Dutta Paritam K, Pehkonen S O, Sharma Virender K, Ray Ajay K
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore.
Environ Sci Technol. 2005 Mar 15;39(6):1827-34. doi: 10.1021/es0489238.
Arsenic contamination has been found in the groundwater of several countries. Photocatalysis can rapidly oxidize arsenite (As(III)) to less labile and less toxic arsenate (As(V)), which then can be removed by adsorption onto photocatalyst surfaces. This study investigates the photocatalytic oxidation of As(III) to As(V) as a function of As(III) concentration, pH, catalyst loading, light intensity, dissolved oxygen concentration, type of TiO2 surfaces, and ferric ions to understand the kinetics and the mechanism of As(III) oxidation in the UV/TiO2 system. Photocatalytic oxidation of As(III) to As(V) takes place in minutes and follows zero-order kinetics. Benzoic acid (BA) was used as a hydroxyl radical (.OH) scavenger to provide evidence for the .OH as the main oxidant for oxidation of As(III). The .OH radical was independently generated by nitrate photolysis, and kinetics of As(III) oxidation by the .OH radical was determined. Formation of salicylic acid (SA) from the oxidation of BA by .OH also demonstrates the involvement of .OH in the mechanism of As(III) oxidation. The effect of Fe(III) on As(III) oxidation at different pH values with and without TiO2 under UV light was examined. The results suggest that .OH is the dominant oxidant for As(III) oxidation. Two commercially available TiO2 suspensions, Degussa P25 and Hombikat UV100, were tested for the removal of arsenic through oxidation of As(III) to As(V) followed by adsorption of As(V) onto TiO2 surfaces. Results showed that complete removal of arsenic below the World Health Organization drinking water limit of 10 microg/L could be achieved.
在多个国家的地下水中都发现了砷污染。光催化能够迅速将亚砷酸盐（As(III)）氧化为较不易迁移且毒性较小的砷酸盐（As(V)），然后可通过吸附在光催化剂表面将其去除。本研究考察了As(III)光催化氧化为As(V)这一过程随As(III)浓度、pH值、催化剂负载量、光照强度、溶解氧浓度、TiO2表面类型以及铁离子的变化情况，以了解UV/TiO2体系中As(III)氧化的动力学和机理。As(III)光催化氧化为As(V)在数分钟内即可完成，且遵循零级动力学。使用苯甲酸（BA）作为羟基自由基（·OH）清除剂，以证明·OH是氧化As(III)的主要氧化剂。·OH自由基通过硝酸盐光解独立产生，并测定了·OH自由基氧化As(III)的动力学。·OH氧化BA生成水杨酸（SA）也证明了·OH参与了As(III)氧化的机理。考察了在紫外光下有无TiO2存在时Fe(III)对不同pH值下As(III)氧化的影响。结果表明，·OH是As(III)氧化的主要氧化剂。测试了两种市售TiO2悬浮液Degussa P25和Hombikat UV100通过将As(III)氧化为As(V)然后将As(V)吸附到TiO2表面来去除砷的效果。结果表明，可实现将砷完全去除至低于世界卫生组织饮用水限值10μg/L。
