Rational Design of High-Concentration Ti3+ in Porous Carbon-Doped TiO2 Nanosheets for Efficient Photocatalytic Ammonia Synthesis.

Photocatalytic ammonia synthesis is exciting but quite challenging with a very moderate yield at present. One of the greatest challenges is to develop highly active centers in a photocatalyst for N-2 reduction under ambient conditions. Herein, porous carbon-doped anatase TiOx (C-TiOx) nanosheets with high-concentration active sites of Ti3+ are presented, which are produced by layered Ti3SiC2 through a reproducible bottom-up approach. It is shown that the high-concentration Ti3+ sites are the major species for the significant increase in N-2 photoreduction activity by the C-TiOx. Such bottom-up substitutional doping of C into TiO2 is responsible for both visible absorption and generation of Ti3+ concentration. Together with the porous nanosheets morphology and the loading of a Ru/RuO2 nanosized cocatalyst for enhanced charge separation and transfer, the optimal C-TiOx with a Ti3+/Ti4+ ratio of 72.1% shows a high NH3 production rate of 109.3 mu mol g(-1) h(-1) under visible-light irradiation and a remarkable apparent quantum efficiency of 1.1% at 400 nm, which is the highest compared to all TiO2-based photocatalysts at present.