Efficient mineralization of organic pollutants in water via a phenol-responsive catalytic ozonation process

Background: Catalytic ozonation process has become one of the most promising technologies in organic wastewater treatment industry due to its high efficiency and rapidity. Some researchers have found that alkaline earth metal oxides can be used to promote the ozonation process to removal organic compound in wastewater. And some of them believe that calcium-based catalysts can effectively catalyze the ozonation reaction, but there are few reports about its reaction mechanism. Methods: In this work, calcium oxide was used as catalyst to study their effect in phenol wastewater and the mechanism of catalytic reaction process. In the catalytic ozonation process, the surface hydroxyl of solid CaO-based catalyst can react as the reaction active sites to promote the formation of free radicals, and the Ca ²⁺ solutes in this system can promote the decomposition of H ₂O ₂ to produce free radicals. At the same time, the addition of calcium oxide-based catalyst also increases the pH of the reaction system, which is conducive to the decomposition of ozone to produce hydroxyl radicals. Owing to the presence of •OH, ¹O ₂ and •O ₂ ⁻, phenol and by-product are decomposed effectively. Significant findings: The experimental results show that the COD removal rate of phenol reached ∼100% in 20 min. And in this study, the mechanism of CaO-based catalysts used in the ozonation process was studied. We found that both of Ca ²⁺ in solution and solid calcium oxide promoted the formation of active free radicals in catalytic ozonation process.