The Preparation Of Bismuth Oxyhalide Composites With Enhanced Photocatalytic Activity For Degradation Of Typical Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons are a typical type of persistent organic pollutant,which are fat-soluble and resistant to degradation.They have been detected in the environment with high residual level.Because most polycyclic aromatic hydrocarbons are carcinogenic,teratogenic and mutagenic,they have been listed as priority pollutants by the US Environmental Protection Agency.In recent years,PAHs pollution has become increasingly serious worldwide.PAHs have polluted lakes,rivers and soils in China to varying degrees.As an advanced oxidation technology for degrading organic pollutants,photocatalysis technology has the advantages of high removal rate,easy operation and no secondary pollution.However,the traditional photocatalysts have the limits of high recombination rate of photogenerated electron-hole pairs and low degradation rate,so many researches is aiming to develop new photocatalysts with wide corresponding range of light and high carrier separation rate.Bismuth oxyhalide photocatalysts have received widespread attention due to their unique layered structure,and bismuth-rich catalysts have also begun to be used in the degradation of organic pollutants due to their appropriate band positions.In this study,typical polycyclic aromatic hydrocarbons(anthracene,methylpyrene,and pyrene)were used as the model pollutants to explore the synthesized new bismuth oxyhalide catalysts and the photocatalytic activity of the bismuth-rich coincident catalyst under simulated sunlight.The reasons for the improvement of catalytic activity,the path of pollutant degradation and the environmental applicability of the catalyst were also explored.(1)A novel solar active AgBr/BiOBr/TiO2 catalyst was synthesized by a facile coprecipitation method for solar-driven water remediation.The synthesized material composed of flower-like TiO2 nanoparticles loaded on BiOBr nanosheets and with homogeneous surface distributed Ag/AgBr nanoparticles.The heterojunction between BiOBr/TiO2 greatly facilitated the charge carrier migration;the introduction of narrow band gap semiconductors(AgBr and BiOBr)promoted the visible light adsorption;and the Ag/AgBr nanoparticles acted as photosensitizer to further improve the light utilization.The new material showed 7.6-and 4.0-times activity of pure TiO2 and BiOBr under solar light,and the contribution of reactive species on anthracene degradation followed the order of h+>O2·->·OH.The degradation mechanism and pathway were proposed based on intermediates analysis and DFT calculation.The QSAR analysis revealed that the environmental risks of contaminants were greatly reduced during the photocatalysis process but some intermediates were still toxic.The high photocatalytic activity,stability and adaptability all indicated that this new material owns great application potential for cost-effective photocatalytic remediation of persistent organic contaminants under solar light.(2)Bi3O4Br nanosheets were synthesized by alkaline hydrothermal method,and Bi3O4Br nanocomposites doped with lattice carbon were synthesized by ultrasonic cell crushing method.The degradation experiment of methylpyrene under simulated sunlight showed that the optimal doping ratio of C was 3.16%.Due to the doping of C,a strong internal electric field was formed between[Bi-O]and[Br]ions,which greatly promoted the separation of photoexcited electrons and holes.The photocatalytic activity of 3.16%C-Bi3O4Br under sunlight was 3.3times that of Bi3O4Br.Quenching experiments showed that the most important active substance in the catalytic system was h+,followed by O2·-radicals,and there was only a very small amount of·OH in the system.Based on the LC-MS results,the possible degradation pathway of methylpyrene was speculated,and the catalytic reaction process could finally mineralize methylpyrene into CO2and H2O.The impact factor experiments of the catalyst proved that low concentration of DOM and SO42-were beneficial to the generation of active free radicals,thus increasing the degradation rate of methylpyrene by 3.16%C-Bi3O4Br.(3)Using glucose as the carbon source,a new series of new photocatalysts of C-doped Bi3O4X with different mass ratios of carbon were synthesized by a combination of ultrasonic disintegration method and hydrothermal method.The pyrene degradation experimental results showed that the photocatalytic activity of 3.16%C-Bi3O4I is 2.1 and 2.5 times higher than that of Bi3O4I and 3.16%C-Bi3O4Br,respectively.In addition,with the increase of atomic numbers of Cl,Br and I,the photocatalytic performance of Bi3O4X is gradually enhanced,and the photocatalytic activity of 3.16%C-Bi3O4X also accords with this regular.Experimental and characterization results showed that c-doping extends the light absorption boundary of Bi3O4I to 678 nm,which improved the visible light utilization rate of the catalysts.At the same time,a strong internal electric field was formed in Bi3O4I nanosheets to promote the separation rate of photogenerated carriers,thus enhancing the photocatalytic performance of 3.16%C-Bi3O4I.The results of radical quenching experiments showed that O2·-was the most important radical in the pyrene degradation system.However,due to the different energy band structure of the catalysts,the main active substance in 3.16%C-Bi3O4Br was h+,and the main active substance in 3.16%C-Bi3O4Cl was ·OH.According to the results of LC-MS,the possible degradation pathway of pyrene was proposed,which provided a new reference for the removal of polycyclic aromatic hydrocarbons in water conditions.