Highly Active Preparation And Application Of Composite Hollow Titania Nanotubes Research

Photocatalysis technology is a promising “green” enviormental treatment, whichrepresent emerging environmental control option for efficient removal of chemicalpollutants. Among the various semiconductors TiO₂in the form of anatase hasattracted wide interest, due to its strong oxidizing power under UV irradiation, itschemical stability and the absence of toxicity. Recently, one dimensional TiO₂nanotubes （TNTs） have been reported that offer a unique combination of widebandgap semiconductor properties with a high surface area and precisely controlledmorphology. For the chemical synthesis of nanotubes, three general approaches havebeen developed, they are template, electrochemical and hydrothermal routes; however,the as prepared products are predominately amorphous phase that show lowphotocatalytic activity. Therefore, since their photocatlytic performance is closelyrelated to crystallinity, additional crystallization is always required for those products.Unfortunately, such materials are also prone to collapse during the calcination process.As a result, the tubular morphology is destroyed, with a significant decrease in SBETand pore volume.In order to overcome this problem, by using a unique chemicalmorphology-freezing method, we obtain TiO₂nanotubes with perfect tubularmorphology. In this paper, the nanotube walls （about1to2nm thick）, are chemically frozen by filling the nanotubes first with carbon then coating with a silica sheath（TNTs@C@SiO₂）. After calcination, open-ended nanotubes （TiNT@@SiO₂） areobtained, with perfect tubular morphology and high crystalline. The effect ofhydrothermal reaction and calcination temperature on morphology and crystalline ofTNTs@C@SiO₂was discussed in details, and the best reaction condition forTiNT@@SiO₂sample with the highest photocatalytic activity was determined at9hours for hydrothermal reaction and at550°C for2hours for following calcination.The sample shows the highest photoactivity of all the samples, which is2timeshigher than that of TiO₂nanorods, and is4times higher than TiO₂nanoparticles （P-25）.Based on the above works, using as prepared TiO₂nanotubes as nanotempletes,under UV light irradiation, only the inner TiO₂surface can photoreduce an H2PtCl6precursor solution to Pt nanoparticles, even Pt nanorods with fine controlled length inthe tube inner channel. Photocatalytic H2-production experiments prove that themethod can efficiently improve the catalytic activity by increasing the ultimateeffective load of Pt. To expose the inside Pt nanoparticles/nanowires, the tubularnanocomposites are etched and removed by HF treatment. Pt nanoparticle/nanowireswith uniform diameter were obtained, which provides a novel template method forpreparing metallic nanoparticles/nanowires.