Production of Activated Carbon from Grape Pomace (<i>Vitis labrusca</i>) by Chemical Activation with ZnCl<sub>2</sub> and Its Application in Phenol Adsorption.

Abstract

This study investigated the production of activated carbon from <i>Vitis labrusca</i> 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 Δ<i>G</i>° values of -18.85, -20.03, and -21.53 kJ mol^-1 at 25, 45, and 55 °C, respectively, Δ<i>H</i>° of 6.2 kJ mol^-1, and Δ<i>S</i>° 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.