Novel Fe₃O₄-Modified Biochar Derived from Citrus Bergamia Peel: A Green Synthesis Approach for Adsorptive Removal of Methylene Blue

The present study reveals the enhanced bio-sorption of methylene blue (MB) from an aqueous solution using iron oxide immobilized citrus bergamia biochar (Fe₃O₄CBC). The adsorption efficiency was increased dramatically from 64 % to 98 % after the magnetic iron oxide modification to citrus bergamia biochar (CBC) due to electrostatic interaction. Physico-chemical alterations of CBC surface prior and post-modification and after dye adsorption were evaluated using the following surface techniques such as FTIR, XRD, SEM, BET, Raman, TGA-DTA, Zeta potential analysis. The retention of C−OH, C=O, C−O, C−H, and Fe₃O₄ groups were confirmed from FTIR spectra. BET analysis revealed that Fe₃O₄CBC showed an elevated surface area of 136.72 m² g⁻¹ with a reduced pore diameter of 3.73 nm than CBC. The Pseudo second order and Langmuir isotherm model was best fitted with R²=0.99 and adsorption capacity of 31 mg/g. The thermodynamic data (ΔS=0.1455 kJ mol⁻¹ K⁻¹, ΔH=33.87 kJ mol⁻¹) revealed the spontaneity, endothermic nature, and feasibility of adsorption process. Regeneration studies revealed that the material has excellent sorption-based performance over five consecutive cycles. The current work demonstrates that Fe₃O₄CBC can serve as a highly efficient, cost-effective, bio adsorbent for the removal of MB with easy magnetic separation from aqueous medium.