High-efficiency electron tandem flow mode on carbon nitride/titanium dioxide heterojunction for visible light nitrogen photofixation

Abstract

Photocatalytic nitrogen fixation is a promising and green approach for converting atmospheric nitrogen to ammonia, which has been considered as a potential way to the energy-intensive Haber-Bosch process. However, the activation of nitrogen by low-cost and visible-light-driven photocatalyst remained a grand challenge. Enlightenment from biological nitrogen fixation, multi-component systems can often achieve higher efficiency when working collaboratively. Herein, we constructed an efficient visible-light-driven carbon nitride/oxygen vacancy titanium dioxide (CN-OvTiO2) heterojunction photocatalyst through a solvent evaporation deposition method, in which CN serves as the light absorption and electron supply components while Ov of TiO2 serves as the active site for N2 activation. A high-efficiency electron tandem flow mode promoting photogenerated charge directional migration from CN to Ov of TiO2 under light irradiation is revealed in this system, which is the key link coupling heterojunction and defects effects. The Ov with high electron density is the active site for nitrogen chemisorption and activation according to the revealed favorable thermodynamics of lower reaction energy and kinetics of enhanced N2 adsorption and N-N polarization. CN-OvTiO2 shows a high quantum yield of 0.15% at 500 nm monochromatic light and a high ammonia production rate of 34 μmol gcat−1 under visible light irradiation, 8.5 times higher than that of pure CN. This work deeply reveals the link and synergy mechanism of heterojunction and defects, and is expected to advance the development of visible-light-driven and low-cost nitrogen fixation catalysts.