Adsorption of methyl green (MG) in aqueous solution by titanium dioxide (TiO2) : kinetics and thermodynamic study

Abstract

Adsorption techniques are widely used to remove certain classes of pollutants from waters, especially those that are not easily biodegradable. In this respect, the removal of Methyl green (MG) from waste water using TiO2 was studied in batch system. This research was carried out to evaluate the capability of TiO2 toward the water treatment relevant to organic MG at batch conditions. The effects of contact time (0–60 min), initial pH (3–11), agitation speed (100–500 rpm), temperature (25–45 °C), adsorbent dosage (0.02–6 g/L), and MG concentration (50–200 mg/L) on the MG adsorption by TiO2 have been studied. The adsorption kinetics in view of four kinetic models, i.e., the pseudo-first-order Lagergren, pseudo-second-order, intra-particle diffusion and Elovich models, was discussed. The adsorption of MG is well described by the pseudo-second-order equation with the best determination coefficient (R2 = 0.999). The experimental isotherm data were analyzed by different models; the adsorption follows the Langmuir and Temkin models, providing a better fit of the equilibrium data. The batch adsorption experiments were carried out to optimize the physical parameters on the MG removal efficiency, and it has been found that 384.615 mg/g at 25 °C is removed. The positive value of the activation energy (Ea = 14.1813 kJ/mol) indicates the endothermic nature and clearly that the randomness is increased at the solid–solution interface during the MG adsorption onto TiO2, indicating that some structural exchange occurs among the active sites of the adsorbent and the MG species