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One-step preparation of MoOx/ZnS/ZnO composite and its excellent performance in piezocatalytic degradation of Rhodamine B under ultrasonic vibration

Song Zheng, Xiaojing Li, Jiayu Zhang, Junfeng Wang, Chunran Zhao, Xin Hu, Ying Wu, Yiming He
Journal of environmental sciences (China) 2023 v.125 pp. 1-13
X-ray diffraction, X-ray photoelectron spectroscopy, adsorption, catalysts, catalytic activity, dielectric spectroscopy, pH, rhodamines, surface area, transmission electron microscopy, ultrasonics, vibration, China
This paper synthesized a new type of ternary piezoelectric catalyst MoOₓ/ZnS/ZnO (MZZ) by a one-step method. The catalytic degradation of Rhodamine B (RhB) solution (10 μg/g, pH = 7.0) shows that the composite catalyst has excellent piezoelectric catalytic activity under ultrasonic vibration (40 kHz). The piezoelectric degradation rate of the optimal sample reached 0.054 min⁻¹, which was about 2.5 times that of pure ZnO. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) technologies were used to analyze the structure, morphology, and interface charge transfer properties of the MZZ piezocatalysts. The results showed that the composite catalyst may have a core-shell structure. ZnS is coated on the surface of ZnO, while MoOₓ adheres to the surface of ZnS. This structure endowed MZZ larger specific surface area than ZnO, which benefits the RhB adsorption. More importantly, the formed heterojunction structure between ZnS and ZnO promotes the separation of positive and negative charges induced by the piezoelectric effect. MoOₓ species may act as a charge trap to further promote more carriers to participate in the reaction. In addition, MoOₓ may also be beneficial in adsorbing dyes. Active species capture experiments show that superoxide radicals and holes are the main active species in piezoelectric catalytic reactions on MZZ catalysts.