Adsorption of malachite green from aqueous solutions onto lotus leaf: equilibrium, kinetic, and thermodynamic studies

The low-cost and highly efficient adsorbents have been investigated to remove dyes from aqueous solution. In this study, lotus leaf was used as a biosorbent for the removal of malachite green (MG) from aqueous solutions. The batch experiments used to investigate the effect of experimental parameters such as contact time, adsorbent dose, initial MG concentration, solution pH, salt ionic strength, and temperature. The Langmuir, Freundlich, Koble-Corrigan and Redlich-Peterson isotherm models were considered to evaluate the adsorption behavior. The adsorption behavior was best described by the Koble-Corrigan, Redlich-Peterson and Langmuir isotherms. The maximum monolayer adsorption capacities of lotus leaf for MG were 105.9, 113.8, and 125.3 mg g(-1) at 296, 306, and 316 K, respectively. The adsorption process followed the pseudo-second-order rate equation which suggested that the adsorption may be a chemisorption process. Thermodynamic parameters of Delta G, Delta H, and Delta S indicated the adsorption process was spontaneous and endothermic. A large number of carbonyl and hydroxyl groups were found on the surface of the lotus leaf through FTIR analysis. The present study suggested that lotus leaf has high potential to be used as low-cost adsorbent for MG removal.