Abstract

Environmental pollution caused by colored effluents is threatening to the world. The aim of this study is to evaluate the applicability of Zinc oxide nanoparticles (ZnO-NPs) for the removal of methylene blue (MB) from aqueous solution and also to study the applicability of the nonlinear and linear adsorption isotherm and kinetic models on the process. The effects of various operating parameters such as pH (3 - 11), ZnO-NPs dosage (0.1 - 0.4 g/L), contact time (30 - 120 min), initial MB concentration (20 - 80 mg/L) on the removal of MB were studied. The adsorption kinetic and isotherm models were examined using the linear and nonlinear regression analyses methods. The results revealed that under optimal conditions of pH 7, ZnO-NPs dosage of 0.2 g/L and contact time of 60 min at concentration of 40 mg/L, the maximum adsorption capacity (q(m)) of MB adsorption on ZnO NPs was 9.6. mg/g and maximum removal was 96.25 . The MB adsorption data was found to follow the Langmuir isotherm model than the Freundlich model using the linear regression analysis method. But the values of the error functions (RAISE, SD, RSS, R-adj(2), and X-red(2)) estimated revealed that the Freundlich isotherm was more suitable for describing the adsorption process. The process of MB adsorption on ZnO-NPs was found to be governed by the pseudo-second-order model using both the linear and nonlinear adsorption models. The rate-determining step is chemisorption. In general, the results indicated that the nonlinear fitting method of the experimental data with the models provided better results. The adsorption of MB on ZnO-NPs was favorable since the intensity of adsorption (n = 9.62) lies within the range of 1-10. The monolayer adsorption capacity (q(m)) for ZnO-NPs with MB was 12.78 mg/g. It could be concluded from the study that ZnO-NPs can be useful for the removal of MB from its aqueous solution.