KNbO(3)/ZnO heterojunction harvesting ultrasonic mechanical energy and solar energy to efficiently degrade methyl orange

In this paper, KNbO(3)/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 KNbO(3)/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 KNbO(3) 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 KNbO(3)/ZnO composite. Owing to the different band potentials of KNbO(3) 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 KNbO(3)/ZnO composite exhibited good catalytic stability during six consecutive uses. Given its advantages of good catalytic activity and stability, the synthesized KNbO(3)/ZnO nanocomposite material has great potential in the further use of solar and mechanical energy to develop new water purification technologies.