End-group and defect analysis of soluble single-walled carbon nanotubes

Current Understanding of Water Properties inside Carbon Nanotubes

Confined water inside carbon nanotubes (CNTs) has attracted a lot of attention in recent years, amassing as a result a very large number of dedicated studies, both theoretical and experimental. This exceptional scientific interest can be understood in terms of the exotic properties of nanoconfined water, as well as the vast array of possible applications of CNTs in a wide range of fields stretching from geology to medicine and biology. This review presents an overreaching narrative of the properties of water in CNTs, based mostly on results from systematic nuclear magnetic resonance (NMR) and molecular dynamics (MD) studies, which together allow the untangling and explanation of many seemingly contradictory results present in the literature. Further, we identify still-debatable issues and open problems, as well as avenues for future studies, both theoretical and experimental.

Rapid and accurate determination of carboxyl groups in carbon materials by headspace gas chromatography

This paper reports a novel and rapid method for determining carboxyl groups in carbon materials by headspace gas chromatography (HS-GC). Taking carboxylated carbon nanotubes (CNTs) as an example, the experiment based on GC measurement of carbon dioxide (CO₂) generated by complete reaction between carboxyl groups and sodium bicarbonate in a sealed vial, which showed that carboxyl groups in CNTs could be completely transformed into CO₂ under the equilibrium temperature at 60 °C for 10 min. The relative standard deviation (RSD) of this method in the repeatability test was less than 1.52%, and the limit of quantitation (LOQ) for carboxyl content was 0.014 mmol/g in CNTs. More significantly, appropriate ultrasound of the sample before headspace injection could greatly improve the detection efficiency by reducing the equilibrium time. All in all, the HS-GC method provides an automated and accurate analysis for testing carboxyl groups in carbon materials, and it is of profound significance to develop a new way for quantitative research of carbon materials.

Conversion of guaiacol as lignin model component using acid-treated, multi-walled carbon nanotubes supported Ru–MnO bimetallic catalysts

Acid-treated, multi-walled carbon nanotube (AMWCNT) supported Ru and MnO bimetallic catalysts were prepared for liquid phase hydrodeoxygenation of guaiacol. The physicochemical properties of the prepared catalysts were characterized by FTIR, XRD, NH3-TPD, CO2-TPD, TEM, and XPS. MnO species were loaded on the inner surface of carbon nanotubes and were helpful for Ru particle dispersion. The 6%Ru-8%MnO/AMWCNTs with smaller Ru particle size, better dispersion, and more basic sites gave the best catalytic performance of 99.38% conversion of guaiacol and 85.84% selectivity to cyclohexanol. The effects of reaction conditions on liquid phase guaiacol hydrodeoxygenation were discussed and a possible reaction path was proposed.

Onion-Like Carbon Nanostructures: An Overview of Bio-Applications

This article presents a brief review of the knowledge concerning onion-like carbons (OLCs). These nanostructures are some of the most fascinating carbon forms due to their unusual structure and physico-chemical properties. Generally, OLCs consist of a hollowspherical fullerene core surrounded by concentric graphitic layers with increasing diameter. Nevertheless, they can have different size, shape and type of core, which determine their physicochemical properties. In this article, we review the most important literature reports in this area and briefly describe these nanostructures, their physical and chemical properties and their potential uses with a focus on biomedicine.

Networks of semiconducting SWNTs: contribution of midgap electronic states to the electrical transport

Single-walled carbon nanotube (SWNT) thin films provide a unique platform for the development of electronic and photonic devices because they combine the advantages of the outstanding physical properties of individual SWNTs with the capabilities of large area thin film manufacturing and patterning technologies. Flexible SWNT thin film based field-effect transistors, sensors, detectors, photovoltaic cells, and light emitting diodes have been already demonstrated, and SWNT thin film transparent, conductive coatings for large area displays and smart windows are under development. While chirally pure SWNTs are not yet commercially available, the marketing of semiconducting (SC) and metallic (MT) SWNTs has facilitated progress toward applications by making available materials of consistent electronic structure. Nevertheless the electrical transport properties of networks of separated SWNTs are inferior to those of individual SWNTs. In particular, for semiconducting SWNTs, which are the subject of this Account, the electrical transport drastically differs from the behavior of traditional semiconductors: for example, the bandgap of germanium (E = 0.66 eV) roughly matches that of individual SC-SWNTs of diameter 1.5 nm, but in the range 300-100 K, the intrinsic carrier concentration in Ge decreases by more than 10 orders of magnitude while the conductivity of a typical SC-SWNT network decreases by less than a factor of 4. Clearly this weak modulation of the conductivity hinders the application of SC-SWNT films as field effect transistors and photodetectors, and it is the purpose of this Account to analyze the mechanism of the electrical transport leading to the unusually weak temperature dependence of the electrical conductivity of such networks. Extrinsic factors such as the contribution of residual amounts of MT-SWNTs arising from incomplete separation and doping of SWNTs are evaluated. However, the observed temperature dependence of the conductivity indicates the presence of midgap electronic states in the semiconducting SWNTs, which provide a source of low-energy excitations, which can contribute to hopping conductance along the nanotubes following fluctuation induced tunneling across the internanotube junctions, which together dominate the low temperature transport and limit the resistivity of the films. At high temperatures, the intrinsic carriers thermally activated across the bandgap as in a traditional semiconductor became available for band transport. The midgap states pin the Fermi level to the middle of the bandgap, and their origin is ascribed to defects in the SWNT walls. The presence of such midgap states has been reported in connection with scanning tunneling spectroscopy experiments, Coulomb blockade observations in low temperature electrical measurements, selective electrochemical deposition imaging, tip-enhanced Raman spectroscopy, high resolution photocurrent spectroscopy, and the modeling of the electronic density of states associated with various defects. Midgap states are present in conventional semiconductors, but what is unusual in the present context is the extent of their contribution to the electrical transport in networks of semiconducting SWNTs. In this Account, we sharpen the focus on the midgap states in SC-SWNTs, their effect on the electronic properties of SC-SWNT networks, and the importance of these effects on efforts to develop electronic and photonic applications of SC-SWNTs.

Dramatic improvement in water retention and proton conductivity in electrically aligned functionalized CNT/SPEEK nanohybrid PEM

Nanohybrid membranes of electrically aligned functionalized carbon nanotube f CNT with sulfonated poly ether ether ketone (SPEEK) have been successfully prepared by solution casting. Functionalization of CNTs was done through a carboxylation and sulfonation route. Further, a constant electric field (500 V·cm(-2)) has been applied to align CNTs in the same direction during the membrane drying process. All the membranes are characterized chemically, thermally, and mechanically by the means of FTIR, DSC, DMA, UTM, SEM, TEM, and AFM techniques. Intermolecular interactions between the components in hybrid membranes are established by FTIR. Physicochemical measurements were done to analyze membrane stability. Membranes are evaluated for proton conductivity (30-90 °C) and methanol crossover resistance to reveal their potential for direct methanol fuel cell application. Incorporation of f CNT reasonably increases the ion-exchange capacity, water retention, and proton conductivity while it reduces the methanol permeability. The maximum proton conductivity has been found in the S-sCNT-5 nanohybrid PEM with higher methanol crossover resistance. The prepared membranes can be also used for electrode material for fuel cells and batteries.

Influence of the carbon nanotube surface modification on the microstructure of thermoplastic binders

The structural properties of polymer nanocomposites based on thermoplastic polyimides filled with surface-modified carbon nanotubes (CNT) have been studied by means of fully-atomistic molecular-dynamics simulations.

Bio-based hyperbranched poly(ester amide)-MWCNT nanocomposites: multimodalities at the biointerface

There has been a growing interest in the use of nanomaterials featuring potent biocompatibility and biodegradability together with the added facet of antibacterial activity, particularly against drug-resistant bacterial species. Addressing these three features at the biointerface, we report the fabrication of multimodal bio-based hyperbranched poly(ester amide) (HBPEA)-microwave functionalized multiwalled carbon nanotube (f-MWCNT) nanocomposites by incorporation of various weight percentages (1, 2.5, and 5 wt%) of the f-MWCNTs into HBPEA by using an ex situ polymerization technique. Fourier transform infrared spectroscopy confirmed the structural changes upon interaction of the f-MWCNTs with HBPEA. The formation of thermosetting nanocomposites resulted in an acceptable improvement of the desired properties including their mechanical properties (∼170%), instrumental for providing mechanical integrity in cultured cells. The nanocomposite films were found to be biocompatible substrates for the in vitro adhesion and proliferation of peripheral blood mononuclear cells (PBMC) with enhanced cell viability correlating with the increase of the f-MWCNT content. The antibacterial results, monitored by a CFU count and the protein concentration, demonstrated that the prepared nanocomposites were more toxic towards Gram positive bacteria and Mycobacterium smegmatis than the Gram negative ones. The damage of bacterial cells upon interaction with the nanocomposites was validated by UV-visible spectroscopy and a SEM study. The antibacterial and biocompatibility studies suggested that these microporous nanocomposite films (3D interconnected porous structures with pore diameters of 5-105 μm and a porosity of 39.90%) possess concurrent long-term lethal activity against the bacterial cells and biocompatibility with PBMC. Thus, the prepared nanocomposites may find potential bio-medical applications, particularly as antimicrobial dressing materials for infected burn wounds.

25th anniversary article: Chemically modified/doped carbon nanotubes & graphene for optimized nanostructures & nanodevices

Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real-life applications without precise controllability of the material structures and properties. This invited article to celebrate the 25th anniversary of Advanced Materials reviews the current research status in the chemical modification/doping of carbon nanotubes and graphene and their relevant applications with optimized structures and properties. A broad aspect of specific correlations between chemical modification/doping schemes of the graphitic carbons with their novel tunable material properties is summarized. An overview of the practical benefits from chemical modification/doping, including the controllability of electronic energy level, charge carrier density, surface energy and surface reactivity for diverse advanced applications is presented, namely flexible electronics/optoelectronics, energy conversion/storage, nanocomposites, and environmental remediation, with a particular emphasis on their optimized interfacial structures and properties. Future research direction is also proposed to surpass existing technological bottlenecks and realize idealized graphitic carbon applications.

High-yield photolytic generation of brominated single-walled carbon nanotubes and their application for gas sensing

We present a facile and efficient photobromination technique for the covalent sidewall functionalization of SWNT using N-bromosuccinamide as the bromine source.

Functionalization of Carboxylated Multi-Wall Nanotubes with Derivatives ofN1-(11H-Indeno[1,2-b]quinoxalin-11-ylidene)benzene-1,4-diamine

Quinoxaline derivatives are compounds with pharmaceutical applications. In this study, derivatives ofN1-(11H-indeno[1,2-b]quinoxalin-11-ylidene)benzene-1,4-diamine were synthesized and attached to carboxylated multi-wall nanotubes (MWNT–COOH). Functionalized carbon nanotubes were characterized by scanning electron microscopy (SEM) to study the shape of structures, transmission electron microscopy (TEM), fast Fourier transform infrared (FT-IR), Raman spectroscopy, and elemental analysis.

Fast carbon nanotube detectors for micro gas chromatographs

Highly sensitive and completely reversible chemiresistor detectors based on carbon nanotubes (CNTs) were fabricated for multi-component chemical analysis. CNT detectors were used in a series configuration with a gas chromatography column and exposed to a mixture of nine different compounds. It is shown that CNT detectors were able to show parts per billion (pbb) sensitivity responses to each individual component of the mixture and detect nine distinct chemical compounds in roughly 210 s when the detector operates in current stimulated desorption (CSD) mode. This is the first demonstration of an uncoated CNT detector to analyze multi-component chemical mixtures providing an alternative yet simple sensing approach for online air quality control and health monitoring applications.

Sonocatalytic epoxidation of alkenes by vanadium-containing polyphosphomolybdate immobilized on multi-wall carbon nanotubes

A Keggin type polyoxometalate (POM) has been immobilized in the unique network structure of multi-wall carbon nanotubes (CNTs). The vanadium-containing polyphosphomolybdate (PVMo) supported on CNTs, which was prepared by a one-step solid-state reaction, was characterized by FT-IR, XRD, SEM and elemental analyses. These uniform nanoparticles have an average size 20-30nm. Furthermore, due to the chemical interaction between PVMo and carboxylic acid groups, PVMo nanoparticles were successfully immobilized on the CNTs. Moreover, the obtained composite was found as an efficient catalyst for oxidation of hydrocarbons under reflux and ultrasonic irradiation (US) conditions.

Sonocatalytic oxidation of olefins catalyzed by heteropolyanion-montmorillonite nanocomposite

A Keggin-type heteropolyanion compound (HPO) was doped within the montmorillonite (MMT) structure by impregnation method. The synthesized catalyst was characterized by FT-IR, XRD, UV-vis, CV, SEM and elemental analysis. Based on chemical adsorption between HPO, and hydroxyl surface groups, HPOs nanoparticles were successfully located on the MMT. Moreover, the obtained nanocomposite was found as an efficient catalyst for oxidation of hydrocarbons under reflux and ultrasonic irradiation conditions.

pH-sensitive intracellular photoluminescence of carbon nanotube-fluorescein conjugates in human ovarian cancer cells

To add to the understanding of the properties of functionalized carbon nanotubes in biological applications, we report a monotonic pH sensitivity of the intracellular fluorescence emission of single-walled carbon nanotube-fluorescein carbazide (SWCNT-FC) conjugates in human ovarian cancer cells. Light-stimulated intracellular hydrolysis of the amide linkage and localized intracellular pH changes are proposed as mechanisms. SWCNT-FC conjugates may serve as intracellular pH sensors.

Enrichment mechanism of semiconducting single-walled carbon nanotubes by surfactant amines

Utilization of single-walled carbon nanotubes (SWNTs) in high-end applications hinges on separating metallic (met-) from semiconducting (sem-) SWNTs. Surfactant amines, like octadecylamine (ODA) have proven instrumental for the selective extraction of sem-SWNTs from tetrahydrofuran (THF) nanotube suspensions. The chemical shift differences along the tail of an asymmetric, diacetylenic surfactant amine were used to probe the molecular dynamics in the presence and absence of nanotubes via NMR. The results suggest that the surfactant amine head is firmly immobilized onto the nanotube surface together with acidic water, while the aliphatic tail progressively gains larger mobility as it gets farther from the SWNT. X-ray and high-resolution TEM studies indicate that the sem-enriched sample is populated mainly by small nanotube bundles containing ca. three SWNTs. Molecular simulations in conjunction with previously determined HNO(3)/H(2)SO(4) oxidation depths for met- and sem-SWNTs indicate that the strong pinning of the amine surfactants on the sem-enriched SWNTs bundles is a result of a well-ordered arrangement of nitrate/amine salts separated with a monomolecular layer of H(2)O. Such continuous 2D arrangement of nitrate/amine salts shields the local environment adjacent to sem-enriched SWNTs bundles and maintains an acidic pH that preserves nanotube oxidation (i.e., SWNT(n+)). This, in turn, results in strong interactions with charge-balancing NO(3)(-) counterions that through their association with neutralized surfactant amines provide effective THF dispersion and consequent sem enrichment.

Single walled carbon nanotube reactivity and cytotoxicity following extended aqueous exposure

Globally carbon nanoparticles are increasingly utilized, yet it is not known if these nanoparticles pose a threat to the environment or human health. This investigation examined 'as-prepared', and acid cleaned carbon nanoparticle physicochemical characteristics (by FTIR, TEM, FESEM, UV-VIS and X-ray microanalysis), and whether these characteristics changed following 2.5-7yr exposure to pH neutral saline or fresh water. To determine if these aqueous aged nanotubes were cytotoxic, these nanotubes were incubated with human epithelial monolayers and analyzed for cell viability (vital staining) and ultrastructural nanoparticle binding/localization (TEM, FESEM). The presence of Ni and Y catalyst, was less damaging to cells than CNT lattice surface oxidation. Extended fresh water storage of oxidized CNTs did not reduce surface reactive groups, nor lessen cell membrane destruction or cell death. However storing oxidized CNTs in saline or NOM significantly reduced CNT-induced cell membrane damage and increased cell survival to control levels.