Studies On Ordered Structure Of Porous Nanocrystalline TiO₂ Films Prepared By Sol-Gel Process

Nanocrystalline TiO2 is an important oxide semiconductor material with direct and wide bandgap, excellent optical, electrical and chemical properties. Recently, research work on the photoelectrochemical properties and functional characteristics of nanocrystalline TiO2 porous films have attracted much attention because these films have a relatively high porosity and specific surface area, and are easy modified with organic functional molecules and semiconductor ultrafine particles, which are desired for many applications, such as solar energy converters, optoelectronic devices and photocatalysts.Up to now, TiO2 porous films have been prepared by various methods. Compared with other methods, the sol-gel method has many prominent advantages, such as simple and convenient process, lower requirement for processing equipments, stoichiometric ratio being easily controlled and large area coating. Additionally, adding organic surfactants (eg. CTAB, PEG) into the sols are novel ways to obtain ordered porous TiO2 films, which is based on the mechanism of phase separation. Using hard templates are also efficient means to prepare inverted TiO2 porous films and TiO2 nanotubes. In this dissertation, research works were focused on these aspects.Ti(OBu)4 was adopted as titanium resource, and cetyltrimethylammonium bromide(CTAB) as cation surfactant was added into the sol. The results showed that pore diameter of TiO2 porous films could be changed from 30nm to 400nm by adjusting CTAB concentration to promote phase separation. Furthermore, it significantly improved the specific surface area of TiO2 porous films by adding alkane into the sol, and the maximum value of specific surface area reached 91.05m2/g. Mixed n-heptanol and ethanol was used as a novel solvent system to prepare porous TiO2 films with highly ordered network structure, in which Ti(OBu)4 was used as the starting material and polyethylene glycol (PEG) was used to realize phase separation. The porous TiO2 film with high pore density and well ordering was obtained by using mixed template of PEG(2000) and PEG(4000) , and its specific surface area was 88.4m2/g.The inverted TiO2 porous films were prepared by using SiO2 spheres colloidal crystal templates. In this experiment, ultrasonic-assisted basic etching was employed in removal of silica spheres templates, and three-dimensionally ordered porous TiO2 films with over 20 layers thickness could be obtained.The preparation of ordered TiO2 nanotube was carried out by sol-dipping method using ZnO rod crystal array as template. The study indicated that suitable concentration of titanium precursor sol was 0.4mol/L~0.6 mol/L, and the appropriate concentration of hydrochloric acid (HCl) used for the etching was 0.3mol/L. The citric acid etching process for removing ZnO rod crystal templates displayed better effects.