Structural evolution and optical properties of C-coated TiO2 nanoparticles prepared by laser pyrolysis

Carbon- coated TiO2 nanoparticles were prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl4 and alternatively C2H4 and C2H4/C2H2 mixtures were used as titanium and carbon precursors, respectively. Optical, morphological and structural properties of the samples have been characterized by X-ray diffraction, transmission electron microscopy, high-resolution electron microscopy, selected area electron diffraction analysis and UV–vis diffuse reflectance spectroscopy. The phase composition of the nanoparticle system contains a mixture of anatase and rutile, with a preponderance of the anatase phase (90%) and with mean particle size of about 20 nm. The effect of increased carbon-dopant concentration on the essential structural properties of C-TiO2 nanopowders has been determined to be a decrease of the TiO2 anatase phase and of the particle mean diameter value (to about 18 nm). For the C-doped TiO2 nanoparticles, the UV–vis diffuse reflectance spectra showed an absorption shift to longer wavelengths, thus demonstrating an enhancement of the absorption in the visible spectrum.