Deep Insight Into The Bromate Reduction Mechanism Induced By Free Radical

In the drinking water disinfection process,ozone oxidation technology is increasingly applied to drinking water treatment processes.The bromine-containing drinking water will generate a Class 2B potential carcinogen,bromate,at the same time as ozone disinfection.Photocatalytic degradation of semiconductors is an effective method to remove bromate from drinking water.As a visible light catalyst,g-C₃N₄ has good chemical stability,thermal stability and semiconducting properties and has an attractive application prospect in the field of photocatalysis.g-C₃N₄ prepared with melamine as precursor is a visible light catalyst.Its phase composition and photocatalysis are determined by X-ray powder diffraction（XRD）,transmission electron microscopy（TEM）and ultraviolet-visible diffuse reflectance spectroscopy（UV-Vis）.The properties were characterized and found that the prepared layered g-C₃N₄ has a stable lamellar structure and a bandgap（².80 eV）of visiblelightresponse.Electronparamagneticresonance（EPR）and photoelectrochemical tests were used to further explore the mechanism of photocatalytic reduction triggered by radicals;the results showed that g-C₃N₄ cannot directly reduce bromate.However,if organic small molecules（such as methanol）exist,the photocatalytic reduction efficiency increases rapidly,and the change of pH has little effect on the degradation effect;the active species produced by the photocatalytic process through electron paramagnetic resonance spectroscopy（EPR）The in-situ measurement shows that g-C₃N₄ has a weak ability to oxidize methanol due to its narrow bandgap,oxidize methanol to the intermediate CH₃O·quinone free radicals,thus reducing bromate;at the same time,it also confirms the photocatalytic generation of photogenerated holes and defects.OH·oxidizes methanol to CH₃O·,which is the main active species for the reduction of bromate rather than photogenerated electrons.In addition,photoelectrochemical tests also show that methanol can promote the separation of photogenerated electrons and holes.In this experiment,graphite carbon nitride was used as a visible light catalyst to investigate the mechanism of photocatalytic reduction of bromate by g-C₃N₄ from the perspective of the oxidation of methanol to produce free radicals,and to promote the application of photocatalytic reduction in water treatment.