Improvement single-wall carbon nanotubes (SWCNTs) based on functionalizing with monomers 2-hydroxyethylmethacryate (HEMA) and N-vinylpyrrolidone (NVP) for pharmaceutical applications as cancer therapy

The functionalized carbon nanotubes play significant roles in the fields such as preparation of composite materials and biological technologies. This paper explains the covalent functionalization of single-wall carbon nanotubes (SWCNTs) with biomedical important monomers, 2-hydroxyethylmethacryate (HEMA) and N-vinylpyrrolidone (NVP) by chemical grafting of HEMA and PVP monomers via free radical polymerization. To get carboxylic acid functionalized SWCNTs, first the nanotubes were oxidized with a mixture of nitric acid and sulfuric acid (1:3). Then, the binding of HEMA and NVP onto the surface of SWCNTs was performed by chemical functionalization of HEMA, NVP with acid chloride-bound carbon nanotube by esterification reaction. These results were confirmed by FT-IR and SEM. The cell culture experiments conducted for pharmaceutical applications were used as cancer therapy.     

Tuning the photophysical properties of soluble single-wall carbon nanotube derivatives by co-functionalization with organic molecules

The photophysical characterization of three soluble derivatives of single-wall carbon nanotubes (SWCNTs), functionalized with poly(ethylene glycol) (PEG), co-functionalized with PEG and aminofluorene and co-functionalized with PEG and aminoanthracene is reported. The peculiar excellent solubility of these derivatives allows, for the first time in covalently functionalized SWCNTs, the study of their excitation dynamics by monitoring the near-infra-red emission. Moreover, the aminoanthracene derivative shows higher photoluminescence efficiency in the visible range than the aminofluorene derivative, demonstrating the possibility to tune extensively the photophysical properties of these functionalized SWCNTs.     

Fabrication of single-walled carbon nanotubes dotted with Au nanocrystals: Potential DNA delivery nanocarriers

Single-walled carbon nanotubes (SWCNTs) dotted with Au nanocrystals (Au-SWCNTs) were fabricated by using a two-phase reduction of hydrogen tetrachloroaurate in the presence of thiol groups anchored to SWCNTs for their potential applications in DNA (deoxyribonucleic acid) delivery. To allow a surface reaction on SWCNTs during the metal nucleation and growth processes, Au nanocrystals were grown using a two-phase system. Raman, XPS and transmission electron microscopy results show that the Au nanocrystals were grafted primarily to the sidewalls of the SWCNTs. DNA probes were immobilized on Au-SWCNTs by the conjugation of DNA functionalized at the 3′ end with a thiol group with Au dots of SWCNTs, followed by hybridizion of complementary oligonucleotides, as verified by fluorescence-based measurements. To investigate whether the target DNA hybridized to DNA probes immobilized on Au-SWCNTs, 618-base-pair fragments of amplified DNA were prepared by polymerase chain reaction using plasmid pET-22b as a template. Atomic force micrograph (AFM) images show that the nanorod-bound DNA is recognizable with excellent specificity, indicating the potential use of such material as a versatile gene delivery carrier in gene-based disease therapy.     

The study of thermodynamics and kinetics methyl orange and malachite green by SWCNTs,SWCNT-COOH and SWCNT-NH2 as adsorbents from aqueous solution

The effective removal of dyes from aqueous wastes is among the most important issues for many industrialized countries. Removal of methyl orange (MO) and malachite green (MG) from aqueous solutions were studied using single-walled carbon nanotubes (SWCNTs), carboxylate functionalized single-walled carbon nanotubes (SWCNT-COOH) and amide functionalized single-walled carbon nanotubes (SWCNT-NH₂). The adsorption process was found to be controlled by temperature, ionic strength, initial concentration, adsorbent dosage and contact time. The microstructure of carbon nanotubes was characterized using SEM and FTIR. The adsorbents studied exhibits high efficiency for MO and MG adsorption and the equilibrium states could be achieved in 20, 20, 15 (min) for SWCNTs, SWCNT-COOH, SWCNT-NH₂, respectively. Adsorption capacity of each adsorbent increased with increasing active groups on the surface of carbon nanotube, where SWCNT-NH₂ was the most effectively adsorbent.     

Environmentally friendly functionalization of single walled carbon nanotubes in molten urea

Using molten urea as the solvent, single walled carbon nanotubes (SWCNTs) are dispersed and functionalized with arenediazonium salts in less than 15 min to afford predominantly unbundled functionalized SWCNTs. This technique provides a rapid and economically viable route to produce covalently functionalized nanotubes in large amounts with an industrially friendly method.     

Nebulization of single-walled carbon nanotubes for respiratory toxicity studies

An ultrafine aerosol consisting of airborne single-walled carbon nanotubes (SWCNTs) was produced by nebulizing functionalized SWCNTs in methanol. Prior to atomization, purified SWCNTs were functionalized with aryl sulfonate groups via a Birch reaction. The functionalized SWCNTs were then dispersed in methanol and nebulized using a TSI-3076 constant output atomizer. Atomic force microscopy of a mica plate placed in the flow revealed both individual and bundled SWCNTs. We anticipate that this method for producing ultrafine mists of SWCNTs will enable respiratory toxicity studies of inhaled ultrafine SWCNT particulate.     

Modifying the electronic properties of single-walled carbon nanotubes using designed surfactant peptides

The electronic properties of carbon nanotubes can be altered significantly by modifying the nanotube surface. In this study, single-walled carbon nanotubes (SWCNTs) were functionalized noncovalently using designed surfactant peptides, and the resultant SWCNT electronic properties were investigated. These peptides have a common amino acid sequence of X(Valine)(5)(Lysine)(2), where X indicates an aromatic amino acid containing either an electron-donating or electron-withdrawing functional group (i.e. p-amino-phenylalanine or p-cyano-phenylalanine). Circular dichroism spectra showed that the surfactant peptides primarily have random coil structures in an aqueous medium, both alone and in the presence of SWCNTs, simplifying analysis of the peptide/SWCNT interaction. The ability of the surfactant peptides to disperse individual SWCNTs in solution was verified using atomic force microscopy and ultraviolet-visible-near-infrared spectroscopy. The electronic properties of the surfactant peptide/SWCNT composites were examined using the observed nanotube Raman tangential band shifts and the observed additional features near the Fermi level in the scanning tunneling spectroscopy dI/dV spectra. The results revealed that SWCNTs functionalized with surfactant peptides containing electron-donor or electron-acceptor functional groups showed n-doped or p-doped altered electronic properties, respectively. This work unveils a facile and versatile approach to modify the intrinsic electronic properties of SWCNTs using a simple peptide structure, which is easily adaptable to obtain peptide/SWCNT composites for the design of tunable nanoscale electronic devices.     

Surfactant-free assembling of functionalized single-walled carbon nanotube buckypapers

The electrical and textural properties of single-walled carbon nanotube buckypapers were tunned through chemical functionalization processes. Single-walled carbon nanotubes (SWCNTs) were covalently functionalized with three different chemical groups: Carboxylic acids (-COOH), benzylamine (-Ph-CH₂-NH₂), and perfluorooctylaniline (-Ph-(CF₂)₇-CF₃). Functionalized SWCNTs were dispersed in water or dimethylformamide (DMF) by sonication treatments without the addition of surfactants or polymers. Carbon nanotube sheets (buckypapers) were prepared by vacuum filtration of the functionalized SWCNT dispersions. The electrical conductivity, textural properties, and processability of the functionalized buckypapers were studied in terms of SWCNT purity, functionalization, and assembling conditions. Carboxylated buckypapers demonstrated very low specific surface areas (< 1 m²/g) and roughness factor (R_a = 14 nm), while aminated and fluorinated buckypapers exhibited roughness factors of around 70 nm and specific surface areas of 160-180 m²/g. Electrical conductivity for carboxylated buckypapers was higher than for as-grown SWCNTs, but for aminated and fluorinated SWCNTs it was lower than for as-grown SWCNTs. This could be interpreted as a chemical inhibition of metallic SWCNTs due to the specificity of the diazonium salts reaction used to prepare the aminated and fluorinated SWCNTs. The utilization of high purity as-grown SWCNTs positively influenced the mechanical characteristics and the electrical conductivity of functionalized buckypapers.     

Effect of montmorillonite and shear stress on the orientation of single walled carbon nanotubes in polypopylene composite fiber

The effect of montmorillonite and shear stress on the orientation of single walled carbon nanotubes and properties of SWCNT/MMT/polypropylene composite was investigated. The effect of functionalization of SWCNT on the orientation was also investigated. Polarized Raman spectroscopy was used to analyze the orientation of the SWCNTs. Orientation of SWCNTs was dependent on the experienced shear stress and functionalization of SWCNTs. The addition of MMT also improved the orientation of functionalized SWCNTs, while its effect was not significant for pristine SWCNTs. The existence of critical shear stress was observed for the orientation of the SWCNTs and the orientation of SWCNTs was found to occur more efficiently above this critical shear stress. Melt viscosity and heat of fusion data also confirmed that the addition of MMT‐induced improved orientation and dispersion of SWCNTs, especially for functionalized SWCNTs. POLYM. ENG. SCI., 54:2455–2459, 2014. © 2013 Society of Plastics Engineers     

Neutralized fluorine radical detection using single-walled carbon nanotube network

It is known that single-walled carbon nanotubes (SWCNTs) can be functionalized by fluorine gas. Here, we report neutralized fluorine radical detection using a matted sheet of SWCNTs, prepared by alternating current dielectrophoresis. Upon exposure to neutralized radicals containing fluorine atoms in a plasma, as model analytes, the conductance of the SWCNT matt showed fast modulation. The transduction mechanism was investigated by electrical transport measurements, X-ray photoelectron spectroscopy and Raman spectroscopy. Metallic nanotubes were shown to react covalently to the near exclusion of semiconducting species. The selectivity was promoted by the curvature-induced strain of the nanotubes. The results open new opportunities for the detection of fluorine radicals at specific locations inside the reaction zone using a simple, miniaturized carbon nanotube network.     

Highly efficient recovery of bioactive ingredients from solid waste of onions onto functionalized SWCNTs supported on amberlite nanocomposite

Preparation of single-walled carbon nanotubes (SWCNTs) with carboxylic (–COOH) acid was executed by functionalization with amine functional groups (–NH2). The obtained functionalized SWCNTs were supported by macroporous resin (amberlite XAD-7HP). The synthesized nanocomposite has been characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) methods. FTIR analysis indicates that functionalized SWCNTs supported onto the amberlite resin were synthesized successfully. The surface morphology of the nanomaterial was also successfully embedded into the amberlite of the functionalized SWCNTs. Huge solid residues of onions are produced as agricultural and food wastes each year. The related biowaste includes biologically active phenolic compounds which have positive effects with strong antioxidant properties on human health when properly isolated and concentrated. In the present research, functionalized SWCNTs have been utilized for the separation of bioactive phenolics from onion waste extracts. Equilibrium (Langmuir, Freundlich and Toth) and kinetic (pseudo-first order, pseudo-second order, intraparticular diffusion and Elovich) models have been applied for analysis and representation of data. Pseudo-second-order model is in good agreement with the experimental data. On the other hand, the equilibrium findings were represented best with Freundlich isotherm model. Additionally, thermodynamic indicators have also demonstrated that the current system is a spontaneous and exothermic chemisorption process.     

d-(+)-Galactose-Conjugated Single-Walled Carbon Nanotubes as New Chemical Probes for Electrochemical Biosensors for the Cancer Marker Galectin-3

d-(+)-Galactose-conjugated single-walled carbon nanotubes (SWCNTs) were synthesized for use as biosensors to detect the cancer marker galectin-3. To investigate the binding of galectin-3 to the d-(+)-galactose-conjugated SWCNTs, an electrochemical biosensor was fabricated by using molybdenum electrodes. The binding affinities of the conjugated SWCNTs to galectin-3 were quantified using electrochemical sensitivity measurements based on the differences in resistance together with typical I-V characterization. The electrochemical sensitivity measurements of the d-(+)-galactose-conjugated SWCNTs differed significantly between the samples with and without galectin-3. This indicates that d-(+)-galactose-conjugated SWCNTs are potentially useful electrochemical biosensors for the detection of cancer marker galectin-3.     

Deposition of functionalized single wall carbon nanotubes through matrix assisted pulsed laser evaporation

Single-wall carbon nanotubes (SWCNTs) functionalized with oxygen-containing groups were deposited onto glass substrates by matrix assisted pulsed laser evaporation (MAPLE). The experiments were performed by subjecting ultraviolet laser pulses (KrF¹ excimer laser, 248 nm wavelength) to frozen SWCNT-toluene targets placed in a parallel plane a few cm in front of the substrate. The morphology, structure, and chemical composition of the deposited materials were studied through atomic force microscopy, high resolution transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The influence of the laser fluence on the material structure was investigated. The results indicate that the functionalized SWCNTs can be transferred by MAPLE at low laser fluences without the alteration of the structure of the initial material used as targets in MAPLE experiments. An increase of the fluence leads to the decomposition of the functional groups, mainly carboxylic acid groups, without degradation of the SWCNT structure whereas, at the highest fluences, the amorphization and even coalescence of the carbon nanotubes takes place.     

Improving the thermal and mechanical properties of poly(vinyl butyral) through the incorporation of acid‐treated single‐walled carbon nanotubes

In this study, to investigate the effect of functionalized carbon nanotubes on the thermal and mechanical properties of the poly(vinyl butyral) (PVB) resin, PVB/functionalized single‐walled carbon nanotube (f‐SWCNT) composites were fabricated by a solution casting method. The functionalized nanotubes were prepared by acid treatment. The formation of oxygen‐containing functional groups on the surface of the nanotubes was confirmed by Fourier transform infrared spectroscopy, energy‐dispersive X‐ray spectroscopy, and scanning electron microscopy (SEM) measurements. SEM analysis also showed that the nanotubes were dispersed well in the PVB matrix. The thermal stability of the composites were investigated with thermogravimetric analysis, and the results show better stability for PVB in the presence of a very low content of the f‐SWCNTs. The prepared composites exhibited a significant increase in the temperature of degradation at 50 wt % loss and also in the onset temperature and decomposition temperature at the maximum rate of weight loss of butyral degradation. A significant enhancement in the mechanical properties was also achieved for these prepared composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40481.     

Construction of a Brönsted-Lewis solid acid catalyst La-PW-SiO2/SWCNTs based on electron withdrawing effect of La(III) on π bond of SWCNTs for biodiesel synthesis from esterification of oleic acid and methanol

A novel solid Brönsted-Lewis acid catalyst La-PW-SiO₂/SWCNTs (single-wall carbon nanotubes) was synthesized from the synergistic modification of H₃PW₁₂O₄₀ (HPW) by single-walled carbon nanotubes functionalized with sidewall hydroxyl groups (SWCNTs–OH) and La³⁺ via sol–gel method. The freshly prepared catalyst was characterized by several methods, and the catalytic activity and stability of it were studied from the esterification of oleic acid and methanol. Results showed that the highest conversion of oleic acid was 93.1% (mass) and maintained as high as 88.7% (mass) after six cycles of La-PW-SiO₂/SWCNTs. The high catalytic activity and stability of La-PW-SiO₂/SWCNTs can be attributed to the strong electron withdrawing effect of La³⁺ on π bond of SWCNTs, because it can facilitate the formation of a large number of strong Lewis acid sites. Therefore, the reduction of catalytic activity of a solid acid catalyst due to the fact that hydration reaction of its Brönsted acid sites can be effectively reduced. La-PW-SiO₂/SWCNTs can be an efficient and economical catalyst, because it shows good catalytic activity and stability.     

Water-soluble carbon nanotubes through sugar azide functionalization

In this work we report a covalent functionalization of pristine single-walled carbon nanotubes (SWCNTs) directly with three sugar azides, 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl, 2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl or 2,3,4,6-tetra-O-acetyl-β-d-mannopyranosyl azide. Microwave-assisted functionalization was carried out for SWCNTs prepared with the HiPCO method. The as-prepared, new type of sugar-functionalized SWCNTs were analyzed by Raman and IR spectroscopy. Deacetylation of the functionalized tubes by sodium methoxide yielded nitrogen-linked, sugar-functionalized carbon nanotubes (CNTs) that formed stable dispersions in water. Reactivity of the sugar azides towards SWCNTs was estimated from the solubility experiments. The water solubility was found to be highest for galactopyranosyl and lowest for gluco- and mannopyranosyl derivatives.     

β-Cyclodextrin non-covalently functionalized single-walled carbon nanotubes bridged by 3,4,9,10-perylene tetracarboxylic acid for ultrasensitive electrochemical sensing of 9-anthracenecarboxylic acid

We report a simple and facile approach for the synthesis of β-cyclodextrin non-covalently functionalized single-walled carbon nanotubes bridged by 3,4,9,10-perylene tetracarboxylic acid (β-CD-PTCA-SWCNTs). Fourier transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy and electrochemical methods were used to characterize the as-prepared functionalized SWCNTs. Furthermore, the β-CD-PTCA-SWCNTs were applied successfully to detect 9-anthracenecarboxylic acid (9-ACA, one derivative of polycyclic aromatic hydrocarbons) by electrochemical methods. The results show that the oxidation peak current of 9-ACA on β-CD-PTCA-SWCNTs modified glassy carbon (GC) electrode is 4.0 and 31.2 times higher than that at the SWCNTs/GC and bare GC electrodes, respectively. The proposed modified electrode has a linear response range of 2.00 to 140.00 nM with a detection limit of 0.65 nM (S/N = 3) towards 9-ACA, which is due to the synergic effects of the SWCNTs (e.g. their good electrochemical properties and large surface area) and β-CD (e.g. a hydrophilic external surface and a high supramolecular recognition and enrichment capability).     

Metal Removal Studies by Composite Membrane of Polysulfone and Functionalized Single-Walled Carbon Nanotubes

Composite nanofiltration membranes were prepared by incorporating single-walled carbon nanotubes (SWNTs) into polysulfone polymer via the phase inversion method. Addition of SWCNTs resulted in the reduction of the pore size due to nanosize (0.7-1.3 nm) diameter of SWCNTs used. The increase in carbon nanotubes makes the surface of the membranes smoother, although the solvent and nonsolvent exchange process becomes slower due to increase in viscosity of the blend solution. The addition of SWCNTs improved the rejection of metal ions, the oxidized functionalized C/PS composite membranes gave 96.8% removal for Cr(VI), 87.6% for As(III), and 94.2% removal for Pb(II) which was just 30.3%, 28.5%, and 28.3%, respectively, with unblended virgin polysulfone membrane.     

Formylation of single-walled carbon nanotubes

Formyl or aldehyde groups are transferred to the surface of single-walled carbon nanotubes (SWCNTs) by reaction of reduced carbon nanotubes with N-formylpiperidine. This could open the way for more versatile chemical modification reactions of carbon nanotubes than is currently possible using functionalization methods reported to date. The formylated SWCNTs were characterized by thermogravimetric analysis-mass spectrometry and Raman, UV-vis-NIR and FTIR spectroscopy. The location and distribution of the functional groups was determined by AFM using electrostatic interactions with gold nanoparticles. The formylated SWCNTs were further derivatized with a fluorescent dye and studied using fluorescence spectroscopy.     

Tailored dielectric and mechanical properties of noncovalently functionalized carbon nanotube/poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) nanocomposites

The preparation of high‐dielectric poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) (SEBS) composites containing functionalized single‐walled carbon nanotubes (f‐SWCNTs) noncovalently appended with dibutyltindilaurate are reported herein. Transmission electron microscopy and X‐ray photoelectron and Raman spectroscopy confirmed the noncovalent functionalization of the SWCNTs. The SEBS‐f‐SWCNT composites exhibited enhanced mechanical properties as well as a stable and high dielectric constant of approximately 1000 at 1 Hz with rather low dielectric loss at 2 wt% filler content. The significantly enhanced dielectric property originates from the noncovalent functionalization of the SWCNTs that ensures good dispersion of the f‐SWCNTs in the polymer matrix. The f‐SWCNTs also acted as a reinforcing filler, thereby enhancing the mechanical properties of the composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013