Studies On Photodegradation Of Organic Pollutants And The Optimized Modification Of Bismuth Oxyhalides

Nowadays,the threat posed to natural water systems by various anthropological processes such as chemical industry production and domestic sewage discharge is increasing.A large amount of organic pollutants is used worldwide and disposed into the environment due to ineffective treatment.Comparing with the traditional methods which have many disadvantages,semiconductor photocatalytic degradation has been known as efficient alternatives in wastewater treatment due to their strong oxidizing capacity and environmentally friendly features.Bismuth oxyhalides（BiOX,X=Cl,Br and I）,as a new family of promising photocatalysts,have been attracting much attention because of its unique physical and chemical properties.The impact factors of photocatalytic degradation efficience of bismuth oxyhalides semiconductor materials were explored in this research.Among bismuth oxyhalides,BiOI has widest light absorption range which makes BiOI a perfect candidate for the photocatalytic process.However,pristine BiOI often suffer from several shortcomings,such as poor quantum yield,low visible light absorption efficiency,lower photo-induced charges separation efficiency and high photo-induced charges recombination resulting in low photocatalytic performance.So,many modification methods have been used to enhance the photocatalytic performance of BiOI,such as co-catalyst,doping,graphene loding etc.Among these methods,doping silver halides into BiOI matrix to construct the heterojunction has the enormous potential to improve the light absorption characteristics and charge separation efficiency.To better know the photocatalytic performance of bismuth oxyhalides（BiOX,X=Cl,Br,I）regulated by incorporation of halides within nanostructures,BiOX nanosheets were synthesized through morphology controllable solvothermal method and characterized systematically.The organic structural property greatly influences the photocatalytic activity of Bi OX:1)as for neutral molecular phenol,BiOX shows photocatalytic activity in the order of BiOCl>BiOBr>BiOI under simulated sun light irradiation,and the photo-oxidation kinetics follow Eley–Rideal mechanism;and2)for adsorbed anionic orange II（OII）and cationic methylene blue（MB）,BiOX shows photocatalytic activity in the order of BiOCl>BiOBr>BiOI,and the photo-oxidation kinetics follow Langmuir-Hinshelwood mechanism.The crystal structure of the catalyst also greatly influences the photocatalytic activity of BiOX:1)The relative photo-oxidation power of O₂^·-radicals or HO·radicals involved in this study were different which were quantitatively detected using typical radical trapping agent,separately;2)The relative photo-oxidation power of photogenerated holes（h⁺）in this study were in the order of BiOCl>BiOBr>BiOI,which may be ascribed to lowering the valence band maximum edge of BiOX through incorporation of halides as the atomic number of halides decreased.This study provides novel explanation for fabricating BiOX heterojunctions with tunable photocatalytic reactivity via regulating the halides ratio.Bismuth oxide iodide（BiOI）is a narrow band gap conductor that can be driven by visible light.In order to efficiently improve its separation efficiency of photogenerated carriers and utilization of visible light,a novel AgI doping Bi OI 3D hierarchical composite（AgI-BiOI）was synthesized via a facile solvothermal method.The crystalline structure,morphology,and chemical composition of AgI-BiOI were thoroughly characterized.The AgI-BiOI with Ag and Bi molar ratio of 1:8（AgI-Bi OI（1-8））shows great enhancement for photocatalytic degradation of bisphenol A（BPA）with the pseudo-first degradation rate constant about 3.7 or 14.5 times than that of pristine BiOI or AgI under simulated solar light Xe lamp irradiation.The synergistic enhancement for BPA photodegradation on AgI-BiOI（1-8）is more obviously under VU-Vis irradiation（Xe lamp）than that of UV or Visible irradiation.The photocatalytic enhancement of AgI-Bi OI1-8 for degradation of BPA is mainly ascribed to the extended light absorption intensity in optical spectrum and accelerated separation efficiency of photo-generated carriers due to the synergistic interaction between AgI and BiOI within the matrix of this heterojunction.Free radical quenching experiments of reactive oxygen species（ROS）involved in this system proved the dominant role of positive holes（h⁺）and superoxide(O₂^·-)radicals being responsible for the photodegradation of BPA rather than that of singlet oxygen（¹O2）and hydroxyl（HO·）radicals,respectively.The AgI-BiOI（1-8）hardly shows any ecotoxicity to C.elegans through lethal experiments.The luminance bacteria acute toxicity of photodegradation intermediates of BPA increases before 30 minutes then reduces significantly with irradiation.The good durability and environmental-friendly characteristics make AgI-BiOI（1-8）catalyst to be a good solar light-driven candidate.