Insight into the isotherm modelling, kinetic and thermodynamic exploration of iron adsorption from aqueous media by activated carbon developed from Limonia acidissima shell

Abstract

The present research article investigated the adsorption of iron ions from aqueous solution using activated carbon as an adsorbent prepared from Limonia acidissima shell by chemical activation technique. Box-Behnken design (BBD) of Response surface methodology (RSM), was employed to optimize the experimental conditions for the preparation of activated carbon. The carbon yield and iodine no. approached 42.74% and 959.42 mg/g under the optimal conditions of IR (23.44%), activation time (39.60 min), and carbonization temperature (418.74 °C). The BET analysis presented that the optimized adsorbent exhibited a high surface area of 1863.49 m2/g. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared absorption spectroscopy (FTIR), Transmission electron microscopy (TEM) and determining the point of zero charge (pHzpc) were employed to characterize the adsorbent. The removal efficacy of the adsorbent for total Fe ion was studied in batch mode as a function of pH, contact time, initial concentration, adsorbent dosage, and temperature. The findings indicated that the adsorption procedure could be well-defined by Langmuir isotherm and pseudo-second-order kinetic model because of the high coefficient of determination (R2) value is 0.99, which is almost close to 1. The maximum adsorption capacity of total Fe ion by optimized activated carbon was determined as 48.5 mg/g. The mean free energy calculated from D-R isotherm implied that the physisorption is the dominant process in adsorption. The thermodynamic calculations suggested the spontaneous nature of the sorption process, along with the exothermic characteristics. According to XPS results, most of the metal ions adsorbed on the carbon surface primarily existed as Fe3+(85.26%) with only (14.38%) remaining as Fe2+. Based on the outcomes of sorption studies, electrostatic interaction and surface complexation are the probable mechanisms for total Fe ion adsorption.