Effect of oxygen vacancies and crystal symmetry on piezocatalytic properties of Bi2WO6 ferroelectric nanosheets for wastewater decontamination†
Piezocatalysis has emerged as a novel technique to make use of mechanical energy in dealing with organic pollutants in wastewater. In this work, ferroelectric Bi2WO6 (BWO) nanosheets with a characteristic layered crystal structure and in-plane polarization were investigated, with special interest in the influence of their crystal symmetry and oxygen vacancies on the piezocatalytic performance. The nanosheets were synthesized by a hydrothermal process along with thermal annealing at different temperatures and atmospheres. The crystal symmetry, grain size and oxygen vacancies of the crystals were characterized by XRD, SEM, XPS and Raman spectroscopy. The piezocatalytic properties were investigated by degrading Rhodamine B (RhB) solution under ultrasonic vibration. The free radicals generated by ultrasonic treatment were detected and characterized using the electron spin resonance (ESR) method. The essential role of hydroxyl radicals in the dye degradation process was demonstrated by controlled experiments with different scavenger additives. The results show that the crystalline size and oxygen vacancies affect the degree of orthorhombic distortion and formation of defect energy levels, respectively, which will further affect the distribution of piezoelectric potential and piezocatalytic activity. This work will enable us to understand the influence of oxygen vacancies and crystal symmetry on piezocatalysis more intuitively and design more efficient piezocatalysts via a heat treatment control strategy.