Is platinum-loaded titania the best material for dye-sensitized hydrogen evolution under visible light?
A dye-sensitized photocatalyst combining Pt-loaded TiOa and Ru(Ⅱ)tris-diimine sensitizer(RuP)was constructed and its activity for photochemical hydrogen evolution was compared with that of Pt-intercalated HCa2Nb3O10 nanosheets.When the sacrificial donor ethylenediaminetetraacetic acid(EDTA)disodium salt dihydrate was used,RuP/Pt/TiO2 showed higher activity than RuP/Pt/HCa2Nb3O10.In contrast,when NaI(a reversible electron donor)was used,RuP/Pt/TiO2 showed little activity due to back electron transfer to the electron acceptor(I2-),which was gener-ated as the oxidation product of I-.By modification with anionic polymers(sodium poly(styrenesulfonate)or sodium polymethacrylate)that could inhibit the scavenging of conduction band electrons by I3-,the H2 production activity from aqueous NaI was improved,but it did not exceed that of RuP/Pt/HCa2Nb3O10.Transient absorption measurements showed that the rate of semiconductor-to-dye back electron transfer was slower in the case of TiO2 than HCa2Nb3O10,but the electron transfer reaction to I2 was much faster.These results indicate that Pt/TiO2 is useful for reactions with sacrificial reductants(e.g.,EDTA),where the back electron transfer reaction to the more reducible product can be neglected.However,more careful design of the catalyst will be nec-essary when a reversible electron donor is employed.
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