Decaffeination of wastewater using activated carbon produced from velvet tamarind-pericarp (Dialium Guineense)

Abstract

Adsorption of caffeine from an aqueous solution was carried out using Velvet Tamarind-Pericarp, activated with H₃PO₄. The adsorbent was characterized using a scanning-electron microscope and the Brunauer-Emmett-Teller. Parameters such as activating agent concentration (80 wt.% in 100 mL solution), initial caffeine concentration of 5-40 g/L, pH of 0-14, and residence time 0-90 minutes, were investigated. Improved adsorptive capacities were seen at increased acid concentrations, with the highest removal rate obtained at a pH of 6. The highest residence time and adsorbent concentrations were obtained at 40 min and 10 g/L. The surface adsorption of the adsorbent obeyed the Langmuir Isotherm, while the regression coefficients conformed to the pseudo-second-order kinetic model for the remediation of caffeine with DG-AC. The highest amount of caffeine removed per gram DG is 72.60 mg.g^-1. From the thermodynamic study, the caffeine adsorption was feasible, spontaneous, entropy-driven, and endothermic. These data show that the use of DG-AC can be a good alternative to other expensive methods for caffeine remediation. The Pseudo - first/second-order kinetic results gave R² values of 0.95 and 0.99, other parameters such as entropy ($\Delta S°)$ and enthalpy ($\Delta H°$) are 0.06 $\left(\frac{kJ}{\mathrm{molK}}\right)$ and (19.21) $\left(\frac{kJ}{\mathrm{molK}}\right).$

Keywords: Caffeine; activated carbon; adsorption; contaminants; velvet tamarind; wastewater.