Visible-light-induced hydrogen evolution from water on hybrid photocatalysts consisting of synthetic chlorophyll-a derivatives with a carboxy group in the 20-substituent adsorbed on semiconductors

Abstract

Chlorophyll (Chl) derivatives have attracted much attention as photosensitizers in dye-sensitized solar cells. In contrast, only a few studies have been reported as Chl-based photosensitizers in photocatalytic hydrogen evolution from water, and therefore systematic studies should be required to obtain the optimal Chl photosensitizers for the photocatalytic water splitting system. In this study, we prepared four carboxylated Chl derivatives with different linkers at the 20-position, and investigated the effects of the linker length and π-conjugation between a chlorin macrocycle and a carboxy anchor. Hydrogen evolution rates on the Pt-loaded TiO2 adsorbing the Chl derivatives are significantly affected by the kind of linkers. The results indicated that (1) π-conjugation of a chlorin moiety with a carboxy anchor and (2) an appropriate linker length are of great importance to the photocatalytic activity probably due to the balance of electron injection to and back electron transfer from TiO2.