Carbon nanotubes can be obtained from variety of the molecular precursors in chemical vapor deposition processes. The low growth temperatures strongly increase the compatibility of carbon nanotubes growth with current complementary metal-oxide-silicon technology for carbon nanotubes-based electronics. Here, we show the low temperature growth of multiwalled carbon nanotubes in acetylene chemical vapor deposition with Fe-Co/MgO. The catalyst mix was active already at 450°C. The higher temperatures growth (500°C and 550°C) were also tested in order to estimate the best thermal condition in respect of the sample quality (via thermogravimetric analyzer) and the sample relative purity (via resonance Raman spectroscopy). High resolution transmission electron microscope was used to determine the morphology of the samples.
In the present study we report resonance Raman study on multiwalled carbon nanotubes treated with HCl, HNO_3 and H_2SO_4. Acids are commonly used in purification procedures in order to remove catalyst particles from the as-produced material. However, it is known that acid treatments in multiwalled carbon nanotubes can induce a surface functionalisation and intercalation of the walls, modifying their electronic properties. Here, we present a comparative study between samples of multiwalled carbon nanotubes modified with the most common acids used in the purification of carbon materials, and the influence of the acid treatment time on their vibronic properties. The samples were analysed via the Raman spectroscopy using the laser length of 785 nm. The presented data reveal the modification of the typical multiwalled carbon nanotubes Raman bands such as: disorder band (D band), the graphite band (G band), and the two-phonon second order Raman band (G' band). The last one shows a broadening effect on its line shape and the appearance of an additional peak. All the treatments enhance the number of defects in the graphitic structure of multiwalled carbon nanotubes.
This paper presents the results of the research on the effect of the two different silanization methods on the thermal and structural properties of oxidized multiwalled carbon nanotubes. As-purified material was oxidized in the mixture of nitric and sulfuric acids. An oxidized material was divided into two parts which underwent two silanization treatments by 3-aminopropyltriethoxysilane (APTES). The first experiment (I) was performed at room temperature in acetone (pH 7) for 30 min. The second experiment (II) involved a hydrolysis of APTES at 40°C in water (pH 4) for 3 h. The functionalization extent of the samples at each step of the preparation was investigated by the Raman spectroscopy. The presence of the functional groups on the nanotubes surface have been studied via the Fourier transform infrared spectroscopy (FT-IR). The quantity of the external moieties introduced on multiwalled carbon nanotubes surface after oxidation process was estimated by the Boehms titration method. The high resolution transmission electron microscopy analysis allowed us to observe the changes of the morphology of the investigated carbon nanotubes. The influence of the silanization processes on the thermal stability of multiwalled carbon nanotubes was thoroughly studied by thermogravimetry analysis. There was observed a significant increase of the thermal stability of the multiwalled carbon nanotubes samples upon silanization treatment in respect of pristine and oxidized multiwalled carbon nanotubes.
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