Preparation And Photocatalytic Properities Of Nb-doped/Self-doped TiO₂

TiO2 represents an effective photocatalyst for environmental purification and for solar energy conversation. Improving the utilization of solar light is one of the focus issues for TiO2 photocatalysis presently. Dopant could adjust the bandgap of TiO2 by introduce bandgap states. Further, the absorption of TiO2 could be extended to visible light area and the utilization of solar energy could be enhanced. In the present paper, we use Nb5+ cationdoped TiO2 and self-dopedTiO2 as research object. And a variety of preparation methods was used to obtain different manners of dopant. The prepared method would affect the formation of defects and the light absorption properties of TiO2. Finally, we struggled to explore the approach to enhance the visible / solar light photocatalytic activity.Visible light responsive Nb-doped TiO2 microspheres were synthesised by ultrasonic spray pyrolysis of Ti-peroxide precursor. The photo-absorption threshold of TiO2 was red-shifted to 580 nm after Nb dopant. Photocatalytic tests of the degradation of gaseous acetaldehyde demonstrate that the Nb-doped TiO2 products exhibit higher photocatalytic activity than that of pristine TiO2 under visible light. However, the material demonstrates an inferior acetaldehyde mineralizationto CO2 performance under visible light and a lower photocatalytic activity under simulated solar light. Correlation between the increased surface photovoltage(SPV) responses in the visible light region illustrates that surface peroxo states promote charge separation, but, surface peroxo states decrease oxidation capacity of photogenerated holes, as well. Furthermore, enhanced photoluminescence in the near-infrared region and reduced SPV response in the UV region as well as photochromic phenomena indicate that Ti3+ defects serve as charge carrier recombination centers, which are responsible for the decreased photocatalytic activity.Nb-doped TiN film was preparaed by magnetronsputtering. Andthe TiN film was annealed in the ambient condition at 400-800?C to obtain Nb-doped TiO2 film. After annealing, we could obtainhighcrystalline qualityNb-doped TiO2(anatase) film with [001] orientation. Comparing with the pristineTiO2, Nb-doped TiO2 processes smaller crystal particlefor film constitution, and increased carrier concentration. Finally, Nb-doped TiO2 exhibited an increased photocatalyticmineralizationof acetaldehyde and significantly enhanced photocatalytic self-cleaning properties.Bulk doping into TiO2 with foreign element would result strong recombination of photogenerated carries. Simple ethanol impregnation followed with mild heat treatment(150-300oC) can render TiO2 nanoparticles colored and enhance visible light photocatalytic activity. The photocatalytic activity for β-naphthol and rhodamine B(RhB) degradation were observed to be dependent on heat-treatment temperature, and the highest activity as well as the most coloration was obtained at temperatures around 200 to 250 oC. Comprehensive analyses investigations as well as first-principle density functional calculation suggest that the simple ethanol impregnation treatment leads to the generation of oxygen vacancy on TiO2 surface which should be responsible for the coloration and enhanced photocatalytic activity.An visible-light-sensitive Fe(III)-species-grafted TiO2-xphotocatalyst(denoted as Fe(III)/TiO2-x) has been prepared via a facileimpregnationmethod. It exhibited higher performance than pristine TiO2 or oxygen defective TiO2-x in visible-light photocatalyticdegradation of β-naphthol. And, β-naphthol was degradated to 80% and 72% within 90 min for the pristine TiO2 and TiO2 with surface oxygen vacancies, under visible light irradiation, while, 31% of the initial β-naphthol concentration was remained in the Fe(III) species grafted sample under the same condition.The high activity of Fe(III)-species-grafted TiO2-xis derived from the surface grafted Fe(III) ions co-catalysts and the generation of surface oxygen vacancies, asthe surface oxygen vacancy produced energy levels below the conduction band of TiO2, which match well with the potential of Fe3+/Fe2+ redox couple in the surface grafted Fe(III) ions. Electrons in the surfacegrafted Fe(III) ions efficiently cause multi-electron reduction of adsorbed oxygen molecules to achieve high photocatalytic activity.