Preparation of activated carbon from Alligator weed (Alternenthera philoxeroids) and its application for tartrazine removal: Isotherm, kinetics and spectroscopic analysis

In this paper, the ability of activated carbon obtained from Alligator weed (AAW) to remove tartrazine from aqueous solutions was investigated. The as-prepared AAW was characterized by SEM, FTIR, BET surface area analyzer, and through the determination of pHzpc. The effect of different operational parameters like pH, initial concentration of tartrazine, contact time, and temperature on the sorption behavior was studied in batch mode. The adsorption of tartrazine was favored in acidic medium. The kinetic data were examined using various models viz. pseudo-first order, pseudo-second order, and intra-particle diffusion models. The fitness of the experimental data with pseudo-second order model was evident from the values of correlation coefficient (R2 > 0.99). The adsorption equilibrium was modeled with the Langmuir and Freundlich isotherm expressions. The isotherm data were better fitted to Freundlich model which indicates heterogeneous nature of the adsorbent. The Freundlich adsorption capacities (KF) were found to be 107.56, 131.67 and 183.4 mg g-1 at 30, 40 and 50 °C, respectively. The negative values of ΔG° and positive value of ΔH° demonstrated that the adsorption of tartrazine onto AAW were spontaneous and endothermic in nature, respectively. The regenerated AAW can be reused 4 times for the adsorption of tartrazine