Magnetic supported activated carbon obtained from walnut shells for bisphenol-a uptake from aqueous solution

This work investigated the usability of activated carbon walnut shell (ACWS) and magnetic activated carbon walnut shell (MACWS) for Bisphenol-A (BPA) elimination from aqueous solution. Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD) were used to study the chemistry of the adsorbents. Batch sorption studies at different temperatures, contact time, adsorbent dosage, pH and varied Bisphenol-A concentrations were performed, while pseudo-first-order and pseudo-second-order kinetics models were deployed to investigate the kinetic data. Equilibrium parameters were computed using the Dubinin-Radushkevich, Freundlich, Temkin and Langmuir isotherms, while Box-Behnken design was used to optimize the adsorption factors. FT-IR report showed the existence of O-H, C=O, C-O and C=C stretches in both adsorbents and Fe-O in MACWS, while XRD revealed an amorphous morphology. BPA removal by ACWS and MACWS with correlation coefficient (R-2) > 0.9 showed that the pseudo-first-order kinetic model was the most appropriate for explaining the kinetic data. Judging from the values of the maximum adsorption capacity (115.85 and 166.67 mg/g for ACWS and MACWS, respectively), it can be inferred that the Langmuir isotherm best describes the equilibrium results. Thermodynamic investigation showed the process of Bisphenol-A uptake to be spontaneous and endothermic with entropy change ( increment S-o) values of 0.033 and 0.039 kJ/mol for ACWS and MACWS, respectively. The data obtained from the kinetics, isotherm and equilibrium studies revealed that ACWS and MACWS adsorbents were effective for the treatment of Bisphenol-A.