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

Herein, we used a hydrothermal method and calcination at different temperatures to synthesize Ca 2 Nb 2 O 7 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 ·O 2 − , 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. We synthesized two paramorphs of Ca 2 Nb 2 O 7 for visible light degradation of tetracycline, and found that pyrochlore phase has better reactivity compared to perovskite phase, which is attributed to the intrinsic oxygen vacancies and lattice disorder of pyrochlore phase.