Selective polycarboxylation of semiconducting single-walled carbon nanotubes by reductive sidewall functionalization

Synthesis of POMOFs with 8-fold helix and its composite with carboxyl functionalized SWCNTs for the voltammetric determination of dopamine

Although many satisfactory studies have been developed for biomolecule detection, the complexity of biofluids still poses a major challenge to improve the performance of nanomaterials as electrochemical sensors. Herein, unprecedented polyoxometalate-based metal-organic frameworks (POMOFs) with 8-fold meso-helical feature, [Ag₅(trz)₄]₂[PMo₁₂O₄₀] (PAZ), were synthesized and explored as electrochemical sensors to detect dopamine (DA). To improve the conductivity of PAZ and the binding ability with single-walled carbon nanotubes (SWCNTs), the nanocomposite of carboxyl functionalized SWCNTs (SWCNTs-COOH) with nano-PAZ (NPAZ), NPAZ@SWCNTs-COOH, was fabricated, and transmission electron microscopy (TEM) shows that NPAZ can interact stably and uniformly with SWCNTs-COOH, owing to more defect sites on the surface of SWCNTs-COOH. The electrochemical result of NPAZ@SWCNTs-COOH/GCE towards detecting DA shows that the linear range was from 0.05 to 100 μM with a detection limit (LOD) of 8.6 nM (S/N = 3). A new electrochemical biosensing platform by combining 8-fold helical POMOFs with SWCNTs-COOH was developed for enhancing detection of dopamine for the first time, exhibiting the lowest detection limit to date.

Effect of conjugation on the vibrational modes of a carbon nanotube dimer

First Principles simulation studies using the density functional theory have been performed to investigate the effect of conjugation on vibrational modes when two CNTs of different chiralities are held together to constitute an inhomogeneous dimer. Raman Spectra of a (5, 0) CNT; a (6,0) CNT and a (5,0)- (6,0) CNT dimer comprising of parallel standing (5,0) and (6,0) CNTs held by weak Van der Waals were simulated. Various vibrational modes in different frequency regions have been discussed in detail. A red shift is observed overall that clearly affirms the stability and existence of the structure formed by conjugation of CNTs. In the RBM (Radial Breathing Mode) region, additional peaks can be seen arising out of the coupled vibrations. D-band peaks of the dimer cover the D-band peaks of both the CNTs as disorder in the constituents reflects in its constitution. In the G-band region of the dimer spectrum, a low wavelength component with Lorentzian shape and a weak high wavelength component with a Breit Wigner Fano (BWF) kind of line-shape suggest metallic nature of the inhomogeneous CNT dimer.

Controlling the Degree of Functionalization: In-Depth Quantification and Side-Product Analysis of Diazonium Chemistry on SWCNTs

We present an in-depth qualitative and quantitative analysis of a reaction between 4-iodobenzenediazonium tetrafluoroborate and single-walled carbon nanotubes (SWCNTs) via thermogravimetric analysis coupled with mass spectrometry (TG-MS) or a gas chromatography and mass spectrometry (TG-GC-MS) as well as Raman spectroscopy. We propose a method for precise determination of the degree of functionalization and quantification of physisorbed aromates, detaching around their boiling point, alongside covalently bonded ones (cleavage over 200 °C). While the presence of some side products like phenol- or biphenyl species could be excluded, residual surfactant and minor amounts of benzene could be identified. A concentration-dependent experiment shows that the degree of functionalization increases with the logarithm of the concentration of applied diazonium salt, which can be exploited to precisely adjust the amount of aryl addends on the nanotube sidewall, up to 1 moiety per 100 carbon atoms.

Modulating Carrier Type for Enhanced Thermoelectric Performance of Single-Walled Carbon Nanotubes/Polyethyleneimine Composites

Thermoelectric (TE) generators consisting of flexible and lightweight p- and n-type single-walled carbon nanotube (SWCNT)-based composites have potential applications in powering wearable electronics using the temperature difference between the human body and the environment. Tuning the TE properties of SWCNTs, particularly p- versus n-type control, is currently of significant interest. Herein, the TE properties of SWCNT-based flexible films consisting of SWCNTs doped with polyethyleneimine (PEI) were evaluated. The carrier type of the SWCNT/PEI composites was modulated by regulating the proportion of SWCNTs and PEI using simple mixing techniques. The as-prepared SWCNT/PEI composite films were switched from p- to n-type by the addition of a high amount of PEI (>13.0 wt.%). Moreover, interconnected SWCNTs networks were formed due to the excellent SWNT dispersion and film formation. These parameters were improved by the addition of PEI and Nafion, which facilitated effective carrier transport. A TE generator with three thermocouples of p- and n-type SWCNT/PEI flexible composite films delivered an open circuit voltage of 17 mV and a maximum output power of 224 nW at the temperature gradient of 50 K. These promising results showed that the flexible SWCNT/PEI composites have potential applications in wearable and autonomous devices.

Adverse Effect of PTFE Stir Bars on the Covalent Functionalization of Carbon and Boron Nitride Nanotubes Using Billups-Birch Reduction Conditions

The functionalization of nanomaterials has long been studied as a way to manipulate and tailor their properties to a desired application. Of the various methods available, the Billups-Birch reduction has become an important and widely used reaction for the functionalization of carbon nanotubes (CNTs) and, more recently, boron nitride nanotubes. However, an easily overlooked source of error when using highly reductive conditions is the utilization of poly(tetrafluoroethylene) (PTFE) stir bars. In this work, we studied the effects of using this kind of stir bar versus using a glass stir bar by measuring the resulting degree of functionalization with 1-bromododecane. Thermogravimetric analysis studies alone could deceive one into thinking that reactions stirred with PTFE stir bars are highly functionalized; however, the utilization of spectroscopic techniques, such as Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, tells otherwise. Furthermore, in the case of CNTs, we determined that using Raman spectroscopy alone for analysis is not sufficient to demonstrate successful chemical modification.

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.

Heptamethine Cyanine Dyes in the Design of Photoactive Carbon Nanomaterials

Near-infrared (NIR) absorbing nanomaterials, built from anionic heptamethine cyanine dyes and single-walled carbon nanotubes or few-layer graphene, are presented. The covalent linkage, using 1,3-dipolar cycloaddition reactions, results in nanoconjugates that synchronize the properties of both materials, as demonstrated by an in-depth characterization study carried out by transmission electron microscopy, atomic force microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. UV-vis-NIR and Raman spectroscopies further confirmed the unique electronic structure of the novel photoactive nanomaterials.

Advanced carbon nanotubes functionalization

Similar to graphene, carbon nanotubes are materials made of pure carbon in its sp² form. Their extended conjugated π-network provides them with remarkable quantum optoelectronic properties. Frustratingly, it also brings drawbacks. The π-π stacking interaction makes as-produced tubes bundle together, blurring all their quantum properties. Functionalization aims at modifying and protecting the tubes while hindering π-π stacking. Several functionalization strategies have been developed to circumvent this limitation in order for nanotubes applications to thrive. In this review, we summarize the different approaches established so far, emphasizing the balance between functionalization efficacy and the preservation of the tubes' properties. Much attention will be given to a functionalization strategy overcoming the covalent-noncovalent dichotomy and to the implementation of two advanced functionalization schemes: (a) conjugation with molecular switches, to yield hybrid nanosystems with chemo-physical properties that can be tuned in a controlled and reversible way, and; (b) plasmonic nanosystems, whose ability to concentrate and enhance the electromagnetic fields can be taken advantage of to enhance the optical response of the tubes.

Increased solubility and fiber spinning of graphenide dispersions aided by crown-ethers

Graphenide solutions in NMP have been prepared by dispersing potassium intercalated graphite with the assistance of 18-crown-6.

Sugar-functionalized triptycenes used for dispersion of single-walled carbon nanotubes in aqueous solution by supramolecular interaction

Two water-soluble sugar-functionalized triptycene derivatives were synthesized and used for dispersion of SWCNTs in aqueous solution via supramolecular interaction.

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.

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.

Filled and peptide-modified single-walled carbon nanotubes: synthesis, characterization, and in vitro test for cancer cell targeting

Multi-functional single-walled carbon nanotubes (SWNTs) with metal endohedral filling and a high degree of polycarboxylation on the sidewalls were synthesized without affecting the SWNTσ-framework.

Brominated single walled carbon nanotubes as versatile precursors for covalent sidewall functionalization

Brominated SWCNTs serve as versatile building blocks for the facile generation of sidewall functionalized SWCNT derivatives.

Tuning the redox activity of encapsulated metal clusters via the metallic and semiconducting character of carbon nanotubes

We demonstrate that reactions confined within single-walled carbon nanotube (SWCNT) channels are modulated by the metallic and semiconducting character of the hosts. In situ Raman and X-ray absorption near-edge structure spectroscopies provide complementary information about the electronic state of carbon nanotubes and the encapsulated rhenium species, which reveal electronic interactions between encapsulated species and nanotubes. More electrons are transferred from metallic tubes (m-SWCNTs) to oxidic rhenium clusters, leading to a lower valence state rhenium oxide than that in semiconducting tubes (s-SWCNTs). Reduction in 3.5% (vol/vol) H2/Ar leads to weakened host-guest electronic interaction. The high valence state Re within s-SWCNTs is more readily reduced when raising the temperature, whereas only a sluggish change is observed for Re within m-SWCNTs. Only at 400 °C does Re reach a similar electronic state (mixture of Re(0) and Re(4+)) in both types of tubes. Subsequent oxidation in 1% O2/Ar does not show changes for Re in s-SWCNTs up to 200 °C. In comparison, m-SWCNTs facilitate the oxidation of reduced rhenium (160 °C). This can be exploited for rational design of active catalysts with stable species as a desired valence state can be obtained by selecting specific-type SWCNTs and a controlled thermal treatment. These results also provide a chemical approach to modulate reversibly the electronic structure of SWCNTs without damaging the sidewalls of SWCNTs.

Increased solubility, liquid-crystalline phase, and selective functionalization of single-walled carbon nanotube polyelectrolyte dispersions

The solubility of single-walled carbon nanotube (SWCNT) polyelectrolytes [K(THF)]nSWCNT in dimethyl sulfoxide (DMSO) was determined by a combination of centrifugation, UV-vis spectral properties, and solution extraction. The SWCNT formed a liquid crystal at a concentration above 3.8 mg/mL. Also, crown ether 18-crown-6 was found to increase the solubility of the SWCNT polyelectrolytes in DMSO. Raman spectroscopy and near-infrared (NIR) fluorescence analyses were applied to study the functionalization of SWCNTs. Small-diameter SWCNTs were found to be preferentially functionalized when the SWCNT polyelectrolytes were dispersed in DMSO.

Wet chemical functionalization of graphene

The fullerenes, carbon nanotubes, and graphene have enriched the family of carbon allotropes over the last few decades. Synthetic carbon allotropes (SCAs) have attracted chemists, physicists, and materials scientists because of the sheer multitude of their aesthetically pleasing structures and, more so, because of their outstanding and often unprecedented properties. They consist of fully conjugated p-electron systems and are considered topologically confined objects in zero, one, or two dimensions. Among the SCAs, graphene shows the greatest potential for high-performance applications, in the field of nanoelectronics, for example. However, significant fundamental research is still required to develop graphene chemistry. Chemical functionalization of graphene will increase its dispersibility in solvents, improve its processing into new materials, and facilitate the combination of graphene's unprecedented properties with those of other compound classes. On the basis of our experience with fullerenes and carbon nanotubes, we have described a series of covalent and noncovalent approaches to generate graphene derivatives. Using water-soluble perylene surfactants, we could efficiently exfoliate graphite in water and prepare substantial amounts of single-layer-graphene (SLG) and few-layer-graphene (FLG). At the same time, this approach leads to noncovalent graphene derivatives because it establishes efficient π-π-stacking interactions between graphene and the aromatic perylene chromophors supported by hydrophobic interactions. To gain efficient access to covalently functionalized graphene we employed graphite intercalation compounds (GICs), where positively charged metal cations are located between the negatively charged graphene sheets. The balanced combination of intercalation combined with repulsion driven by Coulombic interactions facilitated efficient exfoliation and wet chemical functionalization of the electronically activated graphene sheets via trapping with reactive electrophilic addends. For example, the treatment of reduced graphite with aryl diazonium salts with the elimination of N(2) led to the formation of arylated graphene. We obtained alkylated graphene via related trapping reactions with alkyl iodides. These new developments have opened the door for combining the unprecedented properties of graphene with those of other compound classes. We expect that further studies of the principles of graphene reactivity, improved characterization methods, and better synthetic control over graphene derivatives will lead to a whole series of new materials with highly specific functionalities and enormous potential for attractive applications.