Oxalic Acid as a Sacrificial Agent in the Photoreduction of Water Contaminants

Abstract

Oxalic acid (OA) as a sacrificial agent (hole scavenger) in the photoreduction of Cr(VI), was evaluated in a radiation efficient photocatalytic fluidized bed (FB) of a TiO2-quartz sand catalyst composite vis à-vis the homogeneous photoreduction process. The potentiality of OA as catalyst activator via its intimate contact with TiO2 was also explored. Under anoxic conditions the OA was more efficient in the homogeneous photoreduction of Cr(VI) than in the heterogeneous (photocatalytic) reaction system. However, when dissolved oxygen was present in the solution, the reaction rate of the homogeneous reaction was notoriously diminished, thus indicating that oxygen was competing with Cr(VI) in oxidizing the oxalic acid. The pre-exposure of the photocatalyst to an OA solution for designated dwelling times (thus forming a thin, compact overlayer of titanium oxalate) dramatically enhanced the photocatalytic rate, up to the point of clearly overcoming the homogeneous process.