Ultrasound-induced PMS activation for ofloxacin degradation from pharmaceuticals wastewater: DFT calculation, mechanisms and toxicity evolution

The degradation of persistent and refractory pollutants particularly antibiotics from drugs and pharmaceuticals wastewater remains challenging due to their high toxicity. Herein, a hybrid system CuxFe1-xZnO − layer double oxide (LDO)/PMS/US designed for the degradation of ofloxacin (OFC) and total organic carbon (TOC) from drugs and pharmaceuticals wastewater. Catalyst 0.4CFZ-LDO exhibited a remarkable catalytic activity for OFC (98.76 %, 0.0703 min−1) and TOC (76.97 %, 0.0259 min−1) removal, with synergistic index value (OFC, 3.45) and (TOC, 1.69) under the optimum conditions. The quenching experimental study reveals that sulfate radical (SO4•−) was dominant reactive oxygen species (ROS) for OFC and TOC removal. Density functional theory (DFT) demonstrates that strong attacking sites on the OFC structure were C14, C15 and C23 due to high concentration of Fukui index. Based on the as quantitative structure–activity relationship (QSAR) prediction model system 0.4CFZ-LDO/PMS/US potentially reduced the bio-toxicity (acute toxicity, mutagenicity, bioaccumulation factor) after treatment. Furthermore, catalyst 0.4CFZ-LDO demonstrated remarkable stability with minor leaching of metal ions. Critical contribution of Fe3+/Fe2+ and Cu2+/Cu+ surface catalyzed-redox cycle was evaluated with the help of X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, six potential routes of OFC degradation were proposed based on the DFT study, and intermediates were identified by GC–MS analysis. Based on the electrical energy per order (EEO) analysis, economic cost of pharmaceutical wastewater was estimated to be $0.059/L.