High piezo/photocatalytic efficiency of Ag/Bi₅O₇I nanocomposite using mechanical and solar energy for N₂ fixation and methyl orange degradation

In this work, Ag/Bi₅O₇I nanocomposite was prepared and firstly applied in piezo/photocatalytic reduction of N₂ to NH₃ and methyl orange (MO) degradation. Bi₅O₇I was synthesized via a hydrothermal-calcination method and shows nanorods morphology. Ag nanoparticles (NPs) were photo deposited on the Bi₅O₇I nanorods as electron trappers to improve the spatial separation of charge carriers, which was confirmed via XPS, TEM, and electronic chemical analyses. The catalytic test indicates that Bi₅O₇I presents the piezoelectric-like behavior, while the loading of Ag NPs can strengthen the character. Under ultrasonic vibration, the optimal Ag/Bi₅O₇I presents high efficiency in MO degradation. The degradation rate is determined to be 0.033 min^-1, which is 4.7 folds faster than that of Bi₅O₇I. The Ag/Bi₅O₇I also presents a high performance in piezocatalytic N₂ fixation. The piezocatalytic NH₃ generation rate reaches 65.4 μmol L^-1 g^-1 h^-1 with water as a hole scavenger. The addition of methanol can hasten the piezoelectric catalytic reaction. Interestingly, when ultrasonic vibration and light irradiation simultaneously act on the Ag/Bi₅O₇I catalyst, higher performance in NH₃ generation and MO degradation is observed. However, due to the weak adhesion of Ag NPs, some Ag NPs would fall off from the Bi₅O₇I surface under long-term ultrasonic vibration, which would greatly reduce the piezoelectric catalytic performance. This result indicates that a strong binding force is required when preparing the piezoelectric composite catalyst. The current work provides new insights for the development of highly efficient catalysts that can use multiple energies.