Structure and formation mechanism of carbon-doped titanium oxide nanotubes

碳掺杂的氧化钛纳米管是一种有前途的材料，用于几个应用，如质子交换膜燃料电池。纳米管具有高比表面积、良好的导电性和高氧化稳定性，可以在碱性溶液中通过水热法由氧化钛合成。氧化物粉末转化为多壁纳米管，典型内径为310 nm，长度可达500 µm。一个锐钛矿状结构或钛酸盐结构（H2 Ti 3 O 7）的建议的管。在应用方面，文献中报道了用各种元素掺杂所生产的管，包括用碳掺杂。碳的引入对于实现导电性至关重要。碳掺杂的常用方法是在乙炔/氮气流中进行温度处理。然而，这种方法在管上的应用导致烧结和结晶。因此，只有少量的管材可以继续使用。为了避免热后处理的缺点，TH Nürnberg开发了一种新方法。代替管材料，通过碳热处理用碳掺杂氧化钛前体粉末。随后在水热过程中合成管。管的形成过程中讨论有争议的到现在为止，但潜在的应用高度的兴趣。因此，将在不同时间步骤后从工艺中取样研究成型工艺。将对样品的形态、相含量和碳掺入进行研究。这些信息将与诸如离析物浓度、pH值、温度和持续时间等合成参数相关联。在关于形成机理和碳掺入的结果的基础上，进一步优化合成将成为可能，作为应用的先决条件。

Carbon-doped titanium oxide nanotubes are a promising material for several applications such as PEM fuel cells. The nanotubes have a high specific surface area, good electrical conductivity and, as first experiments showed, high oxidation stability.The tubes can be synthesized in alkaline solution via a hydrothermal process from titanium oxide. The oxide powder is transformed into multiwall nanotubes with typical inner diameters of 310 nm and a length up to 500 µm. An anatase-like structure or a titanate structure (H2Ti3O7) is suggested for the tubes. In connection with application, doping of as-produced tubes with various elements is reported in the literature including doping with carbon. The introduction of carbon is essential to achieve electrical conductivity. A common method for carbon doping is a temperature treatment in an acetylene/nitrogen gas flow. Application of this method on tubes leads to sintering and crystallization, however. As a result, only low amounts of tubes persist.To circumvent the disadvantages of thermal post processing, a new method was developed at TH Nürnberg. Instead of the tube material, the titanium oxide precursor powder is doped with carbon via carbothermal treatment. The tubes are synthesized in the hydrothermal process subsequently. The formation process of the tubes is discussed controversially up to now but of high interest for potential application. Therefore, the formation process will be investigated taking samples from the process after various time steps. The samples will be investigated regarding morphology, phase content and carbon incorporation. The information will be correlated with synthesis parameters like concentration of educts, pH value, temperature and duration.On the basis of the results regarding formation mechanism and carbon incorporation further optimization of the synthesis will be possible as a pre-requisite for application.