Defect-engineered micro-sized BaTiO_3-x for enhanced hydrodynamic piezocatalysis and mechanistic insights

Micro-sized piezocatalysts offer an inherent advantage in terms of retrievability compared to nanoscale counterparts, which often require immobilization methods that constrain mechanical deformation and reduce piezocatalytic efficiency. However, their performance remains hindered by low surface area and charge transport efficiency. Therefore, the development of a novel strategy to enhance the performance of micro-sized piezocatalysts remains challenging. Herein, we introduce defect-engineered BaTiO_3-x microspheres (Ov-BaTiO_3-x) synthesized via one-step ultrasonic spray pyrolysis. The oxygen vacancies significantly enhanced electron availability, resulting in a 7.95-fold increase in bisphenol A degradation compared to stoichiometric BaTiO₃. Under hydrodynamic conditions, piezocatalytic performance was primarily governed by electron concentration. To better elucidate this effect, temperature-dependent analysis and Ag nanoparticle modification were conducted. A temperature-dependent study confirmed that an increase in electron concentration induced by thermal excitation activated charge carrier scattering, which in turn reduced piezocatalytic efficiency. Moreover, the reduction in electron concentration caused by Fermi-level alignment between Ag nanoparticles and Ov-BaTiO_3-x impaired piezocatalytic activity. However, at elevated temperatures, these heterojunctions were found to be beneficial by enhancing charge transport efficiency and thereby partially mitigating the performance loss caused by a thermal excitation-induced increase in electron concentration. These findings provide a promising framework for designing efficient and readily recoverable micro-sized piezocatalysts capable of harnessing naturally abundant, low-intensity mechanical energy.