MnO₂-doped Hydrochar composite for peroxymonosulfate activation for norfloxacin degradation: mechanism and toxicity

In this study, peanut shell-derived Hydrochar was synthesized via hydrothermal carbonization and doped with MnO₂ nanorods, which served as a peroxymonosulfate activator for the degradation of norfloxacin. The primary aim was to valorize the natural waste by enhancing its properties for effective PMS activation. The composite was characterized by FTIR, FESEM-EDX, XRD, BET and TGA. The catalytic performance of the MnO₂@HC composite showed an impressive 98.59% degradation of NOR. Optimum batch study conditions were established at pH 3, an MnO₂@HC dosage of 0.07 g L− 1, PMS concentration of 2 mm and a temperature of 50°C. The composite demonstrated strong reusability, with 75% NOR degradation maintained through five cycles. Radical scavenger tests confirmed that SO4●− and •OH radicals were the primary reactive species involved, while O2●− played a minor role in NOR degradation. A degradation pathway was proposed based on High Resolution-Mass Spectrometer (HR-MS) analysis, which identified intermediate products that exhibited reduced toxicity towards aquatic organisms. The mechanism involved cleavage of the quinolone and piperazinyl rings. These results highlight the practical applicability of the MnO₂@HC catalyst in aqueous environments.