Synthesis and characterization of MnOx/TiO2 nanoparticles for photocatalytic oxidation of indigo carmine dye

Manganese (10 wt.%) supported on titania synthesized by sol–gel (Mn/TiO2SG) and impregnation (Mn/TiO2D-imp) methods in addition to their precursors TiO2SG and TiO2D (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/TiO2D-imp indicated the highest activity (98%) comparatively. This was due to 34% of the support titania is covered by Mn species in Mn/TiO2D-imp mainly as Mn2O3 moieties, as validated from IR results (605, 714 cm−1). On the other hand, Mn in Mn/TiO2SG was incorporated in titania lattice mainly in tetrahedral coordination sites as β-MnO2 (655, 693 cm−1) and only exposes surface coverage comprises of 10%. The adsorption of IC dye onto TiO2D 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. TiO2SG and Mn/TiO2SG presented lower activity either in adsorption and photocatalysis compared with Mn/TiO2D-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/TiO2-Dimp was thoroughly investigated and well pH regulated and correlated with ZPC of MnOx species and surface properties.