Methylene Blue Dye Adsorption onto Polyoxometalate Ionic Liquid Supported on Bentonite: Kinetic, Equilibrium and Thermodynamic Studies

The potential of polyoxometalate ionic liquid POM-IL supported on low-cost and available eco-friendly Saudi raw bentonite in the adsorption of MB cationic dye was investigated. For this purpose, TOAx[α-XW11O39]@Bentonite (X = Si, P; TOA = TetraOctylAmmonium), namely SWB and PWB were prepared and characterized by IR, XRD, XRF, SEM, TEM and BET. Batch adsorption experiments showed that SWB and PWB have higher adsorption capacity than the raw bentonite with an enhancement of about 37% for SWB. The adsorption capacities of both SWB and PWB improved with increasing contact time and temperature and decreased with higher salt concentration in solution. The pH is shown to have insignificant effect on the adsorption of MB onto SWB and PWB. This result is quite meaningful in the adsorption process application since it makes pH complicated adjustment of the discharged contaminated water before treatment unnecessary. The Kinetic study expressed that the pseudo-second-order model described the adsorption process better than the pseudo first order. The experimental isotherm data were found to fit the Langmuir model compared to the Freundlich model with a maximum adsorption capacity 277.78 mg/g and 113.6 for PWB and SWB respectively. The thermodynamic parameters illustrated that the adsorption process was favorable, spontaneous and endothermic.