Formation of the Ti4O7 phase through interaction between coated carbon and TiO2

Fine particles of photocatalytic anatase TiO2 prepared through hydrolysis of titanium tetraisopropoxide were coated by carbon. A reduced phase, Ti4O7, was formed through interaction between TiO2 and the coating carbon. EXAFS analysis on this Ti4O7 phase showed an intermediate Ti–Ti distance between those in anatase and rutile, which agreed with the structure composed of two-dimensional slabs of Ti–O octahedra separated by a shear plane. This carboncoated Ti4O7 was confirmed to have photocatalytic activity, even though a little lower than anatase, examining the decomposition of methylene blue in water under UV irradiation.

Carbon coating of photocatalytic anatase-type TiO2 was found to have certain merits: suppression of phase transformation to rutile, maintaining photocatalytic activity even better than without carbon coating, giving adsorptivity, and no degradation of organic binder [8]. In the present work a new photocatalyst of Ti4O7 was formed through the interaction between substrate TiO2 and coated carbon. The formation of Ti4O7 may open a new field of photocatalysts, but the synthesized catalyst was coated by carbon. Therefore, further efforts for the isolation of Ti4O7 are strongly desired in order to study its photocatalytic performance in more detail. An attempt was made to gasify the coated carbon by heating at around 300°C in air, but the isolation of the Ti4O7 phase has not yet succeeded. As a result, TiO2 in the rutile phase was obtained.