Enhanced catalytic activity of ZnO–CuO–Co3O4 composites achieved using a mechanochemical method for effective Fenton-like dye removal: the generation and catalytic mechanism of various superficial active sites

Abstract

Mechanochemical methods are effective in creating active sites of solid catalysts, and have great potential to improve the activity of heterogenous catalysts in advanced oxidative processes of organic wastewater. Herein, ZnO–Co₃O₄–CuO composites were treated using three kinds of grinding methods to adjustably expose the superficial oxygen vacancies and Cu/Co–O dangling bonds according to the grinding strength. In the Fenton-like treatment of organic dye wastewater, the catalytic activity of the composites was accordingly improved, especially in the deep mineralization of wastewater. After the intense trituration of the composites, the formed oxygen vacancies worked as effective sites for the chemisorption of H₂O₂ molecules, while the adjacent Co/Cu sites were simultaneously activated to facilitate the redox cycle of the Fenton-like reactions. In this way, the interfacial electron transfer was dramatically accelerated to transform H₂O₂ molecules into hydroxyl radicals and singlet oxygen which were confirmed as the contributing oxidation species in the degradation of organic dyes. The aforementioned results clarified that the mechanochemical treatment of solid catalysts has a dual function of both the generation of oxygen vacancies and activation of Co/Cu redox sites, which could provide a simple and universal strategy for the catalytic enhancement of Fenton-like catalysts.