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

Abstract

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 N₂ reduction under ambient conditions. Herein, porous carbon-doped anatase TiO_x (C-TiO_x ) nanosheets with high-concentration active sites of Ti³⁺ are presented, which are produced by layered Ti₃ SiC₂ through a reproducible bottom-up approach. It is shown that the high-concentration Ti³⁺ sites are the major species for the significant increase in N₂ photoreduction activity by the C-TiO_x . 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-TiO_x with a Ti³⁺ /Ti⁴⁺ ratio of 72.1% shows a high NH₃ production rate of 109.3 µmol 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.