Sidewall Functionalization Of Carbon Nanotubes Research Articles

Molecular dynamics of reactions between (4,0) zigzag carbon nanotube and hydrogen peroxide under extreme conditions

ABSTRACTSingle-wall carbon nanotubes (CNTs) have been suggested as potential materials for use in next-generation gas sensors. The sidewall functionalisation of CNTs facilitates gas molecule adsorption. In this study, density functional theory (DFT)-based ab initio molecular dynamics simulations are performed for a periodic zigzag single-wall (4,0) CNT surrounded by a monolayer of hydrogen peroxide molecules in an attempt to find conditions that favour sidewall functionalisation. The dependency of dynamics on charge states of the system is examined. It is found negative charges favour reactions that result in the functionalisation of the CNT. First principles molecular dynamics of defect formation yields chemically reasonable structure of stable defects, which can be reproduced in CNTs of any diameter and chirality. The explored hydroxyl and hydroperoxyl defects increase conductivity in a large diameter (10,0) CNT, while decrease conductivities in a small diameter (4,0) CNT.

Sidewall Functionalization of Carbon Nanotubes as a Method of Controlling Structural Transformations of the Magnetically Triggered Nanocontainer: A Molecular Dynamics Study

The magnetically triggered nanocontainer, that is, magnetic nanoparticles covalently linked to carbon nanotube tips, is able to make reversible cycles of capping and uncapping of the nanotube inner cavity. The capped form is when the magnetic nanoparticles adhere to the nanotube tips, whereas the uncapped configuration forms when the magnetic nanoparticle shifts to the nanotube sidewall. The feasibility and likelihood of these two structural forms of the nanocontainer depend on the energetic profile associated with the transitions between them. This paper discusses two approaches for controlling that balance: the covalent functionalization of the nanotube sidewalls by incorporation of polar amide groups and noncovalent functionalization based on adsorption of charged fine colloid nanoparticles. Single- and triple-walled carbon nanotubes were analyzed as was the presence of cisplatin molecules encapsulated in the nanotube inner cavities. Both approaches might result in obtaining the preferred energetic balance, that is, a less stable uncapped state and relatively low activation barrier for spontaneous transition from the uncapped to the capped state. However, adsorption of fine colloids turned out to be too weak to provide long-term stability of the system. Amide functionalization provides the best results in terms of the energetic profile, stability, and other system parameters.

Laser Induced Changes of the Raman Spectra of Pristine and Poly(<i>tert</i>-Butyl Acrylate) Functionalized Carbon Nanotubes

Pristine and poly(tert-butyl acrylate) (PTBA) functionalized carbon nanotubes are continuously exposed to 2.41 eV laser irradiation while collecting Raman spectra. The loss of the intensity of the radial breathing modes (RBMs) of small metallic PTBA functionalized nanotubes is less than that of pristine nanotubes. A reduction of the intensity of the G− band of pristine SWNTs occurs such that the overall shape of the G band evolves to resemble that of the PTBA functionalized sample. Complementing the measurement of the ratio of intensities of the D and G bands, the laser-induced spectral changes provide another way to determine the sidewall functionalization of carbon nanotubes. The laser-induced changes of the G and RBM bands are consistent with the greater sidewall reactivity of small metallic nanotubes toward functionalization with PTBA and reaction with photosensitized oxygen.

Sidewall functionalisation of carbon nanotubes by addition of diarylcarbene derivatives

Functionalisation of carbon nanotubes by carbene derivatives is attracting attention as a way of increasing their dispersibility, processability and also to control the electronic properties of carbon nanotubes. We have explored the functionalisation of a sample containing single- and double-walled carbon nanotubes with different diaryldiazomethane derivatives by using the high reactivity of the intermediate carbenes formed under actinic irradiation to insert to the carbon nanotube structure. Besides characterisation by bulk techniques (Raman, FTIR and TGA), we provide direct evidence on the location of the functional groups on the sidewalls of the carbon nanotubes by an electron microscopy study of a heavy-element tagged sample. The functionalised carbon nanotubes present higher dispersibilities than the purified samples and are prone to further derivatisation, with potential application in the areas of composite materials or molecular electronics.

Covalent Sidewall Functionalization of Carbon Nanotubes by a “Formation−Degradation” Approach

A diazonium salt-based strategy is employed to form a covalently attached multilayer of diphenyl disulfide on the surface of single-walled carbon nanotubes (SWCNTs) or multiwalled carbon nanotubes (MWCNTs). The interlayer S−S bonds are subsequently degraded reductively to produce essentially a single layer of thiophenols (or closely related derivatives) on the nanotube surface. The functionalization is achieved in what is effectively a one-pot procedure since the involved transformations are performed without intermediate workup. This “formation−degradation” modification approach is unique in the sense that it allows the generation of a thin well-defined molecular layer in spite of the involvement of highly reactive radicals in the first step. Transmission electron microscopy and thermogravimetric analyses support the approach proposed and reveal that a significant initial functionalization is achieved. In UV−vis spectroscopy, the disappearance of the Van Hove singularities of the SWCNT after the reaction is consistent with a covalent sidewall functionalization. Moreover, the resulting thin layer of thiophenols is reactive forming Au−S bonds with a macroscopic Au surface. Finally, the peripheral thiophenol groups of the MWCNT are employed as chemical linkers for anchoring gold nanoparticles and rods in a site-selective manner.

Kinetically Controlled Side-Wall Functionalization of Carbon Nanotubes by Nitric Acid Oxidation

The nitric acid oxidation followed by sodium hydroxide washing was applied for functionalization of single-walled carbon nanotubes (SWCNTs), few-walled CNTs (FWCNTs), and multiwalled CNTs (MWCNTs). The surface functionalization of CNTs via acidic oxidation was studied by transmission electron microscopy, Raman scattering spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The oxidation of CNTs involves the exfoliation of functionalized carbon layers into smaller carbonaceous fragments (CF), which might influence the performance of composite materials based on modified CNTs. Optimizing oxidation time increased the selectivity to thermodynamically unstable functionalized CNTs. Thicker CNTs, including FWCNTs and MWCNTs, are better for high-density surface functionalization, due to higher structure stability. It was proposed that a rational selection of the oxidation process and type of CNTs is important for the applications involving CNT-related composite materials.

Carbon nanotube surface science

This paper presents a surface science perspective on sidewall functionalisation of carbon nanotubes. Carbon nanotubes are varyingly described by physicists as extended solids or by organic chemists as molecules. As prototypical nanostructures, they are indeed a little bit of both. Their chemistry and resulting potential applications can only truly be appreciated by combining both perspectives. The emphasis of this review is on the interdependence of topography and electronic structure on one side and chemistry and reactivity of carbon nanotube sidewalls on the other side. A brief introduction to the structure of single-walled carbon nanotubes and related materials (graphite, multi-wall carbon nanotubes and fullerenes) is followed by a review of possible deviations from perfect order in nanotube sidewalls, such as defects, functional groups or non-covalent interactions with nearby entities. We then proceed to review the implications of these deviations on the sidewall local electronic structure and chemical reactivity. Site-dependent functionalisation and induced reactivity on carbon nanotube sidewalls have been proposed theoretically and we have found some initial experimental evidence that this is indeed the case. However, this is a young field and many theoretical and experimental challenges still lie ahead. Understanding site-selectivity of carbon nanotube sidewall functionalisation will allow us to tailor their properties and utilise them as components of more complex nanostructures in the future.

ELECTRONIC-STRUCTURE ENGINEERING OF CARBON NANOTUBES

A review for controlling electronic structures and chirality separation of carbon nanotubes (CNTs) is presented with the subject divided into three topics. The first topic introduces the electronic structures of CNTs and the analytical techniques to identify the chirality of CNTs. The second topic discusses band gap engineering techniques using the sidewall functionalization of CNTs. The third topic concerns several approaches in chiral and diameter-dependent separation of CNTs. The electronic-structure engineering is of critical importance for a variety of technological applications of CNTs including, for example, field-effect transistor, chemical/bio-nanosensors, the electrical conductivity and charge dissipation in polymer/CNT composites, and flexible transparent conducting films. This paper is intended to concisely review the recent advances in the experimental and theoretical CNT researches concerned with the band gap engineering and chiral separation techniques of CNTs.

Reductive Functionalization of Carbon Nanotubes

We present sidewall functionalization of carbon nanotubes via various dissolving metal reduction methods. Carbanion complexes of lithium were prepared in liquid ammonia and THF and reacted with a series of alkyl and aryl halogenides, as well as methanol resulting in the formations of alkylated, arylated, and hydrogenated nanotube derivatives, respectively. The hydrogenation reactions were also performed on graphite. Thermal stabilities and chemical compositions were determined by thermogravimetry‐mass spectrometry (TG‐MS). Characteristic decomposition peaks, observed in the range of 350–600°C, suggest the formation of covalent derivatives upon functionalization. The compositions are 0.01–0.25 side group/carbon depending on the materials. NMR and Raman spectroscopic characterizations show the structural changes due to functionalization.

Organic functionalization of sidewall of carbon nanotubes.

Using density functional theory, we have theoretically studied sidewall functionalization of carbon nanotubes (CNT) with a nucleophilic organic carbene, dipyridyl imidazolidene (DPI). When compared to the dissociated system, formation of the adduct from defect-free (5,5) tube and the DPI is weakly exothermic. However, introduction of (5,7,7,5) defect or nitrogen doping at the CNT stabilizes the adduct in both physical and chemical senses, suggesting a possible way to enrich the chemistry of sidewall functionalization. The work function of the adducts is found to decrease by approximately 0.4 eV per DPI/80 atoms. Upon binding of the DPI, electronic structures are modified in such a way that small gaps are introduced, where the size of the gap depends upon the degree of functionalization.

Sidewall Functionalization of Carbon Nanotubes.

The addition of nitrenes, nucleophilic carbenes, and radicals affords soluble, individual single-walled nanotubes (shown here is a carbene-functionalized adduct) by covalent sidewall functionalization. The characterization, a fundamental problem in nanotube chemistry, is simple to carry out.

Molecular wires, solenoids, and capacitors by sidewall functionalization of carbon nanotubes

Theoretical investigations (density-functional tight binding) about the changes of the properties of single-wall carbon nanotubes (SWNTs) by fluorination are reported. It is shown that a sidewall functionalization of SWNTs may lead to tubes with a wide variety of electronic properties, ranging from insulating over semiconducting to a metallic-like behavior. Therefore, a chemical derivatization of SWNTs may open possibilities for tailoring the electronic properties of nanotubes, providing nanoscale wires, capacitors, and solenoids.