Steady release-activation of hydrogen peroxide and molecular oxygen towards the removal of ciprofloxacin in the FeOCl/CaO2 system

Difficult storage of hydrogen peroxide (H2O2), low production of reactive oxygen species (ROS), and inefficient Fe(II)/Fe(III) recycling limit the application of the Fenton-like process. Calcium peroxide (CaO2) based iron oxychloride (FeOCl) system was developed for solving these deficiencies, and ciprofloxacin (CIP) was effectively degraded within 20 min treatment. 0.33 mmol/L H2O2 and 2.4 mg/L dissolved oxygen (DO) were produced via CaO2. Quenching experiments and electron paramagnetic resonance results confirmed that hydroxyl radicals (·OH) and superoxide anion (·O2-) worked as the main ROS. Density functional theory (DFT) calculations and experimental results suggested that H atoms of H2O2 adsorbed on FeOCl favored the activation of H2O2 into ·OH and DO into ·O2-, and electrophilic Cl and O coordination in FeOCl contributed to the cycle of Fe(II)/Fe(III). ·OH and·O2- were responsible for CIP degradation, and toxicity assessments demonstrated that the developed system reduced the hazard of treated solution. Clarity of FeOCl/CaO2 system triple roles, including H2O2 and O2 production, activation into ROS, and Fe(II)/Fe(III) recycling, facilitates the efficient utilization of O2 in Fenton-like system.