Abstract
Recently, titanium dioxide (TiO2) has been extensively used in various applications such as pigment, photocatalysis, DSSC and Li ion storage devices. In current publications, there are three well known important factors, the phase, morphology and particle size, affecting the performance of TiO2. The research is focused on the syntheses of anatase and brooktie TiO2 with various morphologies and sizes by hydrothermal method using sodium titanate as precursors, alkali metal salts as additives in different pH environment. In addition, the rutile nanowires grown on transparent conductive substrate, was synthesized with solvothermal process. The electrochromic properties of rutile TiO2 nanowires were investigated. Anatase TiO2 with various shapes were synthesized by using sodium titanate as a precursor and different alkali metal salts as additives. {101}-exposed and {301}-exposed anatase TiO2 were synthesized in LiCl and NaCl solution, respectively. The TiO2 with exposed high-index {301} facet has never been reported. The reaction proceeding in KCl solution, the anatase TiO2 with a high aspect ratio elongated along <001> direction were obtained. Anatase TiO2 with a high aspect ratio was obtained in the presence of low charge density high atomic number alkali metal ions, which are not easily absorbed by the {001} planes of anatase, so growth along <001> direction was not restrained. Moreover, the size of anatase could be adjusted by pH values of precursor solution. Reducing pH value of the precursor solution accelerated the dissolving rate of precursor, releasing large amount of nuclei for anatase TiO2, which results in small sized anatase formation. The photodegradation of methylene blue assisted by anatase TiO2 with various exposed faces, reveals that the photoactivity of anatase {101} planes is higher than that of {301} planes. Moreover, submicron-sized TiO2 with high degree of crystallinity has the better photocatalytic performance than that of nano-sized TiO2 with a large amount of defects. With respect to the DSSC fabricated from the various TiO2, the best performance was achieved by using the mixture of nano-sized and submicron-sized rod-like TiO2 as the electrode exhibiting 1.3 times larger efficiency (η = 6.9%) than that of commercial P25 (η = 5.3%). Brookite and anatase TiO2 was synthesized by using sodium titanate as a precursor in sodium fluoride aqueous solution. The ratio of brookite and anatase can be tailored by NaF concentration, and the high quantity brookite TiO2 was acquired in 1M NaF solution. Additionally, the morphology and size of brookite TiO2 can be adjusted by using various acid treated titanates. Micro-sized flower-like brookite was obtained from a weak acid treated titanate, whereas the submicron-sized urchin-like brookite was acquired from a middle acid treated titanate. When a strong acid treated titanate was used, brooktie nanorods with some anatase nanoparticles were obtained. With respect to the phase transformation of brookite with temperature, the micro-sized flower-like brookite remained the same shape and phase even at 800 ℃, but the submicron-sized urchin-like brookite transformed to rutile phase above 750 ℃. Rutile nanowires were grown along the [001] direction and perpendicular to the FTO substrate (R⊥) by solvothermal process using titanium isopropoxide as a precursor in the mixture solution of HCl and IPA. The edge length of the nanowires obtained in IPA is ten times less than that in water. Compared to P25 and rutile nanowire powder coated on FTO, R⊥ have superior electrochromic performance due to its high ionic diffusion rate along rutile [001] direction. Furthermore, a large amount of sodium cations intercalation into TiO2 was first observed at -1.0 V.