Magnetic modification of coffee husk hydrochar for adsorptive removal of methylene blue: Isotherms, kinetics and thermodynamic studies

Abstract The magnetic composite of coffee husk hydrochar-Fe3O4 (MCHH) was synthesized and employed as an adsorbent for the removal of methylene blue (MB) from synthetic wastewater. The coffee husk hydrochar was prepared by hydrothermal carbonization, and magnetic composite was produced through the chemical co-precipitation method. The physicochemical properties of the magnetic composite was analyzed by PZC, PXRD, SEM, FTIR, and VSM. The characterization results indicated successful incorporation of iron oxide particles into coffee husk hydrochar. The influence of adsorbent dose (0.2–1.4 g/L), pH (2−10), initial MB concentration (50–250 mg/L), contact time (0–160 min) and temperature (30–60 °C) on adsorption of MB on MCHH were studied. The adsorption equilibrium and kinetic studies suggested that the Freundlich isotherm model adequately explains the adsorption process and pseudo-second-order kinetic model could be regressed well with the experimental kinetics data. The maximum monolayer adsorption capacity of MB on MCHH was found to be 78 mg/g. Mass transfer analysis was also studied in order to understand the diffusion process in the adsorption process. The thermodynamic parameters are evaluated to elucidate the nature of the adsorption of MB onto MCHH. Good adsorption efficiency and easy recovery ability of MCHH suggests it could be a cost-effective adsorbent for the removal of dyes from wastewater.