One-pot, efficient functionalization of multi-walled carbon nanotubes with diamines by microwave method

Diamines are known to act as a medium to bind miscellaneous compounds to carbon nanotubes (CNT). However, they are commonly applied in a tedious manner. Here, multi-walled carbon nanotubes (MWCNTs) were functionalized by a series of diamine molecules (ethylenediamine, 1,6-hexamethylenediamine and 1,4-diaminobenzen) in a one-pot, rapid microwave-assisted method. Surface functionality groups and morphology of MWCNTs were analyzed by infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results consistently confirmed the formation of diamines functionalities on MWCNTs, while the structure of MWCNT has remained relatively intact. This simple and efficient process may play an important role for realizing miscellaneous functionalization of CNTs.     

Nitrogen-doped carbon nanotubes with tunable structure and high yield produced by ultrasonic spray pyrolysis

Nitrogen-doped carbon nanotubes (CN_x) were prepared by ultrasonic spray pyrolysis from mixtures of imidazole and acetonitrile. Imidazole, as an additive, was used to control the structure and nitrogen doping in CN_x by adjusting its concentration in the mixtures. Scanning electron microscopy observation showed that the addition of imidazole increased the nanotube growth rate and yield, while decreased the nanotube diameter. Transmission electron microscopy study indicated that the addition of imidazole promoted the formation of a dense bamboo-like structure in CN_x. X-ray photoelectron spectroscopy analysis demonstrated that the nitrogen content varied from 3.2 to 5.2 at.% in CN_x obtained with different imidazole concentrations. Raman spectra study showed that the intensity ratio of D to G bands gradually increased, while that of 2D to G bands decreased, due to increasing imidazole concentration. The yield of CN_x made from mixtures of imidazole and acetonitrile can reach 192 mg in 24 min, which is 15 times that of CN_x prepared from only acetonitrile. The aligned CN_x, with controlled nitrogen doping, tunable structure and high yield, may find applications in developing non-noble catalysts and novel catalyst supports for fuel cells.     

A new strategy to assemble CdSe/ZnS quantum dots with multi-walled carbon nanotubes for potential application in imaging and photosensitization

With objective to enhance luminescence intensities of carbon nanotubes (CNTs), we hereby report the attachment of CdSe/ZnS quantum dots (QDs) on to the surface of shortened Multi Walled Carbon Nanotubes (sMWCNTs). The resultant QDs-sMWCNTs nanohybrid complex have been characterized by Fourier transform infrared (FT-IR) spectroscopy, optical microscopy (OM), ultraviolet (UV) light, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) diffraction spectroscopy and thermogravimetric analysis (TGA). Based on IR peaks characteristics of organic functional groups, optical brightness of sMWCNTs under polarized and UV light, the roughness of the sMWCNTs surface as observed in SEM images and black spots observed on the surface of sMWCNTs in TEM images, it is reasonable to conclude that CdSe/ZnS quantum dots (QDs) were attached on to the surface of sMWCNTs. Additionally, signals of Zn, S, Cd and Se along with carbon on the surface of sMWCNTs in EDX data and onset of thermal degradation of QDs-sMWCNTs nanohybrid complex at much lower temperature than that of sMWCNTs under TGA analysis further confirms the formation of QDs-sMWCNTs nanohybrid complex.     

Catalytic activity of Fe, Co and Fe-Co-MCM-41 for the growth of carbon nanotubes by chemical vapour deposition method

Iron, cobalt and a mixture of iron and cobalt incorporated mesoporous MCM-41 molecular sieves were synthesised by hydrothermal method and used to investigate the rules governing their nanotube producing activity. The catalysts were characterised by XRD and N₂ sorption studies. The effect of the catalysts has been investigated for the production of carbon nanotubes at an optimised temperature 750 °C with flow rate of N₂ and C₂H₂ is 140 and 60 ml/min, respectively for a reaction time 10 min. Fe-Co-MCM-41 catalyst was selective for carbon nanotubes with low amount of amorphous carbon with increase in single-walled carbon nanotubes (SWNTs) yield at 750 °C. Formation of nanotubes was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Transmission electron microscope and Raman spectrum was used to follow the quality and nature of carbon nanotubes formed and the graphitic layers and disordered band, which shows the clear evidence for the formation of SWNTs, respectively. The result propose that the diameter of the nanotubes in the range of 0.78-1.35 nm. Using our optimised conditions for this system, Fe-Co-MCM-41 showed the best results for selective SWNTs with high yield when compared with Fe-MCM-41 and Co-MCM-41.