| Due to nontoxicity, chemical stability, cheapness, and excellent photocatalytic degradation of various refractory organic compounds, titanium dioxide (TiO2) has been considered as the most promising photocatalyst for treating contaminated water and polluted air. However, anatase TiO2 can only be induced by ultraviolet (UV) light with the wavelength less than 387.5 nm. Furthermore, TiO2 nanoparticles have a tendency to agglomerate, precipitate, and flow away in liquid suspensions. Therefore, doping modification and immobilization of TiO2 have been widely investigated.In this study, titanium oxoacetate/polyacrylonitrile [TiO(OAc)2/PAN] hybrid nanofibers were fabricated by electrospinning technique. A novel nitrogen-doped TiO2/carbon nanofibers (TiO2-xNx/CNFs) heterostructured photocatalyst was also prepared by subsequent thermal stabilization, ammonification, and calcination. Changes in the morphology, crystal structure, and chemical composition of nanofibers were investigated with TEM, FESEM, XRD, FT-IR, EDX and XPS, respectively. Light response and photocatalytic activity of TiO2-xNx/CNFs were characterized by UV-Vis absorbance spectra and photocatalytic degradation of methylene blue (MB) in aqueous solution under different light irradiations. The results showed that TiO(OAc)2 alignedalong the as-spun PAN nanofibers uniformly and regularly, and led to the reduce of nanofiber diameter from 350～500 nm to 250～400 nm. After the thermal stabilization, the as-spun TiO(OAc)2/PAN nanofibers became smoother, and the average diameter was decreased to 200～300 nm because of physical and chemical shrinkages. The diameter of as-stabilized nanofibers was decreased further to 100～250 nm via NH4OH aqueous solution pretreatment and calcination. After the calcination at 400℃, amorphous titanic ammoniates were converted to anatase TiO2-xNx nanoparticles and transferred to the external surfaces of nanofibers. After calcined at 600℃, about 25 wt. % of anatase TiO2-xNx nanoparticles, with the average grain size of 20 nm, were interspersed on the surfaces of highly-aligned CNFs uniformly. When the temperature was increased to 800℃, abundant micropores and mesopores were formed on the external surfaces of CNFs. However, all the anatase TiO2-xNx would be transformed to rutile TiO2-xNx without photocatalytic activity, and the average grain size was increased to 30～50 nm. Due to the remarkable wider absorbance spectra and enhanced photocatalytic activity of TiO2-xNx, in which the threshold of TiO2 was red-shifted from 390 nm to 500 nm, and the considerable BET specific surface area (130 m2/g), total pore volume (0.34 cm3/g) and adsorption capacity of nanofibers, the TiO2-xNx/CNFs heterostructured photocatalyst calcined at 600℃exhibited excellent photocatalytic activity under UV and visible-light irradiations, and showed much higher photocatalytic efficiency than that of TiO2/CNFs, TiO2-xNx and TiO2 powders.
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