Degradation of tetracycline by visible light using Ca2Nb2O7 composite oxides with perovskite and pyrochlore sub-crystalline phases

Abstract

Herein, we used a hydrothermal method and calcination at different temperatures to synthesize Ca₂Nb₂O₇ composite oxides with two different sub-crystalline phases, namely perovskite and pyrochlore. From the photocatalytic degradation of tetracycline, the catalytic activity of the pyrochlore crystalline phase is higher than that of the perovskite crystalline phase. This is because the pyrochlore phase structure is more disordered, which has abundant oxygen vacancies and can generate more ·O₂⁻, h⁺, and ·OH under visible light irradiation. Additionally, it has a smaller bandgap and a lower valence band energy. The combination of these factors enables the higher reaction activity of the pyrochlore phase structure compared with the perovskite crystalline phase.