Piezophototronic effect in enhancing charge carrier separation and transfer in ZnO/BaTiO3 heterostructures for high-efficiency catalytic oxidation

Rapid charge transfer in various piezoelectric semiconductors is usually limited, which has thus hardly achieved a higher mechanochemical potential elicited by macroscopic polarization for advanced oxidation processes. Here we propose a piezoelectric ZnO/BaTiO3 heterostructure with an elevated macroscopic polarization under ultrasonic activation and, therefore, should be amenable to facilitate photoexcited electron-hole pairs with more efficient separation and transfer; that is, ZnO/BaTiO3 heterostructures have an enhanced piezophototronic effect. Under excitations of concurrent ultrasound at ultrasonic power of 120 W and simulated sunlight at light intensity of 100 mW cm−2 irradiation, the catalytic oxidation capability to dyeing wastewater degradation with ZnO/BaTiO3 is dramatically increased, and its oxidation reaction rate constant can be up to 1.20 × 10−1 min−1, which is 1.50 and 2.00 times that of BaTiO3 and ZnO, respectively. In contrast, ultrasonic agitation or simulated sunlight irradiation of ZnO/BaTiO3 results in an oxidation reaction rate constant of 3.46 × 10−2 or 5.60 × 10−2 min−1, correspondingly, which are both lower than the piezophototronic effect triggered. Additionally, the finite element simulation shows that the as-obtained ZnO/BaTiO3 creates a piezoelectric potential difference of 414.40 mV, which is higher than that of as-obtained BaTiO3 (409.50 mV) and ZnO (33.00 mV). This work will provide references for understanding the correlation between macroscopic polarization and catalytic oxidation processes, and also contribute to the development and applications of multi-energy harvesting piezoelectric materials. Specific ultrasound excitation of ZnO/BaTiO3 heterostructures resulted in a piezoelectric potential difference of 414.40 mV, which is much higher than pure BaTiO3 and ZnO. Consequently, the photoexcited electron–hole pairs can be easily separated and transfer in ZnO/BaTiO3, thus creating more free radicals to accelerate piezophotocatalytic oxidation processes in aqueous solution. [Display omitted] •ZnO/BaTiO3 was prepared by combining solvothermal and impregnation sintering.•ZnO/BaTiO3 has a higher piezoelectric potential difference than BaTiO3 and ZnO.•The flat band potential of ZnO/BaTiO3 is more negative than BaTiO3 and ZnO.•ZnO/BaTiO3 has superior catalytic oxidations initiated by piezophototronic effect.•ZnO/BaTiO3 can efficiently utilize ultrasound and light irradiation simultaneously.