Hollow sphere CuCo2O4 as highly efficient catalyst of microwave-assisted Fenton-like reaction for water treatment

Abstract

In industries with high-value addition, the demand for rapid pollutant breakdown through advanced water treatment techniques is growing. The microwave (MW)-assisted Fenton-like reaction is notable for its exceptionally fast reaction rate, providing enhanced economic benefits, especially in the context of limited factory space. In this research, hollow sphere-shaped CuCo2O4 was synthesized at the various temperature (200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, and 500 °C) and used in a MW-assisted Fenton-like reaction to break down the organic model compound, methyl orange (MO). Unlike typical Fenton reactions that are most effective in acidic conditions (around pH 3), the synthesized CuCo2O4 in this study demonstrated its highest efficiency at a circumneutral pH level (pH 6). It was observed that the majority of MO was oxidized by ∙OH within just 3.5 min under the optical condition (10 mg/L MO, 300 mg/L H2O2, 200 mg/L catalyst, pH 6, 20 °C, 200 W, and total volume of 50 mL). Ex-situ analysis confirmed the gradual generation of oxygen vacancies (OV) with each repeated cycle. The formation of OV enhances the catalyst's MW absorption and oxidation potential, resulting in the superior MO decomposition performance even after the 5th cycle. Although there were minor changes in the shell thickness and smoothness, along with some leaching (1.17 mg Cu/L and 0.01 mg Co/L per cycle), the catalyst continued to comply with the US Environmental Protection Agency (EPA) guidelines for drinking and discharge water.