An effective preparation method of composite photocatalysts for hydrogen evolution using an organic photosensitizer and metal particles assembled on alumina-silica

Abstract

Composite catalysts for photocatalytic hydrogen (H2) evolution were prepared by loading an organic electron donor–acceptor linked dyad [2-phenyl-4-(1-naphthyl)quinolinium ion, QuPh+–NA] as an organic photosensitizer and Pt or Cu particles as H2-evolution catalysts on alumina-silica. The composite catalysts loading Pt particles were prepared by two different methods; first, Pt particles were deposited by reduction of PtCl62− owing to photocatalysis of QuPh+–NA supported on alumina-silica (PD method), and second, alumina-silica was impregnated with the PtCl62− and calcined, and then QuPh+–NA was loaded on the Pt/alumina-silica by a cation exchange method (IMP method). When a composite catalyst was prepared by the IMP method, a high Pt-loading amount of 4.2wt% was necessary to achieve the highest H2-evolution rate of 0.27μmolh−1. On the other hand, a composite catalyst prepared by the PD method exhibited three times faster H2 evolution (0.83μmolh−1) even though the loading amount of Pt was as low as 0.4wt%. The activity of composite catalysts prepared by the PD method highly depends on the electric charges of precursors for Pt particles. A composite catalyst prepared with positively charged Pt(NH3)42+ as a precursor of Pt particles exhibited low catalytic activity with the H2-evolution rate of 0.10μmolh−1, which is significantly lower than the rate (0.27μmolh−1) for the composite catalyst prepared with PtCl62−. However, such precursor-dependence was not observed for composite catalysts employing Cu particles as an H2-evolution catalyst, because the Cu precursors are more labile than the Pt precursors in a reaction solution. The electrostatic interaction between the precursors of metal particles and negatively charged surfaces of alumina-silica should be taken into account to construct efficient H2-evolution catalysts.