Formation of OH Groups and Hydrogen Peroxide Molecules on the Tio2 Anatase Surface: Pseudopotential Calculations

The density functional pseudopotential simulation was carried out to study dissociation of the H2O molecule on the TiO2 anatase surface (pure and W doped). Formation and desorption of the OH groups were studied, and it was shown that the adding of tungsten into titanium dioxide leads to reduction of the desorption energy of OH groups from 6.06 eV to 4.74 eV. Creation of the hydrogen peroxide H2O2 molecules was also investigated. Substitution of Ti with W on the TiO2 anatase surface decreases the formation energy of hydrogen peroxide molecules and moves it up to the range of visible sun light. Decrease of the formation energy of free OH groups and H2O2 molecules, which are fissile oxidizers, increases their quantity in water and promotes increase in effectiveness of organic pollutants decomposition.

Study of the Non-Linearity on TiO2(0 0 1) Surface with Oxygen Defects: A First-Principles Study

First-principles plane-wave pseudopotential calculations were performed to study the energetics and electronic structures of oxygen defects on rutile TiO2(0 0 1). The influence of the material thickness on non-linearity (NL) was studied. With the increase in the thickness, the NL became stronger. Calculating the site-projected density of states by applying an external electric field showed that the NL of the bulk is due to the exchange of electrons between O 2p orbitals and Ti 3d orbitals. Finally, the influence of oxygen defects — oxygen vacancies (Vo), oxygen interstitials (Oi), and oxygen vacancies/oxygen interstitial (Vo[Formula: see text]Oi) pairs (Frenkel pair defects) — on the NL of TiO2 was studied. These results demonstrate that the band gap ([Formula: see text] of TiO2 became gradually narrower as the electric field increased. The Stark effect and defects can lead to the splitting of degenerate energy levels. Stronger electric fields increase the band splitting and reduce [Formula: see text]. With the increase in the Vo concentration, the decrease in the splitting amplitude and width of the energy level lead to weakening of the transfer of electrons between O and Ti atoms and optimizing the NL of TiO2. Therefore, the incorporation of Vo plays a significant role in improving the NL of TiO2.