Photochemical Reduction and Oxidation of Water Including Sacrificial Reagents and Pt/TiO₂ Catalyst

Abstract

Sacrificial reagents (SRs) are extensively used in a variety of photocatalysis systems for hydrogen evolution from water decomposition. It was observed in this work that these SRs, such as Na 2 SO 3, Na 2 S, KI, EDTA-Na, and CH 3 OH have the abilities to reduce H 2 O to H 2, and that AgNO 3 and Fe(NO 3 ) 3 have the abilities to oxidize H 2 O to O 2, even without the presence of photocatalysts. The water reduction and oxidation is attributable to the photochemical property of SRs acting as electron donors (EDs) and as electron scavengers (ESs), respectively, under irradiation. The influence of photochemical reactions of SRs on photocatalytic evolution of H 2 and O 2 could be avoided by using a 300 nm cutoff filter. Comparing the amounts of H 2 or O 2 evolved from the SR aqueous solution without Pt/TiO 2 to those with Pt/TiO 2, CH 3 OH and Fe(NO 3 ) 3 were the most excellent ED and ES, respectively, for photocatalytic reduction and oxidation of water. It was proposed that the photochemistry between SRs and H 2 O should be considered when evaluating the activity of photocatalysts for photocatalytic reduction and oxidation of water into H 2 and O 2 .