Synthesis and Structure of Carbon-doped TiO2 by Carbothermal Treatment

Carbon modified titanium dioxide (TiO2) is a promising candidate for catalytic applications or fuel cells, where the modified oxide could replace currently used catalyst support materials. Carbothermally treated TiO2 was successfully prepared by annealing under acetylene/nitrogen gas flow in a rotary tube furnace. The carbon content in the TiO2 samples ranged from 5 to 14.5 wt.-% as determined by thermogravimetric measurements. The powders showed suppression of the phase transition from anatase to rutile up to a treatment temperature of 825 degrees C. Above 600 degrees C rutile is the thermodynamically stable phase, therefore the suppression must be attributed to either carbon in the lattice or the reducing atmosphere in the furnace. Raman spectra revealed the characteristic G and D bands, indicating the formation of carbonaceous species in the samples. In addition, a shift of the anatase E-g(1) band was observed indicating a lattice disorder pointing toward carbon incorporation into the lattice. Diffuse reflectance spectra show sub band gap absorption together with a shift of the absorption edge. Depending on the extraction method of band gaps from spectra, the band gap values show a decrease or increase with increasing carbon content. Details of the evaluation and interpretation of the spectra are discussed.