Optimization and batch studies on adsorption of malachite green dye using rambutan seed activated carbon

Abstract

Rambutan seeds (Nephelium lappaceum L.)-based activated carbon (RSAC) was prepared using potassium hydroxide (KOH) activation and carbon dioxide (CO2) gasification methods. The adsorbent prepared was characterized using Fourier transform infrared, SEM, proximate analysis, and BET techniques, respectively. The effects of three variable parameters; activation temperature, activation time, and chemical impregnation ratio (IR) (KOH: char by weight) on the preparation of RSAC used for the removal of MG dye was investigated. Based on the central composite design, quadratic and two factor interaction (2FI) models were, respectively, employed to correlate the effect of variable parameters on the preparation of RSAC used for the percentage MG dye removal and activated carbon yield. From the analysis of variance, the most influential factor on each experimental design response was identified. The optimum conditions of MG dye removal by RSAC are: activation temperature (802°C), activation time (1.0 h), and IR (2.4), respectively. The percentage MG dye removal obtained was 91.45% resulting in 22.56% RSAC yield. The percentage error between predicted and experimental results for the removal of MG dye is 2.4%. The effects of operational parameters like pH, initial dye concentration, contact time, and solution temperature were investigated using batch method. Graphical correlations of eight different adsorption isotherm models were carried out. Freundlich isotherm fitted the adsorption data most. The data were also analyzed by the Lagergren pseudo-first-order, Ho Mc Kay pseudo-second-order, Elovich and Avrami kinetic models. Pseudo-second-order kinetic model best represents the kinetic data and the mechanism of adsorption was controlled by both film and intraparticle diffusions. Thermodynamic studies gave negative ∆G° values, indicating that the process of MG dye adsorption onto RSAC was spontaneous. The positive values of ∆H° and ∆S° suggest that the process of dye adsorption was endothermic.