Study On The Degradation Mechanism Of Bromate In Nano-TiO₂ Photocatalytic System

Bromate is one kind of cancer-causing pollutant in water.And the TiO₂ photocatalytic system is an effective method to degrade the bromate..In this thesis,the degradation mechanism of bromate in TiO₂ photocatalytic system was studied,and the possibe influence factor such as holes,electrons,oxygen and hydrogen peroxide were investigated during the TiO₂ photocatalytic reaction.TiO₂ photocatalysis is a unique technique for eliminating environmental contaminants in which oxidation and reduction reactions by holes and electrons could be occurred concurrently.Bromine species have six oxidation states from Br^- to BrO₃^-,and the transformation between different oxidation states of bromine species is complex and controversial.In this study,the lowest oxidation state(Br^-) and the highest oxidation state(BrO₃^-) were used as starting compound for the photocatalytic reaction,to investigate the transformation of bromine species.The experimental results showed that pH was the critical factor which had a huge impact on the hydroxyl radical oxidation and electron reduction resulting in its influence on the transformation of bromine species.The photocatalytic reduction of bromate was the dominant reaction with hydrobromous acid and hydrobromite as the intermediate in a pH range of 3-11. The photogenerated electrons and H₂O₂ play major and minor roles in photocatalytic reduction of BrO₃^-,respectively.The photocatalytic oxidation of Br^- became dominant under strong acidic condition(pH 1.5),while the photocatalytic oxidation and reduction were inhibited under strong basic condition(pH 13.5).Low concentration of organic matters(3 mg/L),which reacted with holes and hydroxyl radicals inhibiting the combination of holes and electrons,promoted the photocatalytic reduction;High concentration of organic matters(30 mg/L) will inhibit the bromate degradation.