Photocatalytic degradation of ciprofloxacin with Fe₂O₃ nanoparticles loaded on graphitic carbon nitride: mineralisation, degradation mechanism and toxicity assessment

Haematite (Fe₂O₃) loaded on graphitic carbon nitride (g-C₃N₄) was synthesised as a new photocatalyst by hydrothermal method, and its photocatalytic activity was evaluated for the degradation of ciprofloxacin (CIP) from aqueous solutions. Structural properties determined by scanning electron microscope (SEM), X-ray powder diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) showed that Fe₂O₃ nanoparticles were successfully prepared and a good interaction occurred between g-C₃N₄ and Fe₂O₃. The g-C₃N₄/Fe₂O₃/UV system showed higher degradation efficiencies than UV and g-C₃N₄/Fe₂O₃ alone. The maximum removal of CIP (100%) and TOC (93.86%) was achieved at pH of 7, photocatalytic dosage of 0.3 g/L, radiation intensity of 36 W, and reaction time of 60 min. The rate of degradation of CIP was investigated by first-order kinetic and its constant rate confirmed the influence of factors. Trapping experiments showed that hole (h⁺), hydroxyl radical (^•OH) and superoxide radical (O₂^•-) were involved in photodegradation of CIP, however, h⁺ and ^•OH plays major role in the degradation of the target pollutant. The excellent stability and recyclability of g-C₃N₄/Fe₂O₃ was confirmed by five consecutive reaction cycles. The energy consumption of the system for different concentrations of CIP (10–50 mg/L) was in the range of 9–44.02 kWh/m³, which emphasises that the g-C₃N₄/Fe₂O₃/UV process is energy-efficient. The BOD₅/COD rate showed that the photocatalytic process can degrade CIP into degradable compounds. The presence of NH₄⁺, NO₃⁻ and F⁻ anions in the treated effluent indicates that CIP is well mineralised. Toxicity experiments performed by Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis) culture suggested the applicability of the g-C₃N₄/Fe₂O₃/UV process as a promising and effective technology for treatment of CIP-containing solution.