Semi‐Synthetic Chlorophyll‐Carotenoid Dyad for Dye‐Sensitized Photocatalytic Hydrogen Evolution

A chlorin‐carotenoid dyad Dyad‐COOH possessing a C32‐carboxylic acid group and a carotenoid moiety at the terminal end of C17‐substituent is synthesized from naturally occurring chlorophyll‐a as a new sensitizer for photocatalytic hydrogen evolution (PHE). Under the same experimental conditions, a maximum turnover number (TON) of PHE based on Dyad‐COOH/Pt/TiO2 is much higher than those of Pt/TiO2‐based photocatalysts sensitized by the corresponding chlorin carboxylic acid (Chl‐COOH) without carotenoid side chain, sole carotenoic acid (Car‐COOH), or their 1:1 (mol/mol) mixture. By co‐adsorbing different types of carboxylic acid, the TON of Chl‐COOH is found to be increased probably due to the suppression of chlorin aggregates on the TiO2 surface. The Dyad‐COOH/Pt/TiO2 exhibits excellent photocatalytic performance with the hydrogen evolution of 9147 µmol g−1 h−1 with TON of 425 when 43 µmol g−1 of dye is loaded on the Pt/TiO2 catalyst, while a better TON of 556 is achieved by preparing the photocatalyst with 10 µmol g−1 of Dyad‐COOH. This study provides new ideas for utilizing traditional photosynthetic dyes to a low‐cost and highly‐efficient photosensitizer for PHE. A chlorin‐carotenoid dyad (Dyad‐COOH) possessing a C32‐carboxylic acid group and a carotenoid moiety at the terminal end of C17‐substituent is synthesized from naturally occurring chlorophyll‐a as a new sensitizer in a Pt/TiO2‐based photocatalytic system for H2 evolution. The Dyad‐COOH/Pt/TiO2 system achieves superior H2 generation activity with ascorbic acid (AA) under visible light irradiation (λ > 420 m).