Synthesis and characterization of MnO x/TiO 2 nanoparticles for photocatalytic oxidation of indigo carmine dye

Abstract

Manganese (10 wt.%) supported on titania synthesized by sol–gel (Mn/TiO 2SG) and impregnation (Mn/TiO 2D-imp) methods in addition to their precursors TiO 2SG and TiO 2D (Degussa) materials were characterized by measuring the surface texturing, Fourier transform infrared spectroscopy, X-ray diffraction, particle size (analyzer) and electrophoretic mobility (zeta potential). These materials were tested for adsorption and mineralization (in the presence of UV irradiation) of indigo carmine (IC) dye. Through comparison of the results, the photocatalytic degradation of Mn/TiO 2D-imp indicated the highest activity (98%) comparatively. This was due to 34% of the support titania is covered by Mn species in Mn/TiO 2D-imp mainly as Mn 2O 3 moieties, as validated from IR results (605, 714 cm −1). On the other hand, Mn in Mn/TiO 2SG was incorporated in titania lattice mainly in tetrahedral coordination sites as β-MnO 2 (655, 693 cm −1) and only exposes surface coverage comprises of 10%. The adsorption of IC dye onto TiO 2D was considerably higher (88%) than rest of materials due to increasing OH groups, large surface to volume ratio and moderate pore radius (33 Ǻ) that was accessible to facile IC diffusion. TiO 2SG and Mn/TiO 2SG presented lower activity either in adsorption and photocatalysis compared with Mn/TiO 2D-imp. There is no apparent size effect on IC degradation over former catalysts since they have comparable values (48–43 nm). The influence of time on the decolorization rate of IC on Mn/TiO 2-Dimp was thoroughly investigated and well pH regulated and correlated with ZPC of MnO x species and surface properties.