Study Of The Mechanism And Doping Effects On The Sol-derived TiO₂ Nanocrystallines At Low Temperature

Nano-scaled TiO₂ materials are expected to play an important role in helping solve many serious environmental and pollution challenges due to its good characteristics of powerful oxidation strength,high chemical stability,and nontoxicity.In the present work,sol method was employed to prepare the TiO₂-based nanocrystallines at low temperature.The formation mechanism of sol-derived TiO₂-based nanocrystallines was studied.Doping was performed to largen the photoresponse range and improves the photocatalytic activity of TiO₂.The structure and photocatalysis mechanism was introduced firstly.Achievments about TiO₂ nanomaterial were summarized.The study of sol-derived TiO₂-based nanocrystallines at low temperature was carried.TiO₂,vanadium doped TiO₂ nanocrystalline and Ag nanoparticle/TiO₂ nanocrystalline composite were prepared by sol method with excessive water.X-Ray diffraction,transmission electron microscopy,scanning electron microscopy,X-ray photoelectron spectroscopy,energy dispersive spectometer,and optical spectra were used to understand the crystallization behavior,microstructure,optical property and photocatalytic activity of TiO₂-based nanocrystallines.Following is the main results.Tetrabutyl titanate was chosen as titanium precursor.TiO₂ nanocrystallines were prepared by sol method at room temperature.The parameter range of molar ratio of water to tetrabutyl titanate and pH was≥40 and≤3,respectively.TiO₂ nanocrystallines showed bi-phase antase and brookite.The crystal particle was 5-6 nm.The formation mechanism is as follows.The fast hydrolysis reaction of tetrabutyl titanate in the excessive water results in the formation of original nuclei or basic units of[TiO₆]octahedra.Subsequently,under enough reaction time,the condensation occurs at interface.These basic units arrange and assemble with each other,result in the formation of crystal structure forms.The photocatalytic activity of as-prepared TiO₂ nanocrystalline is greater than that of P25(Degussa).Vanadium(â…£) oxyacetyl acetonate was used as vanadium source.Vanadium doped TiO₂ nanocrystallines were prepared by sol method at room temperature.The parameter range of molar ratio of water to tetrabutyl titanate and pH was≥200 and≤3, respectively.Vanadium ions are incorporated in the TiO₂ crystal and solid solution Ti_1-xV_xO₂ forms.TiO₂ nanocrystallines showed bi-phase antase and brookite when vanadium content was less than 0.15.Brookite decreases continuously with increasing vanadium content and doesn't form at all when vanadium content is 0.15. The effect of vanadium doping on the formation of vanadium doped TiO₂ nanocrystallines is as follows.In sol system,[TiO₆]and[VO₆]octahedra form simultaneously,and arrange randomly.Under low temperature condition the metastable phase forms.The crystallinity and particle size decrease continuously with increasing vanadium content because acetyl acetone groups retard the hydrolysis of titanium alkoxide.The amount of acetyl acetone groups increases with increasing x,the retarding effect also increases.As-obtained vanadium doped TiO₂ nanocrystallines can photo-degrade methyl orange under daylight.Silver nitrate was used as Ag source.Ag nanoparticle/TiO₂ nanocrystalline composite were prepared by sol method at room temperature.Thus prepared Ag/TiO₂ nanocomposites consisted of metallic Ag and crystal TiO₂ nanoparticles. DEA was necessary to the formation of metallic Ag particles.The size of TiO₂ particles was 5-6 nm,and similar in all Ag/TiO₂ nanocomposites.The size of Ag nanoparticles increased with the increasing Ag content.When molar content of Ag was 0.18,the Ag crystal size was about 6 nm.The agglomerating of Ag crystal particle occurs with the increasing Ag content.The size distribution of Ag particle broadens.As-prepared Ag nanoparticle/TiO₂ nanocrystalline composite Ag/TiO₂ nanocomposite was proven to have better photocatalytic activities than pure TiO₂ obtained at the same condition.TiO₂,vanadium doped TiO₂ nanocrystalline and Ag nanoparticle/TiO₂ nanocrystalline composite films were prepared by spin-coating method using the corresponding sol obtained at room temperature.All film samples showed TiO₂ crystalline.But crystallinity was weak.At the same time,Ag appeared in Ag nanoparticle/TiO₂ nanocrystalline composite film.Either UV or daylight irradiation, the photocatalytic activity of vanadium doped TiO₂ nanocrystalline film was greater than that of Ag nanoparticle/TiO₂ nanocrystalline composite film,and Ag nanoparticle/TiO₂ nanocrystalline composite film was greater than TiO₂ nanocrystalline film.