"Green" functionalization of pristine multi-walled carbon nanotubes with long-chain aliphatic amines.

Short pristine multi-walled carbon nanotubes (MWNTs) were functionalized with a series of long-chain (including polymeric) aliphatic amines, namely octadecylamine (ODA), 1,8-diaminooctane (DO), polyethylene glycol diamine (PEGDA) and polyethylenimine (PEI), via two "green" approaches: (1) gas-phase functionalization (for volatile ODA and DO) and (2) direct heating in the melt (for polymeric PEGDA and PEI). Both of them consist in one-step reaction between MWNTs and amine without the use of organic solvents. The nanostructures obtained were characterized by using infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. It was observed that both solvent-free methods were efficient in the nanotube functionalization, and the nanostructures of variable solubility and morphology were obtained depending on the amines attached. ODA, PEGDA and PEI-functionalized MWNTs were found to be soluble in propanol, meanwhile the MWNTs-PEGDA and MWNTs-PEI were soluble in water as well. The attachment of 1,8-diaminooctane onto MWNTs resulted in cross-linked stable nanostructure.

Fullerene C60 films cross-linked with octane-1,8-dithiol: preparation, characterization and the use as template for chemical deposition of gold nanoparticles.

We report on the preparation of fullerene C60 thin films chemically cross-linked with octane-1,8-dithiol, which are capable of binding gold nanoparticles. The formation of a polymer was directly proved by means of laser desorption/ionization time-of-flight mass spectra, in which we observed the cleavage of fullerene-dithiol polymer at different bonds. Fourier-transform infrared, Raman and UV-visible spectra of the functionalized films exhibited notorious changes due to the formation of new covalent bonds between C60 molecules and bifunctional thiol. We further demonstrated that the dithiol-functionalized fullerene can be employed as a support for stable and homogeneous deposition of gold nanoparticles. Their average size is about 5 nm according to high-resolution transmission electron microscopy observations, and up to 20 nm, as found from scanning tunneling microscopy images. The proposed binding mechanism is through a strong coordination attachment between Au nanoclusters and sulfur donor atoms of the functionalized fullerene, as supported by density functional theory calculations.

Noncovalent functionalization of carbon nanotubes with porphyrins: meso-tetraphenylporphine and its transition metal complexes.

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.

Deposition of gold nanoparticles onto thiol-functionalized multiwalled carbon nanotubes.

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.