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

Abstract

Photocatalytic N ₂ fixation to NH ₃ via defect creation on TiO ₂ to activate ultra-stable N [Private characterTRIPLE BOND, LENGTH AS M-DASH ] 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 TiO ₂ 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 TiO ₂. Motivated by theoretical simulations, we synthesize a phase-selective disordered-anatase/ordered-rutile TiO ₂ photocatalyst (Na-A _d/R _o) by sodium-amine treatment of P25-TiO ₂ under ambient conditions, which exhibits an efficient NH ₃ formation rate of 432 μmol g ⁻¹ h ⁻¹, which is superior to that of any other defect-rich disordered TiO ₂ 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.

Abstract

This work highlights the importance of a rational design for more energetically suitable nitrogen reduction reaction routes and mechanisms by regulating the electronic band structures with phase-selective defect sites.