Preparation And Properties Of Nonmetal Doped Nano-sized TiO₂ With Visible Light Response

TiO₂ is most frequently employed owing to its advantages,such as high photocatalytic activity,structural stability,low cost and non toxicity.Due to its large band gap(3.20eV for anatase),titania could be only activated by UV light,which occupy only about 3-5%in the solar light.And it is difficult to control the proportion of rutile and anatase phase.Moreover, the sizes of titania nanocrystal become bigger and resulted in poor photocatalytic properties when it was used in the environment of high temperature.In order to sovle these problems, many researchers paid their much attention to develop TiO₂ photocatalysts.In this paper,a series of TiO₂ photocatalysts were prepared using reagent grade titanium tetrachloride(TiCl₄) as raw material by a simple hydrolysis method.TiO₂ with small particle sizes,cotrollable structure,high phase stability,visible-light photocatalytic activity were prepared.The photocatalysts were characterized by X-ray diffraction(XRD) analysis, transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FT-IR), UV-vis diffuse reflectance spectrophotometer(UV-Vis DRS),X-ray photoelectron spectroscopy(XPS),and Ultraviolet Raman spectropy(UV-Raman).Phosphor,sulfur and silica doped TiO₂ nanocrystals were synthesized using NaH₂PO₄, Na₂SO₄,Na₂SiO₃ as P,S,Si source respectively.XRD,TEM were employed in the influence analysis of different dopant and dopant amount on particle size and phase composition. UV-Vis was used to analyze the absorption spectra of as-prepared pure TiO₂ and P,S,Si doped TiO₂;XPS was employed to analyze the chemical states of doping P,S and Si on TiO₂ surface and in bulk phase.It shows that P and S dopant is helpful to form anatase phase,and there is also a linear relationship between the dopant amount and the weight ratios of anatase phase.The anatase particles prepared with NaH₂PO₄ show far more enhanced phase stability than the ordinary titania.The phase transformation from anatase to rutile was retarded to 1000℃,which is about 400℃higher than pure titania powders.S-doped TiO₂ are spherical nanoparticles with homogeneous distribution and the addition of S can evidently reduce particle sizes of the sample.The addition of silica into titania is aslo helpful to form anatase content in the sample.The Si-doped TiO₂ we prepared were a series of nanoscale mixed crystal TiO₂ and the grain size in the Si-doped TiO₂ is smaller than the pure TiO₂.It was found that Ti-O-S and Ti-O-Si band were formed.More importantly the dopant all play a key role in expanding the adsorption to visible region.Methyl orange was chosen as the representative of organic pollutants to investigate the photocatalytic activity of the as-prepared pure nanosized TiO₂ and P-doped,S-doped, Si-doped nanosized TiO₂ under irradiation of UV light source and visible LED light source.It shows that doped TiO₂ are superior to the pure TiO₂ under ultraviolet irradiation,most of the doped samples are better than Degussa P25.The 0.8%P-TiO₂,0.8%S-TiO₂ and 0.6%Si-TiO₂ samples exhibited the higher photocatalytic efficiency and the final degradation rate were found to be 96.9%,96.1%and 94.5%within 90 min,while undoped TiO₂ and the Degussa P25 have shown 54.9%and 75.0%degradation rate at the same condition.The doped TiO₂ samples demonstrate considerably high photoactivity under low-power LED light irradiation, while the Degussa P25 and undoped TiO₂ have nearly no activity at all under visible light irradiation.The optimum samples for higher photocatalytic properties were 0.8%P-TiO₂, 0.8%S-TiO₂ and 0.6%Si-TiO₂ sample and the final degradation rate of 0.8%P-TiO₂, 0.8%S-TiO₂ and 0.6%Si-TiO₂ sample were found to be 94.5%,79.5%,82.8%at 4h.It suggested that a best doping concentration exists for every dopant and the possible mechanism of doped TiO₂ for the visible-light activity was discussed.