Study On Photocatalytic Degradation Of Formaldehyde With Titanium Dioxide By The First Principle

Formaldehyde, a harmful substance, affects people's health and endangers our living. It is one of the most hotspot researches to degrade Formaldehyde with catalyst and without causing the secondary pollution. TiO₂ with the advantages of stable, nontoxic, inexpensive and high catalytic activity, it was widely used in the area of management of water, degradation of organic compounds, air purification, self-cleaning, sterilization and so on.However, due to a wide band gap of TiO₂ photocatalyst, which result in a lower rate for the utilization of sunlight, the difficulties which in the experiment are how to improve the rate for utilization of light and find the most stable structure during TiO₂ adsorption CH2O. In this study, Castep module (Cambridge Serial Total Energy Package) of Materials Studio program which based on first principles was used, rutile and anatase TiO₂ was theoretically conducted in the best way of adsorption for before and after adsorption CH₂O, respectively. The spatial and electronic structure also was analysised on fluorine doped anatase TiO₂. The main contents of the paper are as follow.First, the structures of (001), (110) and (100) anatase TiO₂ crystal faces were discussed, It is found that the energy of (001) crystal face is the lowest. The structure of formaldehyde absorbed on the (001) face of anatase by six kinds of modes were optimized, the mode of formaldehyde absorbed on the (001) face of Anatase beside H-C-O is the most stable, the biggest absorption energy, and taking place chemical absorption. When this absorption was conducted, the C-H bond strength weakens, and the bond length increases, while the C-O bond strength increases, and the bond length decreases. Meantime, the overlaps of the electronic clouds between titanium and oxygen atom in neighboring layer, and between titanium and carbon atom in formaldehyde, as well as the new Ti-O and Ti-C bonds were found. The energy gap between the before and after adsorptions on anatase TiO₂(001) is decreased from 2.6 to 2.5 ev, the wave length of adsorption light is increased from 476 to 495 nm.The (001), (100) and (110) surface of rutile TiO₂ were optimized, the results indicate that the most stable surface for adsorption of formaldehyde is (110) surface, the absorption ways for CH₂O adsorption in the rutile TiO₂ (110) surface were physical absorption.The charge density and the density of states for fluorine doped anatase TiO₂ were conducted. The results indicate that, F and Ti atoms form covalent bonds after F replacing O atoms. The band gap of TiO₂ became narrow, which makes it possible to make TiO₂ in the sunlight on the absorption of visible light, improve the photocatalytic efficiency consequently.