Theory Study On Trifluoroacetic Acid Adsorbedon TiO₂Surface

Trifluoroacetic Acid（TFA）is the simplest of Perfluorinated Carb-Oxylic Acids. TFA, as a harmful substances affects people’s health andendangers their living, is difficult to be decomposed because of its persis-tent and bioaccumulative properties. The method and mechanism on theTFA decomposition is a hot issue. With the advantages of stable, nontox-ic, inexpensive and high catalytic activity, TiO₂was widely used in thearea of sewage treatment, degradation of organic compounds, air purifica-tion, self-cleaning and sterilization of water and so on.In the paper, surface action of the strutctures of Fe doped anataseTiO₂, rutile TiO₂and brookite TiO₂before and after, as well as adsorpti-on TFA, respectively, were investigated by Castep module （CambridgeSerial Total Energy Package） of Materials Studio program which basedon Density Functional Theory（DFT）. The spatial and electronic structureof nonmetal doped brookite TiO₂were analysed. The main contents of thepaper are as follow.First, the twelve surfaces of Anatase TiO₂（101）,（001）,（110）,（210）,Rutile TiO₂（110）,（001）,（101）,（210） and Brookite TiO₂（210）,（101）,（001）,（110）, as well as the stablest types, geometries and electronicstructures of Trifluoroacetic Acid （TFA） adsorption on TiO₂were optimi-zed with CASTEP program. It is found that the stable surface for adsorpt-ion of TFA are anatase（101）, rutile（110） and brookite （210）. In order tofind the best adsorption site, the absorption ways of TFA were calculatedin the stablest surfaces, and analysed by the charge density, density ofstates and band structure. It is found that the all absorption ways werephysical adsorption.The spatial and electronic structure of Fe doped anatase TiO₂（101）, rutile TiO₂（110）and brookite TiO₂（210） were discussed. It shows that the3d orbital of Fe inserts to the conduction band（CB） or valence band（VB）of TiO₂, which leads to the increasing width of CB or forming impurityenergy level, respectively. It may lead to the narrowing of the band gap inFe/TiO₂and the increasing of the photocataltic efficiencyies. In comparis-on with direct adsorption, the TFA adsorption on Fe/Rutile （110） and Fe-Anatase （101） crystal face are chemical adsorption, but the adsorption onFe/Bookite （210） crystal face is physical adsorption.Electronic structure of TFA adsorption on nonmetal （N，S，F） dopedbrookite TiO₂（210） before and after were researched. It shows that the2porbital of N, S inserts to the valence band（VB） of TiO₂, which leads to theincreasing width of VB. It may lead to the narrowing of the band gap inN/TiO₂and S/TiO₂. The photocatalytic efficiencyies are increased. It isfound that the2p orbital of F inserts to the valence band（VB） of TiO₂, itmay lead to the widening of the band gap in F/TiO₂. The photocatalyticefficiencyies are decreased. In comparison with the direct adsorption,theTFA adsorption on N/Brookite （210） and F/Brookite（210） crystal face arechemical adsorption, and on S/Bookite （210） crystal face is physicaladsorption.