Platinum-like Behavior of Reduced Graphene Oxide as a Cocatalyst on TiO2 for the Efficient Photocatalytic Oxidation of Arsenite

The preoxidation of arsenite [As(III)] to arsenate [As(V)] is usually needed for efficient removal of arsenic from water, and TiO2-based photocatalytic oxidation has been investigated as an environmentally benign process for this purpose. The oxidation efficiency can be markedly enhanced when using platinum (Pt) as a cocatalyst, but its expensive material cost hinders its practical application. Herein, we prepared the reduced graphene oxide (rGO) hybridized with TiO2 as a low-cost alternative to Pt and achieved a highly enhanced activity for the photocatalytic oxidation of As(III), which is comparable to that of Pt/TiO2. While either superoxide or hydroxyl radical can be involved as a main oxidant depending on the experimental condition, this study shows that not only superoxide but also hydroxyl radicals (or hole) can be directly involved in As(III) photo-oxidation when rGO is present as a cocatalyst. The photocatalytic activity, - charge transfer characteristics, and arsenic oxidation mechanism observed with rGO-loaded TiO2 are very similar to those of Pt/TiO2. The nanocomposite of rGO/TiO2 that consists of earth-abundant elements only is proposed as a practical environmental photocatalyst for pretreating As(III)-contaminated water.