Clarifying the locations of precious metals in sol gel derived nano-TiO2

Titania is a cheap and nontoxic polymorphic material of current interest for a variety of technological applications. Generally, TiO2, with a band gap of 3.2 eV, can only be excited by a small UV fraction of solar light, which accounts for only 3-5% of the solar energy. Various strategies have been pursued including doping with metallic elements (e.g., iron) or nonmetallic elements (e.g., nitrogen). In the present work TiO2 was doped with palladium (Pd), platinum (Pt), silver (Ag) and gold (Au) at doping levels of 5% weight, following the standard sol-gel methods. Structural characterization was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy (RS) and X-ray absorption near edge structure (XANES). Palladium and silver initially form oxides but annealing at high temperatures, convert to Pd and Ag metals whereas traces of Au and Pt are observed even at lower temperatures.