(361g) In-Situ Generated Hydrogen Driven Reductive Photocatalysis

Photocatalytic removal of organic contaminants is of great interest since UV light is a readily available energy source. However most photocatalytic reactions are oxidative in nature and result in toxic by-products. We develop a bifunctional semiconductor-metal composite material that functions as a reduction photocatalyst using in-situ generated hydrogen (H₂). The Pd-on-Au/TiO₂ catalyst (0.1wt% Pd, 1wt% Au) was synthesized by reducing dihydrogen tetrachloropalladate (II) onto a commercially available Au/TiO₂ catalyst. As the test reaction, the hydrodechlorination of trichloroethene (TCE, a common groundwater contaminant) was observed to occur in batch reactor studies, under both aerated and deaerated conditions upon illumination with a 400 W xenon light source. Analysis of the reactor headspace confirmed that reductive hydrodechlorination products are formed. No photocatalytic TCE oxidation is observed. Control experiments without TCE reveal that in-situ H₂ is generated by photocatalytic water splitting, irrespective of the presence of air. Other catalysts such as commercially available Au/TiO₂ and Pd/TiO₂ were also investigated. We therefore infer that Pd-on-Au/TiO₂ simultaneously photocatalyzed water splitting and catalyzed reductive TCE hydrodechlorination in the same batch reactor. Extension of this study to other bifunctional semiconductor-metal systems and groundwater contaminants could significantly simplify future remediation efforts.