Removal of methylene blue from aqueous solutions by an adsorbent based on metal-organic framework and polyoxometalate

A metal-organic framework (Cu-3(BTC)(2), BTC = 1,3,5-benzenetricarboxylate) composite based on polyoxometalate (H6P2W18O62) was synthesized by a simple one-pot solvent-thermal method and applied as an adsorbent to remove methylene blue (MB) from aqueous solution. The chemical structure, morphology and thermostability of the composite were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Thermogravimetric Analysis (TG) and N-2 adsorption-desorption isotherms. The removal rate of the composite H6P2W18O62@Cu-3(BTC)(2) was greater than that of the pure Cu-3(BTC)(2), especially at higher initial concentrations, showing that the adsorption performance of porous Cu-3(BTC)(2) can be improved through the modification of H6P2W18O62. The effect factors containing the initial concentration, contact time, initial solution pH and temperature of MB adsorption onto the composite were systematically explored. The experimental isotherm data was found to fit the Freundlich model well and the process of MB adsorption onto H6P2W18O62@Cu-3(BTC)(2) was controlled by the pseudo-second-order kinetic model. The thermodynamic parameters illustrated that the adsorption was spontaneous and exothermic process. These results show that designing a metal-organic framework composite is a quite promising strategy to achieve extreme application for metal-organic framework. (C) 2015 Elsevier B.V. All rights reserved.