Piezo-Photocatalytic Decomposition of Metronidazole Using ZnO Microtetrapods under Simulated Sunlight

The article presents the results of a study on the effect of ultrasonic exposure on the process of photocatalytic decomposition of metronidazole using ZnO microtetrapods under simultaneous irradiation with artificial sunlight. The synthesized zinc oxide microtetrapods had pronounced sharp tips, clear facets, and edges, indicating their high crystalline perfection. This unique morphology of ZnO microtetrapods provides the material with high catalytic activity in both photocatalytic and piezocatalytic processes. The Raman spectrum of ZnO microtetrapods showed distinct peaks corresponding to the transverse E and high-frequency E modes. The high intensity of the E mode indicates the crystalline perfection of ZnO microtetrapods. The enhancement of the intensity of the transverse optical mode A is observed at the tip of the tetrapod and is absent at the base. It has been shown that the use of ZnO microtetrapods achieves significant efficiency in the decomposition of metronidazole due to the combined effect of light and ultrasound, creating a piezoelectric field on the surface of ZnO. This piezoelectric field promotes the spatial separation of photogenerated charges and reduces the likelihood of their recombination, significantly increasing the rate of decomposition of the target pollutant. The rate constant for the decomposition of metronidazole in piezophotocatalysis is higher than the rate constants for photolysis, sonolysis, sonophotolysis, piezocatalysis, and photocatalysis by 1254, 35, 17, 8, and 4 times, respectively.