Magnetically modified orange peel powder: A sustainable and recoverable adsorbent for enhanced removal of Rhodamine B

Orange peel powder (OPP) has been widely explored for dye adsorption; however, its limited adsorption capacity and poor separation efficiency restrict its practical applicability. In this study, magnetic Fe₃O₄ nanoparticles were successfully integrated with OPP through a green synthesis approach, yielding a mesoporous composite (OPP- Fe₃O₄), which was evaluated for the removal of Rhodamine B (RhB) dye. Comprehensive characterization confirmed the successful formation of the mesoporous OPP-Fe₃O₄ structure. Adsorption experiments revealed a high removal efficiency of 93.5% under optimized conditions. The adsorption behavior aligned most closely with the Freundlich isotherm and the pseudo-second-order kinetic model, indicating a heterogeneous adsorption surface and a mechanism dominated by chemisorption. Thermodynamic analysis further verified that the adsorption process is both spontaneous and exothermic. The maximum adsorption capacity (q_max) was determined to be 61.087 mg g⁻¹. Additionally, the mesoporous OPP-Fe₃O₄ composite exhibited excellent durability and recyclability, maintaining high adsorption efficiency over five consecutive adsorption-desorption cycles. The optimized adsorption performance is attributed to the strong interaction, increased surface area, porous architecture, and the presence of additional reactive centers generated through the synergistic interaction between OPP and Fe₃O₄, all of which collectively improve adsorption efficiency. Overall, this study demonstrates a green and effective synthesis route for magnetically modified orange peel powder, producing a mesoporous, high-surface-area material with strong adsorption capability and excellent recyclability for next-generation environmental applications.