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Vasilios Georgakilas

Publications and source records attributed to Vasilios Georgakilas.

17 recordsLinked to original sources
PubMed2006

Clay-fulleropyrrolidine nanocomposites.

In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C(60) differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C(60)-based organic/clay hybrid materials.

Aluminum Silicates↗
PubMed2005

Nanoscale organization of a phthalocyanine-fullerene system: remarkable stabilization of charges in photoactive 1-D nanotubules.

Induction of self-organization between zinc phthalocyanine (ZnPc) and C60 moieties in a novel amphiphilic ZnPc-C60 salt results in uniformly nanostructured 1-D nanotubules. Their photoreactivity, in terms of ultrafast charge separation (i.e., approximately 1012 s-1) and ultraslow charge recombination (i.e., approximately 103 s-1), is remarkable. In addition, the observed ZnPc*+-C60*- lifetime of 1.4 ms implies, relative to that of the monomeric ZnPc-C60 ( approximately 3 ns), an impressive stabilization of 6 orders of magnitude.

Journal Article↗
PubMed2005

Ordering fullerene materials at nanometer dimensions.

The combination of the hydrophobic fullerene core with hydrophilic functional groups of both ionic and nonionic nature produces organized structures with sizes that range from nanometer to micrometer length scales. The driving force toward this spontaneous organization is the amphiphilic character of the fullerene derivatives. To control both shape and size of the supramolecular assemblies and ultimately their function, important parameters that must be tuned are (i) the balance between the hydrophobic and the hydrophilic moieties, (ii) the effect of the environment, typically provided by simple solvents, (iii) the interface on which the aggregation occurs or, more precisely, surface templating effects, and (iv) the solvation process.

Air↗
PubMed2005

Thermal stripping of supramolecular structures: C60 nanorods.

The investigated ionic C60 derivative self-assembles into nanorods. When the functional side groups are removed by heating the nanorods to 623 K, they retain their shape. Utilization of lithographic markers allows the study of identical nanostructures before and after heat treatment by dynamic mode atomic force microscopy. Various independent techniques, including Raman spectroscopy and mass spectroscopy demonstrate that the shape-preserving mechanism is a thermal-stripping process, stabilizing the original supramolecular morphology. The latter implies two coherent sub-processes: detachment of the side groups and oligopolymerization running in parallel, eventually yielding rod-shaped C60 polymers. Synthesizing fullerenic polymers in this way can lead to several applications.

Carbon↗
PubMed2004

Incorporation of fullerene derivatives into smectite clays: a new family of organic-inorganic nanocomposites.

Three fulleropyrrolidine derivatives, characterized by the presence of positive charges, were introduced in the interlayer space of montmorillonite. The composites were characterized by powder X-ray diffraction and differential thermal and thermogravimetric (DTA-TGA) analysis, in conjunction with FTIR, UV-Vis, Raman, and (57)Fe-Mössbauer spectroscopies. Organophilic derivatives were intercalated into organically modified clays, while water-soluble fulleropyrrolidines were introduced into the clay galleries through ion exchange. The experiments, complemented by computer simulations, show that not all the clay-clay platelets are intercalated by the fullerene derivatives and that a sizable amount of charge transfer takes place between the host and the guests.

Journal Article↗
PubMed2004

Cyclic voltammetry and bulk electronic properties of soluble carbon nanotubes.

The bulk electronic properties of pyrrolidine-functionalized nanotubes are obtained from cyclic voltammetry measurements and discussed in the light of quantum chemical calculations. The functionalization is found to preserve the metallic character and to hardly affect the average density of electronic states.

Journal Article↗
PubMed2003

Organic functionalization and optical properties of carbon onions.

We report, for the first time, the organic functionalization of carbon onions. The functionalization was achieved via 1,3-dipolar cycloaddition of azomethine ylides to a mixture of amorphous carbon and concentric fullerenes. Once functionalized, the onions become soluble in organic solvents and it is possible to purify them from the rest of carbon. Their nonlinear optical properties have been studied in solution for application as broadband optical limiters. It was found that the functionalized onions are an example of soluble material that functions equally well in both the visible and the NIR regions.

Journal Article↗
PubMed2003

Soluble carbon nanotubes.

Carbon nanotubes have attracted great interdisciplinary interest because of their unique structure and properties. However, carbon-nanotube research is challenged by several problems, such as: i) mass production of material, ii) control of length, diameter, and chirality, and iii) manipulation for use in diverse technological fields. Issues regarding the synthesis and purification as well as the functionalization and solubilization of carbon nanotubes are relevant topics in this rapidly growing field. In this paper, covalent and noncovalent approaches to functionalized and solubilized nanotubes are examined in detail, with particular emphasis on the change of properties that accompany the chemical modification.

Journal Article↗
PubMed2003

Clays as a host matrix in the synthesis of organic macrocycles.

A new approach for the synthesis of amide macrocycles, based on the use of organo-clay derivatives as controlling template, is proposed as an alternative to the rotaxane method. Dications of p-xylylene diamine inserted in the clay interlayer space act as molding pillars around which neutral diamine molecules are erected via hydrogen bonding and pi-pi interactions to form supramolecular arrays. Condensation of diamines in the supramolecular arrays with diacetyl dichlorides yields various tetramide macrocycles in good yields. Shape, aromaticity and dimensions of the reactants are factors affecting the condensation reaction.

Journal Article↗
PubMed2002

Purification of HiPCO carbon nanotubes via organic functionalization.

We report a new method for the purification of HiPCO single-wall carbon nanotubes (SWNT), which consists of the following sequence: (a) organic functionalization of the as-produced nanotubes (pristine tubes, p-SWNT), (b) purification of the soluble functionalized nanotubes (f-SWNT), (c) removal of the functional groups and recovery of purified nanotubes (r-SWNT) by thermal treatment at 350 degrees C, followed by annealing to 900 degrees C. Each of these steps contributes to the purification, but only their sequential combination leads to high-purity materials. Organic functionalization makes the SWNT more easy to handle, which results in a better manipulation for potential practical uses. The electronic properties of the purified tubes are investigated via Raman and NIR spectroscopies along with transmission electron microscopy.

Journal Article↗
PubMed2002

Supramolecular self-assembled fullerene nanostructures.

Four ionic fullerene derivatives, which are relatively soluble in polar solvents, are shown to organize into morphologically different nanoscale structures. Spheres, nanorods, and nanotubules form in water depending on the side chain appendage of the fullerene spheroid. Images at different nanoscale structures were obtained via transmission electron microscopy. Also, computer simulations were used for investigating the relative spatial arrangements. The efficient method to fabricate almost perfect and uniformly shaped nanotubular crystals, which order spontaneously by self-assembly, opens the way to the possibility of exploiting the fullerene properties at the nanometer scale.

Carbon↗
PubMed2002

Organic functionalization of carbon nanotubes.

A very general and versatile method for functionalizing different types of carbon nanotubes is described, using the 1,3-dipolar cycloaddition of azomethine ylides. Approximately one organic group per 100 carbon atoms of the nanotube is introduced, to yield remakably soluble bundles of nanotubes, as seen in transmission electron micrographs. The solubilization of the nanotubes generates a novel, interesting class of materials, which combines the properties of the nanotubes and the organic moiety, thus offering new opportunities for applications in materials science, including the preparation of nanocomposites.

Journal Article↗