Carbon-coated anatase: the role of the carbon layer for photocatalytic performance

Carbon-coated anatase-type TiO2 was prepared by the heat treatment of powder mixtures of photocatalyst TiO2 (ST-01) with different carbon precursors, poly(vinyl alcohol), hydroxyl propyl cellulose and poly(ethylene terephthalate), at a temperature between 700 and 900 °C for 1 h in an Ar gas flow. Since the carbon layers formed on the TiO2 particles were porous, the samples prepared showed a high adsorptivity, in addition to the photoactivity of TiO2. The carbon coating was shown to suppress the phase transition from photoactive anatase to much less active rutile, but seemed to reduce the amount of UV radiation reaching the surface of the TiO2 particles. A balance among different factors controlled by the carbon layer on the TiO2 particles was required to get high photocatalytic performance, i.e., high rate constant for the photodecomposition of methylene blue. On the sample prepared at 850 °C with a carbon content of about 3.5 wt%, the highest rate constant in the present work was obtained, in which the transition from anatase to rutile was suppressed and carbon layer was thin enough to transmit UV rays.