Slow-release of hydrogen peroxide from PDA-coated calcium peroxide for enhanced dye wastewater decolourisation removal

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In Fenton-like systems, a slow-release of hydrogen peroxide (H2O2) is of great value in improving the sustainable treatment of pollutants. In this study, calcium peroxide (CaO2) was first synthesized by different methods, and its slow-release performance of H2O2 was evaluated. Then CaO2@PDA composites (referred to as CP-X, X represent the mass ratio of Polydopamine (PDA) to CaO2 were prepared by using a simple precipitation method. And the H2O2 slow-release experimental result indicates that the average release rate of the prepared CP-1.0 is 0.19 mmol·g-1·min-1 within 130 min. The release of H2O2 from CP-1.0 is consistent with the biexponential biphasic kinetic model, where water molecules and H2O2 osmotic diffusion are the main factors affecting the rate of H2O2 release. Decolourisation removal of crystalline violet (CV) solution was carried out using CP-1.0 as oxidants. Under the conditions of 0.02 g CP-1.0, pH = 6.5, and 20°C, more than 98.0% of CV solution (30 mg/L) was removaled within 30 min. Then, possible degradation pathways were postulated using a combination of density functional theory (DFT) and liquid chromatography mass spectrometry (LC-MS). Finally, the decolourisation degradation mechanism was proposed according to the active species quenching experiments and Electron Paramagnetic Resonance (EPR) analysis. This study presents novel insights into the removal of emerging pollutants in aqueous media by CaO2-based Fenton-like systems.