Efficient photocatalytic nitrogen fixation over up-conversion nonlinear optical material Pr3+:LiNbO3 under visible light irradiation

Ammonia (NH3) synthesis is a critical chemical process to develop nitrogen-containing commodities which remains a significant challenge in chemistry and industry. Photocatalysis reduction has been deemed as one of the most promising strategies for N2 fixation under mild conditions. Herein, a series of Pr doped LiNbO3 (Pr3+:LiNbO3) were synthesized by a facile sol–gel method. Results showed that the Pr3+:LiNbO3 upconverted visible light into ultraviolet light and had the highest up-conversion efficiency when the molar ratio of Pr3+ was 2.5 mol%. In addition, the oxygen vacancies generated by the incorporation of Pr3+ into the LiNbO3 crystal lattice acted as active sites boosting the adsorption and activation of N2. The NH4+ production rate reached the highest of 30.72 μmol/L, attributed to the synergistic effects combining spontaneous polarization of the nonlinear optical (NLO) material LiNbO3 and up-conversion luminescence of Pr3+, which not only broaden the adsorption range of solar light but also enhance the charge separation. The up-conversion NLO material Pr3+:LiNbO3 in this study provides a novel alternative for guiding the design of ammonia synthesis photocatalyst.