value, nutrient substances and toxic substances; the growth and reproduction of microorganisms requires a certain time, and the treatment cycle is long, and a large amount of residual sludge generated in the treatment process needs to be properly treated.

[0005] Photocatalysis is a new environmental management technology, and its core is photocatalyst. Photocatalyst is usually based on semiconductor materials, which can absorb photon energy to excite the internal electron transition of the material and form photo-generated electrons and photo-generated holes. These photo-generated electrons and photo-generated holes have strong reducing and oxidizing properties, and can react with water molecules and oxygen adsorbed on the surface of the catalyst to generate ·OH and other strong oxidizing substances. These free radicals can oxidize and decompose organic pollutants into harmless substances such as water and carbon dioxide. The reaction process of photocatalysis can be carried out at room temperature without secondary pollution, and the rate is fast and the effect is little affected by repeated catalysis.

[0006] The conduction band edge position of BiOI is lower than the reduction potential of hydrogen, which leads to the inability of BiOI to split water to produce hydrogen. The band gap of pure BiOI is narrow, resulting in low quantum efficiency of BiOI. In order to improve these deficiencies, researchers have conducted various modification studies on BiOI, including: constructing heterojunction, ion doping, noble metal loading, etc. Studies have shown that most of the prepared composite photocatalysts exhibit better stability and separation ability of photo-generated carriers than pure BiOI. BiOI is simple to prepare and easy to operate, and the equipment cost is low, but the narrow band gap also leads to problems such as easy recombination of photo-generated carriers. Modification can improve its own properties, expose more effective crystal faces, and improve photocatalytic efficiency. AgI has a localized surface plasmon resonance effect, which can enhance the absorption of composite materials in the visible light range, and at the same time it acts as a capture center and transmission channel for photo-generated carriers, reducing the recombination rate of electrons and holes. The rich active sites on the surface of AgI promote the adsorption and activation of reactants, accelerate the photocatalytic reaction rate and improve the selectivity. In the composite material, the synergistic effect of AgI and other materials improves the stability of the photocatalytic system under light conditions, reduces the decomposition or deactivation of AgI. The combination of BiOI and AgI can further improve the catalytic effect.

[0007] Among the existing photocatalytic technologies for organic matter, for example, Chinese patent application CN115193453A provides a biochar-based photocatalyst, which is based on biochar and loaded with BiOCl and AgI on the surface; when used, the photocatalyst is directly added to the contaminated water body, and photocatalytic degradation is carried out under the irradiation of a 500 W xenon lamp and a 420 nm filter.

[0008] For example, Chinese patent application CN109046396A provides a Z-type photocatalyst with the general structure of BiOY n I 1-n / Ag / AgI-x. This photocatalyst can be used to degrade organic dyes, organic pollutants or antibiotics, etc.

[0009] For example, the silver iodide nanoparticle modified bismuth oxybromide composite photocatalyst provided by the Chinese authorized patent CN107961800B is a composite photocatalyst taking bismuth oxybromide BiOBr as a carrier and having silver iodide AgI nanoparticles modified on the BiOBr. However, the photocatalyst provided by the patent is used for degrading antibiotic wastewater, but not methylene blue.

[0010] For example, the AgI / BiOBr heterojunction photocatalyst provided by the Chinese patent application CN108620097A is added to water containing target pollutants (such as 17β-estradiol (E2), 17α-ethynyl estradiol (EE2), bisphenol A (BPA), estrone (E1), rhodamine B (RhB), methyl orange (MO), methylene blue (MB), etc.) and degrades the target pollutants under light irradiation. However, the patent does not provide the degradation effect and removal rate of methylene blue, and the photocatalytic effect is unknown.

[0011] However, through research, it is found that simply combining BiOI and AgI has relatively limited degradation efficiency of methylene blue. The research results of the above patent also show that BiOI and AgI need to be modified by a certain process to significantly improve the removal effect of methylene blue. SUMMARY

[0012] The present application provides a BiOI-based composite photocatalyst and a method for photocatalytic degradation of methylene blue. The present application finds that the prepared BiOI photocatalyst or AgI / BiOI composite photocatalyst can significantly catalyze and promote the degradation of methylene blue in wastewater by hydrogen peroxide, compared with the use of hydrogen peroxide, BiOI or AgI / BiOI composite photocatalyst alone, and has a higher degradation rate of methylene blue under light irradiation. The present application is specifically implemented by the following technologies.

[0013] The present application provides a method for photocatalytic degradation of methylene blue, adjusting the pH value of methylene blue wastewater to be ≤7.0, adding BiOI photocatalyst or AgI / BiOI composite photocatalyst and hydrogen peroxide working solution to the methylene blue wastewater, and performing light treatment for not less than 40 min to complete the photocatalytic degradation of methylene blue.

[0014] In the present application, when hydrogen peroxide degrades wastewater, the BiOI photocatalyst or AgI / BiOI composite photocatalyst is added and irradiated, and the electrons in the valence band are excited to the conduction band by absorbing light energy to form an electron-hole pair. The photo-generated hole has strong oxidizing property and can react with water molecules or hydrogen peroxide to generate hydroxyl radicals; and the hydroxyl radical is a very efficient oxidant and can selectively oxidize and decompose organic pollutants. The photo-generated electrons e -The BiOI can catalyze hydrogen peroxide to generate ·OH, and therefore, the presence of the BiOI can enhance the response capability of the composite catalyst to visible light, and more photo-generated electrons e can be generated under visible light excitation - and holes h + The noble metal (such as Au, Ag, Pd, etc.) can be loaded on the surface of the semiconductor to effectively transfer the charges at the interface, thereby improving the photocatalytic activity. The Fermi level of the BiOI is generally lower than that of the noble metal, and the combination of the BiOI and the noble metal can form a Schottky barrier of holes on the surface, and at this time, the chemical potentials of the holes are the same, so that a large number of e can be generated under visible light excitation - / h + The photo-generated electrons e - can excite H2O2 to generate a large amount of ·OH, and the holes h + can also react with H2O to generate ·OH, and the contact interface can greatly improve the photocatalytic performance of the composite material as an electron capture center; and the presence of the AgI can effectively inhibit the separation of the photo-generated electrons and holes, and the two promote each other, and the hydrogen peroxide and the dye molecules promote the degradation.

[0015] It is found through experiments that, under the condition of pH>7, the degradation rate of the methylene blue is 44.6% (BiOI photocatalyst is used) and 52.1% (AgI / BiOI composite photocatalyst is used) by using the above method. Since the decomposition rate of hydrogen peroxide is relatively fast, although the hydroxyl radicals can be generated, the hydroxyl radicals may react with other ions to generate species with low activity, and the degradation rate is relatively fast in the first 30 min. However, since the alkaline environment significantly affects the activity of the catalyst, the degradation rate tends to be flat with the increase of time, the degradation rate becomes slow, and the degradation rate is not high. Under the condition of pH<7, the BiOI photocatalyst and the AgI / BiOI composite photocatalyst catalyze the hydrogen peroxide to oxidize and degrade the methylene blue, and under the acidic condition, the photocatalyst can catalyze the hydrogen peroxide to generate a large amount of hydroxyl radicals, thereby accelerating the oxidation rate and increasing the degradation rate.

[0016] It is found through experiments that, under the condition of pH>7, the degradation rate of the methylene blue is 44.6% (BiOI photocatalyst is used) and 52.1% (AgI / BiOI composite photocatalyst is used) by using the above method. Since the decomposition rate of hydrogen peroxide is relatively fast, although the hydroxyl radicals can be generated, the hydroxyl radicals may react with other ions to generate species with low activity, and the degradation rate is relatively fast in the first 30 min. However, since the alkaline environment significantly affects the activity of the catalyst, the degradation rate tends to be flat with the increase of time, the degradation rate becomes slow, and the degradation rate is not high. Under the condition of pH<7, the BiOI photocatalyst and the AgI / BiOI composite photocatalyst catalyze the hydrogen peroxide to oxidize and degrade the methylene blue, and under the acidic condition, the photocatalyst can catalyze the hydrogen peroxide to generate a large amount of hydroxyl radicals, thereby accelerating the oxidation rate and increasing the degradation rate.

[0017] Further, the concentration of the methylene blue in the methylene blue wastewater is 20 mg / L.

[0018] Further, the adding amount of the hydrogen peroxide working solution is 0.2-0.5 ml / L based on the volume of the methylene blue wastewater.

[0019] Further, the adding amount of the hydrogen peroxide working solution is 0.4 ml / L based on the volume of the methylene blue wastewater.

[0020] The present application finds through experiments that when the concentration of hydrogen peroxide is 0.2-0.5 ml / L, the degradation rate of methylene blue is faster. When the concentration of hydrogen peroxide in the system is moderate, the number of generated hydroxyl radicals increases with the increase of the concentration, which can improve the degradation efficiency of methylene blue. However, excessive hydrogen peroxide will cause its own decomposition reaction to generate oxygen and water, resulting in a decrease in effective ingredients and a decrease in the degradation ability of methylene blue. Experiments show that when the concentration of hydrogen peroxide is 0.4 ml / L, the degradation effect of methylene blue is the best.

[0021] Further, when the BiOI photocatalyst is selected, the concentration of the BiOI photocatalyst is 0.1-0.7 g / L.

[0022] Further, the concentration of the BiOI photocatalyst is 0.5 g / L.

[0023] The present application finds through experiments that the effect of BiOI catalyzing hydrogen peroxide to degrade methylene blue wastewater is remarkable. The greater the concentration of the catalyst, the higher the efficiency of catalyzing hydrogen peroxide to degrade methylene blue. This is because increasing the amount of catalyst will increase more catalytically active centers, so the contact probability of active centers and reactants will be larger, and therefore the degradation rate is higher. When the concentration of the BiOI photocatalyst exceeds a certain limit (0.5 g / L), the activity of the BiOI photocatalyst catalyzing hydrogen peroxide to degrade methylene blue decreases.

[0024] Further, when the AgI / BiOI composite photocatalyst is selected, the concentration of the AgI / BiOI composite photocatalyst is 0.1-0.5 g / L.

[0025] Further, the concentration of the AgI / BiOI composite photocatalyst is 0.3 g / L.

[0026] The application finds through experimental verification that, with the increase of the concentration of the AgI / BiOI composite photocatalyst, more photoactive sites can be provided to react with hydrogen peroxide, the contact probability of active sites and reactants is increased, the generation of hydroxyl radicals is accelerated, and thus the degradation rate is improved. However, when the concentration of the AgI / BiOI composite photocatalyst exceeds a certain limit, the active sites on the surface of the catalyst can be saturated by reactants or intermediate products, which can cause the activity of the AgI / BiOI composite photocatalyst to decrease and the degradation rate to slow down. Excessive catalyst can react with the generated hydroxyl radicals to generate species with low activity, thereby affecting the degradation rate.

[0027] Further, the preparation method of the BiOI photocatalyst is as follows: bismuth nitrate is dissolved in ethylene glycol, and potassium iodide solution is added dropwise while stirring in the dark, and the stirring is performed at 90 DEG C for 2 hours; after cooling, the product is washed and dried to obtain the BiOI photocatalyst.

[0028] Optionally, in the reaction system of the preparation method of the BiOI photocatalyst, the concentration of bismuth nitrate is 5.3 g / L.

[0029] Optionally, in the reaction system of the preparation method of the BiOI photocatalyst, the concentration of potassium iodide is 39.8 g / L.

[0030] Further, the preparation method of the AgI / BiOI composite photocatalyst is as follows: bismuth nitrate is dissolved in ethylene glycol, silver nitrate solution is added, and potassium iodide solution is added dropwise while stirring in the dark, and the stirring is performed at 90 DEG C for 2 hours; after cooling, the product is washed and dried to obtain the AgI / BiOI composite photocatalyst.

[0031] Optionally, in the reaction system of the preparation method of the AgI / BiOI composite photocatalyst, the concentration of bismuth nitrate is 5.3 g / L.

[0032] Optionally, in the reaction system of the preparation method of the AgI / BiOI composite photocatalyst, the concentration of silver nitrate is 2.5 g / L.

[0033] Optionally, in the reaction system of the preparation method of the AgI / BiOI composite photocatalyst, the concentration of potassium iodide is 39.8 g / L.

[0034] The application also provides a photocatalyst for degrading methylene blue, which is composed of the BiOI photocatalyst or the AgI / BiOI composite photocatalyst and hydrogen peroxide.

[0035] The BiOI photocatalyst and the AgI / BiOI composite photocatalyst are both prepared by the above method.

[0036] The application also provides application of the AgI / BiOI composite photocatalyst and H2O2 in combination in photocatalytic degradation of methylene blue.

[0037] Compared with the prior art, the application has the advantages that the AgI / BiOI composite photocatalyst has photocatalytic activity on methylene blue, and can be combined with hydrogen peroxide to have a degradation efficiency on methylene blue in wastewater which is 98.0% at most, which is higher than that of the single application. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is an XRD pattern of the BiOI catalyst.

[0039] Figure 2 is an XRD pattern of the AgI / BiOI composite photocatalyst.

[0040] Figure 3 is an ultraviolet-visible spectrum of methylene blue.

[0041] Figure 4 is a standard curve of methylene blue.

[0042] Figure 5 is a comparison chart of degradation rates of the AgI / BiOI composite photocatalyst and no catalyst, wherein the mass concentration of MB is 20 mg / L, the volume is 100 mL, the pH is 4, the catalyst dosage is 0.3 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition is used.

[0043] Figure 6 is an influence chart of different catalysts on the degradation rate of methylene blue under the optimal conditions of the catalysts, wherein the mass concentration of MB is 20 mg / L, the volume is 100 ml, the hydrogen peroxide dosage is 0.4 ml / L, the pH is 4, the AgI / BiOI catalyst dosage is 0.3 g / L, the pH is 6, the BiOI catalyst dosage is 0.5 g / L, and the room temperature condition is used.

[0044] Figure 7 is an influence chart of different catalysts on the degradation rate of methylene blue under the same conditions, wherein the mass concentration of MB is 20 mg / L, the volume is 100 ml, the pH is 4, the catalyst dosage is 0.3 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition is used.

[0045] Figure 8 The left chart of is an influence chart of different pHs on the degradation rate of methylene blue, wherein the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition is used.Figure 8 The right graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition.

[0046] Figure 9 The left graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition. Figure 9 The right graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition.

[0047] Figure 10 The left graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition. Figure 10 The right graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition.

[0048] Figure 11 The left graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition. Figure 11 The right graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition.

[0049] Figure 12 The left graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition. Figure 12 The right graph of Figure 1 is a sampling graph at pH 6; in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, the hydrogen peroxide dosage is 0.4 ml / L, and the room temperature condition.

[0050] Figure 13The left graph of Figure 1 is the effect of different hydrogen peroxide dosages on the degradation rate of methylene blue, the mass concentration of MB is 20 mg / L, the volume is 100 mL, pH = 4, the catalyst dosage is 0.3 g / L, and the room temperature condition. Figure 13 The right graph of Figure 1 is the sampling graph when the hydrogen peroxide dosage is 0.4 ml / L, in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, pH = 4, the catalyst dosage is 0.3 g / L, and the room temperature condition.

[0051] Figure 14 Figure 2 is a comparison chart of the effect of BiOI catalytic hydrogen peroxide under light and no light conditions, in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, the catalyst dosage is 0.5 g / L, pH = 6, and the hydrogen peroxide dosage is 0.4 ml / L under room temperature condition.

[0052] Figure 15 Figure 3 is a comparison chart of the effect of AgI / BiOI catalytic hydrogen peroxide under light and no light conditions, in the graph, the mass concentration of MB is 20 mg / L, the volume is 100 mL, pH = 4, the catalyst dosage is 0.3 g / L, and the hydrogen peroxide dosage is 0.4 ml / L under room temperature condition.

[0053] Figure 16 Figure 4 is the adsorption effect of the BiOI photocatalyst on methylene blue.

[0054] Figure 17 Figure 5 is the adsorption effect of the AgI / BiOI composite photocatalyst on methylene blue. DETAILED DESCRIPTION

[0055] The technical solutions of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0056] In some embodiments of the present application, the method for photocatalytic degradation of methylene blue is provided, first adjusting the pH value of the methylene blue wastewater to be less than or equal to 7.0, then adding BiOI photocatalyst or AgI / BiOI composite photocatalyst and H2O2 into the methylene blue wastewater, and irradiating for not less than 40 min to complete the photocatalytic degradation of methylene blue.

[0057] Optionally, the concentration of methylene blue in the methylene blue wastewater is 20 mg / L.

[0058] Optionally, the addition amount of the hydrogen peroxide working solution is 0.2-0.5 ml / L based on the volume of the methylene blue wastewater.

[0059] Specifically, the hydrogen peroxide working solution is added in an amount of 0.4 ml / L, based on the volume of the methylene blue wastewater.

[0060] Optionally, when the BiOI photocatalyst is selected, the concentration of the BiOI photocatalyst is 0.1-0.7 g / L.

[0061] Specifically, the concentration of the BiOI photocatalyst is 0.5 g / L.

[0062] Optionally, when the AgI / BiOI composite photocatalyst is selected, the concentration of the AgI / BiOI composite photocatalyst is 0.1-0.5 g / L.

[0063] Specifically, the concentration of the AgI / BiOI composite photocatalyst is 0.3 g / L.

[0064] In some other embodiments of the present application, the BiOI photocatalyst is prepared by dissolving bismuth nitrate in ethylene glycol, adding potassium iodide solution dropwise while stirring in the dark, and stirring at 90℃ for 2 hours; after cooling, the product is washed and dried to obtain the BiOI photocatalyst.

[0065] Optionally, in the reaction system of the preparation method of the BiOI photocatalyst, the concentration of bismuth nitrate is 5.3 g / L.

[0066] Optionally, in the reaction system of the preparation method of the BiOI photocatalyst, the concentration of potassium iodide is 39.8 g / L.

[0067] In some other embodiments of the present application, the AgI / BiOI composite photocatalyst is prepared by dissolving bismuth nitrate in ethylene glycol, adding silver nitrate solution, adding potassium iodide solution dropwise while stirring in the dark, and stirring at 90℃ for 2 hours; after cooling, the product is washed and dried to obtain the AgI / BiOI composite photocatalyst.

[0068] Optionally, in the preparation method of the AgI / BiOI composite photocatalyst, the concentration of bismuth nitrate is 5.3 g / L.

[0069] Optionally, in the preparation method of the AgI / BiOI composite photocatalyst, the concentration of silver nitrate is 2.5 g / L.

[0070] Optionally, in the preparation method of the AgI / BiOI composite photocatalyst, the concentration of potassium iodide is 39.8 g / L.

[0071] Table 1 Information of experimental reagents

[0072]

[0073] Table 2 Experimental instrument information

[0074]

[0075] In the following specific implementation cases, the preparation methods of the BiOI catalyst and the AgI / BiOI composite photocatalyst are as follows.

[0076] The preparation method of the BiOI catalyst is as follows: (1) 0.24 g of bismuth nitrate pentahydrate is added to 45 ml of ethylene glycol; stirring in the dark, 25 ml of a solution of 0.996 g of KI is slowly added in the middle; that is, the concentration of bismuth nitrate in the final reaction system is 5.3 g / L, and the concentration of potassium iodide is 39.8 g / L; (2) stirring for 30 min in the dark and light-proof condition, then 90°C water bath and mechanical stirring for 2 h; (3) after cooling, the obtained product is washed alternately with ethanol and deionized water, and dried at 60°C for 12 h to obtain the BiOI catalyst, which is an orange powder after grinding.

[0077] The preparation method of the AgI / BiOI composite photocatalyst is as follows: (1) 0.24 g of bismuth nitrate pentahydrate is added to 45 ml of ethylene glycol; then a mixture of 0.063 g of silver nitrate and 25 ml of ultrapure water is added, stirring in the dark, 25 ml of a solution of 0.996 g of KI is slowly added in the middle; that is, the concentration of bismuth nitrate in the final reaction system is 5.3 g / L, the concentration of silver nitrate is 2.5 g / L, and the concentration of potassium iodide is 39.8 g / L; (2) stirring for 30 min in the dark and light-proof condition, then 90°C water bath and mechanical stirring for 2 h; (3) after cooling, the obtained product is washed alternately with ethanol and deionized water, and dried at 60°C for 12 h to obtain the AgI / BiOI composite photocatalyst, which is a red-brown powder after grinding.

[0078] The structural properties of the BiOI catalyst and the AgI / BiOI composite photocatalyst are characterized by XRD, as shown in the following Figure 1 and 2 . Figure 1 It shows obvious diffraction peaks at 31.651°, 33.180°, 39.345°, 51.361°, 55.161°, etc., which are consistent with the standard BiOI peak positions. Figure 2 It shows obvious diffraction peaks at 19.422°, 29.714°, 31.699°, 37.130°, 41.557°, etc., which are consistent with the standard AgI / BiOI peak positions, indicating that it is a composite substance composed of AgI and BiOI.

[0079] In the following specific implementation cases, methylene blue simulated wastewater is used as the experimental research object when studying the degradation effect of the catalyst and the catalytic method on methylene blue.

[0080] The preparation method of the following specific implementation case of methylene blue simulated wastewater (methylene blue concentration 20 mg / L) is as follows: accurately weigh 0.0200 g of analytical pure methylene blue solid, dissolve it with deionized water, and dilute to 1000 mL in a brown volumetric flask. In order to avoid the influence of light on its stability, the solution needs to be stored in a cool place to ensure its effectiveness and accuracy in subsequent experiments.

[0081] Test example 1: drawing of methylene blue standard curve

[0082] In this test example, UV-vis spectroscopy was used to scan the full spectrum of methylene blue (MB) solution. The results showed that the maximum absorption peak was at 664 nm, as shown in Figure 3 By measuring the absorbance at different time points and applying Lambert-Beer's law, the degradation rate E of MB was calculated. The calculation formula is as follows:

[0083]

[0084] In the formula: C0 is the initial concentration of methylene blue, mg / L, C is the concentration of methylene blue after reaction, mg / L.

[0085] The standard curve of concentration (mg / L) vs. absorbance (A) was drawn by configuring 1, 2, 3, 4, 5 mg / L methylene blue standard solution in turn, as shown in Figure 4

[0086] This method not only effectively verifies the spectral characteristics of methylene blue, but also provides important experimental basis for subsequent degradation research. The experimental results show that the application of UV-vis method in dye degradation monitoring has good accuracy and reliability, and provides effective technical support for environmental pollution control.

[0087] Test example 2: adsorption effect of different catalysts

[0088] 1. Take 100 mL of MB wastewater with initial concentration of 20 mg / L into a 100 mL conical flask, the reaction temperature is 20℃, the catalyst (BiOI photocatalyst or AgI / BiOI composite photocatalyst) concentration is 0.3 g / L, the magnetic stirrer is stirred, and the sample is taken every 10 min for 50 min.

[0089] The experimental results are as follows: Figure 16 and 17 ​As shown in the figure, it can be seen that the adsorption rate of BiOI photocatalyst and AgI / BiOI composite photocatalyst fluctuates around 0. The experimental results show that the BiOI photocatalyst and the AgI / BiOI composite photocatalyst have no adsorption, and it is speculated that they may have water absorption, so that the concentration of wastewater becomes larger, and the adsorption rate is negative. This also shows that the BiOI photocatalyst and the AgI / BiOI composite photocatalyst provided by the application are directly used for catalyzing hydrogen peroxide to degrade methylene blue, rather than adsorbing methylene blue.

[0090] Test Example 3: Study on the degradation effect of methylene blue using different catalysts

[0091] 1. Test method

[0092] This test example studies the degradation effect of methylene blue in methylene blue simulated wastewater using hydrogen peroxide alone, BiOI catalyst alone, AgI / BiOI composite photocatalyst alone, hydrogen peroxide+BiOI catalyst, and hydrogen peroxide+AgI / BiOI composite photocatalyst. The following tests all use 100 ml of methylene blue simulated wastewater with a concentration of 20 mg / L. After 0, 30, 60, 90, 120 and 150 minutes of photodegradation reaction, 1 sample is taken each time, and the degradation rate of the sample is analyzed using a UV-visible spectrophotometer.

[0093] (1) Using hydrogen peroxide alone

[0094] Hydrogen peroxide is added to the methylene blue simulated wastewater to make the concentration of hydrogen peroxide in the system 0.4 ml / L, and 1 mol / L sodium hydroxide solution and 1 mol / L H2SO4 solution are used to adjust the reaction system to maintain pH=4.0. One group is placed in the dark, and the other group is irradiated with a purple light to degrade. After 0, 30, 60, 90, 120 and 150 minutes of reaction, 1 sample is taken each time to detect the degradation rate.

[0095] (2) Using BiOI catalyst alone

[0096] BiOI catalyst is added to the methylene blue simulated wastewater to make the concentration of BiOI catalyst in the system 0.5 g / L, and a magnetic stirrer is used for stirring, and a sample is taken every 10 minutes for 50 minutes.

[0097] (3) Using AgI / BiOI composite photocatalyst alone

[0098] BiOI catalyst is added to the methylene blue simulated wastewater to make the concentration of BiOI catalyst in the system 0.3 g / L, and a magnetic stirrer is used for stirring, and a sample is taken every 10 minutes for 50 minutes.

[0099] (4) Hydrogen peroxide+BiOI catalyst

[0100] In methylene blue simulated wastewater, hydrogen peroxide and BiOI catalyst were added, the concentration of hydrogen peroxide in the system was 0.4 ml / L, and the concentration of BiOI catalyst was 0.5 g / L. 1 mol / L sodium hydroxide solution and 1 mol / L H2SO4 solution were used to adjust the reaction system to maintain pH=6.0.

[0101] (5) hydrogen peroxide + AgI / BiOI composite photocatalyst

[0102] In methylene blue simulated wastewater, hydrogen peroxide and AgI / BiOI composite photocatalyst were added, the concentration of hydrogen peroxide in the system was 0.4 ml / L, and the concentration of AgI / BiOI composite photocatalyst was 0.3 g / L. 1 mol / L sodium hydroxide solution and 1 mol / L H2SO4 solution were used to adjust the reaction system to maintain pH=4.0. At 0, 10, 20, 30, 40, 50, 60 min, 1 sample was taken to detect the degradation rate.

[0103] 2, analysis of test results

[0104] As shown in Figure 5 , the degradation rate and degradation rate of AgI / BiOI composite photocatalyst are significantly better than that of hydrogen peroxide alone (without BiOI catalyst or AgI / BiOI composite photocatalyst). After adding AgI / BiOI composite photocatalyst, the degradation rate is faster in the first 30 min, and the degradation rate becomes flat after 30 min, and finally tends to 98.0 %.

[0105] According to Figure 6 , the degradation rate of BiOI catalyst is lower than that of AgI / BiOI composite photocatalyst in the first 120 min, but the degradation rate of BiOI catalyst is higher than that of AgI / BiOI composite photocatalyst in this period. After 120 min, the degradation rate of BiOI catalyst is significantly lower than that of AgI / BiOI composite photocatalyst, and the degradation rate of BiOI catalyst tends to be flat and lower than that of AgI / BiOI composite photocatalyst. After 150 min, the degradation of AgI / BiOI composite photocatalyst gradually becomes flat. The final degradation rate of BiOI catalyst is 94.2 %, while the final degradation rate of AgI / BiOI composite photocatalyst is 98.0 %.

[0106] Under the same conditions as Figure 7As shown, the degradation rate of the AgI / BiOI composite photocatalyst reached 98.0% at 150 minutes, while the degradation rate of BiOI reached 59.6% at 150 minutes, so the degradation rate of the AgI / BiOI composite photocatalyst was obviously higher than that of BiOI. AgI and BiOI have matching band potentials, and under the excitation of visible light, the intermediate band electrons will jump to the conduction band to generate photoelectrons with reducing power and photoholes with oxidizing power, respectively. The single BiOI material has always had the problem of easy recombination of photoelectron-hole pairs, so the AgI / BiOI composite catalyst system is selected. The photoelectrons of AgI migrate to the conduction band of BiOI, and at the same time, the photoholes of BiOI also migrate to the valence band of AgI, thereby realizing efficient separation of electrons and holes in the system. The electrons transferred to BiOI can reduce molecular oxygen in the solution to generate superoxide radicals, which are then converted into hydroxyl radicals; and the separated photoholes will also oxidize OHˉ to form hydroxyl radicals. The active radicals generated by the two pathways jointly act on the degradation process of methylene blue, so that the AgI / BiOI composite catalyst exhibits significantly better photocatalytic performance than single AgI or BiOI.

[0107] Through the above analysis, the degradation effect of the AgI / BiOI composite photocatalyst is better than that of the single BiOI catalyst.

[0108] Test Example 4: Study on the effect of pH value of the reaction system on the degradation of methylene blue by hydrogen peroxide, BiOI photocatalyst or AgI / BiOI composite photocatalyst

[0109] 1. Test method

[0110] A number of groups of methylene blue simulated wastewater were selected. Hydrogen peroxide, BiOI photocatalyst or AgI / BiOI composite photocatalyst was added to the methylene blue simulated wastewater, so that the concentration of hydrogen peroxide in the system was 0.4 ml / L, the concentration of BiOI photocatalyst was 0.5 g / L, and the concentration of AgI / BiOI composite photocatalyst was 0.3 g / L. Ammonia and 1 mol / L H2SO4 solution were used to adjust and maintain the pH of each group of reaction system to be 2.0, 4.0, 6.0, 7.0 and 9.0, respectively. After light treatment for 0, 30, 60, 90, 120 and 150 minutes, each sample was taken to detect the degradation rate.

[0111] 2. Analysis of test results

[0112] (1) Using hydrogen peroxide and BiOI photocatalyst

[0113] As follows Figure 8As shown in the left figure, the pH of the reaction system has a significant impact on the degradation efficiency of hydrogen peroxide. Under conditions of pH > 7, the degradation rate is only 44.6%, with hydrogen peroxide decomposing into oxygen and water, leading to a decrease in the concentration of hydroxyl radicals and thus poor degradation. Under conditions of pH ≤ 7, the BiOI photocatalyst catalyzes the generation of a large number of hydroxyl radicals from hydrogen peroxide, and under acidic conditions, H... + It can inhibit the hydrolysis of hydrogen peroxide, thus increasing the degradation rate. However, as the concentration of hydroxyl radicals increases, the degradation rate gradually levels off. The degradation rate is 94.2% at pH 6, with the best degradation effect observed in methylene blue wastewater.

[0114] Initially, the methylene blue wastewater solution was blue at pH 6. As the concentration of hydroxyl radicals increased, the solution gradually lightened to a pale blue, eventually becoming transparent and colorless. Figure 8 As shown in the right figure.

[0115] (2) Using AgI / BiOI composite photocatalyst

[0116] as follows Figure 9 As shown in the left figure, the degradation rate was 52.1% under pH>7 conditions. Hydrogen peroxide itself decomposes relatively quickly. Although it can generate hydroxyl radicals, these radicals may react with other ions to form less reactive species. The degradation rate was rapid before 30 minutes, but under alkaline conditions, the catalyst activity was low, and the degradation rate tended to plateau over time, resulting in a slower degradation rate and lower overall degradation. Under pH≤7 conditions, the AgI / BiOI composite photocatalyst catalyzed the oxidation of hydrogen peroxide. Hydrogen peroxide was more stable under acidic conditions, resulting in better catalyst activity, accelerated oxidation rate, and higher degradation rate. The best degradation effect for methylene wastewater was achieved at pH=4, reaching 98.0%.

[0117] Initially, the methylene blue wastewater solution was blue at pH 4. As the concentration of hydroxyl radicals increased, the solution gradually lightened to a pale blue, eventually becoming transparent and colorless. Figure 9 As shown in the right figure.

[0118] Experimental Example 5: Effect of the amount of BiOI photocatalyst or AgI / BiOI composite photocatalyst in the reaction system on the degradation effect of methylene blue.

[0119] 1. Test Methods

[0120] Select several groups of methylene blue simulated wastewater. In the methylene blue simulated wastewater, hydrogen peroxide is added, and BiOI photocatalyst or AgI / BiOI composite photocatalyst is also added; the concentration of hydrogen peroxide in the system is 0.4 ml / L; the concentrations of BiOI photocatalyst in each group are 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, and 0.7 g / L, respectively; the concentrations of AgI / BiOI composite photocatalyst in each group are 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, and 0.5 g / L, respectively. Ammonia and 1 mol / L H2SO4 solution are used to adjust and maintain the pH of each group of reaction systems to 4.0. After 0, 30, 60, 90, 120, and 150 min of light treatment, each sample is taken once to detect the degradation rate.

[0121] 2. Test results

[0122] (1) Using hydrogen peroxide and BiOI photocatalyst

[0123] As shown in the left graph of Figure 10 . The greater the concentration of BiOI photocatalyst, the greater the degradation rate of hydrogen peroxide. This is because increasing the amount of BiOI photocatalyst increases the number of catalytically active centers, thereby increasing the probability of contact between active centers and reactants, resulting in a higher degradation rate. The degradation rate is relatively fast within the first 30 min, and then the degradation rate becomes flat, but when the concentration of BiOI photocatalyst is 0.5 g / L, the degradation rate can reach 94.2 %, the effect is the best, and the degradation rate is also relatively fast.

[0124] At the beginning, when the concentration of BiOI photocatalyst is 0.5 g / L, the methylene blue wastewater solution is blue, and as the concentration of hydroxyl radicals increases, the solution gradually becomes light blue, and finally becomes transparent and colorless, as shown in the right graph of Figure 10 .

[0125] (2) Using AgI / BiOI composite photocatalyst

[0126] The experimental results of catalyzing hydrogen peroxide by adding different amounts of catalyst are as follows Figure 11As shown in the left figure, when the catalyst concentration is 0.3 g / L, the degradation rate is relatively fast in the first 30 minutes. Although the degradation rate decreases somewhat thereafter, the degradation rate still shows an upward trend, eventually approaching 98.0%. Increasing the catalyst dosage can provide more photoactive sites and hydrogen peroxide for interaction, increasing the contact probability between the active centers and reactants, accelerating the generation of hydroxyl radicals, and thus improving the degradation rate. However, when the catalyst dosage exceeds a certain limit, the active sites on the catalyst surface may be saturated by reactants or intermediate products, leading to a decrease in catalyst activity and a slowdown in the degradation rate. Excess catalyst may react with the generated hydroxyl radicals to form species with lower activity, thereby affecting the degradation rate.

[0127] Initially, when the concentration of the methylene blue wastewater catalyst was 0.3 g / L, the solution was blue. As the concentration of hydroxyl radicals increased, the solution gradually lightened to a pale blue, eventually becoming transparent and colorless. Figure 11 As shown in the right figure.

[0128] Experimental Example 6: Effect of the Amount of Hydrogen Peroxide in the Reaction System on the Degradation of Methylene Blue

[0129] 1. Test Methods

[0130] Several groups of simulated methylene blue wastewater were selected. Hydrogen peroxide was added to the simulated methylene blue wastewater, along with either BiOI photocatalyst or AgI / BiOI composite photocatalyst, to achieve the following concentrations in each reaction system: 0.1 ml / L, 0.2 ml / L, 0.3 ml / L, 0.4 ml / L, and 0.5 ml / L; 0.5 g / L for BiOI photocatalyst; and 0.3 g / L for AgI / BiOI composite photocatalyst. The pH of each reaction system was adjusted to 4.0 using ammonia and 1 mol / L H₂SO₄ solution. Samples were taken at 0, 30, 60, 90, 120, and 150 min after light treatment to determine the degradation rate.

[0131] 2. Test Results

[0132] (1) Using hydrogen peroxide and BiOI photocatalyst

[0133] Experimental results are as follows Figure 12As shown in the left figure, increasing the concentration of hydrogen peroxide generates a large number of hydroxyl radicals, which increases the probability of contact between oxide species (such as hydroxyl radicals, peroxide radicals·OOH, etc.) and reactants, thus enhancing the oxidation capacity of the system. The large number of hydroxyl radicals oxidizes and decomposes methylene blue, increasing the degradation rate. However, excessively high hydrogen peroxide concentrations actually decrease the degradation rate, possibly because excess hydrogen peroxide reacts to generate other less reactive substances, thereby reducing reaction efficiency. The highest degradation rate of methylene blue (94.2%) was achieved when the hydrogen peroxide concentration was 0.4 ml / L, demonstrating the best effect.

[0134] Initially, the methylene blue wastewater solution was blue when the hydrogen peroxide concentration was 0.4 ml / L. As the concentration of hydroxyl radicals increased, the solution gradually lightened to a light blue-green, eventually becoming transparent and colorless. Figure 12 As shown in the right figure.

[0135] (2) Using AgI / BiOI composite photocatalyst

[0136] Experimental results are as follows Figure 13 As shown in the left figure, under a hydrogen peroxide concentration of 0.4 ml / L, the degradation rate of methylene blue was relatively fast in the first 30 minutes. After 30 minutes, the degradation rate decreased, but the degradation rate still slowly increased, eventually approaching 98.0%. When the amount of hydrogen peroxide is moderate, the number of hydroxyl radicals generated increases with its concentration, which improves the degradation efficiency of methylene blue. However, excessive hydrogen peroxide will trigger its own decomposition reaction, generating oxygen and water, leading to a reduction in the effective components and decreasing the degradation ability of methylene blue. Experiments show that the degradation effect of methylene blue is best when the hydrogen peroxide concentration is 0.4 ml / L.

[0137] Initially, the methylene blue wastewater solution was blue when the hydrogen peroxide concentration was 0.4 ml / L. As the concentration of hydroxyl radicals increased, the solution gradually lightened to a light blue-green, eventually becoming transparent and colorless. Figure 13 As shown in the right figure.

[0138] Experimental Example 7: Effect of light on the degradation of methylene blue by hydrogen peroxide and AgI / BiOI composite photocatalyst

[0139] 1. Test Methods

[0140] Four groups of methylene blue simulated wastewater were selected. Hydrogen peroxide was added to the methylene blue simulated wastewater, and BiOI photocatalyst (2 groups) or AgI / BiOI composite photocatalyst (2 groups) was also added, so that the concentration of hydrogen peroxide in each group of reaction system was 0.4 ml / L, the concentration of BiOI photocatalyst in 2 groups was 0.5 g / L, and the concentration of AgI / BiOI composite photocatalyst in the other 2 groups was 0.3 g / L. Ammonia and 1 mol / L H2SO4 solution were used to adjust and maintain the pH of each group of reaction system to 4.0. One group was subjected to light treatment, and the other group was placed in a dark environment. After 0, 30, 60, 90, 120, and 150 minutes of reaction, each sample was taken to detect the degradation rate.

[0141] 2. Test results

[0142] (1) Using hydrogen peroxide and BiOI photocatalyst

[0143] The experimental results are shown in Table 1. Figure 14 As can be seen, under the condition of light, the degradation rate of methylene blue gradually increased to 94.2%, while the degradation rate without light was slow and the degradation rate was low, which was 3.6%. It can be seen that light is conducive to the combination of BiOI photocatalyst and hydrogen peroxide, and reactive free radicals are produced in the reaction.

[0144] (2) Using AgI / BiOI composite photocatalyst

[0145] The experimental results are shown in Table 2. Figure 15 As can be seen, under the condition of light, the degradation rate of methylene blue gradually increased to 98.0%, while the degradation rate without light was slow and the degradation rate was low, which was 3.6%. It can be seen that light is conducive to the combination of AgI / BiOI composite photocatalyst and hydrogen peroxide, and reactive free radicals are produced in the reaction.

[0146] In summary, AgI / BiOI composite photocatalyst has better effect on methylene blue wastewater treatment. When the mass concentration of methylene blue MB is 20 mg / L, the volume is 100 mL, the catalyst concentration is 0.3 g / L, the pH is 4, and the hydrogen peroxide concentration is 0.4 ml / L under light, the AgI / BiOI catalytic hydrogen peroxide oxidation of methylene blue wastewater is the best, and the degradation rate can reach 98.0%. The degradation rate of BiOI catalytic hydrogen peroxide oxidation of methylene blue wastewater is only 59.6%. Therefore, the effect of AgI / BiOI composite photocatalyst on the degradation of methylene blue wastewater by hydrogen peroxide is better than that of bismuth iodine oxide catalyst. Under the optimal conditions, the effect of AgI / BiOI composite photocatalyst on the degradation of methylene blue wastewater by hydrogen peroxide is also better than that of bismuth iodine oxide catalyst, and the degradation rate of the former is 98.0%, while that of the latter is 94.2%. Moreover, under the condition of light, the effect of degrading wastewater is better than that in the dark.

[0147] Photocatalytic degradation of wastewater by hydrogen peroxide is a new water treatment technology, which has the advantages of simple operation and wide application range. This technology can effectively degrade organic pollutants in water through the generation of hydroxyl radicals by photocatalysts, significantly improving the degradation efficiency. In addition, the photocatalytic process does not produce secondary pollution, ensuring the safety of the environment. The innovation and efficiency of this method make it show broad application prospects in the field of wastewater treatment, providing a new way to solve water pollution problems. The photocatalytic degradation of methylene blue wastewater by hydrogen peroxide is affected by many factors. This experiment explores the influence of different amounts of hydrogen peroxide, pH, and different amounts of catalysts. According to the experimental results, the degradation effect under light is better than that without light, and the absorbance of methylene blue in the dark is basically unchanged. The effect of adding hydrogen peroxide alone is not as good as adding catalysts. Under the conditions of BiOI concentration of 0.5 g / L, pH=6, hydrogen peroxide addition of 0.4 ml / L, and methylene blue concentration of 20 mg / L, the decomposition effect of hydrogen peroxide on methylene blue wastewater is the best under light conditions, and the degradation rate can reach 94.2 %. Under the conditions of AgI / BiOI composite catalyst concentration of 0.3 g / L, pH=4, hydrogen peroxide addition of 0.4 ml / L, and methylene blue concentration of 20 mg / L, the decomposition effect of hydrogen peroxide on methylene blue wastewater is the best under light conditions, and the degradation rate is 98.0 %. Under the optimal and same conditions, AgI / BiOI composite catalyst can more effectively catalyze hydrogen peroxide to generate hydroxyl radicals, improve the degradation efficiency, and the degradation rate can reach 98.0 %, which is better.

[0148] Photocatalytic oxidation technology plays an important role in treating dye wastewater, which can effectively degrade harmful dyes. However, current experimental studies mostly use methylene blue as simulated wastewater, lacking universality for actual industrial wastewater. Therefore, future research should focus on improving this point to improve the application effect of photocatalytic technology in diversified dye wastewater treatment, so as to better meet the environmental protection needs and promote the progress of industrial wastewater treatment technology. The chemical composition of actual output dye wastewater is complex, and the actual application rules and technology of photocatalytic oxidation technology have not been fully mastered. Deepen the research on the mechanism of photocatalytic oxidation, and at present there is still a lack of tracking of reaction intermediates and active products in the photocatalytic degradation system, which needs to expand the research on the mechanism and reaction kinetics of photocatalytic reaction, provide basis for the treatment of mixed industrial wastewater, and prepare more effective and targeted catalysts. The current experiment has not studied the influence of temperature, so it is necessary to further explore the best conditions. ③ The research on the industrialization process of photocatalytic oxidation is gradually focusing on improving the cost performance and simplifying the steps to meet market demand. By optimizing the process and materials, researchers are committed to improving the application efficiency of photocatalytic technology and promoting its wide application in the field of environmental governance. In the future, we should continue to develop new high-efficiency photocatalysts, improve catalyst stability, reduce costs, and combine with other technologies. With the continuous deepening of research, photocatalyst catalytic hydrogen peroxide degradation wastewater technology will play an increasingly important role in wastewater treatment.

[0149] The above specific embodiments describe the implementation of the present application in detail, but the present application is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concepts of the present application, the technical solutions of the present application can be modified and changed in many ways, and these simple modifications all belong to the protection scope of the present application.

Claims

1. A method for photocatalytic degradation of methylene blue, characterized in that, Adjust the pH of the methylene blue wastewater to ≤7.0, add BiOI photocatalyst or AgI / BiOI composite photocatalyst and hydrogen peroxide working solution to the methylene blue wastewater, and irradiate for no less than 40 min to complete the photocatalytic degradation of methylene blue.

2. The method for photocatalytic degradation of methylene blue according to claim 1, characterized in that, The concentration of methylene blue in the methylene blue wastewater was 20 mg / L.

3. The method for photocatalytic degradation of methylene blue according to claim 1, characterized in that, The amount of hydrogen peroxide working solution added is 0.2-0.5 ml / L, based on the volume of the methylene blue wastewater.

4. The method for photocatalytic degradation of methylene blue according to claim 3, characterized in that, Based on the volume of the methylene blue wastewater, the amount of hydrogen peroxide working solution added is 0.4 ml / L.

5. The method for photocatalytic degradation of methylene blue according to claim 1, characterized in that, When the BiOI photocatalyst is selected, the concentration of the BiOI photocatalyst is 0.1-0.7 g / L; when the AgI / BiOI composite photocatalyst is selected, the concentration of the AgI / BiOI composite photocatalyst is 0.1-0.5 g / L.

6. The method for photocatalytic degradation of methylene blue according to claim 4, characterized in that, The concentration of the BiOI photocatalyst is 0.5 g / L, and the concentration of the AgI / BiOI composite photocatalyst is 0.3 g / L.

7. The method for photocatalytic degradation of methylene blue according to claim 1, characterized in that, The preparation method of the BiOI photocatalyst is as follows: Bismuth nitrate is dissolved in ethylene glycol, and potassium iodide solution is added dropwise while stirring in the dark. The mixture is stirred at a constant temperature of 90°C for 2 hours. After cooling, the product is washed and dried to obtain the BiOI photocatalyst. The preparation method of the AgI / BiOI composite photocatalyst is as follows: bismuth nitrate is dissolved in ethylene glycol, silver nitrate solution is added, potassium iodide solution is added dropwise while stirring in the dark, and the mixture is stirred at a constant temperature of 90°C for 2 hours. After cooling, the washed product was dried to obtain the AgI / BiOI composite photocatalyst.

8. A photocatalyst for degrading methylene blue, characterized in that, The photocatalyst is composed of BiOI photocatalyst or AgI / BiOI composite photocatalyst and hydrogen peroxide.

9. The use of the photocatalyst according to claim 8 in the photocatalytic degradation of methylene blue.

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