Preparation and characterization of a nano-sized Mo/Ti mixed photocatalyst

Nano-sized molybdenum-doped TiO(2) (Mo/Ti) mixed oxide photocatalysts were prepared with the Mo(5+) content varying from 0 up to 2.5 mol%, to shift the absorption onset into the visible region and to enhance the efficiency of photocatalytic activity by retarding the (e(-)-h(+)) recombination. Prepared Mo/Ti mixed oxides were characterized by ultraviolet and visible spectroscopy (UV/VIS), transmission electron microscopy-electron diffraction pattern (TEM-EDP), X-ray diffraction(XRD), energy dispersive X-ray (EDAX) and X-ray photoelectron spectroscopy (XPS). Photonic efficiency was also investigated with the degradation rate of dichloroacetate (DCA) and light intensity measured by actinometry. TEM-EDP and XRD patterns showed that particles were in the form of anatase with the diameter of ca. 4 nm. The appreciable red-shift in the UV/VIS absorption spectra was monitored at each preparation stage - aging and dialyzing. The red-shift varied with addition of Mo, in the case of 2.5% Mo/Ti the UV/VIS absorption started at around 0.22 eV less than in nano-sized pure TiO(2) (about 3.42 eV). EDAX verified that the amount of Mo in the prepared mixed oxides was as required, and XPS analysis revealed that Mo(V) existed in the TiO(2) lattice. The measured photonic efficiency increased to 0.28 with DCA at 0.5 mol% Mo, and then decreased as the Mo content increased above 0.5 mol% Mo. This could be explained in terms of the changing prevailing phenomena - electron trapping and recombination - as the amount of dopant increased in terms of the distance between the trapped sites of the charge carriers. (C) 2000 Elsevier Science B.V. All rights reserved.