Mixed Conducting Perovskite Materials as Superior Catalysts for Fast Aqueous-Phase Advanced Oxidation: A Mechanistic Study

A mixed ionic-electronic conducting (MIEC) double perovskite, PrBaCo₂O_5+δ (PBC), was synthesized and evaluated as the heterogeneous catalyst to generate radicals from peroxymonosulfate (PMS) for the oxidative degradation of organic wastes in aqueous solution. A superior catalytic activity was obtained for PBC, which was much higher than that of the most popular Co₃O₄ nanocatalyst. More importantly, a detailed mechanism of PMS activation on the MIEC perovskite was proposed. Electron paramagnetic resonance (EPR) and radical competitive reactions suggested that both sulfate radicals (SO₄^•-) and hydroxyl radicals (^•OH) participated in and played important roles in the catalytic oxidation processes. Oxygen temperature-programmed desorption (O₂-TPD) demonstrated that the PBC perovskite oxide is capable of facilitating an easier valence-state change of the B-site cation (cobalt ions) to mediate a redox process. Additionally, the oxygen vacancies could facilitate the bonding with PMS molecules and promote the reactivity of cobalt ions for PMS activation. Electrochemical impedance spectroscopy (EIS) was also performed to evidence charge transfer and surface reaction rates of the PBC catalyst that are much faster than those of Co₃O₄. Additionally, suppressed cobalt leaching was also achieved through tailoring the pH value of the reaction solution. This study provides insight into MIEC perovskites in catalytic reactions and applications.