The Preparation, Characterization And Photocatalytic Performance Of TiO₂ Nanotubes

As a type of environmentally and friendly functional material, TiO₂ nanomaterials had attracted much attention due to the non-toxic, cheap raw materials, and strong chemical stability. TiO₂ nanotubes had become one of research hotspots in recent years because of the special tubular structure and larger specific surface area compared with other TiO₂ nanostructures. Therefore, it had a better prospect in photocatalysis, solar cells, sensor, the application of biological medicine and other fields. Hydrothermal method, with the advantages of low cost, simple operation, was one of the most commonly used methods to prepare one-dimensional TiO₂ nanomaterials. In this work, we investigated the affection of hydrothermal parameters on the performance of TiO₂ nanotubes. Base on this basis, we also optimized the parameters of hydrothermal synthesis process for TiO₂ nanotubes. In addition, we also studied the formation mechanism of TiO₂ nanotubes. The properties of as-prepared products were characterized by XRD, BET, TEM, UV-vis adsorption, PL and photoelectrochemistry testing. The photocatalytic activity was evaluated by photocatalytic hydrogen production. In specific, the research contents were as follows:（1） The TiO₂ nanotube（ TNT） was prepared by hydrothermal method, using P25 TiO₂ as raw materials. By single factor control method, this paper mainly investigated the influence of hydrothermal process conditions such as lye concentration, lye volume, thermal response time, dosage of raw material P25 TiO₂ and the times of alkali liquor circulation. The results showed that TiO₂ nanotubes prepared with NaOH（ 110 m L, 10 M） and 1.5 g P25 TiO₂ dicating 48 h at 150 ℃had optimal performance. The photocatalytic activity of TiO₂ nanomaterials prepared respectively by reducing lye concentration, decreasing lye volume, shortening hydrothermal response time and increasing the raw material P25 TiO₂ was dropped, and when the lye concentration decreased to 5 M, samples included most of broken nanotubes and some particles. And when lye used two times, nanotubes formed were irregular and the photocatalytic activity declined. The results proved that although above-mentioned preparation process parameters adjustment of TiO₂ nanotubes could reduce the preparation cost in some degree, it was unfavorably to form nanotubes with regular shape and the same photocatalytic activity with previous.（2） It was difficult on the technology to directly observe the morphology of intermediate during hydrothermal response process due to the high temperature and high pressure conditions. Therefore, whether the formation mechanism of TiO₂ nanotubes was in the hydrothermal process or proton exchange process had been controversially since the hydrothermal preparation of TiO₂ nanotubes was reported in 1988. In this work, we investigated the influence of mechanical force in the process of proton exchange to product morphology using the sodium titanate prepared by the same hydrothermal response condition as raw materials. Research finding that pure titanate nanotubes were gotten when the pickling stirring speed was 0 r/min; the tubular structure declined constantly and nano banded structure was increasing with the increase of the pickling stirring speed. When pickling stirring speed increased to 600 r/min, nanotubes almost disappeared, titanate nanobelts became more and more normal. It showed that the acid treatment process had a vital influence for the morphology formation of hydrothermal product, at the same time, the result also suggested indirectly that the formation process of TiO₂ nanotubes was proton exchange process at room temperature, rather than the hydrothermal process with high temperature and high pressure conditions.