Kinetic and thermodynamic studies on the adsorption of xylenol orange onto MIL-101 (Cr)

A highly porous metal-organic framework (MOF) material based on chromium-benzenedicarboxylates (MIL-101) was applied to the adsorption of xylenol orange (XO) from aqueous solution. Adsorption kinetics and isotherms were determined from the experimental data, and the results showed that pseudo-second-order kinetic model and Langmuir adsorption isotherm matched well for the adsorption of XO onto MIL-101. Thermodynamic parameters including free energy, enthalpy, and entropy of adsorption were obtained, and all the results were in favor of the adsorption. It was found that the adsorbed amounts decreased with increasing pH value of the XO solution, which indicates that the mechanism may be the charge interactions between the dye stuffs and the adsorbents. The used MIL-101 could be regenerated by washing with a dilute concentration of NaOH solution. Compared with other adsorbents like active carbon and MCM-41, especially in high concentrations of XO, MIL-101 demonstrated a superior dye adsorption capability. (C) 2011 Elsevier B.V. All rights reserved.