Black TiO2(B)/anatase bicrystalline TiO2–xnanofibers with enhanced photocatalytic performance

Black TiO2(B)/anatase bicrystalline TiO2–xnanofibers were synthesized from a porous titanate derivative by calcination in H2, and were characterized using field-emission scanning electron microscopy, Raman spectroscopy, N2adsorption-desorption analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet-visible diffuse reflection spectroscopy and photoluminescence measurements. Characterization results showed that no Ti3+was present on the surface of black bicrystalline TiO2–xand oxygen vacancies were distributed in the bulk of both TiO2(B) and anatase phases. The O/Ti atom stoichiometric ratio of black bicrystalline TiO2–xwas estimated to be 1.97 from the difference of mass loss between black bicrystalline TiO2–xand white bicrystalline TiO2without oxygen vacancies. The photocatalytic activity of black bicrystalline TiO2–xwas 4.2 times higher than that of white bicrystalline TiO2and 10.5 times higher than that of anatase TiO2. The high photocatalytic activity of black bicrystalline TiO2–xwas attributed to its effective separation of electrons and holes, which may be related to the effects of both bicrystalline structure and oxygen vacancies. Black bicrystalline TiO2–xalso exhibited good photocatalytic activity after recycling ten times. The black bicrystalline TiO2–xnanofibers show potential for use in environmental and energy applications.