Synthesis of algal–bacterial sludge activated carbon/Fe₃O₄ nanocomposite and its potential in antibiotic ciprofloxacin removal by simultaneous adsorption and heterogeneous Fenton catalytic degradation

The extensive use of pharmaceuticals has increased their presence in the environment, posing significant ecological and public health concerns. The current study reports the magnetic nanocomposite (M-ABAC) synthesis using the algal–bacterial sludge as the precursor for activated carbon and evaluates its potential in fluoroquinolone antibiotics removal. The activated carbon from algal–bacterial sludge was composited with Fe₃O₄ nanoparticles using the co-precipitation method. The M-ABAC was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX), Brunauer–Emmett–Teller (BET) analysis, and vibrating sample magnetometry (VSM). M-ABAC was employed for antibiotic ciprofloxacin (CIP) removal by combined adsorption and heterogenous Fenton degradation. The adsorption studies reveal that the Langmuir isotherm best fits the experimental data, with a maximum adsorption capacity of 81.6 mg/g. Pseudo-second-order kinetic model well describes adsorption kinetics. Fenton catalytic degradation was performed using H₂O₂ as the activating agent. The optimal H₂O₂ dosage was observed to be 10 mM. A CIP adsorptive removal efficiency of 75% was observed at 2 g/L dosage of M-ABAC in a 200 ppm CIP solution. Simultaneous adsorption and Fenton catalytic degradation further enhanced the removal efficiency to 92%. Radical scavengers experiment revealed that the hydroxyl radical (•OH) was the dominant reactive oxidation species. The degradation products of the CIP were identified using liquid chromatography quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS). The possible CIP degradation mechanisms include decarboxylation, piperazine moiety degradation, defluorination, and hydroxylation.