Photocatalytic Degradation Mechanism Of Bismuth-based Composites For Organic Pollutants In Water

The crisis of energy shortage,water environment pollution and ecological destruction has caused serious concern in the growing industrial development.Antibiotics in water bodies destroy the ecological environment on which human beings live,and the production of"super bacteria"threatens people’s health all the time.People hope to use a low-energy and low-cost way to remove antibiotics from water bodies.The utilization of solar energy may be an ideal and promising strategy to solve the environmental crisis.As a new type of environment-friendly technology,semiconductor-based photocatalysis is expected to apply sunlight to energy conversion,pollutant degradation,and organic matter synthesis.Therefore,how to prepare photocatalysts that respond to visible light and have excellent photocatalytic properties is a major challenge in the field of photocatalytic research.In this paper,the bismuth-based material was used as the substrate to improve the catalytic activity of the material for doxycycline hydrochloride in water by constructing a heterojunction.The details are as follows:（1）The precursor g-C₃N₄ was perforated with Na HCO₃ without using a template or strong acid to obtain porous g-C₃N₄（PCN）with high specific surface area.Subsequently,Bi₄O₅I₂/PCN photocatalysts with different ratios were prepared by ethylene glycol（EG）-assisted hydrothermal method.Within 90 min,the degradation rate of doxycycline hydrochloride by BCN15（Bi₄O₅I₂/15wt.%PCN）reached 82.3%.They are 1.5 times and4.6 times that of pure Bi₄O₅I₂ and PCN,respectively.The enhanced photocatalytic activity is mainly attributed to the separation and mobility of photogenerated carriers.Meanwhile,the activity trapping experiments showed that superoxide radical（·O₂-）was the main group for the Bi₄O₅I₂/PCN catalyst to effectively degrade doxycycline hydrochloride.Toxicity analysis proves that Bi₄O₅I₂/g-C₃N₄ is a green photocatalyst.（2）A new Bi₅O₇I/Bi OCl heterojunction photocatalyst was prepared by in-situ co-precipitation method,which overcomes the shortcomings of small specific surface area,fast photogenerated carrier recombination,and slow charge transfer speed.The photodegradation rate of doxycycline hydrochloride by BB-40（Bi₅O₇I/40wt.%Bi OCl）reached 83.0%within 90 min,and the inhibition rate to Escherichia coli was 99.92%.The possible degradation pathway of doxycycline hydrochloride was proposed by liquid chromatography-mass spectrometry（LC-MS）analysis.·OH and h⁺play a major role in the photocatalytic degradation process.The biological toxicity test showed that the toxicity of doxycycline hydrochloride after photodegradation was obviously weakened.This strategy provides a green and low toxicity pathway for the application of bismuth-rich materials in the fields of environmental remediation and photocatalytic disinfection.