Magnetic Fe ₃ O ₄ Nanocubes Coated with Silica and Nb-Doped TiO ₂ for Recyclable Photocatalytic Degradation of Ciprofloxacin

Antibiotics, recognized as “emerging contaminants”, have been detected in increasing concentrations within aquatic ecosystems, contributing to elevated pollution levels and accelerating the development of antimicrobial resistance. Ciprofloxacin (CIP), one of the most prescribed antibiotics globally, exemplifies this challenge due to its persistence and resistance to conventional wastewater treatment methods. The inefficiency of existing water treatment approaches, often reliant on harmful chemical agents, exacerbates both health and environmental risks, underscoring the need for a sustainable, effective, and eco-friendly solution for antibiotic remediation. This study addresses this critical issue by synthesizing strongly magnetic iron oxide nanocubes (Fe 3 O 4 NCs) coated with silica (SiO 2 ) and niobium-doped titanium dioxide (Nb-TiO 2 )─Fe 3 O 4 @SiO 2 @Nb-TiO 2 ─as a photocatalyst for CIP degradation under visible-light irradiation. The magnetic Fe 3 O 4 core enables easy recovery and reuse of the nanoparticles (NPs), while Nb-TiO 2 doping improves photocatalytic performance by reducing the bandgap and extending light absorption into the visible spectrum. The intermediate SiO 2 shell mitigates interparticle interactions of the magnetic core and promotes the formation of a more crystalline TiO 2 structure. Results demonstrate that the synthesized NPs remove from 90 to 96% of CIP across initial concentrations of 5 to 40 ppm under visible light. The degradation followed pseudo-first-order kinetics, with the rate constant increasing as the initial CIP concentration decreased. The catalysts retained their activity over five reuse cycles, highlighting their durability and potential as a sustainable solution for antibiotic removal. This study emphasizes the integration of magnetic nanotechnology and photocatalysis as an innovative, recoverable, and environmentally friendly approach to water treatment, contributing to global efforts to safeguard public health and water resources.