Study Of The Behaviors Of Hydrogen In Titanium Dioxide

Few researches have been devoted to effect of hydrogen on oxides which were supposed not to react with each other. Hydrogen has long been discovered to influence harmfully properties of materials in processes of metallurgical operation, acid pickling, electroplating and soldering, which has greatly stimulates research interest in microscopically form of hydrogen atoms in metals as well as their diffusion and drifting mechanisms. However, recent studies actually shows hydrogen plays subtle roles in determining electrical, magnetic and optical properties of oxides. This work mainly studies behaviors of hydrogen atoms in rutile TiO2. There exist four parts contained in this thesis:invasion of hydrogen into TiO2, existence form of hydrogen defect in TiO2, diffusion process into TiO2, and modification of TiO2due to H defects. The following conclusions are made via experimental approaches in conjunction with density functional theory (DFT) calculation.1. According to two different methods of introducing H atoms into TiO2, two different existence forms of H atoms are proposed and are studied by DFT calculation as well as by experiments and. There are mainly two possible positions for H atoms in the TiO2. First H atoms tend to occupy the sites of oxygen vacancies and second H atoms also tend to occupy the interstitial positions. Introduced hydrogen atoms during annealing process at high temperature tend to occupy oxygen vacancy site and exhibit negative chemical valence as H". Hydrogen atoms introduced by electrochemical method occupy interstitial positions in TiO2, forming weak O-H bonds with the nearby oxygen ion as H+.2. Diffusion of hydrogen atoms in TiO2mainly depends on temperature and time. We have measured hydrogen content and permeation rate in TiO2samples during annealing process in H2atmosphere at different temperatures and time. It is found that the hydrogen content in TiO2sample was increased with the increase in annealing time at the beginning and was to be stable after50hours annealing. The annealing temperature was set from200to1000℃. Hydrogen content in TiO2ceramics are higher than that in TiO2single crystals in lower temperature annealing process while the situation reversed in higher temperature annealing process. Through measuring the permeation rate of hydrogen in TiO2film, we obtained the activation energy of hydrogen penetration.3. We have researched the influence of hydrogen on physical properties of TiO2in the following three aspects:electrical properties, optical properties and its hydrophobic and hydrophilic properties. Study on the electrical properties shows that conductivity of TiO2increases after hydrogen defects are introduced into TiO2and TiO2samples are changed from insulative semiconductors to conductors. Study on optical properties shows the band structure of TiO2, especially the top of valence band, could be controlled by hydrogenation process. The band gap of TiO2can be narrowed and absorption rate of visible light was enhanced. Study on the hydrophobic and hydrophilic shows hydrogenation can enhance the hydrophobicproperties of the surface of TiO2.Our study could help to deepen understanding of hydrogen influence on electronic structure as well as physical properties of TiO2and advance application of these unique materials in the field of energy harvest, environment protection and so on. It also provides an experimental and theoretical basis for the research of effects of hydrogen on other oxide materials such as ZnO and helps applications of these oxide materials.