Defective Single-walled Carbon Nanotubes Research Articles

Enhancing near-infrared photoluminescence from single-walled carbon nanotubes by defect-engineering using benzoyl peroxide

Single-walled carbon nanotubes (SWCNTs) have been modified with ester groups using typical organic radical chemistry. Consequently, traps for mobile excitons have been created, which enhanced the optical properties of the material. The proposed methodology combines the benefits of mainstream approaches to create luminescent defects in SWCNTs while it simultaneously avoids their limitations. A step change was achieved when the aqueous medium was abandoned. The selection of an appropriate organic solvent enabled much more facile modification of SWCNTs. The presented technique is quick and versatile as it can engage numerous reactants to tune the light emission capabilities of SWCNTs. Importantly, it can also utilize SWCNTs sorted by chirality using conjugated polymers to enhance their light emission capabilities. Such differentiation is conducted in organic solvents, so monochiral SWCNT can be directly functionalized using the demonstrated concept in the same medium without the need to redisperse the material in water.

Nonlocal beam model and FEM of free vibration for pristine and defective CNTs

The natural frequencies of defective single-walled carbon nanotubes are studied and compared with the values for pristine structures. In order to capture the size-dependent effects in carbon nanotubes, nonlocal stress gradient theory within a Euler-Bernoulli beam model is involved. The analytical computations are compared with finite element analysis of a structural model of carbon nanotubes. The numerical analysis of free vibrations is applied to predict the value of the nonlocal parameter. The eigenfrequencies obtained from finite element analysis are much lower compared with analytical computations of local (classical) beam model. For defective structures having small vacancy, a slight decrease in the eigenfrequencies is observed. All studied boundary conditions indicated the higher the nonlocal parameter is, the lower the natural frequencies are.

Role of defects in the sensing mechanism of CNTFET gas sensors

In nanotechnology, understanding the effect of interfaces and defects becomes critically important in determining a material's properties and device performance. Many one-dimensional and two-dimensional materials exhibit excellent physical, electrical, thermal, and optical properties, making them highly desirable for a wide array of applications. However, their low dimensionality also means their performance can be susceptible to defects in the material and the interfaces they form with other device components. Carbon nanotubes are often used in sensing applications, typically, in a field-effect transistor configuration (CNTFET). The interface between the contact electrode metal and the nanotube forms a Schottky barrier, which plays an important role in both transistor and sensor characteristics. Modifications to this interface by the environment can modulate the barrier and produce a change in device characteristics. Transistor operation can also be modified by the presence of defects in the carbon nanotube sidewall structure. This paper explores how defects in single-wall carbon nanotubes can affect the sensing mechanism of CNTFET gas sensing devices. Gas exposure measurements were performed on as-grown near pristine (low defect) nanotube devices and compared with plasma irradiated, highly defective nanotube devices. By utilizing selective passivation to isolate structural components that contribute to the sensing mechanism, the study shows that the presence of defects, and their relative densities, has a critical role in gas sensing performance. Recognizing the presence of these defects, even in as-grown nanotubes, can help reconcile seemingly contradictory results in the literature regarding the gas sensing mechanism. This work represents an important step toward understanding the effect of both interfaces and defects for carbon nanotube sensor development.

Buckling Failure Analysis of Defective Carbon Nanotubes Using Molecular Dynamics Simulation

Buckling failure under axial compression of defective single-walled carbon nanotubes (SWCNT) having (n, n) and (n, 0)-helicity is studied. Different types of vacancy defects such as monovacancy, bivacancies and tetravacancies as well as topological defect such as Stone–Thrower–Wales with their symmetric and asymmetric distribution are considered. The influence of these initial manufacturing defects on the compression properties is closely studied. The simulation results for armchair (11, 11) and zigzag (19, 0) tubes show that even a single missing atom reduces the buckling capacity of SWCNT. In general, buckling properties deteriorate higher by increasing the missing atoms and asymmetry distribution of vacancy cluster. Further, both vacancy defects and topological defects affect the compression capacity considerably. Zigzag carbon nanotubes (CNTs) have higher compression strength but are more sensitive to vacancy defects than compared to their armchair counterparts. STW defect has more detrimental effect on buckling capacity of armchair SWCNTs than its defective zigzag SWCNT counterparts.

Photoexcited Aromatic Reactants Give Multicolor Carbon Nanotube Fluorescence from Quantum Defects.

Covalent functionalization of single-wall carbon nanotubes (SWCNTs) can be valuable for modifying their electronic properties and creating fluorescent quantum defects. We report here a previously unreported category of such reactions involving interactions of photoexcited aromatic compounds with SWCNT sidewalls. When aqueous suspensions of SWCNTs are exposed to organic aromatic compounds and then irradiated by UV light, fluorescent defects are formed in the nanotubes at rates that depend on the aromatic ring substituents. In reactions with aniline or iodoaniline, strong spectral sidebands appear within 1 min. Total SWCNT photoluminescence can be enhanced by a factor as large as ∼5. Notably, emission spectra of reacted SWCNTs depend on the presence or absence of dissolved oxygen during the reaction. For (6,5) SWCNTs, treatment when oxygen is present gives an additional emission band red-shifted by 160 meV from the pristine position, whereas treatment without oxygen leads to two additional emission bands red-shifted by 140 and 270 meV. Variance spectroscopy shows the presence of individual "multicolor" nanotubes with three distinct emission bands (pristine plus two shifted). The facile generation of dual fluorescent quantum defects in SWCNTs provides emission closer to standard telecom wavelengths, advancing the prospects for applications as single-photon sources in quantum information processing.

The study of the interaction mechanism between bovine serum albumin and single-walled carbon nanotubes depending on their diameter and concentration in solid nanocomposites by vibrational spectroscopy.

The results of the study of composites based on bovine serum albumin (BSA) and single-walled carbon nanotubes (SWCNT) are presented. Nanocomposites were created by evaporation of the water-albumin dispersion with nanotubes using diode laser with temperature control. Two types of nanotubes were used. SWCNT I were synthesized using the electric arc method, SWCNT II were synthesized using the gas phase method. SWCNT I had a diameter and length less than SWCNT II. The mechanism of interaction between BSA and SWCNT in solid nanocomposites is considered. An experimental and theoretical studies of the interaction between aspartic (Asp) and glutamic (Glu) amino acids located on the outer surface of BSA and nanotubes using of vibrational spectroscopy (Fourier-transform infrared (FTIR) and Raman spectroscopy) was carried out. The possibility of nanotubes functionalization by oxygen atoms of negative amino acid residues Asp and Glu, which are on the outer surface of BSA, is shown by molecular modeling. The formation of covalent bonds between BSA and SWCNT in nanocomposites with different concentrations of nanotubes (0.01, 0.1 and 1 g/l) was confirmed by vibrational spectra. The covalent interaction between BSA with SWCNT under the laser irradiation leads to the conformational changes in the secondary and tertiary structures of albumin. This is confirmed by a significant decrease in the intensity of the absorption bands in the high-frequency region. The calculation of the vibrational spectra of the three Glycine:Glycine, Glutamic acid:Threonine and Aspartic acid:Lysine complexes, which take into account hydrogen, ion-dipole and ion-ion bonds, showed that a disturbance in the intermolecular interaction between amino acid residues led to significant decrease in the intensity of absorption bands in the region of stretching vibrations bonds OH and NH. From the Raman spectra, it was found that a significant number of defects in SWCNT is caused by the covalent attachment of oxygen atoms to the graphene surface of nanotubes. An increase in the diameter of nanotubes (4 nm) has practically no effect on the absorption spectrum of nanocomposite, while measuring the concentration of SWCNT affects the FTIR spectra. This confirmed the hydrophobic interaction between BSA and SWCNT. Thus, it was shown that BSA solid nanocomposites with CNTs can interact either with the help of hydrophobic forces or with the formation of covalent bonds, which depends on the diameter of the used nanotubes. The viability of connective fibroblast tissue cells on nanocomposites with both types of SWCNT was demonstrated. It was found that nanocomposites based on SWCNT I provide slightly better compatibility of their structure with fibroblasts. It allows to achieve better cell adhesion to the nanocomposite surface. These criteria make extensive use of scaffold nanocomposites in biomedicine, depending on the requirements for their quality and application.

Electroless Deposition of Cu-SWCNT Composites

In this work, as-received HiPCO single walled carbon nanotubes (SWCNTs) are incorporated in a controllable manner at various concentrations into Cu-SWCNT composites via electroless plating, by varying the related reaction times, with polyethylene glycol (PEG) used as a dispersing agent. The resultant samples were analyzed using scanning electron microscopy (SEM) for morphology assessment, energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) for elemental analysis, X-ray diffraction (XRD) for the assessment of crystal phase identification, and Raman spectroscopy for the confirmation of the presence of the incorporated SWCNTs. The Cu-SWCNT composites were found to contain carbon, catalytic iron (associated with the raw, as-received SWCNTs), oxygen, and copper; the latter was found to be inversely proportional to carbon and iron contents. The oxygen (associated with both the SWCNT defect sites and oxidized copper surfaces) remained more or less constant regardless of the proportion of SWCNTs in the composites. The Raman IG:ID ratio remains within the experimental error constant, indicating that the electroless deposition does not have a deleterious effect on the SWCNTs. At short deposition times, SEM revealed a relatively dense structure comprising a distinctive fibrous morphology, suggestive of an underlying SWCNT substrate coated with copper; however, with increasing deposition, a more porous morphology is observed. The size of the granular particles increases up until 10 min of reaction, after which time it remains unchanged.

The nature of small molecules adsorbed on defective carbon nanotubes.

In this work, we perform a comprehensive theoretical study on adsorption of representative 10-electron molecules H2O, CH4 and NH3 onto defective single-walled carbon nanotubes. Results of adsorption energy and charge transfer reveal the existence of both chemical adsorption (CA) and physical adsorption (PA). While PA processes are common for all molecules, CA could be further achieved by the polar molecule NH3, whose lone-pair electrons makes it easier to be bonded with the defective nanotube. Our systematic work could contribute to the understanding on intermolecular interactions and the design of future molecular detectors.

Mediatorless, Reversible Optical Nanosensor Enabled through Enzymatic Pocket Doping

Single-walled carbon nanotubes (SWCNTs) exhibit intrinsic near-infrared fluorescence that benefits from indefinite photostability and tissue transparency, offering a promising basis for in vivo biosensing. Existing SWCNT optical sensors that rely on charge transfer for signal transduction often require exogenous mediators that compromise the stability and biocompatibility of the sensors. This study presents a reversible, mediatorless, near-infrared glucose sensor based on glucose oxidase-wrapped SWCNTs (GOx-SWCNTs). GOx-SWCNTs undergo a selective fluorescence increase in the presence of aldohexoses, with the strongest response toward glucose. When incorporated into a custom-built membrane device, the sensor demonstrates a monotonic increase in initial response rates with increasing glucose concentrations between 3 × 10−3 and 30 × 10−3 M and an apparent Michaelis–Menten constant of KM(app) ≈ 13.9 × 10−3 M. A combination of fluorescence, absorption, and Raman spectroscopy measurements suggests a fluorescence enhancement mechanism based on localized enzymatic doping of SWCNT defect sites that does not rely on added mediators. Removal of glucose reverses the doping effects, resulting in full recovery of the fluorescence intensity. The cyclic addition and removal of glucose is shown to successively enhance and recover fluorescence, demonstrating reversibility that serves as a prerequisite for continuous glucose monitoring.

The stability of multiple carbon ad-dimer defects in single-walled carbon nanotubes as a function of its distance from the nanotube end

Single-walled carbon nanotubes (SWCNTs) are considered as one of the most promising materials for a diverse range of applications. The multiple carbon ad-dimer defects in SWCNTs are particularly attractive structures. By using density functional theory calculations, the structural and electronic properties of a (4, 4) SWCNT with the positions of the defect states induced by multiple carbon ad-dimers and the chemisorption of hydrogen and fluorine on the surface of these nanotubes were studied. The results indicate that nanotubes with multiple carbon ad-dimers defect exhibit a higher reactivity than perfect ones. The chemisorptions of hydrogen and fluorine atoms can enhance the stability of defective SWCNTs. The reaction energy of chemisorption of hydrogen and fluorine atoms is almost independent of the positions of the defect states.

Study on the detection behavior of defect-rich single-walled carbon nanotubes toward perchlorate

Defect-rich single-walled carbon nanotubes (SWCNTs) were prepared by a water vapor flow-assisted chemical vapor deposition process. The correlation between defect density and water flow was quantitively studied using Raman spectrum. The detection capabilities of defective SWCNTs films toward perchlorate anions were investigated. It was found the defect-rich SWCNTs could adsorb more perchlorate anions owing to the strong chemical bonding between anions and defective sites. However, the detective response of defective SWCNTs toward perchlorate was not in compliance with anion adsorption. A tradeoff phenomenon between response and adsorption was found as the defect density of SWCNTs increased. This work is expected to provide a guidance to the future design of SWCNTs based ion detector.

Raman active modes in defective peapods

The vibrational properties of defective single-walled carbon nanotube filled with C60 fullerene is the subject of the current study. For this aim we use the spectral moments method in the framework of the bond-polarization theory to calculate the non-resonant Raman spectra of hexa-vacancy defective C60 peapods. Essentially, the vibrational properties are closely coupled with the atomic structure of the system. The evolution of the Raman spectrum as a function of the spatial arrangement of defects in carbon nanotubes is discussed. This work provides benchmark theoretical results to understand the experimental data of defective C60 peapods. #single_wall_carbon_nanotube #C60_peapods #hexa-vacancy_defect #Raman_spectroscopy #pectral_moment_method

Optical transitions of native defects in single-walled carbon nanotubes: Time-dependent density functional theory study

ABSTRACTOptical transitions of a pristine (8,0) single-walled carbon nanotube (SWCNT) and the (8,0) SWCNT containing three types of defects were calculated based on electronic structures obtained using the density functional theory (DFT) corrected by the van der Waals (vdW) interactions. The photon absorption energies (PAE) of the pristine (8,0) SWCNT and defected (8,0) SWCNTs were calculated using time-dependent density functional theory (TDDFT). We found that all three defects studied, namely, single vacancy, diatom vacancy, and Stone-Wales, have characteristic PAEs lower than the PAE of the pristine SWCNT. The calculated PAE could be used to identify native defects in semiconducting (8,0) SWCNT.

Obtaining global equations for the Young’s modulus of perfect and defective carbon nanotubes

There are limited studies which have extracted global equations for calculation of Young’s modulus (E) in both pristine and defective carbon nanotubes (CNT), especially when a combination of different defects such as atom-vacancy and-misplacement exist simultaneously in the studied CNT. In this study, the finite element method was used to investigate E for a large set of perfect and defective single walled carbon nanotubes (2440 finite element models), including armchair, zigzag and chiral tubes. The obtained results were then employed as the basis for achieving accurate global equations for calculation of E in perfect and defective carbon nanotubes at various defect percentages. Despite most previous studies, which were based on the tube’s diameter, the chiral indices (n, m) have been considered here as variables to predict the stiffness of carbon nanotubes. The achieved equations showed to be accurate, with maximum errors below 2% and 10% for perfect and defective tubes, respectively, compared to FE results. Based on the obtained equations, a computer execution file was developed which is capable of calculating E when different percentages of defects are introduced to the structure. The results show that unlike single defect states, the existence of any combination of atom vacancy and atom misplacement defects causes dramatic reduction in the stiffness of carbon nanotubes. Furthermore, the role of vacancy defects in the reduction of tube’s elastic properties revealed to be more significant than misplacement defects. The results not only demonstrate that edge defects influence Young’s modulus more noticeably, but also confirm previous works showing that armchair edged structures are less vulnerable to defects, as compared to zigzag.

Adsorption and Diffusion of Fluids in Defective Carbon Nanotubes: Insights from Molecular Simulations.

Single-walled carbon nanotubes (SWNTs) have been shown from both simulations and experiments to have remarkably low resistance to gas and liquid transport. This has been attributed to the remarkably smooth interior surface of pristine SWNTs. However, real SWNTs are known to have various defects that depend on the synthesis method and procedure used to activate the SWNTs. In this paper, we study adsorption and transport properties of atomic and molecular fluids in SWNTs having vacancy point defects. We construct models of defective nanotubes that have either unrelaxed defects, where the overall structure of the SWNT is not changed, or reconstructed defects, where the bonding topology and therefore the shape of the SWNT is allowed to change. Furthermore, we include partial atomic charges on the SWNT carbon atoms due to the reconstructed defects. We consider adsorption and diffusion of Ar atoms and CO2 and H2O molecules as examples of a noble gas, a linear quadrupolar fluid, and a polar fluid. Adsorption isotherms were found to be fairly insensitive to the defects, even for the case of water in the charged, reconstructed SWNT. We have computed both the self-diffusivities and corrected diffusivities (which are directly related to the transport diffusivities) for each of these fluids. In general, we found that at zero loading that defects can dramatically reduce the self- and corrected diffusivities. However, at high, liquidlike loadings, the self-diffusion coefficients for pristine and defective nanotubes are very similar, indicating that fluid-fluid collisions dominate the dynamics over the fluid-SWNT collisions. In contrast, the corrected diffusion coefficients can be more than an order of magnitude lower for water in defective SWNTs. This dramatic decrease in the transport diffusion is due to the formation of an ordered structure of water, which forms around a local defect site. It is therefore important to properly characterize the level and types of defects when accurate transport diffusivities are needed.

Mediatorless, Reversible Optical Nanosensor Enabled through Enzymatic Pocket Doping.

Single-walled carbon nanotubes (SWCNTs) exhibit intrinsic near-infrared fluorescence that benefits from indefinite photostability and tissue transparency, offering a promising basis for in vivo biosensing. Existing SWCNT optical sensors that rely on charge transfer for signal transduction often require exogenous mediators that compromise the stability and biocompatibility of the sensors. This study presents a reversible, mediatorless, near-infrared glucose sensor based on glucose oxidase-wrapped SWCNTs (GOx-SWCNTs). GOx-SWCNTs undergo a selective fluorescence increase in the presence of aldohexoses, with the strongest response toward glucose. When incorporated into a custom-built membrane device, the sensor demonstrates a monotonic increase in initial response rates with increasing glucose concentrations between 3 × 10-3 and 30 × 10-3 m and an apparent Michaelis-Menten constant of KM (app) ≈ 13.9 × 10-3 m. A combination of fluorescence, absorption, and Raman spectroscopy measurements suggests a fluorescence enhancement mechanism based on localized enzymatic doping of SWCNT defect sites that does not rely on added mediators. Removal of glucose reverses the doping effects, resulting in full recovery of the fluorescence intensity. The cyclic addition and removal of glucose is shown to successively enhance and recover fluorescence, demonstrating reversibility that serves as a prerequisite for continuous glucose monitoring.

Characteristics of lithium adsorption near divacancy defects on carbon nanotubes (7,7)

First-principles modeling is used to study the lithium adsorption on defective single-walled carbon nanotube (SWCNT). The article considers SWCNTs (7,7) with divacancy defects (2V defect) in the model with periodic boundary conditions. Due to the use of these conditions, the article discusses the problem of proper sizing of the defective tube fragment subject to modeling. Special attention is paid to the search for stable equilibrium positions (adsorption sites) for the lithium atom interacting with the defective tube and the evaluation of the configurations with the lowest energy of these sites. It is shown that all the adsorption sites located near the defect within the first three environments of carboatomic 6-rings are more energetically favorable for adsorption than the adsorption sites on the defectless tube section. Most energetically favorable are the sites above the 8- and 5-rings forming the 2V-defect. During external adsorption, the adsorption site occurs above each 6-ring within the defect. During internal adsorption, most of the 6-rings of the first defect coordination environment cannot keep the lithium atom rolling down into the defect area. The identified regularities are of direct interest in relation to the search for perspective materials for lithium-ion batteries.

Rhodium clustering process on defective (8,0) SWCNT: Analysis of chemical and physical properties using density functional theory

The Spin-polarized density functional theory is used to study the effect of a single vacancy in a (8,0) single-walled carbon nanotube (SWCNT) on the Rh clustering process. The vacancy is considered oxygenated and non-oxygenated and, in each case, different Rhn cluster sizes (n=1–4) are taken into account. For the analysis of these systems some physical and chemical properties are calculated, such as binding energy (Eb), work function (WF), magnetic moment, charge transfer, bond length, band gap (Eg), and density of state (DOS). From this analysis it can be concluded that: a single Rh atom and Rh2 dimer are adsorbed on vacancy without oxygen, whereas Rh3 and Rh4 clusters prefer to be adsorbed on oxygenated vacancy. In all cases, Rh adsorption induces a magnetic moment. When the Rh atom and Rh2 dimer are bonded to the defective SWCNT, it has been found that they show a semiconductor behavior that could be interesting to use in the spintronic area. In the case of Rh3 and Rh4 clusters our results show a metallic behavior suggesting that these systems are good candidates for nanotube contact.

Evaluation of Elastic moduli for different Patterns of Stone-Thrower-Wales Defect in Carbon Nanotubes/epoxy Composites

A pristine Carbon nanotube (CNTs) possesses exceptional mechanical properties. However, the performance of CNTs get affected from defects such as vacancies, Stone-Thrower-Wales (S-T-W), hybridization and doping which can appear during production. The study conducted here is based on molecular dynamics (MD) simulations performed on S-T-W defected single-walled carbon nanotubes (SWCNTs) and their corresponding epoxy composites. A (6, 6) armchair SWCNT has been used in this study with the defect ratio (DR) varies from 1 to 5.0% for S-T-W defects. S-T-W defects in two (type-I and type-II) different forms has also been modeled and simulated for their various mechanical properties. Results have also been obtained for S-T-W defective SWCNT/epoxy composites. A continuous degradation of elastic moduli in S-T-W type-II defective SWCNTs and their composites has been observed for increased DR. Maximum reduction of 25.4% in failure strain was noticed in type-II S-T-W defect pattern for their maximum DRs, when compared with pristine SWCNTs. A maximum drop of 32% has also been noticed in moduli of the composite made by the reinforcement of type-II S-T-W patterns when compared with pristine SWCNT/epoxy composite. Therefore, comparative approach of this study leads to more reliable design of epoxy nanocomposites.

Hydrogen storage capacity of bundles of single-walled carbon nanotubes with defects

We study the hydrogen storage capacity of bundles of single-walled carbon nanotubes (SWCNT) at 80 and 298 K using molecular dynamics simulations. The effect of packing on the storage capacity of the bundles is studied using triangular and square arrays of nanotubes with various separation distance between adjacent nanotubes. The gravimetric storage capacity of the bundles increases with the separation distance between individual nanotubes. At low temperature, the storage capacity of bundles is significantly lower than for isolated SWCNT as the intertube distance is smaller than the adsorbed layer thickness of hydrogen. At high temperature, the adsorbed layer thickness corresponds to only a monolayer of hydrogen around SWCNTs, and hence, hydrogen is captured in the interstitial spaces within the bundle. As the groove volume in the square array is higher than that in the triangular array, the storage capacity of the bundle with square array is higher. An introduction of the Stone–Wales defects on the surface of nanotubes further increases the storage capacity of the bundle due to the higher binding energy of the 8-member rings of the defective SWCNTs. We also observe that more hydrogen molecules are packed in the interstitial spaces due to the deformation of the nanotubes caused by the presence of defective sites. Copyright © 2016 John Wiley & Sons, Ltd.