Adsorption, Thermodynamics and Kinetics of Methylene Blue on Nano Structured ZnO Crystals

Abstract

This investigation was concern to study the removal of methylene blue pollutants from aqueous solution using nano ZnO synthesized from raw materials of zinc oxide. The equilibrium adsorption data were analyzed using adsorption models of Langmuir, Freundlich and Temkin. The thermodynamic and kinetics parameters were calculated using adsorption process on nano ZnO for the methylene blue solution at different temperatures. It was found that a ZnO at nano level has a very significant adsorption for methylene blue compared to that of raw materials. The results showed that the model isotherms are fitting very well with the experimental data. The specific adsorption percentage of methylene blue was highly affected by addition of nano ZnO and decreasing with temperature compared to that of control sample. It has been found that the adsorption capacity was increased by increasing the methylene blue concentrations, and these values indicated that the methylene blue adsorption onto nano ZnO was spontaneous and endothermic in nature. All values of Gibbs functions were negative with values of -15 and -17 kJmol-1 for temperatures of 293 to 323K, while values of enthalpy and entropy about -33 kJmol-1 and 72 JK-1 mol-1 for nano ZnO respectively. These results indicated that the adsorption process was feasible, spontaneous and exothermic. Kinetic Study showed that the value of the rate constant is 0.338 min-1.