Production of Activated Carbon from Grape Pomace ( Vitis labrusca ) by Chemical Activation with ZnCl 2 and Its Application in Phenol Adsorption

This study investigated the production of activated carbon from Vitis labrusca grape pomace through chemical activation with ZnCl2 and subsequent carbonization at varying temperatures and times using a fractional factorial design. The best performance for phenol adsorption was obtained at 800 °C for 120 min, achieving a maximum adsorption capacity of 54.04 mg g-1. The activated carbon presented a high specific surface area (1017.58 m2 g-1), meso- and micro-porous structure (type I and IVa isotherms with H4 hysteresis), oxygenated functional groups, and thermal stability. Adsorption kinetics were studied at different phenol concentrations (50-150 mg L-1), and the experimental data were fitted to pseudo-first-order, pseudo-second-order, and Elovich models. The results revealed that the pseudo-second-order model better described the kinetic data. Regarding the equilibrium studies, the maximum adsorption capacity was 180 mg g-1. Isotherm modeling indicated that the Freundlich model was the most appropriate. Thermodynamic analysis indicated that the adsorption process is spontaneous and favorable, with ΔG° values of -18.85, -20.03, and -21.53 kJ mol-1 at 25, 45, and 55 °C, respectively, ΔH° of 6.2 kJ mol-1, and ΔS° of 83.8 J mol-1 K-1 at 45 °C, demonstrating that higher temperatures enhance adsorption. Reuse tests showed that after five adsorption-desorption cycles, the adsorbent maintained its mechanical integrity and physical stability. These findings confirm that grape-pomace-derived activated carbon is a sustainable and effective material for phenol removal from aqueous solutions.