Modification Design Of Bismuth Based Photocatalysts And Removal Of Organic Pollutants

Organic pollutants are various and stable in chemical structure,which cause serious harm to ecological environment after polluting water.As a green technology with important application prospect,photocatalytic technology has been applied more and more in the treatment of dye,pesticide and antibiotic in wastewater.At present,metal-organic coordination polymers have been widely used in the field of photocatalysis due to their variety,controllable structure,high thermal stability and large specific surface area.Bismuth-based materials have become promising visible light response photocatalysts due to their narrow band gap.However,few reports have been reported on bismuth-containing coordination polymers combined with the advantages of the two materials,and there is no in-depth discussion on their photocatalytic properties.Aiming at these problems,three types of bismuth-based bimetal coordination polymers and their derivatives were constructed in this paper for the removal of organic pollutants in water.1.A novel bismuth-cobalt bimetallic coordination polymer（BiCo-MCP）was prepared by hydrothermal method.Its molecular formula is BiCo C₂₁H₁₇N₃O₁₆.The crystal structure,morphology,size and band gap width of the materials were characterized by single crystal XRD,SEM,UV,FTIR and BET.The band gap was calculated as 1.65 e V and applied to the removal of Rh B and imidacloprid.The value-added effects of p H value and H₂O₂on the degradation of Rh B and imidacloprid was investigated,and the photocatalytic degradation mechanism of imidacloprid by BiCo-MCP was revealed.The results showed that the removal rates of Rh B and imidacloprid could be increased to 98%and 75.8%respectively by changing the p H value of the solution under simulated sunlight irradiation.The removal rate of imidacloprid could be increased to 81%by introducing H₂O₂.BiCo-MCP was used as photocatalytic to degrade imidacloprid wastewater,the final degradation products were inorganic ions,avoiding the formation of various organic intermediates.BiCo-MCP has good stability under acidic and neutral conditions,and it can still maintain good photocatalytic performance after three cycles.2.BiCo-MCP/Gr composite graphene material was prepared by hydrothermal method.Its morphology,structure and band gap width were characterized.The band gap of BiCo-MCP/Gr is about 1.5 e V.Using Rh B and imidacloprid as target pollutants,the photocatalytic performance of BiCo-MCP/Gr composite was investigated.The photocatalytic properties of the composites were studied with Rh B and imidacloprid as target pollutants.The experimental results showed that when the concentration of Rh B slution was 10 mg·L^-1,the degradation rate could reach 72.2%after two hours of illumination.By adjusting the p H value of Rh B solution to 2.3,under the same conditions,the degradation rate could reach 95.2%,and the removal rate reached 70.35%after 15 min of dark reaction.No desorption phenomenon was found when the dark reaction time was prolonged.When the catalyst dosage was increased to 1.5 mg·L^-1,Rh B could be completely removed within 30min in the dark reaction stage,and the cycle was constant for three times.3.A bimetallic oxide of feldspar type bismuth cobalt was prepared by pyrolysis of BiCo-MCP,whose chemical formula is Bi_12.7CO_0.3O_19.35.The structure,composition,morphology,band gap width and specific surface area were characterized by XRD,SEM,UV,XPS and BET.With Rh B and imidacloprid as the target pollutants,the effects of pyrolysis temperature and time on the composition,morphology and photocatalytic properties were studied.At the same time,experiments were designed to change the p H value of the target pollutants,improve the degradation rate of the target pollutants,and reveal the degradation path and mechanism under different p H conditions.The results show that the material prepared at700℃for 30 min has the best morphology and photocatalytic performance.The p H value of the target pollutants solution have a great influence on the photocatalytic performance,especially when the p H=1.86 or 11.0,the photocatalytic degradation rate of imidacloprid can reach more than 96%,while the catalytic degradation of Rh B can reach 100%removal within30 minutes.The oxidation reaction of imidacloprid played a leading role in acidic conditions,and the intermediate product was 6-chlorotinaldehyde.The reduction reaction played a leading role under alkaline conditions and the intermediate product was2-chloro-5-（（4,5-dihydro-1H-imidazolyl）methyl）pyridine.The results of HPLC and TOC tests showed that the intermediates were unstable and eventually mineralized into CO₂,H₂O and inorganic salts.The cyclic stability of Bi_12.7Co_0.3O_19.35material shows that it was very stable under alkaline conditions,and its photocatalytic performance remains unchanged after three cycles.4.Two bismuth-based bimetallic organic oxides BiMn-MOO and BiCu-MOO were prepared.Their molecular formulas are Bi₂Mn C₁₈H₆O₁₃and Bi₃Cu C₁₀H₃N₄O₁₁,respectively.The structure,morphology,size and band gap were characterized by XRD,SEM,EDS and UV.The photocatalytic degradation of dye methylene blue,Rh B and neonicotinoid pesticides imidacloprid,thiamethoxam and clothianidin were studied.The influence of p H value of solution and amount of catalyst on photocatalytic performance was investigated.The results showed that two bismuth-based bimetallic organic oxides could effectively remove three neonicotinoid pesticides.The degradation ability is related to the structure of the three pesticides.The factors affecting the degradation rates of the three pesticides were studied.The optimal degradation conditions were determined as follows:the dosage of BiMn-MOO was1 g·L^-1,the p H value of solution was below 2.6,and the degradation rates of imidacloprid and clothianidin were increased to 91.9%and 81.2%,but the degradation rates of thiamethoxam was decreased to 40.6%.The degradation rates of Rh B,imidacloprid and thianidin reached100%,76.93%and 41.23%,respectively,when the dosage of BiCu-MOO was 1 g·L^-1and the p H value of solution was 1.82.5.A mullite bismuth manganese bimetal oxide with molecular formula of Bi₂Mn₄O₁₀was prepared by high temperature pyrolysis of BiMn-MOO.The structure,composition,morphology and band gap were characterized by XRD,SEM,EDS,UV and FTIR.The effects of different pyrolysis temperatures on the composition,morphology and photocatalytic properties of materials with imidacloprid,clothianidin and thiamethoxam as target pollutants were studied.It was found that compared with BiMn-MOO,BiMn-MOO500 and BiMn-MOO700,BiMn-MOO600 exhibits the best photocatalytic performance,which was attributed to the morphology and composition of the porous surface.XRD analysis shows that BiMn-MOO600 was composed of Bi₂Mn₄O₁₀and a small amount of Bi₂O₃,both of which were good bismuth-based semiconductor materials.When the concentration of BiMn-MOO600 was1g·L^-1,the concentration of pollutant solution was 10 mg·L^-1,and the reaction time was 360min under visible light,the degradation rates of imidacloprid,clothianidin and thiamethoxam could reach 48.7%,58.2%and 83.1%,respectively.By testing the TOC and TN of the solution before and after the reaction,it was found that the photocatalytic degradation rate of the three neonicotinoid insecticides was up to 74.34%.The active substances involved in the photocatalytic reaction were investigated.The results showed that photoinduced holes（h⁺）,·OH and·O₂^-were all important active substances in the photocatalytic reaction,and their active order was·O₂^->h⁺>·OH,further revealing the reaction mechanism.BiMn-MOO600 has good stability.The morphology and structure of catalyst do not change before and after the reaction,and the photocatalytic performance remains unchanged after three cycles.