Enhanced adsorptive and photocatalytic achievements in removal of methylene blue by incorporating tungstophosphoric acid–TiO 2 into MCM-41

Abstract

The use of titania-dispersed materials in photocatalytic processes has been proposed as an alternative to the conventional bare TiO 2, in order to modify the surface area and activity of the catalyst. A homogeneously dispersed Keggin unit into TiO 2 was synthesized using tungstophosphoric acid (TPA) and titanium tetraisopropoxide. This compound was then loaded into MCM-41 by dispersing it in a suspension containing the mesoporous phase. Two other titanium-containing MCM-41 catalysts, Ti–MCM-41 and TiO 2/MCM-41 were also prepared using isomorphous substitution synthesis method and impregnation method, respectively, for the sake of comparison. The prepared photocatalysts were characterized by X-ray diffraction (XRD), nitrogen physisorption (BET) and chemical analysis. The catalysts were used to study degradation of methylene blue (MB) in aqueous solution. XRD result shows a pure anatase crystalline phase for TPA-containing TiO 2 indicating that there is good molecular distribution of tungstophosphoric acid into TiO 2 structure. Supported TPA–TiO 2 into MCM-41 shows both TPA–TiO 2 and MCM-41 characteristic X-ray reflections in the high-angle and low-angle parts of the XRD patterns, respectively. The experimental results show that adsorption is a major constituent in the elimination of MB from the dye solutions by the TPA-containing materials. Exploitation of both adsorption and photocatalytic processes speeds up the removal of the dye using the TPA–TiO 2-loaded MCM-41 photocatalyst. The elimination of MB is completed within 15 min for a 30 mg l −1 MB solution containing a catalyst dose of 100 mg/100 ml. The efficiencies of the other photocatalysts such as commercial TiO 2, Ti–MCM-41, TiO 2/MCM-41 and TPA–TiO 2 for adsorption and degradation of MB were also studied and compared with that of the prepared catalyst.