KNbO3/ZnO heterojunction harvesting ultrasonic mechanical energy and solar energy to efficiently degrade methyl orange

[Display omitted] •KNbO3/ZnO composite was prepared via a two-step hydrothermal method.•KNbO3/ZnO can utilize solar and vibration energy to catalyze the degradation of MO.•KNbO3/ZnO presented much better performance in piezo/photocatalytic MO degradation than ZnO or KNbO3.•The enhanced performance was mainly ascribed to the improved charge separation. In this paper, KNbO3/ZnO nanocomposite was synthesized and used in piezo/photocatalytic degradation of methyl orange (MO) under simulated sunlight and ultrasonic vibration. Under simulated solar light, the optimal KNbO3/ZnO sample presented a MO degradation rate of 0.047 min−1, which is 2.47 times higher than that of ZnO. The promotion effect of KNbO3 on ZnO was also observed in the piezoelectric catalytic reaction. In addition, the co-utilization of solar and mechanical energy can further increase the MO degradation rate. Piezoelectric property and photoresponse capability are the origins of the piezo/photo catalytic behavior of the KNbO3/ZnO composite. Owing to the different band potentials of KNbO3 and ZnO, the electric potential field at their interface can drive the second distribution of the photo/piezoinduced charge carriers and hence promote the photo/piezocatalytic activity. This phenomenon was verified by the analysis on transient photocurrent and piezocurrent response. Trapping experiments on reactive species were also conducted. Superoxide radicals, holes, and hydroxyl radicals were found to be the main reactive species during the photo/piezocatalytic reaction. Recycling test showed that the KNbO3/ZnO composite exhibited good catalytic stability during six consecutive uses. Given its advantages of good catalytic activity and stability, the synthesized KNbO3/ZnO nanocomposite material has great potential in the further use of solar and mechanical energy to develop new water purification technologies.