Phase-selective active sites on ordered/disordered titanium dioxide enable exceptional photocatalytic ammonia synthesis

Abstract

© The Royal Society of Chemistry 2021. Photocatalytic N-2 fixation to NH3 via defect creation on TiO2 to activate ultra-stable N N has drawn enormous scientific attention, but poor selectivity and low yield rate are the major bottlenecks. Additionally, whether N-2 preferentially adsorbs on phase-selective defect sites on TiO2 in correlation with appropriate band alignment has yet to be explored. Herein, theoretical predictions reveal that the defect sites on disordered anatase (A(d)) preferentially exhibit higher N-2 adsorption ability with a reduced energy barrier for a potential-determining-step (*N-2 to NNH*) than the disordered rutile (R-d) phase of TiO2. Motivated by theoretical simulations, we synthesize a phase-selective disordered-anatase/orderedrutile TiO2 photocatalyst (Na-A(d)/R-o)by sodium-amine treatment of P25-TiO2 under ambient conditions, which exhibits an efficient NH3 formation rate of 432 mu mol g(-1) h(-1), which is superior to that of any other defect-rich disordered TiO2 under solar illumination with a high apparent quantum efficiency of 13.6% at 340 nm. The multi-synergistic effects including selective N-2 chemisorption on the defect sites of Na-A(d) with enhanced visible-light absorption, suitable band alignment, and rapid interfacial charge separation with R-o enable substantially enhanced N-2 fixation.