Novel magnetic coffee waste nanocomposite as effective bioadsorbent for Pb(II) removal from aqueous solutions

In this study, highly abundant coffee waste was taken as a matrix to synthesize a novel magnetic coffee waste (MCW) by dispersing Fe₃O₄ nanoparticles on its surface via a single pot precipitation method. The potential of MCW to remove Pb (II) from aqueous solution (Pb II) was assessed. The synthesized adsorbent was characterized using XRD, FTIR and SEM-EDX for envisaging the role of surface structures and functional groups in the sorption process. Various operating conditions including effect of Fe₃O₄-loading, solution pH, contact time, adsorbent dosage, initial Pb (II) concentration and temperature on the sorption of Pb (II) from aqueous solution were studied. The sorption data were fitted using Freundlich, Langmuir, Temkin and Dubinin-Radushkevich (D-R) adsorption models. Langmuir isotherm best fitted the experimental data with R² > 0.99 and maximum Pb (II) adsorption capacity of 41.15 mg/g at 25 °C indicating monolayer adsorption. Analysis of kinetic data using pseudo first-order, pseudo second-order and intra-particle diffusion models, revealed that sorption of Pb (II) onto MCW followed pseudo-second order kinetics; demonstrating the chemisorption nature of sorption. Intra-particle diffusion model, clearly depicts that diffusion is not the only rate limiting step in the sorption. Thermodynamic analysis revealed that sorption is endothermic and spontaneous in nature. MCW's showed remarkable potential to be used as an adsorbent for the removal of Pb (II) from aqueous solutions with the advantage of easy separation using magnetic forces.