A noble-metal-free artificial photosynthesis system with TiO2 as electron relay for efficient photocatalytic hydrogen evolution

Artificial photosynthesis (AP) systems for hydrogen production are currently attracting immense attention due to their huge potential to convert solar energy into chemical fuels. We developed an efficient AP system containing fluorescein (FL) as photosensitizer, a simple nickel complex (Ni(TEOA)(2)(Cl)(2), Nil) as catalyst, TiO2 as electron relay, and triethanolamine (TEOA) as sacrificial electron donor for H-2 generation from a fully aqueous solution. This FL/Nil/TiO2 system exhibits considerable photocatalytic activity and stability under visible light, with turnover number (TON, based on Nil) of 740 after 24 h irradiation, which is 200% that of the FL/Nil system. The efficient photocatalytic performance should be attributed to efficient electron transfer from FL to Nil as well as TiO2-mediated electron transfer from FL to the nickel metal generated in situ onto TiO2 by photoreduction of Nil, leading to the increased oxidative quenching of FL* by TiO2 and then the inhibited generation of unstable FL- intermediates by reductive quenching. The present study successfully fabricated a typical AP system for visible-light-driven H-2 generation and introduced a feasible and facile strategy for designing high-performance AP systems for mediator-engineered electron transfer processes. (C) 2016 Elsevier Inc. All rights reserved.