Low-temperature Synthesis, Structure Characterization And Properties Of Nonmetal-doped TiO₂ Powders And Films

Since Fijishima found out that hydrogen could be generated from water by TiO₂ electrode in 1972,TiO₂ photocatalyst has been widely studied. Up to now, TiO₂-based semiconducting photocatalysis technology has been shown to be potentially advantageous for environmental remediation as it can lead to mineralization of pollutants with the use of light as the energy source. However, the wide application of TiO₂ as photocatalyst is hampered due to several typical deficiencies. One of its deficiencies is that TiO₂ can work only under ultraviolet (UV) light (wavelengthλ<387.5 nm) due to its wide bandgap of 3.2 eV, which means only 4-6% of the incoming solar energy on the earth surface can be utilized.Many attempts have been made to improve the optical response of TiO₂ under visible light excitation. Among them the doping of TiO₂ with nonmetal is an effective approach. However, their photocatalytic activity must be improved. Based on the development of nonmetal-doped and codoped TiO₂ in the world, this dissertation presents some effective routes for preparation of N-doped, C-dopoed and F-N-, S-N-codoped TiO₂ photocatalysts. The as-prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption/desorption measurements (BET), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-vis optical measurements. The photocatalytic activity of the doped and codoped TiO₂ photocatalysts was evaluated by the degradation of methyl orange (MO) under visible light irradiation. The main contents of this dissertation are listed as follows:(1) Anatase F-N-codoped TiO₂ photocatalysts were prepared by a chemical process at low temperature using TiCl₄ and NH₄F as titanium and fluorine, nitrogen sources, respectively. The effects of NH₄F/TiO₂ molar ratio, synthesis temperatures and addition of surfactant CTAB on the structure and photocatalytic activity of codoped TiO₂ photocatalysts were systematically discussed. The F-N-codoping could extend the absorbance spectra of TiO₂ into visible region up to 620 nm. The increasing dosage of surfactant CTAB not only enhanced the visible absorption ability but also produced more typical mesoporous structure. The results of degradation of MO solution showed that the F-N-codoped TiO₂ photocatalysts exhibited much higher visible-light-induced catalytic activities than that of Degussa P25 and the as-prepared pure TiO₂.(2)N-doped and S-N-codoped TiO₂ photocatalysts were prepared by a chemical process at low temperature using TiCl₄ and thiourea as titanium, nitrogen and sulfur sources, respectively. The N-doping and N-S-codoping extended the absorbance spectra of TiO₂ into visible region up to 570 nm. Different dosages of thiourea and synthesis temperatures affected the structure and properties of as-prepared samples. The N-S-codoped TiO₂ prepared at 40℃exhibited the highest visible-light-induced activity, which was much higher than that of pure TiO₂ and Degussa P25 TiO₂ photocatalysts.(3)The visible-light-activated C-doped anatase TiO₂ sol, powders and films have been synthesized from TiCl₄ and carbonic ink by using a sol-gel route. The obtained semitransparent C-doped anatase TiO₂ sol can maintain homogeneous dispersion for more than two years without sedimentation and delamination phenomena. The annealing temperature affected the structure and photocatalytic activity of the as-prepared samples.The C-doped TiO₂ films exhibited much higher photocatalytic activities than that of pure TiO₂ film prepared at the same conditions.(4)C-modified TiO₂ films have been deposited on slide glass substrates by magnetron reactive co-sputtering using titanium and graphite as targets. The oxygen partial pressure and R.F. power affected the surface structure and wettability of C-modified TiO₂ films. The as-prepared film structure transferred from rutile-anatase composite to anatase phase with the increasing oxygen partial pressure. The wettability of C-modified film prepared at the oxygen partial pressure of 0.05 Pa showed high hydrophobic properties.