Preparation And Photocatalytic Properties Of Aligned TiO₂ Nanotubes

TiO2 has a unique characteristic of photoelectric conversion, its transformation efficiency is related to the size and morphology. Harmful substances can be decomposed by the nanometer sized TiO2 particles, lines, or tubes under uv or visible lights. They will make contribution to purifying environment and are filled with enormous potential in environmental protection. In the present work, aligned TiO2 nanotubes with different morphologies were prepared by adjusting the process conditions during anodic oxidation. The relationship between photocatalytic performance and morphologies of TiO2 nanotubes were discussed after investigating different morphologies and photocatalytic property of TiO2 nanotubes.First, TiO2 nanotubes were prepared by using anodic oxidation method. The influe ence of the type of electrolyte, the voltage of anodic oxidation and the time of anodi c oxidation on the surface morphologies was examined. The growing mechanism of na notubes when using the ethylene glycol solution of NH4F and NH4CI as an electrolyte was analyzed. When we use a glycol solution NH4F as the electrolyte and anodizing 30min, the diameter and the tube length of TiO2 nanotubes were increasing as the vo ltage of anodic oxidation increases. In the case of using glycol solution NH4F as the electrolyte and setting the anodic oxidation voltage to 100V, the inflence of the anodi c oxidation time on the TiO2 nanotube surface topography was observed. We found th at the nano-tube length and diameter increases with time history in a certain time. Ho wever, when the anodic oxidation reaction proceeds to 45 min, some nano-grass nan otubes appear on the surface and hinder the growth of nanotubes.With the increase o f the anodic oxidation time, the nanotubes eventually stop growing.Secondly, using the change of anodization voltage and time, we prepared the bam boo-like TiO2 nanotubes and analyzed the growth mechanism. Anodizing in an ethylen e glycol solution of NH4F, oxidizing 2min at the voltage of 120V, turning the anodi zing voltage to 20V and oxidizing 15min and then we found that the tube section wil 1 grow at a high voltage and the bamboo section will grow at a low voltage, and fin ally bamboo-like nanotubes were formed.Finally, we explored the effects of different morphologies of TiO2 nanotube on p hotocatalytic properties by the experiment of photocatalytic decomposition of formaldeh yde.Before the nano-grass appearing on the nanotube surface, the tube length and dia meter of the nanotubes.the surface area and the photocatalytic conversion rate increas ed with the increase of anodization time. While with the emergence of nano-grass, the actual reaction area decreased and the photocatalytic efficiency reduced. When the an odic oxidation voltage was set to 100V and the anodization time was set to 30min, th e photocatalytic conversion rate could achieve 89%. Compared with the single TiO2 na notubes of equal length, the bamboo-like TiO2 nanotubes will have greater surface area, and the nano-grass will not appear on its surface with the increase of oxidation time, so it has the better photocatalytic effect.