Hydrothermal Synthsis And Photocatalytic Activity Of TiO₂ Nanotube

In this paper, TiO₂ nanotube was prepared by hydrothermal method with TiO₂ powder and KOH solution. The effects of reaction temperature and time were studied on the structure and morphology of the samples by characterizing with powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). And the formation mechanism and conditions of TiO₂ nanotubes were investigated. Nitride calcination was used to treat TiO₂ nanotubes, finaly the N-doped TiO₂ nanotube was obtained successfully. The N doping mechanism and optical absorption were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectrophotometry and UV-Vis absorption spectroscopy. At last, N-doped TiO₂ nanotubes was applied for quick determination of Chemical Oxidation Demard (COD).Comparing samples prepared at different temperature for same time, it was found that the anatase was obtained easily at low temperature and the rutile was obtained easily at high temperature; nanotubes could not be formed completely at too low temperature, while the structure of nanotubes would be broken up at too high temperature; with increasing temperature, the TiO₂ nanotube grew wider. The best temperature rang was from 130℃to 160℃. When the reaction temperature was increased to 190℃, the sample composed was burnt out and was not tubular structure anymore. A very long time of hydrothermal reaction, the nanotube may change to nanorod.A general formation mechanism of TiO₂ nanotubes was proposed in terms of the detailed observation of the products via characterizing the microstructure and morphology of samples. The overall formation can be summarized with three successive steps: 1. Layeded TiO₂ formation; 2. Formation of nanotube via trititanate splitting and multilayer scrolling process of nano-planes around the c axis. 3. Lengthing process.N-doped TiO₂ nanotube with different N doption were synthesized by varying the ratio of the amount TiO₂ nanotube to that of ammonia. The results showed that the scrytal coefficient was different with standard data. So it was proposed that the variation was caused by N doption. Moreover, the replacement of N to O in TiO₂ lattice resulted in narrowing the energy gap, and increasing shine optical absorption.As a type of high efficient photocatalyst, TiO₂ nanotube was applied to determine COD of waste water. When COD range from 3 to 10, the COD was in a linear relation with absorbance change. The limit was 0.1mg/L.