We attempted the direct solvent-free amination of closed caps of multiwalled carbon nanotubes (MWNTs) with octadecylamine (ODA), which is essentially similar to the amination of spherical fullerenes. Thermogravimetric analysis revealed a relatively high content of organics in the product of derivatization (ODA-MWNTs), suggesting that a large ODA fraction is distributed over MWNT sidewalls through chemical attachment. This was confirmed by high-resolution transmission electron microscopy observations. Quantum chemical calculations showed that the presence of pyracylene units in the closed caps is not crucial for the amine addition, although the site specificity of the reaction does depend on the mutual position of five-membered rings. If the caps contain pyracylene units, then the addition preferentially takes place on their 6,6 bonds; if they do not, then the preferential reaction sites are C−C bonds of the pentagons. Whereas ideal nanotube sidewalls composed of solely benzene rings were found to be inert with respect to amines, the real nanotube sidewalls must contain numerous reactive five-membered rings as defects. ODA-MWNTs exhibited enhanced dispersibility/solubility in propanol. The proposed amination reaction is the most direct link between carbon nanotube and fullerene chemistry, contrary to all derivatization methods designed previously.
Gold nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWNTs) functionalized with aliphatic bifunctional thiols (1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 2-aminoethanethiol) through a direct solvent-free procedure. Small gold particles, with a narrow particle size distribution around 1.7 nm, were obtained on 1,6-hexanedithiol-functionalized MWNTs. For MWNTs functionalized with the aminothiol, the average Au particle size was larger, 5.5 nm, apparently due to a coalescence phenomenon. Gatan image filter (GIF) observations show that sulfur is at the nanotube surface with a non-homogeneous distribution. A higher sulfur concentration was observed around the gold nanoparticles' location.
The few-layer graphene, produced by exfoliation of graphite in 4-methylanisole, was noncovalently functionalized with the Ni(ii) complex of 5,7,12,14-tetramethyldibenzo-1,4,8,11-tetraazacyclotetradeca-3,5,7,10,12,14-hexaene (Ni(ii)-tetramethyldibenzotetraaza[14]annulene, or NiTMTAA), which is a simple model of more complex porphyrins and phthalocyanines. The resulting hybrid materials with different content of NiTMTAA were characterized by means of thermogravimetric analysis, scanning and transmission electron microscopy (SEM and TEM, respectively), atomic force microscopy (AFM), energy dispersive X-ray, Fourier-transform infrared (FTIR), Raman and UV-visible spectroscopy, as well as fluorescence and conductivity measurements. Additional information on the mechanisms of NiTMTAA interaction with graphene was obtained from density functional theory (DFT) and molecular mechanics (MM) calculations. Both experimental and theoretical results suggest that NiTMTAA forms a full double-sided adsorption layer on the graphene surface. The presence of NiTMTAA molecules in the hybrid materials obtained manifests itself in the appearance of characteristic bands in all types of electromagnetic spectra recorded; in FTIR, they are relatively weak as compared to graphene absorption bands, but dominate in Raman spectra. The morphology of the nanohybrids observed by SEM, TEM and AFM, as well as their electrical conductivity, depends on the NiTMTAA content. According to the results of DFT calculations of NiTMTAA adsorption on different graphene models, flat orientation of the complex with respect to graphene is energetically preferable, with a little difference depending on whether benzo or methyl groups contact the sheet.
Noncovalent functionalization of carbon nanotubes with meso-tetraphenylporphine (H2TPP) and its metal(II) complexes NiTPP and CoTPP was studied by means of different experimental techniques and theoretical calculations. As follows from the experimental adsorption curves, free H2TPP ligand exhibits the strongest adsorption of three porphyrins tested, followed by CoTPP and NiTPP. At the highest porphyrin concentrations studied, the adsorption at multi-walled carbon nanotubes was about 2% (by weight) for H2TPP, 1% for CoTPP, and 0.5% for NiTPP. Transmission electron microscopy observations revealed carbon nanotubes with a variable degree of surface coverage with porphyrin molecules. According to scanning electron microscopy, the nanotubes glue together rather than debundle; apparently, a large porphyrin excess resulting in polymolecular adsorption is essential for exfoliation/debundling of the nanotube ropes. The nanotube/porphyrins hybrids were studied by infrared and Raman spectroscopy, as well as by scanning tunneling microscopy. Electronic structure calculations were performed at the B3LYP/LANL2MB theoretical level with the unsubstituted porphine (H2P) and its Co(II) complex, on one hand, and open-end armchair (5,5) (ANT) and zigzag (8,0) (ZNT) SWNT models, on the other hand. The interaction of H2P with ANT was found to be by 3.9 kcal mol(-1) stronger than that of CoP. At the same time, CoP+ZNT complex is more stable by 42.7 kcal mol(-1) as compared to H2P+ZNT According to these calculated results, the free porphyrins interact less selectively with zigzag and armchair (i.e., semiconducting and metallic) nanotubes, whereas the difference becomes very large for the metal porphyrins. HOMO-LUMO structure, electrostatic potential and spin density distribution for the paramagnetic cobalt(II) complexes were analyzed.
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