Theoretical Study On Trifluoroacetic Acid Adsorbed On Nonmetal And Metal Doped Anatase Surface With Density Functional

Trifluoroacetic acid (TFA) is an organic acid that endanger people’s health and ecosystems, which is difficult to be decomposed because of its high energy C-F bond. Photocatalytic degradation method is one of the most effective means. Due to the outstanding photocatalytic property, low-cost, nontoxicity and chemical stability, TiO2is considered as the heart of photocatalysis field. However, the wide intrinsic band gap of TiO2(anatase:3.2eV) only allows the absorption of the ultraviolet light (λ≤387.5nm) in the solar irradiation. It is realistic importance for the finding a photocatalyst which can catalyze the degradation of TFA in visible light and cannot bring the second pollution.In the paper, the surface action of the structures of non-metal and metal single doped and co-doped anatase TiO2, as well as adsorption TFA were investigated by Castep program which based on Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA), respectively.The structures of TFA adsorption on nonmetal (N、S、F) doped anatase TiO2(101) surface were optimized, respectively. It shows that the N/Anatase (101) surface has strong electron interaction with TFA, the C-C, C-F, O-H bonds of TFA were activated greatly, and the released energy is the highest. TFA adsorption on S/Anatase (101), as a physical adsorption, has weak electron interaction, and the released energy is less than40kJ/mol. TFA adsorption on F/Anatase (101) is a chemical adsorption, and the electron interaction is relatively weak. When TFA was degraded on the surface of the best optimized N/Anatase (101), the3d electron of Ti migrate to TFA. The reaction belongs to a reduction reaction.The electronic structure and optical absorption of different atomic fraction for Bi(1.39%、2.08%、2.17%) doped anatase TiO2were studied. It is found that the band gaps for the anatase were narrowed gradually with the increasing concentration of Bi doped, and the optical absorption intensity was increased gradually in500-700nm. The2.08%Bi is the best doping proportion. The4.17%Bi doped anatase can’t promote the separation of photogenerated electron-hole pairs effectively. The Bi doped anatase surface has little effect to degrade TFA. It is a simple physical adsorption.The structure of TFA adsorption on Bi(2.08%)/N co-doped anatase TiO2(101) surface were researched. It shows that, when the Bi is doped(Tl) on (101)surface of anatase, the structure effect to anatase is very small, and the degradation of TFA is weaker than the N-doped anatase surface. The activation of the C-C, C-F, O-H bond of TFA in the Bi doped(T2) in (101) anatase are more greater than in Bi or N single doped. The N2p electron migrates to the top of the valence band(VB). The Bi6s electron migrates to the bandgap. The band gap energy decreases from2.59eV to1.62eV, while the photocatalytic wavelength increases from478.8nm to765.4nm. When TFA was degraded on the Bi/N(T2) anatase (101) surface, the electron of the bottom surface migrates to TFA, and the reaction belongs to a reduction reaction.The electronic structures and optical absorption of Pt/N co-doped anatase were explored. It was found that the the band gap energy for the Pt/N-codoped is less than the Pt/N single doped, and the new impurity energy level between the valence band and the conduction band is made. It results in the red shift of the absorption wavelength and the separation of photogenerated electron-hole pairs effectively. The Pt/N co-doping could further improve the performance of the catalyst comparing to the Pt or N single doped.