A novel heterojunction ZnO/CuO piezoelectric catalysts: fabrication, optical properties and piezoelectric catalytic activity for efficient degradation of methylene blue

The heterojunction ZnO/CuO piezoelectric catalysts with different Zn/Cu molar ratios were synthesized by one-step polyacrylamide gel method. Various characterization techniques have been used to explore the phase structure and purity, composition, morphology, charge state, electronic energy level, optical and photoluminescence properties and piezoelectric catalytic activity of the heterojunction ZnO/CuO piezoelectric catalysts. Phase structure and purity analysis shows that the intensity of CuO diffraction peak increases gradually with the increasing of the content of Cu ion. The surface morphology observation shows that the particle size of the heterojunction ZnO/CuO piezoelectric catalysts increases with the increasing of Cu content. The optical properties analysis shows that the optical band gap (Eg) of ZnO/CuO decreases with the increasing of the content of Cu ion. The photoluminescence spectra of the heterojunction ZnO/CuO piezoelectric catalysts show two emission peaks at 470 and 484 nm can be ascribed to the intrinsic defects such as oxygen vacancies and the near-band-edge emission, respectively. The heterojunction ZnO/CuO (nZn:nCu=9:1) piezoelectric catalysts exhibits highest degradation percentage of 71.06% and the optimum catalyst content, initial dye concentration, vibration time, ultrasonic power and frequency is 1 g/L, 5 mg/L, 140 min, 180 W and 40 kHz, respectively. This work will provide technical references for understanding the contribute between ZnO and CuO, and the coupling effect between piezoelectric and electrochemistry, and also explore to the development and applications of heterojunction piezoelectric catalysts.