Amino-functionalized Multi-walled Carbon Nanotubes Research Articles

Preparation of multi-walled carbon nanotubes grafted with synthetic poly(l-lysine) through surface-initiated ring-opening polymerization

A surface-initiated ring-opening polymerization approach was used to functionalize multi-walled carbon nanotubes (MWNTs) with linear poly(l-lysine) (PLL). The oxidized MWNTs, which resulted from the treatment of MWNTs with mixed concentrated sulfuric acid and nitric acid, were converted into amino-functionalized MWNTs (MWNT-NH2) by the amidation of carboxylic group on MWNT surface with excess 1,6-diaminohexane. Surface-initiated ring-opening polymerization of ɛ-(benzyloxycarbonyl)-l-lysine N-carboxyanhydride with MWNT-NH2 as the initiator resulted in MWNTs grafted with poly(ɛ-(benzyloxycarbonyl)-l-lysine) (MWNT-g-PLys(Z)). After the acidolysis of benzylcarbamate group of the grafting poly(ɛ-(benzyloxycarbonyl)-l-lysine) chain, water-soluble MWNTs grafted with PLL (MWNT-g-PLL) were obtained. The successful grafting was confirmed by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, elemental analyses, high-resolution transmission electron microscopy (HRTEM) and field-emission scanning electron microscopy. HRTEM indicates that MWNTs were enveloped by PLL layer. The as-prepared MWNT-g-PLys(Z) and MWNT-g-PLL exhibited excellent ability to disperse homogeneously in THF and water, respectively.

The reinforcement role of different amino-functionalized multi-walled carbon nanotubes in epoxy nanocomposites

Functionalization with different amino groups of multi-walled carbon nanotubes was achieved and nanotube-reinforced epoxy nanocomposites were prepared by mixing amino-functionalized multi-walled carbon nanotubes with epoxy resin. Differential scanning calorimetry, thermogravimetric analysis and bending tests were used to investigate the thermal and mechanical properties of the nanocomposites. The results showed that different kinds of amino-functionalized multi-walled carbon nanotubes would have different effects on the thermal and mechanical properties of the nanocomposites. The reinforcement mechanism of amino-functionalized multi-walled carbon nanotubes in epoxy resin was discussed.

Thermo-physical properties of epoxy nanocomposites reinforced with amino-functionalized multi-walled carbon nanotubes

The modification of multi-walled carbon nanotubes (MWNTs) with amine groups was investigated by FTIR, Raman spectroscopy and XPS after such steps as carboxylation, acylation and amidation. Nanotube-reinforced epoxy polymer composites were prepared by mixing amino-functionalized MWNTs with epoxy resin and curing agent. DSC, TGA, SEM and flexural test were used to investigate the thermal and mechanical properties of the composites. The results showed that amino-functionalized MWNTs could enhance the interfacial adhesion between the nanotubes and the matrix, thus greatly improve the thermal and mechanical properties of the resin epoxy bulk material.

Thermal degradation behavior of multi-walled carbon nanotubes/polyamide 6 composites

This paper focuses on the thermal degradation behavior of multi-walled carbon nanotubes (MWNTs)/polyamide 6 (PA6) composites under air and nitrogen atmosphere using thermogravimetric analysis (TGA). The results show that the dispersion of amino-functionalized MWNTs (f-MWNTs) in PA6 is more homogeneous than purified MWNTs (p-MWNTs). The presence of MWNTs improves the thermal stability of PA6 under air obviously, but has little effect on the thermal degradation behavior of PA6 under nitrogen atmosphere. The activation energies for degradation under air, E a, estimated by Kissinger method, are 153, 165 and 169 kJ/mol for neat PA6, p-MWNTs/PA6 and f-MWNTs/PA6 composites, respectively. The p-MWNTs/PA6 composites show two-step degradation not only under air but also under nitrogen atmosphere, however, neat PA6 and the f-MWNTs/PA6 composites exhibit two-step degradation only under air.

Carbon Nanotube Delivery of the GFP Gene into Mammalian Cells

Exogenous-gene expression and manipulation in mammalian cells has become a mainstay of biomedical research. Consequently, improving methods for efficient gene transfer to a broad range of cell types is of great interest and remains a high priority. Several classes of transfection methods have been developed, which include traditional cationic moleculemediated agents, such as Lipofectamine 20000 and FuGENE 6, viral-vector systems, and the “gene gun” approach. With the rapid development of nanobiotechnology, a variety of new materials, such as gold nanoparticles, silica nanoparticles, polymers, nanogels, and dendrimers have been investigated as biocompatible transporters. Recently, carbon nanotube—a well-studied nanomaterial— have been investigated for their ability to interact with and affect living systems. For instance, carbon nanotubes have been found to enhance DNA amplification in PCR and affect the growth pattern of neurons. Pantarotto et al. have reported the internalization of fluorescein isothiocynate (FITC) labeled nanotubes and nanotube delivery of the gene that encodes b-galactosidase into cells, with no apparent toxic effects. Kam et al. have studied the mechanism of protein-conjugated carbon nanotube uptake into cells via the endocytic pathway. Here we present our finding that amino-functionalized multiwalled carbon nanotubes (NH2-MWCNTs) are able to interact with plasmid DNA and deliver the green fluorescence protein (GFP) gene into cultured human cells. Our data strongly suggest that carbon nanotubes can be considered as a new carrier for the delivery of biomolecules, such as DNA, proteins, and peptides into mammalian cells. Therefore, this novel system might have potential applications in biology and therapy, including vaccine and gene delivery. In order to increase their biocompatibility, we introduced amino-, carboxyl-, hydroxyl-, and alkyl groups onto the surface of MWCNTs. COOH-MWCNTs were first prepared by nitric / sulfuric acid oxidation, and then NH2and CH3CH2CH2-groups were added. Finally, we obtained four types of MWCNTs with different chemical groups on their surface. Functionalized MWCNTs were observed under an electron microscope and were found to be 60–70 nm in diameter and 1–2 mm in length. Although we did not find a significant difference in size between the NH2-MWCNTs and NH2-MWCNT–DNAs, the latter appeared to have the tendency to aggregate (Figure 1B). In order to test the DNA-binding ability of amino-, carboxyl-, hydroxyl-, and alkyl-group-modified MWCNTs, we incubated them with pEGFPN1-plasmid DNA, and MWCNT–DNA mixtures were analyzed by agarose-gel electrophoresis. The results show that only NH2-MWCNT bound to DNA (Figure 2); since the NH2-MWCNT–DNA complex was too big to run into the

Multiamino-functionalized carbon nanotubes and their applications in loading quantum dots and magnetic nanoparticles

Two strategies were employed to synthesize amino-functionalized multiwalled carbon nanotubes (MWNTs). In the first strategy, we grew poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) from the surfaces of MWNTs by in situ atom transfer radical polymerization (ATRP), then allowed the polymer chains to react with methyl iodide to acquire cationic polyamine coated-carbon nanotubes (MWNT-PAmMeI). Three samples with different amounts of grafted polyamine were obtained. TGA measurements showed that the content of PDMAEMA was ca. 25, 60 and 80% by mass. The chemical structure, morphology and nanostructures of the polyamine-grafted MWNTs were confirmed by 1H NMR spectroscopy, SEM and TEM. In the second strategy, we prepared amino-functionalized MWNTs (MWNT-NH2) by reacting acyl chloride-containing MWNTs with para-phenylenediamine in the presence of pyridine. The resulting polyamine- and amino-functionalized MWNTs were then used as templates to load CdTe quantum dots (QDs) and Fe3O4 magnetic nanoparticles by the electrostatic self-assembly approach, affording MWNT/CdTe and MWNT/Fe3O4 nanohybrids. TEM, EDS and XRD showed the structure and components of the obtained nanohybrids. Luminescence measurements indicated that the MWNT/CdTe complexes based on MWNT-PAmMeI could retain the luminescent properties of the QDs, which showed an emission peak at a wavelength of 550 nm, while the photoluminescence (PL) of the MWNT-NH2/CdTe composites can be hardly detected.

Polyurea-Functionalized Multiwalled Carbon Nanotubes: Synthesis, Morphology, and Raman Spectroscopy

An in situ polycondensation approach was applied to functionalize multiwalled carbon nanotubes (MWNTs), resulting in various linear or hyperbranched polycondensed polymers [e.g., polyureas, polyurethanes, and poly(urea-urethane)-bonded carbon nanotubes]. The quantity of the grafted polymer can be easily controlled by the feed ratio of monomers. As a typical example, the polyurea-functionalized MWNTs were measured and characterized in detail. The oxidized MWNTs (MWNT-COOH) were converted into acyl chloride-functionalized MWNTs (MWNT-COCl) by reaction with neat thionyl chloride (SOCl2). MWNT-COCl was reacted with excess 1,6-diaminohexane, affording amino-functionalized MWNTs (MWNT-NH2). In the presence of MWNT-NH2, the polyurea was covalently coated onto the surfaces of the nanotube by in situ polycondensation of diisocyanate [e.g., 4,4'-methylenebis(phenylisocyanate)] and 1,6-diaminohexane, followed by the removal of free polymer via repeated filtering and solvent washing. The coated polyurea content can be controlled to some extent by adjusting the feed ratio of the isocyanato and amino groups. The structure and morphology of the resulting nanocomposites were characterized by FTIR, NMR, Raman, confocal Raman, TEM, EDS, and SEM measurements. The polyurea-coated MWNTs showed interesting self-assembled flat- or flowerlike morphologies in the solid state. The signals corresponding to that of the D and G bands of the carbon nanotubes were strongly attenuated after polyurea was chemically tethered to the MWNT surfaces. Comparative experiments showed that the grafted polymer species and structures have a strong effect on the Raman signals of polymer-functionalized MWNTs.

Polyurea-Functionalized Multiwalled Carbon Nanotubes

An in situ polycondensation approach was applied to functionalize multiwalled carbon nanotubes (MWNTs), resulting in various linear or hyperbranched polycondensed polymers [e.g., polyureas, polyurethanes, and poly(urea-urethane)-bonded carbon nanotubes]. The quantity of the grafted polymer can be easily controlled by the feed ratio of monomers. As a typical example, the polyurea-functionalized MWNTs were measured and characterized in detail. The oxidized MWNTs (MWNT-COOH) were converted into acyl chloride-functionalized MWNTs (MWNT-COCl) by reaction with neat thionyl chloride (SOCl2). MWNT-COCl was reacted with excess 1,6-diaminohexane, affording amino-functionalized MWNTs (MWNT-NH2). In the presence of MWNT-NH2, the polyurea was covalently coated onto the surfaces of the nanotube by in situ polycondensation of diisocyanate [e.g., 4,4‘-methylenebis(phenylisocyanate)] and 1,6-diaminohexane, followed by the removal of free polymer via repeated filtering and solvent washing. The coated polyurea content can be controlled to some extent by adjusting the feed ratio of the isocyanato and amino groups. The structure and morphology of the resulting nanocomposites were characterized by FTIR, NMR, Raman, confocal Raman, TEM, EDS, and SEM measurements. The polyurea-coated MWNTs showed interesting self-assembled flat- or flowerlike morphologies in the solid state. The signals corresponding to that of the D and G bands of the carbon nanotubes were strongly attenuated after polyurea was chemically tethered to the MWNT surfaces. Comparative experiments showed that the grafted polymer species and structures have a strong effect on the Raman signals of polymer-functionalized MWNTs.

Characterization of Covalent Functionalized Carbon Nanotubes

The characterization of chemically modified carbon nanotubes has been achieved using 13C nuclear magnetic resonance (NMR) spectroscopy. Amino-functionalized multiwall carbon nanotubes (MWNT−NH2) were reacted with a 13C terephthalic acid. Covalent attachment of the acid to the nanotubes is confirmed by 13C NMR and 2D NMR through the presence of amide grouping resonances.

Interconnecting carbon nanotubes with an inorganic metal complex.

Intermolecular carbon nanotube junctions were formed through amide linkage of amino functionalized multiwall carbon nanotubes and [Ru (dcbpy)(bpy)2](PF6)2, an inorganic metal complex. Nanotube interconnects were visualized using atomic force microscopy. Absorption and emission spectroscopy showed significant changes between starting products and the resulting ruthenium nanotube complex, indicative of successful chemical modification.