Insight into the formation of carbon-doped titanate nanotubes

The formation of carbon-doped titanate nanotubes has been studied by using a simplified synthesis approach and extracting samples at different stages during the formation. The hydrothermal synthesis was conducted in a rotary evaporator with a PFA flask under ambient conditions. The resulting samples have been analyzed regarding their morphology, structure and surface area using X-ray diffraction, scanning electron microscopy and gas adsorption measurements. The results show the formation of high surface area nanosheets after a synthesis time as short as 2 h. Even though the surface area at this stage has already reached 212 m 2 /g, a change in morphology to elongated structures is not observed until 4 h of synthesis, suggesting the formation of the nanotubes during this phase. From that moment on, the d 100 value, corresponding to the layer spacing between the nanotube layers, is further decreasing. Additionally, the formation of bundles with longer synthesis times was observed. This effect is discussed to be caused by a self-assembly process of nanotubes assisted by the continuous rotation of the flask in the rotary evaporator. The analysis of the final sample after 24 h revealed remaining carbon shells from the precursor powder. The presence of Ti O C bonds observed by X-ray photoelectron spectroscopy proved the incorporation of carbon in the nanotube structure. • Analysis of the titanate nanotube formation during a synthesis inside a PFA flask • Fast formation of layered structure followed by roll-up into nanotubes during synthesis • Ostwald ripening and oriented attachment mechanisms causing elongation of nanotubes • Ti O C bond observed in XPS proving the incorporation of carbon in the nanotubes