Defective Single-walled Carbon Nanotubes Research Articles

The Decompositions of Fluorescent Defects and Pristine Structure in (6,5) Carbon Nanotubes Using Various Oxidants

Fluorescent quantum defects in single-wall carbon nanotubes (SWCNTs) are outstanding candidates as fluorophores for in vivo biomedical imaging applications such as image-guided surgeries and single-cell tracking. Their longer wavelength emission in the short-wave infrared penetrates biological tissues deeper than visible and NIR light. In addition, fluorescent quantum defects can enhance fluorescence brightness by a factor of ~9 compared to the pristine SWCNT emission. Besides their exceeding optical properties, the degradations of SWCNTs in biological and environmental systems are also of importance, but still not well understood yet. This study utilizes sodium hypochlorite (NaClO) and hydrogen peroxide (H2O2) to examine the chemical decompositions of pristine and defect-containing SWCNTs. We found that the oxidation rate of NaClO is ~5 times faster than that of H2O2, showing an obvious oxidant-dependent degradation kinetics. It is also worth mentioning that when using NaClO as the oxidant, the oxidation rate is significantly increased under acidic conditions, probably due to the increased concentration of hypochlorous acid (HOCl). In contrast, H2O2 prefers to oxidize the pristine structure. It is also found that SWCNT coating materials including SDS, SC, and ssDNA might protect the surface structures, especially the defects, from oxidant attacks. We believe our study will lead to a better understanding of the SWCNT degradation, providing valuable insights for future clinical applications.

Modeling Electrochemical Vacancy Regeneration in Single-Walled Carbon Nanotubes.

Synthesis-induced defects in single-walled carbon nanotubes (SWCNTs) enable diverse catalytic reactions, but the nature of catalytic intermediates and how active species regeneration occurs are unclear. Using a quantum mechanics/molecular mechanics (QM/MM) hybrid methodology based on density functional theory (DFT) and a classical force-field, we explore the reactivity and electrochemical regeneration of a vacancy defect in a zigzag SWCNT. Our findings indicate that hydrolysis of the defect forms a ketone group on one carbon atom and C-H bonds on two adjacent carbons. Applying an electrochemical potential of ESHE = -0.740 V triggers a proton-coupled electron transfer (PCET), converting the ketone to a hydroxyl group. Further reduction at ESHE = -1.08 V induces another PCET, expelling the hydroxyl as water and forming an active carbon with carbene character that can react with hydrogen peroxide and perchlorate. The hydrogen atoms on neighboring carbons prevent further water dissociation, maintaining the catalytic vacancy.

A First-Principles Study on the Anchoring Properties of Defective Single-Walled Carbon Nanotubes for Lithium-Sulfur Batteries

The application of lithium-sulfur (Li–S) batteries is impeded by the significant polysulfide shuttling phenomenon. Developing suitable anchoring material is an effective way to restrain this behavior. In this work, the anchoring performance of lithium polysulfide (LiPSs) on defective single-wall carbon nanotubes (DSWNT) is investigated by density functional theory. The results demonstrate that the DSWNT with three carbon vacancies (DSWNT-3) has the highest forming capacity and the strongest adsorption capacity, indicating it has the best anchoring effect of LiPSs. As the anchoring material of the cathode, DSWNT-3 has greater energy than solvent molecules to inhibit the dissolution of long-chain polysulfides. In general, DSWNT-3 demonstrates notable efficacy as an anchoring material for Li–S batteries, which establishes a theoretical foundation for exploring the anchoring characteristics of defects and their application in the cathode of Li–S batteries.

Purification of carbon nanotubes for dissolution in chlorosulfonic acid

Carbon nanotubes (CNTs) can be scalably processed into high-performance fiber with a low environmental footprint by solution spinning from chlorosulfonic acid (CSA). CNTs are produced by numerous manufacturers, but CNTs typically need to undergo purification to improve solubility in CSA. For over two decades, oxidative techniques have been used to remove amorphous carbon species to improve CNT dissolution in acid. However, more recent work has attributed the improved solubility after single-walled carbon nanotube (SWCNT) oxidation to the inclusion of oxygen groups in the sidewall of the SWCNT. Here, we refute the recent claim that oxidation incorporates oxygen into the sidewall of CNTs to improve CNT dissolution to CSA. Instead, we provide experimental evidence in support of classical purification literature: at the appropriate time and temperature, oxidation removes amorphous carbon shells and defective SWCNTs without oxidizing the SWCNT sidewall. Once these amorphous carbon shells are removed, CSA can access and protonate the sp2-bonded carbon sites, which results in SWCNT dissolution. Additionally, we explore how oxidation conditions impact SWCNT aspect ratio (length of CNT divided by CNT diameter), which directly controls macroscale fiber properties.

Quantum Defect Sensitization via Phase-Changing Supercharged Antibody Fragments.

Quantum defects in single-walled carbon nanotubes promote exciton localization, which enables potential applications in biodevices and quantum light sources. However, the effects of local electric fields on the emissive energy states of quantum defects and how they can be controlled are unexplored. Here, we investigate quantum defect sensitization by engineering an intrinsically disordered protein to undergo a phase change at a quantum defect site. We designed a supercharged single-chain antibody fragment (scFv) to enable a full ligand-induced folding transition from an intrinsically disordered state to a compact folded state in the presence of a cytokine. The supercharged scFv was conjugated to a quantum defect to induce a substantial local electric change upon ligand binding. Employing the detection of a proinflammatory biomarker, interleukin-6, as a representative model system, supercharged scFv-coupled quantum defects exhibited robust fluorescence wavelength shifts concomitant with the protein folding transition. Quantum chemical simulations suggest that the quantum defects amplify the optical response to the localization of charges produced upon the antigen-induced folding of the proteins, which is difficult to achieve in unmodified nanotubes. These findings portend new approaches to modulate quantum defect emission for biomarker sensing and protein biophysics and to engineer proteins to modulate binding signal transduction.

Topology of boron substitutional defects in single-walled carbon nanotubes: A first-principles study

This is a theoretical study of boron-doped single-walled carbon nanotubes. The same topology of primitive nanodomains, located at different positions on single-walled carbon nanotubes, leads to different electronic band structures. We propose a ϕ term. Density functional theory was corrected for van der Waals interactions and used to carry out the periodic boundary condition geometry optimization, where boron formed the topologies of primitive nanodomains. The calculated bulk structure and local structure spectroscopic parameters can be used for comparison with experimental results to confirm the theoretical models.

How to recognize clustering of luminescent defects in single-wall carbon nanotubes.

Semiconducting single-wall carbon nanotubes (SWCNTs) are a promising material platform for near-infrared in vivo imaging, optical sensing, and single-photon emission at telecommunication wavelengths. The functionalization of SWCNTs with luminescent defects can lead to significantly enhanced photoluminescence (PL) properties due to efficient trapping of highly mobile excitons and red-shifted emission from these trap states. Among the most studied luminescent defect types are oxygen and aryl defects that have largely similar optical properties. So far, no direct comparison between SWCNTs functionalized with oxygen and aryl defects under identical conditions has been performed. Here, we employ a combination of spectroscopic techniques to quantify the number of defects, their distribution along the nanotubes and thus their exciton trapping efficiencies. The different slopes of Raman D/G+ ratios versus calculated defect densities from PL quantum yield measurements indicate substantial dissimilarities between oxygen and aryl defects. Supported by statistical analysis of single-nanotube PL spectra at cryogenic temperatures they reveal clustering of oxygen defects. The clustering of 2-3 oxygen defects, which act as a single exciton trap, occurs irrespective of the functionalization method and thus enables the use of simple equations to determine the density of oxygen defects and defect clusters in SWCNTs based on standard Raman spectroscopy. The presented analytical approach is a versatile and sensitive tool to study defect distribution and clustering in SWCNTs and can be applied to any new functionalization method.

Broadband Full-Spectrum Raman Excitation Mapping Reveals Intricate Optoelectronic-Vibrational Resonance Structure of Chirality-Pure Single-Walled Carbon Nanotubes.

The Raman excitation spectra of chirality-pure (6,5), (7,5), and (8,3) single-walled carbon nanotubes (SWCNTs) are explored for homogeneous solid film samples over broad excitation energy and scattering energy ranges using a rapid and relatively simple full spectrum Raman excitation mapping technique. Identification of variation in scattering intensity with sample type and phonon energy related to different vibrational bands is clearly realized. Excitation profiles are found to vary strongly for different phonon modes. Some modes' Raman excitation profiles are extracted, with the G band profile compared to earlier work. Other modes, such as the M and iTOLA modes, have quite sharp resonance profiles and strong resonances. Conventional fixed wavelength Raman spectroscopy can miss these effects on the scattering intensities entirely due to the significant intensity changes observed for small variations in excitation wavelength. Peak intensities for phonon modes traceable to a pristine carbon lattice forming a SWCNT sidewall were greater for high-crystallinity materials. In the case of highly defective SWCNTs, the scattering intensities of the G band and the defect-related D band are demonstrated to be affected both in absolute intensities and in relative ratio, with the ratio that would be measured by single wavelength Raman scattering dependent on the excitation wavelength due to differences in the resonance energy profiles of the two bands. Lastly it is shown that the approach of this contribution yields a clear path toward increasing the rigor and quantification of resonance Raman scattering intensity measurements through tractable corrections of excitation and emission side variations in efficiency with excitation wavelength.

Oxygen Defects in Single-Wall Carbon Nanotubes for Near-Infrared Light Emitters

A new peak with an increased intensity was observed in the photoluminescence (PL) spectra of single-walled carbon nanotubes (SWCNTs), exposed to UV irradiation in the presence of sodium hypochlorite. It was concluded on the basis of the spectroscopic data that the new PL peak is associated with oxygen defects in the SWCNT structure. The impact of environmental acidity on the optical properties of oxygen-doped SWCNTs (O-SWNTs) was investigated. An increased sensitivity of the new PL peak to the pH of the medium was observed. It was concluded that the usage of a pH-neutral medium is of crucial importance for the creation of IR light sources based on O-SWNTs. Keywords: single-walled carbon nanotubes, photoluminescence, localized exciton, acidity, infrared light emitters.

Thermal defect healing of single-walled carbon nanotubes assisted by supplying carbon-containing reactants

We experimentally investigated the effect of carbon-containing reactants (C2H2) on healing the defects in single-walled carbon nanotubes (SWCNTs) by thermal processes at high temperatures (∼1100 °C). Introducing C2H2 notably improved the crystallinity of healed SWCNTs compared with the thermal process in Ar ambient without C2H2. The defect healing rate increased with increasing C2H2 partial pressure, and the healing effect of C2H2 was more remarkable for relatively thinner SWCNTs (<1.1 nm). Combined with the relevant theoretical work reported previously, we propose a healing model in which C2H2 helps to heal the vacancy defects and increases the healing rate at high temperatures.

A continuum-discrete multiscale coupling method for pristine and defected single-walled carbon nanotubes

A continuum-discrete multiscale coupling (CDMC) method is developed for predicting the large deformation and buckling behaviors of pristine and defected single-walled carbon nanotubes (SWCNTs). With the use of the moving least squares (MLS) approximation as the linkage for the deformations of the discrete atomic structure and the corresponding continuum model, the delicate microstructures of pristine or defected SWCNTs which possess abnormal properties can be involved accurately in the mechanic model built by this CDMC method. Based on the proposed CDMC method, a variationally consistent meshless computational scheme is developed. As the degree of freedom of SWCNTs can be chosen freely in the context of CDMC method, the numerical computational efficiency is higher than that of the fully atomistic simulations. Various numerical tests are carried out for simulating the nonlinear large and buckling deformations of SWCNTs. The results compared with those of the fully atomistic simulations show that CDMC method is accurate and efficient for predicting the nonlinear mechanical properties of pristine and defective SWCNTs and has great potential for dealing with large scale boundary problems.

Temperature dependence of Raman shift in defective single-walled carbon nanotubes

Raman scatterings of both pristine and defective single-walled carbon nanotubes were measured. Defects on carbon nanotubes (CNTs) were induced by UV/O3 treatment, and the correlation between the temperature dependence of the Raman shift of the G-band and the crystallinity of CNTs was investigated. In the temperature range of 250–600 K, a gradual negative change in the slope was observed; the linear shift of the Raman G-band frequency with respect to temperature increased as the crystallinity deteriorated. This phenomenon is attributed to the increase in the fourth-order phonon–phonon scattering interaction resulting from the induced defects.

The role of topological defects on the mechanical properties of single-walled carbon nanotubes

ABSTRACT Carbon nanotubes (CNTs) are among the most employed nanomaterials in developing new technologies. Their applicability requires a fundamental understanding of the chirality and defect effects on the mechanical properties. In this study, molecular dynamics (MD) simulations were performed to investigate the mechanical response of defective single-walled carbon nanotubes (SWCNTs) under tension loading. The Stones-Wales, monovacancy, and the divacancy reconstructions (585, 555777, and 555567777) defects were considered. In addition, we investigated the influence of the adaptive intermolecular reactive bond order (AIREBO) potential cut-off radii on the defect formation energy of SWCNTs. Our results reveal that the tensile strength properties are notably dependent on the chirality and defect configurations at strains over 8%. Energetically favourable defects have a high impact on the mechanical response of SWCNTs. A combination of certain defects may lead the control on the fracture pattern of the SWCNTs, which can significantly contribute to the designing of innovative nanostructures with tailored properties.

Room temperature hydrogen storage in defective single-walled carbon nanotubes: a molecular dynamics study

Hydrogen has the potential to be an alternative source of energy. However, most of the research on hydrogen storage carried out in the past is based on low temperature (<80 K) whereas storage near room temperature is desired. Here, we report room-temperature hydrogen storage capacity of defective single-walled carbon nanotubes (SWCNT) investigated using molecular dynamics simulations and density functional theory. Four different types of defective SWCNTs are considered to study room temperature hydrogen storage. We observed maximum adsorption capacity of SWCNT with 5 and 8-membered ring defects, namely, D1. The SWCNT with other three defects studied here, Stone-Wales with 5- and 7-membered ring defect (D2), 5-membered ring defect (D3), and 3-, 5- and 8-membered ring defect (D4) have negative adsorption effect compared to the defect-free SWCNT. The highest gravimetric capacity of 1.82 wt.% is found for the D1 defective SWCNT at room temperature, 298 K and 140 atm. The DFT calculations show that hydrogen adsorption strongly depends on the type of defect where the 8-membered ring has the highest adsorption energy and the 3-membered ring has the lowest adsorption energy. A combination of 5- and 8-membered defective rings can increase hydrogen adsorption significantly even at room temperature.

Identification of vacancy defects in carbon nanotubes using vibration analysis and machine learning

Point vacancies are the most common defects in a carbon nanotube (CNT) lattice. However, there is no standard technique to identify these defects. Moreover, the effect of such vacancies on the vibrational properties of CNTs is unknown. Therefore, this paper presents the first-ever technique for identification of vacancy defects in single-walled carbon nanotubes (SWCNT) using their vibrational analyses and machine learning. 240 SWCNT samples were modelled using molecular-structural-mechanics-approach and their modes obtained using finite element analyses. Then, an analytical expression for fundamental vibration frequency of a vacancy defective SWCNT was derived using log-linear multiple regression. This frequency is found to decrease with: (i) increase in the magnitude of point vacancies; (ii) decrease in diameter; and (iii) increase in length. A polynomial support vector machine (SVM) was developed that successfully classifies pristine and vacancy defective SWCNT samples at test accuracy greater than 90%. The proposed technique for identification of point vacancies combines the developed SVM classification with inverse estimation using the derived expression. This technique will be useful for the most crucial characterization of SWCNTs, i.e., characterizing pristine and vacancy defective samples. The derived expression will be useful in predicting vibration response of vacancy defective SWCNTs, and deciding their applications.

(Invited) Quantum Light Emission from Coupled Defect-States in DNA-Functionalized Carbon Nanotubes

Solid-state single-photon sources are the essential building block for quantum photonics and quantum information technologies. The report here illustrates an advanced perspective of implanting coupled fluorescent quantum defects in single-wall carbon nanotubes (SWCNTs) through chemical reactions between the nanotube sidewall and the guanine nucleotides in single-stranded DNA (ssDNA) that coats the nanotube. Through low-temperature photoluminescence spectroscopy and photon correlation experiments, we have revealed that multiple guanine defects within a single ssDNA strand couple together to form a cumulative deep trapping potential supporting a localized quantum state that is capable of room-temperature single-photon emission. Helical wrapping of multiple ssDNA strands in single nanotubes allows a series of exciton localization sites to be created along the length of the SWCNTs. Such unique exciton trapping potential landscape gives rise to previously inaccessible intrinsic emission characteristics including coupling of multiple spatially separated quantum emitters. Our joint experimental and computational studies together reveal quantum emission properties from multiple spatially patterned covalent defects in SWCNTs, identify capture of the band-edge exciton as the underlying cause of the cross-correlated photon emission and open a distinctive prospect for tailoring chemically altered nanotubes as quantum light emitters.

Thermal conductivity of perfect and defective carbon nanotubes functionalized with carbene: a molecular dynamics study

ABSTRACT Thermal transport issues are one of the major concerns of scientists as the size decreases. To this end, the thermal conductivity of perfect and defective single-walled carbon nanotubes (SWCNTs) functionalized with carbene, which is an important functional group in nanodevices, is investigated. A series of molecular dynamics (MD) simulations are performed and the thermal conductivity is determined by the approach introduced by Muller-Plathe. The results demonstrate that functionalization decreases the thermal conductivity. Also, the thermal conductivity of functionalized SWCNT declines as the weight percentage of functional group increases. Additionally, it is shown that increasing the weight percentage decreases the sensitivity of thermal conductivity. According to the obtained results, simulation temperature does not affect the thermal conductivity of functionalized SWCNTs considerably compared to pure ones. Finally, it is revealed that the presence of vacancy defect reduces the thermal conductivity of functionalized SWCNTs.

Correlation between the air stability of n-type thermoelectric properties and defects in single-walled carbon nanotubes with anionic surfactants

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials for use as sustainable power sources for the Internet of Things technology due to their flexibility and excellent thermoelectric properties near 300 K. One of the most important challenges in the development of SWCNTs is achieving n-type thermoelectric properties with long air stability. Here, we investigated the correlation between the air stability of the n-type property and the defects of SWCNTs using two types of SWCNTs with different defect densities. SWCNT films with anionic surfactants were prepared using drop-casting, followed by heat treatment. Both types of SWCNT films exhibited approximately the same n-type Seebeck coefficient values at appropriate heat treatment temperatures. The SWCNT films with low defect density exhibited high electrical conductivity, but the n-type Seebeck coefficient was converted into a p-type one at 14 d. Conversely, the SWCNT films with high defect density exhibited low electrical conductivities but maintained the n-type Seebeck coefficient for 35 d. Therefore, the defect density of SWCNTs impacted the air-stability of the thermoelectric properties. This phenomenon possibly indicates that SWCNT films with high defect density were homogeneously coated with surfactants, thus preventing oxygen atoms from adhering to the film.

Sp3-Functionalization of Single-Walled Carbon Nanotubes Creates Localized Spins.

Chemical functionalization-introduced sp3 quantum defects in single-walled carbon nanotubes (SWCNTs) have shown compelling optical properties for their potential applications in quantum information science and bioimaging. Here, we utilize temperature- and power-dependent electron spin resonance measurements to study the fundamental spin properties of SWCNTs functionalized with well-controlled densities of sp3 quantum defects. Signatures of isolated spins that are highly localized at the sp3 defect sites are observed, which we further confirm with density functional theory calculations. Applying temperature-dependent line width analysis and power-saturation measurements, we estimate the spin-lattice relaxation time T1 and spin dephasing time T2 to be around 9 μs and 40 ns, respectively. These findings of the localized spin states that are associated with the sp3 quantum defects not only deepen our understanding of the molecular structures of the quantum defects but could also have strong implications for their applications in quantum information science.

Population of Exciton–Polaritons via Luminescent sp3 Defects in Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWCNTs) are an interesting material for strong-light matter coupling due to their stable excitons, narrow emission in the near-infrared region, and high charge carrier mobilities. Furthermore, they have emerged as quantum light sources as a result of the controlled introduction of luminescent quantum defects (sp3 defects) with red-shifted transitions that enable single-photon emission. The complex photophysics of SWCNTs and the overall goal of polariton condensation pose the question of how exciton–polaritons are populated and how the process might be optimized. The contributions of possible relaxation processes, i.e., scattering with acoustic phonons, vibrationally assisted scattering, and radiative pumping, are investigated using angle-resolved reflectivity and time-resolved photoluminescence measurements on microcavities with a wide range of detunings. We show that the predominant population mechanism for SWCNT exciton–polaritons in planar microcavities is radiative pumping. Consequently, the limitation of polariton population due to the low photoluminescence quantum yield of nanotubes can be overcome by luminescent sp3 defects. Without changing the polariton branch structure, radiative pumping through these emissive defects leads to an up to 10-fold increase of the polariton population for detunings with a large photon fraction. Thus, the controlled and tunable functionalization of SWCNTs with sp3 defects presents a viable route toward bright and efficient polariton devices.