Sidewalls Of Carbon Nanotubes Research Articles

Noncovalent functionalization of pristine CVD single-walled carbon nanotubes with 3d metal(II) phthalocyanines by adsorption from the gas phase

Noncovalent hybrids of carbon nanotubes (CNTs) with phthalocyanines (Pcs) is a subject of growing research effort focused on the development of new efficient organic photovoltaic cells, heterogeneous catalysts, lithium batteries, gas sensors, field effect transistors, among other possible applications. The main advantage of using unsubstituted Pcs is their very moderate cost and easy commercial availability. Unfortunately, the deposition of unsubstituted Pcs onto CNT sidewalls via the traditional liquid-phase strategy proves to be very problematic due to an extremely poor solubility of Pcs. At the same time, unsubstituted free-base H2Pc ligand and many of its transition metal complexes exhibit high thermal stability and volatility under reduced pressure, which allows for their physical vapor deposition onto solid surfaces. In the present work, we demonstrated the possibility of simple, fast, efficient and environmentally friendly noncovalent functionalization of single-walled CNTs (SWNTs) with a series of 3d metal(II) phthalocyanines Me(II)Pc, where Me = Co, Ni, Cu and Zn. The functionalization can be performed at 400–500 °C under moderate vacuum, and takes about 2–3 h only. The nanohybrids obtained were characterized by means of Fourier-transform infrared, Raman, UV–vis and energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), scanning and transmission electron microscopy. TGA suggested that Pc weight content is 30%, 17% and 35% for NiPc, CuPc and ZnPc, respectively (CoPc exhibited anomalous behavior), which is close to the estimates from EDS spectra of 24–39%, 27–36% and 27–44% for CoPc, CuPc and ZnPc, respectively. A strong increase in intensity of D band in the Raman spectra of SWNT‒Pc hybrids, as compared to that of pristine nanotubes, was interpreted as very strong interactions between Pc molecules and SWNT sidewalls. Very high absolute values of binding energies of 32.46–37.12 kcal/mol and the patterns of HOMO and LUMO distribution, calculated at the PBE-D/DNP level of density functional theory, also suggested that the interactions between metal phthalocyanines studied and nanotube sidewalls are very strong.

Functionalized Carbon Nanotubes with Ni(II) Bipyridine Complexes as Efficient Catalysts for the Alkaline Oxygen Evolution Reaction

Among current technologies for hydrogen production as an environmentally friendly fuel, water splitting has attracted increasing attention. However, the efficiency of water electrolysis is severely limited by the large anodic overpotential and sluggish reaction rate of the oxygen evolution reaction (OER). To overcome this issue, the development of efficient electrocatalyst materials for the OER has drawn much attention. Here, we show that organometallic Ni(II) complexes immobilized on the sidewalls of multiwalled carbon nanotubes (MWNTs) serve as highly active and stable OER electrocatalysts. This class of electrocatalyst materials is synthesized by covalent functionalization of the MWNTs with organometallic Ni bipyridine (bipy) complexes. The Ni-bipy-MWNT catalyst generates a current density of 10 mA cm–2 at overpotentials of 310 and 290 mV in 0.1 and 1 M NaOH, respectively, with a low Tafel slope of ∼35 mV dec–1, placing the material among the most active OER electrocatalysts reported so far. Different ...

Photophysical Properties of Porphyrin Dimer–Single-Walled Carbon Nanotube Linked Systems

Porphyrin dimers were covalently grafted onto electron-accepting single-walled carbon nanotube (SWNT) sidewalls by direct aryl radical addition reaction with an m- or p-phenylene linker with the help of π–π interaction between the porphyrins. A splitting of the porphyrin Soret band and DFT calculations supported the selective formation of the porphyrin dimers on the sidewall of SWNTs. Photoexcitation of the porphyrin dimers on the SWNT resulted in the formation of the exciplex state, which directly decayed to the ground state without yielding the complete charge-separated state. Lifetimes of the porphyrin dimer–SWNT exciplex were longer than that of a porphyrin monomer–SWNT exciplex due to the stabilization by π-electron interaction over two porphyrin rings. In addition, the weaker electronic coupling through the meta-linkage than the para-one may be responsible for the exciplex lifetime of the porphyrin dimer–SWNT with the m-phenylene linker (49 ps) longer than that with the p-phenylene one (24 ps). The ...

Synthesis of a poly(amidoamine) dendrimer having a 1,10-bis(decyloxy)decane core and its use in fabrication of carbon nanotube/calcium carbonate hybrids through biomimetic mineralization

A new dendritic dispersant of carbon nanotubes (CNTs) was synthesized and applied for the noncovalent functionalization of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The 1,10-bis(decyloxy)decane core of the poly(amidoamine) dendrimer strongly adhered to the sidewalls of CNTs to form CNT/dendrimer supramolecular nanocomposites having many carboxyl groups (–COOH) on the surface. Then, crystallization of calcium carbonate (CaCO3) by the CO2 diffusion technique in aqueous environments using the CNT/dendrimer supramolecular nanocomposites as scaffolds afforded monodisperse spherical CNT/CaCO3 nanohybrids consisting of CNTs and calcite nanocrystals. The morphologies of the SWCNT/CaCO3 hybrids and MWCNT/CaCO3 hybrids were almost the same.

The functionalization of carbon nanotubes to enhance the efficacy of the anticancer drug paclitaxel: a molecular dynamics simulation study.

Carbon nanotubes (CNTs) are widely used in drug delivery systems (DDSs) due to their unique chemical and physical properties. Investigation of interactions between biomolecules and CNTs is an interesting and important subject in biological applications. In this study, we used molecular dynamics (MD) simulation to investigate the adsorption mechanism of the anticancer drug paclitaxel (PTX) on pristine and functionalized CNTs (f-CNT) in aqueous solutions. Our theoretical results show that PTX can be adsorbed on sidewalls of CNT in different methods. In the case of f-CNTs, PTX can be adsorbed on the functional groups due to the existence of polar interactions. These interactions in the CNT functionalized with polyethylene glycol (PEG), are more than the other investigated systems. Furthermore, it was found that the solubility of CNTs in aqueous solution is increased by functionalization. This is related to the intermolecular hydrogen bonds between functional groups and solvent molecules. The PEG group has the greatest effect on the solubility of the CNT in aqueous solution due to more polar interactions.

Characteristics of hydrogen plasma treated carbon nanotubes and their influence on the mechanical properties of polyetherimide-based nanocomposites

The structural phase transformation and etching of the sidewalls of multi-walled carbon nanotubes (MWCNTs) by hydrogen plasma and the effect on the dispersion and mechanical properties of polyetherimide (PEI) composites was investigated. Surface-modified MWCNTs with various plasma treatment times were characterized using FESEM, HRTEM, Raman spectroscopy, FT-IR, and XPS. The results showed that plasma treatment facilitates the attachment of functional groups while damaging and detaching the sidewalls of the MWCNTs and modifying the crystallinity of the graphene layer. The mechanical properties of the PEI composites with the modified MWCNTs depended on the degree of damage to the surface and crystallinity modification of the MWCNTs. Hydrogen plasma treatment led to a significant improvement in the dispersion and mechanical properties of PEI/MWCNT composites due to the surface modification of the MWCNTs.

Electrochemical Activation of Single-Walled Carbon Nanotubes with Pseudo-Atomic-Scale Platinum for the Hydrogen Evolution Reaction

The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. Platinum-based materials are the most active electrocatalysts for catalyzing HER, but reducing the use of Pt is required because of the high price and scarcity of Pt. Here, we achieve pseudo-atomic-scale dispersion of Pt, i.e. individual atoms or subnanometer clusters, on the sidewalls of single-walled carbon nanotubes (SWNTs) with a simple and readily upscalable electroplating deposition method. These SWNTs activated with an ultralow amount of Pt exhibit activity similar to that of commercial Pt/C with a notably higher (∼66–333-fold) Pt loading for catalyzing the HER under the acidic conditions required in proton exchange membrane technology. These catalysts resemble pseudo-atomic-scale Pt systems which are mainly composed of a few to tens of Pt atoms dispersed on the sidewalls of the SWNTs. The Pt loading is only 0.19–0.75 atom % at the electrode surface,...

Interaction between NiOx and MWСNT in NiOx/MWСNTs composite: XANES and XPS study

The current work presents the investigation of the interaction between NiOx and multi-walled carbon nanotube (MWCNTs) sidewall in NiOx/MWCNT nanocomposite, synthesized by electrochemical metal oxidation and dispersion method using the near edge X-ray absorption fine structure (XANES) and X-ray photoelectron spectroscopies. Scanning electron microscopy (SEM) illustrated that formation of the NiOx/MWCNT composite leads to decreasing of the NiOx sheets size and their dispersion among nanotubes. Comparison of the C K-edge XANES spectra of the initial high-purified MWCNTs with NiOx/MWCNTs indicates significant shape changes of the nanocomposite spectrum. Changes in π resonance and inter-resonance region of C K-edge XANES spectrum showed the appearance of new chemical bonds in the carbon nanotubes as result of formation of NiOx/MWCNTs nanocomposite, associated with partial chemical interaction of NiOx with CNT walls. The chemical state of Ni in the composite compound is 2+ and there is Ni with different oxygen surroundings in the NiOx/MWCNT nanocomposite.

Explosion Study of Nitromethane Confined in Carbon Nanotube Nanocontainer via Reactive Molecular Dynamics

Explosion dynamics of confined nitromethane (NM) fluid has been investigated by using nonequilibrium reactive molecular dynamics. For the confinement, NM was encapsulated into a nanocontainer, which is the capped (20, 20) armchair carbon nanotube (CNT). After thermal energy was injected into confined NM at various densities, the nanobomb consisting of NM and CNT was fully decomposed including bursting phenomena. We found that the time for explosion was reduced as density and initial temperature increased. While NM was being decomposed into intermediates, defects of Stone–Wales type (5–7 carbon atoms ring) or high-order rings were randomly formed at the cap and side wall of CNT. Subsequently, the intermediates functionalized carbon atoms at the defects, from which nanoholes were evolved. The CNT burst when the size of nanohole became about 8 A. Further, we demonstrated that defective CNT with vacancy exploded faster because carbon atoms at defect sites played a seed role to make nanoholes. This theoretical...

Terahertz conductivity engineering in surface decorated carbon nanotube films by gold nanoparticles.

We report the controllable conductivity of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes with their surface walls decorated by gold nanoparticles (Au NPs) with varying concentration in terahertz (THz) frequency range. Colloidal Au NPs of nominal diameter ∼15 nm are synthesized by the reduction of gold chloride solution using tri-sodium citrate. A simple chemical route is followed to attach Au NPs on the surfaces of both types of carbon nanotubes (CNTs). The attachment of Au NPs on the sidewalls of CNTs is confirmed by UV-visible spectroscopy and scanning electron microscope images. THz spectroscopic measurements are carried out at room temperature in transmission geometry in the frequency range of 0.3-2.0THz. It is found that the THz conductivity of the surface decorated SWNT composites can either be increased or decreased by ±15% than that of the as-prepared SWNT composites by carefully choosing the Au NP concentration. The conductivity variation is qualitatively explained in terms of carrier trapping potential for low Au NP density, and alternative carrier conduction pathways at higher Au NP density and analyzed with the help of a modified universal dielectric relaxation model.

Selective Adsorption and Separation through Molecular Filtration by Hyperbranched Poly(ether amine)/Carbon Nanotube Ultrathin Membranes.

In response to the increasing public awareness of serious dye-contained wastewater contamination, we herein fabricated a novel anthracene-containing hyperbranched poly(ether amine) (hPEA-AN)/carbon nanotube (CNT) ultrathin membrane (UTM), which combined both the merits of the conventional dye adsorption strategy and membrane filtration process, to implement efficient selective adsorption of dye molecules and also the separation of dye mixtures by molecular filtration. Taking advantage of the π-π stacking interactions between anthracene and CNT sidewalls and hydrophobic interactions, CNTs were coated tightly with hPEA-AN to form the hPEA-AN@CNT complex, which can be well-dispersed very stably in water. The formation of the hPEA-AN@CNT complex was confirmed using X-ray photoelectron spectroscopy, Raman spectra, fluorescence spectra, and thermogravimetric analysis. Meanwhile, a simple filtration process was applied to prepare hPEA-AN@CNT UTMs with a thickness of 1.5 μm, which can be further cross-linked through photodimerization of anthracene moieties. The UTMs represented selective adsorption behaviors toward hydrophilic dyes even with similar backbones and the same charge states, namely, they showed high adsorption capacities (Qeq) toward eosin B, erythrosin B (ETB), 4',5'-dibromofluorescein, and Evans blue (EVB) dyes up to 300 μmol/g while showing low adsorption capacities toward calcein (Cal), methyl red, and Ponceau S dyes. On the basis of this unique selective adsorption, molecular filtration was then realized toward mixed ETB/Cal and EVB/Cal dyes, with a separation efficiency of up to 100% and regeneration without an obvious efficiency decrease.

Enhancement of Photoluminescence from Semiconducting Nanotubes in Aqueous Suspensions due to Cysteine and Dithiothreitol Doping: Influence of the Sonication Treatment.

The influence of tip sonication duration on the spectral characteristics of carbon single-walled nanotubes (SWNTs) in aqueous suspension with single-stranded DNA (ssDNA) has been studied by NIR luminescence, NIR absorption, and Raman spectroscopy. It was revealed that prolongation of sonication leads to weakening of the SWNT polymer coverage and appearance of additional defects on the nanotube surface. Prolongation of the tip sonication treatment of SWNT/ssDNA from 30 to 90 min leads to the increase of the number of individual nanotubes in the aqueous suspension, but it significantly decreases the photoluminescence (PL) from semiconducting SWNTs because more defects are formed on the nanotube surface. At probing the SWNT/ssDNA emission with cysteine or dithiothreitol (DTT) doping the nanotube aqueous suspension showed the different PL intensity enhancement depending on the duration of the sonication treatment and on the ability of these reducing agents to passivate emission-quenching defects on the carbon nanotube sidewall. The magnitude of the PL enhancement rises with sonication prolongation and depends on the nanotube chirality. Tight and ordered polymer coverage of (6,4) nanotubes hampers the access of the reducing agent to emission-quenching defects on the nanotube surface and provides the weaker PL intensity increasing while (7,5) nanotubes show the strongest reaction to the doping effect. The comparison of cysteine and DTT ability to passivate the emission-quenching defects showed the higher efficiency of DTT doping. This prevailing is explained by the stronger reducing activity of DTT which is determined by a lower redox potential of this molecule.

Tuning the carbon nanotube photoluminescence enhancement at addition of cysteine through the change of external conditions

The enhancement of the photoluminescence (PL) from the semiconducting single-walled carbon nanotubes suspended with single-stranded DNA (ssDNA) in water observed after amino acids doping is the largest at cysteine addition. The PL intensity increased through the passivation of p-defects on the carbon nanotube sidewall by the cysteine molecules due to thiol group. The effect of several external factors on the cysteine-induced enhancement of PL from carbon nanotubes covered with ssDNA was studied: UV irradiation, tip or bath sonication treatment of the suspension, the ionic strength and pH of aqueous suspension. It turned out that all these factors have an essential influence on the dependence of the PL enhancement on the cysteine concentration through inducing of additional defects on nanotube as well as a change of the nanotube surface coverage with polymer. The obtained experimental results demonstrated that PL from carbon nanotubes can be exploited successfully for the monitoring of cysteine concentration in aqueous solution.

A MnO2/Graphene Oxide/Multi-Walled Carbon Nanotubes-Sulfur Composite with Dual-Efficient Polysulfide Adsorption for Improving Lithium-Sulfur Batteries.

Lithium-sulfur batteries can potentially be used as a chemical power source because of their high energy density. However, the sulfur cathode has several shortcomings, including fast capacity attenuation, poor electrochemical activity, and low Coulombic efficiency. Herein, multi-walled carbon nanotubes (CNTs), graphene oxide (GO), and manganese dioxide are introduced to the sulfur cathode. A MnO2/GO/CNTs-S composite with a unique three-dimensional (3D) architecture was synthesized by a one-pot chemical method and heat treatment approach. In this structure, the innermost CNTs work as a conducting additive and backbone to form a conducting network. The MnO2/GO nanosheets anchored on the sidewalls of CNTs have a dual-efficient absorption capability for polysulfide intermediates as well as afford adequate space for sulfur loading. The outmost nanosized sulfur particles are well-distributed on the surface of the MnO2/GO nanosheets and provide a short transmission path for Li+ and the electrons. The sulfur content in the MnO2/GO/CNTs-S composite is as high as 80 wt %, and the as-designed MnO2/GO/CNTs-S cathode displays excellent comprehensive performance. The initial specific capacities are up to 1500, 1300, 1150, 1048, and 960 mAh g-1 at discharging rates of 0.05, 0.1, 0.2, 0.5, and 1 C, respectively. Moreover, the composite cathode shows a good cycle performance: the specific capacity remains at 963.5 mAh g-1 at 0.2 C after 100 cycles when the area density of sulfur is 2.8 mg cm-2.

A Fully-Sealed Carbon-Nanotube Cold-Cathode Terahertz Gyrotron.

Gigahertz to terahertz radiation sources based on cold-cathode vacuum electron technology are pursued, because its unique characteristics of instant switch-on and power saving are important to military and space applications. Gigahertz gyrotron was reported using carbon nanotube (CNT) cold-cathode. It is reported here in first time that a fully-sealed CNT cold-cathode 0.22 THz-gyrotron is realized, typically with output power of 500 mW. To achieve this, we have studied mechanisms responsible for CNTs growth on curved shape metal surface, field emission from the sidewall of a CNT, and crystallized interface junction between CNT and substrate material. We have obtained uniform growth of CNTs on and direct growth from cone-cylinder stainless-steel electrode surface, and field emission from both tips and sidewalls of CNTs. It is essential for the success of a CNT terahertz gyrotron to have such high quality, high emitting performance CNTs. Also, we have developed a magnetic injection electron gun using CNT cold-cathode to exploit the advantages of such a conventional gun design, so that a large area emitting surface is utilized to deliver large current for electron beam. The results indicate that higher output power and higher radiation frequency terahertz gyrotron may be made using CNT cold-cathode electron gun.

Scanning Electrochemical Microscopy of Carbon Nanomaterials and Graphite.

Carbon materials are tremendously important as electrode materials in both fundamental and applied electrochemistry. Recently, significant attention has been given not only to traditional carbon materials, but also to carbon nanomaterials for various electrochemical applications in energy conversion and storage as well as sensing. Importantly, many of these applications require fast electron-transfer (ET) reactions between a carbon surface and a redox-active molecule in solution. It, however, has not been well understood how heterogeneous ET kinetics at a carbon/solution interface is affected by the electronic structure, defect, and contamination of the carbon surface. Problematically, it is highly challenging to measure the intrinsic electrochemical reactivity of a carbon surface, which is readily passivated by adventitious organic contaminants. This Account summarizes our recent studies of carbon nanomaterials and graphite by scanning electrochemical microscopy (SECM) not only to reveal the fast ET kinetics of simple ferrocene derivatives at their graphitic surfaces, but also to obtain mechanistic insights into their extraordinary electrochemical reactivity. Specifically, we implemented new principles and technologies to reliably and reproducibly enable nanoscale SECM measurements. We took advantage of a new SECM imaging principle to resolve the high reactivity of the sidewall of individual single walled carbon nanotubes. In addition, we developed SECM-based nanogap voltammetry to find that monolayer graphene grown by chemical vapor deposition yields an unprecedentedly high standard ET rate constant, k(0), of ≥25 cm/s, which was >1000 times higher than that reported in the literature. Remarkably, the nonideal asymmetry of paired nanogap voltammograms revealed that the high reactivity of graphitic surfaces is compromised by their contamination with airborne hydrocarbons. Most recently, we protected the clean surface of highly oriented pyrolytic graphite from the airborne contaminants during its exfoliation and handling by forming a water adlayer to obtain a reliable k(0) value of ≥12 cm/s from symmetric pairs of nanogap voltammograms. We envision that SECM of clean graphitic surfaces will enable us to reliably address not only effects of their electronic structures on their electrochemical reactivity, but also the activity of carbon-based or carbon-supported electrocatalysts for fuel cells and batteries.

Remarkably enhanced photocatalytic activity by sulfur-doped titanium dioxide in nanohybrids with carbon nanotubes

TiO2 doped S nanohybrids with carbon nanotubes (CNTs) were synthesized with CNTs, thiourea and TiO2 nanoparticles. The result indicated that the TiO2 nanoparticles with about 8nm in size are attached on the sidewall of CNTs. The nanohybrids material can absorb at longer wavelength and the absorption even covers the whole range of visible region than that only TiO2 nanoparticles. Application of the catalysts to photocatalytic degradation of methylene blue (MB) was tested under visible light irradiation. The result suggests that a high MB degradation activity of S-TiO2/CNTs due to a reduce band gap of TiO2 when S is doped, and the decrease in the possibility of electron–hole recombination by CNTs. In addition, the density functional-theory (DFT) calculations of the electronic band structures and density of states (DOS) to understand the bonding states between TiO2 and CNTs, proved that the TiO2/CNTs system is stable.

Conjugation of insulin onto the sidewalls of single-walled carbon nanotubes through functionalization and diimide-activated amidation

PurposeThe high aspect ratio of carbon nanotubes (CNTs) allows the attachment of compounds that enhance the functionality of the drug vehicle. Considering this, use of CNTs as a multifunctional insulin carrier may be an interesting prospect to explore.Materials and methodsThe carboxylic acid groups were functionalized on the sidewalls of single-walled CNTs (SWCNTs) followed by diimidation to form amide bonds with the amine groups of the insulin.ResultsScanning transmission electron microscopy and transmission electron microscopy establish clear conjugation of insulin onto the surface of nanotube sidewalls. The incorporation of insulin further increased the solubility of SWCNTs in biological solution for the tested period of 5 months. Bicinchoninic acid assay confirms that 0.42 mg of insulin could be attached to every 1 mg of carboxylated SWCNTs.ConclusionWith the successful conjugation of insulin to SWCNTs, it opens up the potential use of SWCNTs as an insulin carrier which in need of further biological studies.

Probing Diels–Alder reactivity on a model CNT sidewall

We have synthesized a cycloparaphenylene containing a perylene motif that is a model for a carbon nanotube sidewall. The reactivity of the sidewall model towards a Diels–Alder reaction using a masked acetylene was examined and similar reactivity was observed between the macrocyclic and planar substrate. This study suggests that a Diels–Alder reaction is a viable method for carbon nanotube growth using an appropriate template.

Carbon nanobuds based on carbon nanotube caps: a first-principles study.

Based on density functional theory calculations, we here show that the formation of a fullerene C60 carbon "nanobud" (CNB) on carbon nanotube (CNT) caps is energetically more favorable than that on CNT sidewalls. The dominant CNB formation mode for CNT caps is found to be the [2 + 2] cycloaddition reaction as in the conventional CNT sidewall case. However, it is identified to be exothermic in contrast to the endothermic reaction on CNT sidewalls. Computed reaction pathways further demonstrate that the formation (dissociation) barrier for the CNT cap-based CNB is slightly lower (significantly higher) than that of the CNT sidewall-based CNB, indicating an easier CNB formation as well as a higher structural stability. Additionally, performing matrix Green's function calculations, we study the charge transport properties of the CNB/metal electrode interfaces, and show that the C60 bonding to the CNT cap or open end induces resonant transmissions near the Fermi level. It is also found that the good electronic linkage in the CNT cap-C60 cycloaddition bonds results in the absence of quantum interference patterns, which contrasts with the case of the CNB formed on an open-ended CNT that shows a Fano resonance profile.