Degradation of ciprofloxacin using CoFe2O4@three-dimensional TiO2@graphene aerogels composite: kinetic, reusability, mineralization, degradation pathway, and toxicity assessment

Abstract

An investigation into the degradation of ciprofloxacin (CIP) under visible light was carried out using an efficient photocatalyst, i.e., CoFe₂O₄@3D-TiO₂@GA, synthesized by doping CoFe₂O₄@three-dimensional-TiO₂ into a hierarchical porous graphene aerogel. Optimal conditions for achieving complete removal of CIP involved a reaction time of 60 min, a catalyst dose of 0.6 g/L, an initial CIP concentration of 25 mg/L, and a solution pH range of 3–5. The reusability of CoFe₂O₄@3D-TiO₂@GA was observed to remain high even after four consecutive cycles, as the CIP degradation only slightly decreased from 94.3 to 87.1%. Following a 2-h photocatalytic degradation process, the intermediate products within the CIP solution no longer posed a threat to E. coli. The TOC analysis confirmed that CIP achieved 86% total mineralization. In the raw sewage, the BOD₅/COD and BOD₅/TOC ratios were 0.774 and 0.232, respectively. However, after a 120-min photocatalytic reaction, these ratios increased to 1.38 and 0.754, respectively. These findings suggest that non-biological sewage can be successfully transformed into biodegradable effluent through photocatalytic degradation. The photocatalytic process has a reaction rate coefficient that is 8.7 to 20.7 times higher than the adsorption process, depending on the concentration. The half-life constant is 117.4 min for the optimal concentration of 10 mg/L for the adsorption process, while for the photocatalytic process, it is 6.24 min. The research has highlighted the importance of integrating adsorption and photocatalysis, whereby primary reactive oxidative species, including superoxide and hydroxyl radicals, were identified. The study presents a pioneering approach for producing CoFe₂O₄@3D-TiO₂@GA, which has promising potential for environmental applications utilizing visible light.

Graphical abstract