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

The synergistic effect of high electron density of Ov induced by the accurate electron transformation from CN to Ov and enhanced nitrogen adsorption and activation by Ov promotes the visible light nitrogen photofixation. • An efficient visible-light-driven heterojunction photocatalyst was constructed. • A high-efficiency electron tandem flow mode is revealed in this system. • Electron tandem flow is the key link coupling heterojunction and defects effects. • The O defects with high electron density is the active site for nitrogen activation. • CN-OvTiO 2 catalyst exhibits high activity and quantum yield for N 2 photofixation. 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-OvTiO 2 ) heterojunction photocatalyst through a solvent evaporation deposition method, in which CN serves as the light absorption and electron supply components while Ov of TiO 2 serves as the active site for N 2 activation. A high-efficiency electron tandem flow mode promoting photogenerated charge directional migration from CN to Ov of TiO 2 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 N 2 adsorption and N-N polarization. CN-OvTiO 2 shows a high quantum yield of 0.15% at 500 nm monochromatic light and a high ammonia production rate of 34 μmol g cat −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.