Photocatalytic removal of Cr(VI) using cobalt ferrite-coated recycled cigarette butts under visible light:...

This study investigates the efficiency of a photocatalytic process utilizing a cobalt ferrite nanocomposite coated on recycled cigarette butts for the removal of hexavalent chromium Cr(VI) from aqueous environments under visible light. The variables under investigation were optimized using a entral composite design (CCD) within the framework of the response surface methodology (RSM). XRD, FTIR, SEM, and EDX mapping were employed to determine the structural, functional groups, morphology and compositional attributes of the synthesized nanocomposite. At the established optimal parameters (pH 2, 20 mg/L Cr(VI), 1.5 g/L catalyst dosage, and a reaction time of 120 min) the synthesized nanocomposite achieved a 95.49% photocatalytic reduction. Furthermore, the influence of environmental parameters, including purging gases, H₂O₂, organic compound types, various anions, radical scavengers, and catalyst recyclability, on the photocatalytic reduction of Cr(VI) was examined under optimal conditions. The value and accuracy of the proposed model were statistically evaluated based on the coefficient of determination (R²) and analysis of variance (ANOVA). The Visible/CoFe₂O₄-RCBs system demonstrated superior performance in Cr(VI) removal and optimal electrical energy consumption compared to other visible-light processes, achieving an energy efficiency of 6.89 × 10⁻^⁵ mg/J. The operational cost of this system was calculated at US$33.50 per kilogram, indicating its practical and economic viability compared to other visible-light systems. Furthermore, toxicity analysis using Daphnia magna confirmed a significant reduction in toxicity after treatment. Overall, the findings of this research indicate that the CoFe₂O₄-RCBs nanocomposite can serve as an effective, environmentally friendly, and promising catalyst for the removal of hexavalent chromium from contaminated water.