Preparation andcharacterization of carboncoated TiO2 photocatalysts

Carbon-coated TiO2 were prepared by a simple heat treatment of the powder mixtures of anatase-type TiO2 (ST-01) with carbon precursor, poly (vinyl alcohol) (PVA), hydroxyl propyl cellrose (HPC) and poly (ethylene telephtalate) (PET) etc., at a temperature of 700 to 900°C. Diffuse optical reflectance spectra for carbon-coated TiO2 clearly showed the absorption edge for anatase-type structure, overlapping with absorption due to coated carbon over all wavelength of 220-850nm. Photocatalytic activity of carbon-coated TiO2 was evaluated through the determination of rate constant k for the decomposition of four model pollutants in water, methylene blue (MB), reactive black 5 (RB-5), phenol (Ph) and iminoctadine triacetate (IT), under UV irradiation. For MB most of carbon-coated TiO2 showed higher activity than the pristine anatase powder, but for others carbon-coated anatase gave either comparable or smaller rate constant for their photodecomposition. Photocatalytic activity defined by rate constant k for pollutants decomposition was found to depend strongly on crystallinity of anatase phase, which was evaluated by full width at half maximum intensity (FWHM) of 101 diffraction line; a maximum of k at an apparent FWHM of about 0.6° in 2θ (CuKα) for four pollutants. Adsorptivity of carbon-coated TiO2 photocatlysts was determined and discussed on the relations to BET surface area, amount of carbon coated and also rate constant k for the decomposition of MB, RB5, Ph and IT. Adsorptivity of carbon-coated catalysts depends strongly on the adsorbate (pollutant) but also on the surface nature of carbon layer on TiO2 particles. The relations between adsorptivity and rate constant k for four pollutants looked similar, suggesting that the pollutant adsorbed in the larger amount being decomposed with the higher rate. In order to check cyclic performance of carbon-coated TiO2, the photocatalysts were repeatedly used either in powder or fixed on one side of double-sided organic adhesive tape. It was proven that the carbon-coated TiO2 could be resisted to the multiple usage without marked deterioration in rate constant. The merits and demerits of carbon coating on photocatalyst TiO2 particles were discussed.