Scalable method for the reductive dissolution, purification, and separation of single-walled carbon nanotubes

Nanotechnological advances in cancer: therapy a comprehensive review of carbon nanotube applications

Nanotechnology is revolutionising different areas from manufacturing to therapeutics in the health field. Carbon nanotubes (CNTs), a promising drug candidate in nanomedicine, have attracted attention due to their excellent and unique mechanical, electronic, and physicochemical properties. This emerging nanomaterial has attracted a wide range of scientific interest in the last decade. Carbon nanotubes have many potential applications in cancer therapy, such as imaging, drug delivery, and combination therapy. Carbon nanotubes can be used as carriers for drug delivery systems by carrying anticancer drugs and enabling targeted release to improve therapeutic efficacy and reduce adverse effects on healthy tissues. In addition, carbon nanotubes can be combined with other therapeutic approaches, such as photothermal and photodynamic therapies, to work synergistically to destroy cancer cells. Carbon nanotubes have great potential as promising nanomaterials in the field of nanomedicine, offering new opportunities and properties for future cancer treatments. In this paper, the main focus is on the application of carbon nanotubes in cancer diagnostics, targeted therapies, and toxicity evaluation of carbon nanotubes at the biological level to ensure the safety and real-life and clinical applications of carbon nanotubes.

Functionalization of Carbon Nanotubes Surface by Aryl Groups: A Review

The review is devoted to the methods of introducing aryl functional groups to the CNT surface. Arylated nanotubes are characterized by extended solubility, and are widely used in photoelectronics, semiconductor technology, and bioelectrocatalysis. The main emphasis is on arylation methods according to the radical mechanism, such as the Gomberg-Bachmann and Billups reactions, and the decomposition of peroxides. At the same time, less common approaches are also considered. For each of the described reactions, a mechanism is presented in the context of the effect on the properties of functionalized nanotubes and their application. As a result, this will allow us to choose the optimal modification method for specific practical tasks.

New nitrides: from high pressure-high temperature synthesis to layered nanomaterials and energy applications

We describe work carried out within our group to explore new transition metal and main group nitride phases synthesized using high pressure-high temperature techniques using X-ray diffraction and spectroscopy at synchrotron sources in the USA, UK and France to establish their structures and physical properties. Along with previously published data, we also highlight additional results that have not been presented elsewhere and that represent new areas for further exploration. We also describe new work being carried out to explore the properties of carbon nitride materials being developed for energy applications and the nature of few-layered carbon nitride nanomaterials with atomically ordered structures that form solutions in polar liquids via thermodynamically driven exfoliation. This article is part of the theme issue 'Fifty years of synchrotron science: achievements and opportunities'.

Reductive diazotation of carbon nanotubes: an experimental and theoretical selectivity study

The reaction of negatively charged SWCNTs with diazonium salts was analyzed in a combined experimental and computational DFT study.

The reaction of neutral single-walled carbon nanotubes (SWCNTs) with diazonium salts proceeds with a high selectivity towards metallic carbon nanotube species; this reaction is well-understood and the mechanism has been elucidated. In the present joint theoretical and experimental study, we investigate the reaction of negatively charged SWCNTs – carbon nanotubides – with diazonium salts. Our density functional theory calculations predict a stronger binding of the aryl diazonium cations to charged metallic SWCNTs species and therefore lead to a preferential addend binding in the course of the reaction. The Raman resonance profile analysis on the reductive arylation of carbon nanotubides obtained by the solid state intercalation approach with potassium in varying concentrations confirms the predicted preferred functionalization of metallic carbon nanotubes. Furthermore, we were also able to show that the selectivity for metallic SWCNT species could be further increased when low potassium concentrations (K : C < 1 : 200) are used for an initial selective charging of the metallic species. Further insights into the nature of the bound addends were obtained by coupled thermogravimetric analysis of the functionalized samples.

Depleting Depletion: Maintaining Single-Walled Carbon Nanotube Dispersions after Graft-To Polymer Functionalization

Grafting polymers onto single-walled carbon nanotubes (SWCNTs) usefully alters properties but does not typically yield stable, solvated species directly. Despite the expectation of steric stabilization, a damaging (re)dispersion step is usually necessary. Here, poly(vinyl acetate)s (PVAc's) of varying molecular weights are grafted to individualized, reduced SWCNTs at different concentrations to examine the extent of reaction and degree of solvation. The use of higher polymer concentrations leads to an increase in grafting ratio (weight fraction of grafted polymer relative to the SWCNT framework), approaching the limit of random sequentially adsorbed Flory "mushrooms" on the surface. However, at higher polymer concentrations, a larger percentage of SWCNTs precipitate during the reaction; an effect which is more significant for larger weight polymers. The precipitation is attributed to depletion interactions generated by ungrafted homopolymer overcoming Coulombic repulsion of adjacent like-charged SWCNTs; a simple model is proposed. Larger polymers and greater degrees of functionalization favor stable solvation, but larger and more concentrated homopolymers increase depletion aggregation. By using low concentrations (25 μM) of larger molecular weight PVAc (10 kDa), up to 65% of grafted SWCNTs were retained in solution (at 65 μg mL^-1) directly after the reaction.

Sulfonitric Treatment of Multiwalled Carbon Nanotubes and Their Dispersibility in Water

In this study, Multiwalled carbon nanotubes (MWCNTs) were oxidized by a mixture of sulfuric acid and nitric acid (V:V = 3:1) at 70 °C for 1, 2, and 4 h, respectively. The oxidized MWCNTs were characterized by N₂ adsorption, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), and Raman spectroscopy to determine the oxidation degree. The dispersion of the MWCNTs was investigated by UV-vis-NIR, SEM, and dynamic light scattering measurements. Results show that sulfonitric treatment increased the surface area and total pore volume and reduced the average pore diameter of MWCNTs. The treatment promoted the formation of oxidized species on the surface MWCNTs, as identified by FT-IR, TGA, and X-ray photoelectron spectroscopy measurements, and more oxygen-containing functional groups were generated when treatment time was extended. Moreover, a general relationship between oxidation degree and dispersibility of MWCNTs in water was established. UV-vis-NIR and dynamic light scattering measurements and SEM images revealed that MWCNTs with higher oxidation degree showed better dispersibility in water.

Hydroxide Ions Stabilize Open Carbon Nanotubes in Degassed Water

The main hurdle preventing the widespread use of single-walled carbon nanotubes remains the lack of methods with which to produce formulations of pristine, unshortened, unfunctionalized, individualized single-walled carbon nanotubes, thus preserving their extraordinary properties. In particular, sonication leads to shortening, which is detrimental to percolation properties (electrical, thermal, mechanical, etc.). Using reductive dissolution and transfer into degassed water, open-ended, water-filled nanotubes can be dispersed as individualized nanotubes in water-dimethyl sulfoxide mixtures, avoiding the use of sonication and surfactant. Closed nanotubes, however, aggregate immediately upon contact with water. Photoluminescence and absorption spectroscopy both point out a very high degree of individualization while retaining lengths of several microns. The resulting transparent conducting films are 1 order of magnitude more conductive than surfactant-based blanks at equal transmittance.

Dopant-Modulated Conjugated Polymer Enrichment of Semiconducting SWCNTs

Conjugated polymer extraction (CPE) is a low-cost, scalable process that can enrich single-walled carbon nanotube (SWCNT) materials in organic media. For other separation methods in aqueous phases, redox chemistry and/or pH control dramatically affect the sorting process of the SWCNTs. We have previously determined that the CPE process can be fine-tuned by adjusting the pH on the tube surface. Here, we systematically studied the effect of redox chemistry on the CPE process by adding organic p-/n-dopants. At a very strong p-/n-doping level, static repulsions dominated the interactions between the tubes and the CPE lost selectivity. When the doping level changed from a medium p-doping to a neutral state, the yield of CPE increased and the selectivity was compromised. We also observed chiral selectivity when a weak p-dopant was used. A photoluminescence excitation mapping under different titration conditions provided more insight into the doping level of the tubes relative to their diameters, chiralities, and redox potentials. We proposed a mechanism for the CPE process. The semiconducting and metallic tubes are separated because of their different solubilities, which are determined by the bundling energy between the tubes and are related to their doping level in polymer solutions.

Overcoming Catalyst Residue Inhibition of the Functionalization of Single-Walled Carbon Nanotubes via the Billups-Birch Reduction

The Billups-Birch Reduction chemistry has been shown to functionalize single-walled carbon nanotubes (SWCNTs) without damaging the sidewalls, but has challenges in scalability. Currently published work uses a large mole ratio of Li to carbon atoms in the SWCNT (Li:C) to account for lithium amide formation, however this increases the cost and hazard of the reaction. We report here the systematic understanding of the effect of various parameters on the extent of functionalization using resonant Raman spectroscopy. Addition of 1-iodododecane yielded alkyl-functionalized SWCNTs, which were isolated by solvent extraction and evaporation, and purified by a hydrocarbon wash. The presence of SWCNT growth catalyst residue (Fe) was shown to have a strong adverse effect on SWCNT functionalization. Chlorination-based SWCNT purification reduced the amount of residual Fe, and achieve a maximum I_D/I_G ratio using a Li:C ratio of 6:1 in a reaction time of 30 min. This result is consistent with published literature requiring 20-fold mole equivalents of Li per mole SWCNT with a reaction time of over 12 h. This new understanding of the factors influencing the functionalization chemistry will help cut down material and process costs, and also increase the selectivity of the reaction toward the desired product.

Reductive dissolution of supergrowth carbon nanotubes for tougher nanocomposites by reactive coagulation spinning

Long single-walled carbon nanotubes, with lengths >10 μm, can be spontaneously dissolved by stirring in a sodium naphthalide N,N-dimethylacetamide solution, yielding solutions of individualised nanotubide ions at concentrations up to 0.74 mg mL^-1. This process was directly compared to ultrasonication and found to be less damaging while maintaining greater intrinsic length, with increased individualisation, yield, and concentration. Nanotubide solutions were spun into fibres using a new reactive coagulation process, which covalently grafts a poly(vinyl chloride) matrix to the nanotubes directly at the point of fibre formation. The grafting process insulated the nanotubes electrically, significantly enhancing the dielectric constant to 340% of the bulk polymer. For comparison, samples were prepared using both Supergrowth nanotubes and conventional shorter commercial single-walled carbon nanotubes. The resulting nanocomposites showed similar, high loadings (ca. 20 wt%), but the fibres formed with Supergrowth nanotubes showed significantly greater failure strain (up to ∼25%), and hence more than double the toughness (30.8 MJ m^-3), compared to composites containing typical ∼1 μm SWCNTs.

Chemical routes to discharging graphenides

Chemical and electrochemical reduction methods allow the dispersion, processing, and/or functionalization of discrete sp²-hybridised nanocarbons, including fullerenes, nanotubes and graphenes. Electron transfer to the nanocarbon raises the Fermi energy, creating nanocarbon anions and thereby activating an array of possible covalent reactions. The Fermi level may then be partially or fully lowered by intended functionalization reactions, but in general, techniques are required to remove excess charge without inadvertent covalent reactions that potentially degrade the nanocarbon properties of interest. Here, simple and effective chemical discharging routes are demonstrated for graphenide polyelectrolytes and are expected to apply to other systems, particularly nanotubides. The discharging process is inherently linked to the reduction potentials of such chemical discharging agents and the unusual fundamental chemistry of charged nanocarbons.

Challenges in Liquid-Phase Exfoliation, Processing, and Assembly of Pristine Graphene

Recent developments in the exfoliation, dispersion, and processing of pristine graphene (i.e., non-oxidized graphene) are described. General metrics are outlined that can be used to assess the quality and processability of various "graphene" products, as well as metrics that determine the potential for industrial scale-up. The pristine graphene production process is categorized from a chemical engineering point of view with three key steps: i) pretreatment, ii) exfoliation, and iii) separation. How pristine graphene colloidal stability is distinct from the exfoliation step and is dependent upon graphene interactions with solvents and dispersants are extensively reviewed. Finally, the challenges and opportunities of using pristine graphene as nanofillers in polymer composites, as well as as building blocks for macrostructure assemblies are summarized in the context of large-scale production.

Reductively PEGylated carbon nanomaterials and their use to nucleate 3D protein crystals: a comparison of dimensionality

A range of carbon nanomaterials, with varying dimensionality, were dispersed by a non-damaging and versatile chemical reduction route, and subsequently grafted by reaction with methoxy polyethylene glycol (mPEG) monobromides. The use of carbon nanomaterials with different geometries provides both a systematic comparison of surface modification chemistry and the opportunity to study factors affecting specific applications. Multi-walled carbon nanotubes, single-walled carbon nanotubes, graphite nanoplatelets, exfoliated few layer graphite and carbon black were functionalized with mPEG-Br, yielding grafting ratios relative to the nanocarbon framework between ca. 7 and 135 wt%; the products were characterised by Raman spectroscopy, TGA-MS, and electron microscopy. The functionalized materials were tested as nucleants by subjecting them to rigorous protein crystallization studies. Sparsely functionalized flat sheet geometries proved exceptionally effective at inducing crystallization of six proteins. This new class of nucleant, based on PEG grafted graphene-related materials, can be widely applied to promote the growth of 3D crystals suitable for X-ray crystallography. The association of the protein ferritin with functionalized exfoliated few layer graphite was directly visualized by transmission electron microscopy, illustrating the formation of ordered clusters of protein molecules critical to successful nucleation.

Carbon nanotube anions for the preparation of gold nanoparticle–nanocarbon hybrids

This methodology highlights the unusual chemistry of negatively charged carbon nanotubes and provides a blueprint for the generation of hybrid nanomaterials.

The dispersion, solubilization and stabilization in “solution” of single-walled carbon nanotubes

Methods for the solubilization and dispersion of single-walled carbon nanotubes in water and organic solvents by physical and chemical methods have been reviewed.

Covalent Functionalization of Boron Nitride Nanotubes via Reduction Chemistry

Boron nitride nanotubes (BNNTs) exhibit a range of properties that hold great potential for many fields of science and technology; however, they have inherently low chemical reactivity, making functionalization for specific applications difficult. Here we propose that covalent functionalization of BNNTs via reduction chemistry could be a highly promising and viable strategy. Through density functional theory calculations of the electron affinity of BNNTs and their binding energies with various radicals, we reveal that their chemical reactivity can be significantly enhanced via reducing the nanotubes (i.e., negatively charging). For example, a 5.5-fold enhancement in reactivity of reduced BNNTs toward NH2 radicals was predicted relative to their neutral counterparts. The localization characteristics of the BNNT π electron system lead the excess electrons to fill the empty p orbitals of boron sites, which promote covalent bond formation with an unpaired electron from a radical molecule. In support of our theoretical findings, we also experimentally investigated the covalent alkylation of BNNTs via reduction chemistry using 1-bromohexane. The thermogravimetric measurements showed a considerable weight loss (12-14%) only for samples alkylated using reduced BNNTs, suggesting their significantly improved reactivity over neutral BNNTs. This finding will provide an insight in developing an effective route to chemical functionalization of BNNTs.

Carbon Nanotube Flexible and Stretchable Electronics

The low-cost and large-area manufacturing of flexible and stretchable electronics using printing processes could radically change people's perspectives on electronics and substantially expand the spectrum of potential applications. Examples range from personalized wearable electronics to large-area smart wallpapers and from interactive bio-inspired robots to implantable health/medical apparatus. Owing to its one-dimensional structure and superior electrical property, carbon nanotube is one of the most promising material platforms for flexible and stretchable electronics. Here in this paper, we review the recent progress in this field. Applications of single-wall carbon nanotube networks as channel semiconductor in flexible thin-film transistors and integrated circuits, as stretchable conductors in various sensors, and as channel material in stretchable transistors will be discussed. Lastly, state-of-the-art advancement on printing process, which is ideal for large-scale fabrication of flexible and stretchable electronics, will also be reviewed in detail.

Aligned Carbon Nanotube Thin Films from Liquid Crystal Polyelectrolyte Inks

Single walled carbon nanotube thin films are fabricated by solution shearing from high concentration sodium nanotubide polyelectrolyte inks. The solutions are produced by simple stirring of the nanotubes with elemental sodium in dimethylacetamide, and the nanotubes are thus not subject to any sonication-induced damage. At such elevated concentrations (∼4 mg mL(-1)), the solutions exist in the liquid crystal phase and during deposition this order is transferred to the films, which are well aligned in the direction of shear with a 2D nematic order parameter of ∼0.7 determined by polarized absorption measurements. Compared to similarly formed films made from superacids, the polyelectrolyte films contain smaller bundles and a much narrower distribution of bundle diameters. After p-doping with an organic oxidizer, the films exhibit a very high DC electrical to optical conductivity ratio of σ(DC)/σ(OP) ∼ 35, corresponding to a calculated DC conductivity of over 7000 S cm(-1). When very thin (T550 ∼ 96%), smooth (RMS roughness, R(q) ∼ 2.2 nm), and highly aligned films made via this new route are used as the front electrodes of carbon nanotube-silicon solar cells, the power conversion efficiency is almost an order of magnitude greater than that obtained when using the much rougher (R(q) ∼ 20-30 nm) and less conductive (peak σ(DC)/σ(OP) ∼ 2.5) films formed by common vacuum filtration of the same starting material, and having the same transmittance.

Carbon nanotubides: an alternative for dispersion, functionalization and composites fabrication

In this review, we systematically describe the state-of-knowledge in the area of carbon nanotubides (CNTDs). CNTDs can be used for achieving highly concentrated dispersions of SWCNTs and can also be used as an important intermediate for covalent chemical modification. In recent years, researchers have used SWCNTDs as starting materials for the functionalization of SWCNTs with functionalities such as alkyl chains, carboxylic acids, sulfide, amino, hydroxyl, silyl, bromide, ethers, ketones and polymers. Also, we discussed the observed selectivity on the covalent functionalization towards certain classes of CNTs. Finally, we describe the use of SWCNTDs in the manufacture of fibers, films and other functional materials.

Sonochemical degradation of N-methylpyrrolidone and its influence on single walled carbon nanotube dispersion

Sonicating pure N-methyl pyrrolidone (NMP) rapidly produces contaminating organic nanoparticles, at increasing concentration with time, as investigated by AFM, as well as UV-vis, IR and NMR spectroscopies. The contamination issue affects carbon nanotube, and likely other nanomaterial, dispersions processed by sonication in organic solvents.

DEVICE TECHNOLOGY. Nanomaterials in transistors: From high-performance to thin-film applications

For more than 50 years, silicon transistors have been continuously shrunk to meet the projections of Moore's law but are now reaching fundamental limits on speed and power use. With these limits at hand, nanomaterials offer great promise for improving transistor performance and adding new applications through the coming decades. With different transistors needed in everything from high-performance servers to thin-film display backplanes, it is important to understand the targeted application needs when considering new material options. Here the distinction between high-performance and thin-film transistors is reviewed, along with the benefits and challenges to using nanomaterials in such transistors. In particular, progress on carbon nanotubes, as well as graphene and related materials (including transition metal dichalcogenides and X-enes), outlines the advances and further research needed to enable their use in transistors for high-performance computing, thin films, or completely new technologies such as flexible and transparent devices.

A one-step route to solubilised, purified or functionalised single-walled carbon nanotubes

Reductive dissolution is a promising processing route for single walled carbon nanotubes (SWCNTs) that avoids the damage caused by ultrasonication and aggressive oxidation whilst simultaneously allowing access to a wealth of SWCNT functionalisation reactions. Here, reductive dissolution has been simplified to a single one-pot reaction through the use of sodium naphthalide in dimethylacetamide allowing direct synthesis of SWCNT Na+ solutions. Gram quantities of SWCNTs can be dissolved at concentrations over 2 mg mL-1. These reduced SWCNT solutions can easily be functionalised through the addition of alkyl halides; reducing steric bulk of the grafting moiety and increasing polarisability of the leaving group increases the extent of functionalisation. An optimised absolute sodium concentration of 25 mM is shown to be more important than carbon to metal ratio in determining the maximum degree of functionalisation. This novel dissolution system can be modified for use as a non-destructive purification route for raw SWCNT powder by adjusting the degree of charging to dissolve carbonaceous impurities, catalyst particles and defective material, before processing the remaining SWCNTs.

Reductive dismantling and functionalization of carbon nanohorns

Aggregated carbon nanohorns (CNHs) spontaneously dismantle in organic solvents upon reduction with potassium naphthalenide; the reduced CNHs can be further functionalized via addition of electrophiles.

Investigating linear and nonlinear viscoelastic behaviour and microstructures of gelatin-multiwalled carbon nanotube composites

The linear and nonlinear rheology of physically-crosslinked-gelatin gel-multiwalled carbon nanotube (MWNT), chemically-crosslinked-gelatin gel-MWNT, and chemically–physically-crosslinked-gelatin gel-MWNT composites, are investigated.

Macroscopic nanotube fibers spun from single-walled carbon nanotube polyelectrolytes

In this work, single-walled carbon nanotube (SWCNT) fibers were produced from SWCNT polyelectrolyte dispersions stabilized by crown ether in dimethyl sulfoxide and coagulated into aqueous solutions. The SWCNT polyelectrolyte dispersions had concentrations up to 52 mg/mL and showed liquid crystalline behavior under polarized optical microscopy. The produced SWCNT fibers are neat (i.e., not forming composites with polymers) and showed a tensile strength up to 124 MPa and a Young's modulus of 14 GPa. This tensile strength is comparable to those of SWCNT fibers spun from strong acids. Conductivities on the order of 10(4) S/m were obtained by doping the fibers with iodine.

Methods for Dispersion of Carbon Nanotubes in Water and Common Solvents

Contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed. Main attention is paid to ultrasonic, plasma techniques and other physical techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and organic salts, mineral and organic acids, oxides, inorganic and organic peroxides, organic sulfonates, polymers, dyes, natural products, biomolecules, and coordination compounds).

Solubilization of fullerenes, carbon nanotubes, and graphene

Processing of novel carbon forms, i.e. fullerenes, nanotubes and graphene, in solution is described. C60 and higher fullerenes appear to be the only truly soluble forms of pure carbon. Ways to disperse carbon nanotubes and graphene are reviewed. True solutions of carbon nanotubes and graphene can be obtained by reductive dissolution, leading to solution of polyelectrolyte nanocarbons of high concentrations without damaging the nanocarbon. Finally it is shown that these solutions allow to obtain high performing materials such as highly conducting transparent electrodes.

Probing the charging mechanisms of carbon nanomaterial polyelectrolytes

Chemical charging of single-walled carbon nanotubes (SWCNTs) and graphenes to generate soluble salts shows great promise as a processing route for electronic applications, but raises fundamental questions. The reduction potentials of highly-charged nanocarbon polyelectrolyte ions were investigated by considering their chemical reactivity towards metal salts/complexes in forming metal nanoparticles. The redox activity, degree of functionalisation and charge utilisation were quantified via the relative metal nanoparticle content, established using thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The fundamental relationship between the intrinsic nanocarbon electronic density of states and Coulombic effects during charging is highlighted as an important area for future research.

Single walled carbon nanotube growth and chirality dependence on catalyst composition

Vertical arrays of single walled carbon nanotubes (VA-SWNTs) were grown using bi-metallic nanoparticle pro-catalysts. Iron oxide particles were doped with varying quantities of first row transition metals (Mn, Co, Ni, and Cu) for a comparative study of the growth of nanotubes. VA-CNT samples were verified using scanning electron microscopy, and characterized using resonance Raman spectroscopy. The length of the VA-CNTs is used as a measure of catalyst activity: the presence of dopants results in a change in the CNT length and length distribution. Cross correlation of the Raman spectra reveal variations in the distribution of radial breathing mode peaks according to the pro-catalyst composition. The formation of various chirality nanotubes is constant between repetitive runs with a particular catalyst, but may be controlled by the identity and concentration of the metal dopants within the iron catalyst. These results demonstrate that the composition of the catalyst is a major driving force toward type selective growth of nanotubes.

Electrochemical processing of discrete single-walled carbon nanotube anions

The dissolution of single-walled carbon nanotubes (SWCNTs) remains a fundamental challenge, reliant on aggressive chemistry or ultrasonication and lengthy ultracentrifugation. In contrast, simple nonaqueous electrochemical reduction leads to spontaneous dissolution of individualized SWCNTs from raw, unprocessed powders. The intrinsic electrochemical stability and conductivity of these nanomaterials allow their electrochemical dissolution from a pure SWCNT cathode to form solutions of individually separate and distinct (i.e., discrete) nanotube anions with varying charge density. The integrity of the SWCNT sp² framework during the charge/discharge process is demonstrated by optical spectroscopy data. Other than a reversible change in redox/solvation state, there is no obvious chemical functionalization of the structure, suggesting an analogy to conventional atomic electrochemical dissolution. The heterogeneity of as-synthesized SWCNT samples leads to the sequential dissolution of distinct fractions over time, with fine control over the electrochemical potential. Initial preferential dissolution of defective nanotubes and carbonaceous debris provides a simple, nondestructive means to purify raw materials without recourse to the usual, damaging, competitive oxidation reactions. Neutral SWCNTs can be recovered either by electroplating at an anode or by reaction with a suitable electrophile.

Deconstructing graphite: graphenide solutions

Growing interest in graphene over past few years has prompted researchers to find new routes for producing this material other than mechanical exfoliation or growth from silicon carbide. Chemical vapor deposition on metallic substrates now allows researchers to produce continuous graphene films over large areas. In parallel, researchers will need liquid, large scale, formulations of graphene to produce functional graphene materials that take advantage of graphene's mechanical, electrical, and barrier properties. In this Account, we describe methods for creating graphene solutions from graphite. Graphite provides a cheap source of carbon, but graphite is insoluble. With extensive sonication, it can be dispersed in organic solvents or water with adequate additives. Nevertheless, this process usually creates cracks and defects in the graphite. On the other hand, graphite intercalation compounds (GICs) provide a means to dissolve rather than disperse graphite. GICS can be obtained through the reaction of alkali metals with graphite. These compounds are a source of graphenide salts and also serve as an excellent electronic model of graphene due to the decoupling between graphene layers. The graphenide macroions, negatively charged graphene sheets, form supple two-dimensional polyelectrolytes that spontaneously dissolve in some organic solvents. The entropic gain from the dissolution of counterions and the increased degrees of freedom of graphene in solution drives this process. Notably, we can obtain graphenide solutions in easily processable solvents with low boiling points such as tetrahydrofuran or cyclopentylmethylether. We performed a statistical analysis of high resolution transmission electronic micrographs of graphene sheets deposited on grids from GICs solution to show that the dissolved material has been fully exfoliated. The thickness distribution peaks with single layers and includes a few double- or triple-layer objects. Light scattering analysis of the solutions shows the presence of two-dimensional objects. The typical size of the dissolved flakes can be determined by either static or dynamic light scattering (DLS) using models available in the literature for disk-shape objects. A mean lateral size of ca. 1 μm is typically observed. We also used DLS to monitor the reaggregation that occurs as these sensitive solutions are exposed to air. The graphenide solutions reported in this Account can be used to deposit random arrays of graphene flakes and large single flakes of a lateral size of tens of micrometers onto different substrates. Using the graphenide solutions described in this Account, we foresee the large-scale production of graphene-based printings, coatings, and composites.

On the unzipping of multiwalled carbon nanotubes

Graphene nanoribbons (GNRs) are very interesting structures which can retain graphene's high carrier mobility while presenting a finite bandgap. These properties make GNRs very valuable materials for the building of nanodevices. Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for GNR controlled and large-scale production, although some of the details of the CNT unzipping processes are not completely known. In this work we have investigated CNT unzipping processes through fully atomistic molecular dynamics simulations using reactive force fields (ReaxFF). Multiwalled CNTs of different dimensions and chiralities under induced mechanical stretching were considered. Our results show that fracture patterns and stress profiles are highly CNT chirality dependent. Our results also show that the 'crests' (partially unzipped CNT regions presenting high curvature), originating from defective CNT areas, can act as a guide for the unzipping processes, which can explain the almost perfectly linear cuts frequently observed in unzipped CNTs.