Selective removal of dual dyes from aqueous solutions using Metal Organic Framework (MIL-53(Al))

Abstract

The adsorption process of the cationic dye Malachite Green (MG) and the anionic dye Methyl Orange (MO) onto a MOF, namely, MIL-53(Al) was studied under several experimental parameters. Batch experiments were performed to investigate the feasibility of this MOF as possible adsorbent for the removal of MG and MO from both single and binary-dye aqueous solutions. Experimental results revealed that MIL-53(Al) can quickly bind to both types of dyes with high removal efficiency of more than 95%. The effects of different parameters such as adsorbent dosage, initial concentration of dye solution, pH of the solution, and temperature on the adsorption process were examined. Adsorption kinetic data were then fitted using pseudo first-order, pseudo second-order, and elovich models, showing that pseudo second-order model had the best fit for both dyes among the other models in both single and binary-dye systems with R2>0.996. Moreover, adsorption isotherm models of Langmuir and Freundlich were studied and the isotherm data was found to be in good agreement with the Freundlich isotherm for both dyes. Thermodynamics studies of change in Gibbs free energy, enthalpy, and entropy were carried out and showed that the adsorption of both dyes was endothermic and spontaneous. The selectivity test for an equimolar binary-dye solution containing both MG and MO suggested the higher affinity of MIL-53(Al) towards MO over MG, as it reached a value of 13.58 at the optimum conditions. Finally, excellent reusability of MIL-53(Al) was shown by utilizing it for 4 cycles of adsorption-desorption with almost no reduction in the adsorption capacity, bringing about additional examination of its applicability.