Synthesis And Application Research Of Single Crystalline TiO₂ Nanostructure

TiO₂, with a wide direct band gap is an important semiconducting material, which is environmentally Friendly, and abundant in resources. TiO₂ nanocrystalline is widely used in highly-efficient photocatalytic, dye-sensitized solar cells, sensors, and so forth. In this aticle, TiO₂ nano-flower and nanowire arrays were prepared by hydrothermal method. Then the discipline of technological conditions's influence in TiO₂ nano-flower and nanowire bundle arrays film was studied systematically. Also, the photoelectricity conversion perfirmance, photocatalytic performance and field emission performance were studied. The contents are as follows:Vertically aligned single-crystalline TiO₂ nano-flower and nanowire bundle arrays were synthesized on transparent conductive fluorine-doped tin oxide (FTO) substrates by hydrothermal method with the precursors of hydrochloric acid, tetrabutyl titanate, and deionized water. TiO₂ nanowire bundle arrays were prepared, when the FTO was layed vertical or sloping beyond the wall of super high pressure teflon reaction pot, and TiO₂ nano-flowers made up of nanorods with flat tetragonal crystallographic planes were prepared, when the FTO was layed horizontal in the wall of super high pressure teflon reaction pot.The structure and mophology of TiO₂ nanocrystallines have been analyzed by scanning electron microscope(SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results revealed that the TiO₂ nanowire bundle arrays prepared on FTO were rutile, and comformed with the single crystalline nanowire whose diameter is between 4～6 nm. The TiO₂ nanowire grew firstly along the crystal plane of (110), the distance of which was 0.325nm. The structure of nanorod of TiO₂ nano-flower was as same as the nanowire of TiO₂ nanowire bundle arrays.The structure and mophology of TiO₂ nanowire bundle arrays and nano-flower influenced by the density of tetrabutyl titanate, the value of PH of precursor,reaction time, and so forth was studied in this aticle.The results show that as the density of tetrabutyl titanate increases, the diameter of TiO₂ nanowire bundle arrays increases and the amount of nanowire in each area; and that the average diameter of nanowire decreased from 230nm to 10nm and the density increased from 16/μm2 to 68/μm2, as the amount of hydrochloric acid increased; and that the TiO₂ nanowire bundle arrays grew slower and slower as the time expanded, for which, the length of nanowire was 4.1μm, when growing 16h later, and it wouldn't grew any longer after 16h.The right density of hydrochloric acid was the inportant factor in the growth of TiO₂ nanowire bundle arrays. In the hydrothermal reaction, hydrochloric acid is believed to play a dual role here:(1) With the formation of TiO₂ nanocrystal, the Cl- ion can selectively adsorb onto the (110) crystal plane and suppress further growth of this plane, resulting in anisotropic growth in the [001] direction. Thus, according to the crystal-symmetry and surface-energy considerations. (2) It regulates the value of PH, slows down hydrolysis of titanium butoxide and restricts the supply of the growth units.the presence of an abundant amount of H+ from the hydrochloric acid significantly slows down hydrolysis of titanium butoxide and restricts the supply of the growth units. As the amount of hydrochloric acid raises, hydrolysis of titanium butoxide and the growth of nanowire slows down, the diameter of nanowire becomes smaller.The dye-sensitized nanocrystalline solar cell is fabricated with the TiO₂ nanocrystal as the anode, and the influence of length and diameterof nanowire in the performance of DSSCs was studied. The highest photoconversion efficiency is 2.15%. The photocatalytic effects of TiO₂ nanocrystal in rhodamine B and methyl orange under visible light indicates as folows:for rhodamine B, the photocatalytic effects of TiO₂ nanowire bundle arrays is stronger than TiO₂ nano-flower, and the diameter smaller, its effects stronger; for methyl orange the photocatalytic effects of TiO₂ nanowire bundle arrays is weaker than TiO₂ nano-flower. For the field emission performance of TiO₂ nanowire bundle arrays, it shows a turn-on field of 5.7 V/m and a threshold field of 9.5 V/m at a current density of 10 mA/cm2 and indicates good stability of field emission. The low synthesis temperature and good field emission performance show that the TiO₂ nanowire bundle arrays have good potential application in field emission cold cathode devices.