Facile Preparation of Fe3O4@SiO2 Derived from Iron-Rich Sludge as Magnetic Catalyst for the Degradation of Organic Contaminants by Peroxymonosulfate Activation

Iron-rich sludge, generated during flocculation/sedimentation processes by using Fe-based coagulant in drinking water treatment plants, could be used as a precursor to prepare an effective peroxymonosulfate (PMS) activator (Fe3O4@SiO2) for the ciprofloxacin (CIP) degradation via facile hydrothermal treatment. The catalytic performances of raw iron-rich sludge and Fe3O4@SiO2 were evaluated. The removal rate of CIP in Fe3O4@SiO2/PMS system increased from 44.7% to 82.8% within 60 min compared with the raw iron-rich sludge. The effects of PMS, catalyst loadings, temperature, and initial pH on the CIP degradation were examined, demonstrating that acidic conditions and higher temperatures were beneficial for CIP degradation. Both sulfate radicals (SO4•−) and hydroxyl radicals (•OH) contributed to the CIP degradation, and SO4•− was predominated in the Fe3O4@SiO2/PMS system, which was confirmed by the result of electron paramagnetic resonance (EPR) analysis and radical quenching tests. The mechanisms of the PMS activation process by Fe3O4@SiO2 were elucidated, and the influencing factors were among which the role of the iron mineral phase was emphatically explored. This study provides a facile method to convert the recycled waste iron-rich sludge to magnetic heterogeneous catalysts for CIP degradation with PMS activation.