Carbon-doped titania was fabricated via carbothermal treatment in nitrogen–acetylene gas flow and further used as a precursor for multiwalled titanate nanotube (TNT) synthesis via alkaline hydrothermal route. Investigation of the reaction products after hydrothermal treatment of carbon-doped titania using Transmission electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller method shows the successful formation of TNTs. The presence of carbon was proved although the type of incorporation could not be certified. All samples show approximately the same carbon content before and after hydrothermal treatment. An increasing pretreatment temperature of titania precursor powders yields more secondary products in the nanotube samples, indicating lower reactivity of the titanium oxycarbide phase during hydrothermal treatment. In this study, TNTs with 6 wt% carbon and with the highest specific surface area of 340 m2/g were formed via hydrothermal treatment of carbon-doped titania precursor powder exposed to 700 °C during carbothermal pretreatment.
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 m2/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 d100 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.
Carbon‐doped TiO2 nanoparticles were prepared by a facile carbothermal treatment at different temperatures. The synthesis was conducted in a rotary tube furnace under an acetylene/nitrogen gas flow. A detailed analysis of the morphology of the particles revealed a layered graphene structure surrounding the TiO2core with a temperature‐shell thickness of 1–1.5 nm. The material exhibits a significant shift in the Raman Eg(1) mode toward higher wavenumbers. High carbon contents were determined by X‐ray photoelectron spectroscopy. This led to the conclusion that in addition to the carbon in the shell, carbon is also incorporated into the TiO2 structure. Substitutional doping in favor of titanium or oxygen atoms could be excluded based on XPS measurements due to the absence of Ti–C bonds and the lack of changes in lattice parameters of the unit cell or microstrain. An interstitial incorporation of carbon is therefore most likely. Either the incorporation of carbon or the carbon shell suppressed the phase transition from anatase to the thermodynamically stable rutile which is expected above 600 Celsius. Additionally, the process inhibits the crystallite growth at higher treatment temperatures.
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