Sol-gel combined mechano-thermal synthesis of Y2O3, CeO2, and PdO partially coated ZnO for sulfamethazine and basic yellow 28 photodegradation under UV and visible light

Abstract

The presence of organic pollutants in marine systems has made wastewater treatment extremely complicated, due to the release of a series of harmful contaminants into the ocean and causing direct damage to humans and the aquatic ecosystem. The present research aims to examine the impact of ZnO partial coating with different nonmetric layers based on CeO2, Y2O3, or PdO for water-charged organic contaminants treatment, using a photocatalysis process. In this vision, the photodegradation of two organic pollutants, sulfamethazine (SMZ) and basic yellow 28 (BY28), using ZnO and ZnO partially coated with cerium, yttrium or palladium oxides was studied. These materials have been successfully synthesized by the combination of both sol-gel and mechano-thermal methods. The prepared catalysts were characterized using X-ray diffraction, scanning electron microscopy SEM-EDX, UV diffuse reflectance spectra (DRS), and X-ray photoelectron spectroscopy analysis (XPS). The XRD measurements discovered that all the synthesized photocatalysts have the hexagonal crystal system of ZnO, and the crystallite size value is calculated to be 36 nm. EDX results affirmed the existence of yttrium, cerium and palladium elements in the prepared ZnO/Y2O3, ZnO/CeO2, and ZnO/PdO materials, respectively, with good dispersion and homogeneity. The XPS spectra of ZnO/Y2O3, ZnO/CeO2, and ZnO/PdO, confirmed the presence of Zn, O, Y, Ce, and Pd elements, where they are, excited as Zn2+, Y3+, Ce4+, and Pd2+ oxidation state, respectively. The photoactivity tests demonstrate that the partial coating increases the degradation efficiency of ZnO, with a total photodegradation of BY28 and SMZ under UV irradiation. Moreover, ZnO/PdO under visible light degrades 94% of BY28 in 120 min and 60% of SMZ in 180 min due to the effective separation of photo-induced charge carriers between PdO and ZnO.