Lime-Juice-Assisted Synthesis of Magnetically Recoverable CoFe2O4/Chitosan Nanocomposites for Visible-Light Removal of Methylene Blue

A lime-juice-assisted route was used to synthesize CoFe2O4 nanoparticles, which were subsequently immobilized in a chitosan matrix to obtain a magnetically recoverable CoFe2O4/chitosan (CoFe2O4/CS) nanocomposite for methylene blue (MB) removal under visible light. X-ray diffraction confirmed the cubic spinel phase and its retention after composite formation, while FTIR and XPS supported interfacial interactions between CoFe2O4 and the amino/hydroxyl functionalities of chitosan. Electron microscopy showed predominantly spherical-to-quasi-spherical ferrite nanoparticles (approximately 10–20 nm) distributed on the polymer matrix with reduced agglomeration. Chitosan incorporation decreased the BET surface area from 81.9 to 51.3 m2 g−1 and the saturation magnetization from 51.5 to 31.4 emu g−1, but the nanocomposite remained readily separable with an external magnet. The optical band gap increased from 2.17 to 2.61 eV, whereas photoluminescence quenching was consistent with altered radiative charge-carrier behavior. At pH 9, an initial MB concentration of 20 mg L−1, and a catalyst dosage of 0.7 g L−1, the composite achieved 98.5% MB removal within 120 min under a 30 W visible-light LED, with a pseudo-first-order rate constant of 0.035 min−1. Removal remained at 90.3% after five cycles. Scavenger tests indicated major contributions from pathways involving h+ and •OH. These findings support further evaluation of bio-assisted CoFe2O4/CS nanocomposites as magnetically recoverable photocatalysts for MB-containing wastewater treatment.