Equilibrium, Kinetic and Thermodynamic Studies on the Adsorption of Direct Dye onto a Novel Green Adsorbent Developed from Uncaria Gambir Extract

Uncaria gambir extract was chemically modified for the purpose of developing a novel green adsorbent. The modified gambir adsorbent was characterised by FTIR, SEM-EDX and pHzpc, and its potential for the removal of Direct Red 23 from aqueous solution was investigated. The results showed that the equilibrium data were well described by the Langmuir isotherm model, with a maximum adsorption capacity of 26.67 mg/g. The kinetics of adsorption of Direct Red 23 followed a pseudo-second-order kinetic model. Thermodynamic parameters such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) were studied, and the adsorption process of Direct Red 23 was found to be endothermic and spontaneous.