Studies On Hydrothermal Synthesis Of Nanosized Titanium Dioxide With Different Crystal Structures And Their Photocatalytic Activities

Titanium dioxide has wide application fields as an important inorganic functional material including storing and utilizing solar energy, photovoltaic conversion, chromatic change by light, photocatalytic degradation to various pollutants and so on. So there have been focused on the preparation, phase transformation and catalytic performance of nanosized powders, films and doped composites of TiO₂ via physical and chemical methods. Currently, it is received more and more attentions for the synthesis and study of nanosized TiO₂ with different crystal structures and their derivates such as nanotube, nanorod and nanowire by using hydrothermal or solvothermal method.In this paper, it is found that the pure rutile and mixed crystallite of anatase and rutile with different ratio can be synthesized under hydrothermal and solvothermal conditions using water and alcohol with different carbon numbers as solvent. It is noted that anatase gradually transformed into rutile increasing carbon number of alcohol under alcohol-thermal conditions. It may be correlated with the variety of pH values arisen from the steric effect of. carbon chains of alcohol on the hydrolysis reaction of precursor. The mixed crystallite consisting of anatase (80.5%) and rutile (19.5%) has the best photocatalytic activity using methanol as solvent. TiO₂ is gradually transformed from anatase into rutile while increasing the amount of hexamethylene tetramine (HMT) in the methanol solvent. Consequently, rutile transformed into brookite up to the pH value of 10 and brookite became more while continuously increasing the amount of HMT. So it is concluded that anatase is easier to form at lower pH value, but rutile at higher pH value. Ascent of base strength from increase of pressure can promote the formation of brookite. The mixed crystallite consisting of brookite and anatase has the best photocatalytic activity in the all samples. That anatase gradually transforming into rutile occurred as elevating temperature in the methanol solvent. It indicated that rutile with thermodynamic stability is prone to form at higher temperature. The relationship between phase composition of TiO₂ and its photocatalytic activity is as following: Mixed crystallite (anatase+brookite) > Mixed crystallite (anatase+rutile) > Anatase > Rutile.In this thesis, the TiO₂/ZrP composite catalyst has been also discussed. The TiO₂/ZrP and Ag-TiO₂/ZrP composite catalyst has been synthesized successfully, and we find that the Ag-TiO₂/ZrP composite has the higher photocatalytic activity.And the TiO₂ nanotube has been also studied. The diameter of obtained TiO₂ nanotube was about 10nm and the length is in the range of 500nm～1μm. Ag- TiO₂ nanotube is also synthesized, and we find that the Ag- TiO₂ nanotube has the higher photocatalytic activity. By comparing the photocatalytic activity of different TiO₂ nanotube synthesized with different raw material amount of TiO₂, we found that the photocatalytic activity of TiO₂ nanotube increased with the increase of raw material amount of TiO₂.