Assessment of the adsorption capacity of phenol on magnetic activated carbon

Abstract

In this work, an alternative utilization of agro-industrial waste coconut endocarp (Cocos nucifera L.) as raw material for the synthesis of magnetic adsorbent aiming the phenol removal is proposed. The synthetized adsorbent, denominated magnetic activated carbon (MAC), was prepared by coprecipitation of cobalt ferrite (CoFe2O4) onto activated carbon surface obtained by carbonization of coconut endocarp. Characterization of MAC was carried out by point of zero charge (PZC), Brunauer, Emmett, and Teller (BET) surface area, scanning electron microscopy (SEM), x-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), x-ray diffractometry (XRD) analysis, and magnetization curves. Adsorption experiments were performed in batch system to evaluate kinetics and equilibrium of phenol adsorption. Adsorbent regeneration method was proposed to evaluate the reutilization of MAC in successive cycles of adsorption–desorption. Results showed that obtained magnetic compounds present cubic phase structure covered in activated carbon surface. MAC has microporous structure with functional groups like carbonyl and hydroxyl that can behave as adsorption sites. Kinetic studies indicate that adsorption rate increased rapidly around the initial 60 min, reaching equilibrium at 240 min; following pseudo-first-order and pseudo-second-order kinetic models in characterization concentrations of 50 and 100 mg L−1, only the second-order model fit the kinetic data at 150 mg L−1, while both models were outside the chi-square interval at 200 and 230 mg L−1. The adsorption equilibrium is represented by Langmuir isotherm with high adsorption capacity of 116.0 ± 3.61 mg g−1. The desorption experiments revealed that adsorption capacities of MAC still viable after three adsorption–desorption cycles. It was observed that chemical affinity of small concentrations of methanol with phenol allowed to exert greater desorption capacity to other solvents with permanence of adsorbed phenol of 17.5 mg g−1.