Functionalization of carbon nanotubes by combination of controlled radical polymerization and "grafting to" method

This paper reviews the recent advances in non-covalent and covalent tethering of small molecules and polymer chains onto carbon nanotube (CNT) and its derivatives. The functionalized CNT has recently attracted great attention because of an increasing number of its potential applications. In non-covalent functionalization of CNT, the sp²-hybridized network plays a crucial role. The non-covalent grafting of small molecules and polymers can mainly be carried out through hydrogen bonding and π-stacking interactions. In covalent functionalization of CNT, condensation, cycloaddition, and addition reactions play a key role. Polymer modification has been reported by using three main methods of "grafting from", "grafting through", and also "grafting to". The "grafting from" and "grafting through" rely on propagation of polymer chains in the presence of CNT modified with initiator and double bond moieties, respectively. In "grafting to" method, which is the main aim of this review, the pre-fabricated polymer chains are mainly grafted onto the surface using coupling reactions. The coupling reactions are used for grafting pre-fabricated polymer chains and also small molecules onto CNT. Recent studies on grafting polymer chains onto CNT via "grafting to" method have focused on the pre-fabricated polymer chains by conventional and controlled radical polymerization (CRP) methods. CRP includes reversible activation, atom transfer, degenerative (exchange) chain transfer, and reversible chain transfer mechanisms, and could result in polymer-grafted CNT with narrow polydispersity index of the grafted polymer chains. Based on the mentioned mechanisms, nitroxide-mediated polymerization, atom transfer radical polymerization, and reversible addition-fragmentation chain transfer are known as the three commonly used CRP methods. Such polymer-modified CNT has lots of applications in batteries, biomedical fields, sensors, filtration, solar cells, etc.

Bidirectional charge-transfer behavior in carbon-based hybrid nanomaterials

In recent years there has been a growing interest in finding materials revealing bidirectional charge-transfer characteristics, that is, materials behaving as an electron donor or an acceptor in the presence of redox and photoactive addends, for optoelectronic applications. In this respect, carbon-based nanostructures, such as graphene and carbon nanotubes, have emerged as promising nanomaterials for the development of hybrid systems for bidirectional charge transfer, whose behaviour can be switched from donor-type to acceptor-type by simply changing the electroactive counterpart to which they are anchored. In this review we provide an overview of the main advances that have been made over the past few years in carbon-based hybrid architectures involving different types of carbon nanostructures and photosensitizers. In particular, carbon nanotube and graphene-based hybrid systems will be highlighted.

Photo-assisted electrochemical abatement of trifluralin using a cathode containing a C60-carbon nanotubes composite

This work reports the potential application of modified gas-diffusion electrode (GDE) with C₆₀-CNT composite, as a stable and efficient cathode material for degradation of trifluralin (TRL) pesticide by photo-assisted electrochemical (PE) process. C₆₀-CNT composite was prepared and characterized. Subsequently, a novel C₆₀-CNT composite modified GDE cathode was developed and the electrochemical and physical characteristics of the modified GDEs were studied. C₆₀-CNT composite/GDE showed great efficiencies for electro-generating H₂O₂, owing to huge surface area and high conductivity. Afterwards, a comparative study of TRL oxidation via photolysis, anodic oxidation (AO) and PE processes using C₆₀-CNT composite/GDE revealed the degradation percentages of 42.2, 48.5 and 93.4%, respectively, after 180 min of treatment. The TRL degradation followed a pseudo-first-order kinetics, being faster in the order: photolysis < AO < PE. The effects of various operational conditions were assessed on the degradation of TRL. From the results, PE process using C₆₀-CNT composite/GDE exhibited great performance for the degradation of TRL (20 mg L^-1) under its original pH, Na₂SO₄ electrolyte concentration of 0.05 mol L^-1, applied current intensity of 300 mA, and flow rate of 12.5 L h^-1. TOC results displayed that 92.8% of TRL was mineralized after 8 h of PE process. In addition, a plausible pathway for mineralization of TRL was proposed according to the identified by-products detected by means of gas chromatography-mass spectroscopy (GC-MS), High-performance liquid chromatography (HPLC) and ion chromatography analyses.

The impact of copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition in fullerene chemistry

Click reactions largely cross the borders of organic synthetic chemistry and are now at the forefront of many interdisciplinary studies at the interfaces between chemistry, physics, and biology. As part of this research, our group is involved in a program on the development of clickable fullerene building blocks and their application in the preparation of a large variety of new advanced materials and bioactive compounds. Importantly, the introduction of the click chemistry concept in fullerene chemistry allowed us to produce compounds that would barely be accessible by using the classical tools of fullerene chemistry. This is particularly the case for the conjugation of fullerenes with other carbon nanoforms, such as carbon nanohorns and graphene. It is also the case for most of the sophisticated molecular ensembles constructed from clickable fullerene hexa-adduct building blocks. In this paper, we have summarized our ongoing progress in this particular field.

Emergent Properties and Toxicological Considerations for Nanohybrid Materials in Aquatic Systems

Conjugation of multiple nanomaterials has become the focus of recent materials development. This new material class is commonly known as nanohybrids or "horizon nanomaterials". Conjugation of metal/metal oxides with carbonaceous nanomaterials and overcoating or doping of one metal with another have been pursued to enhance material performance and/or incorporate multifunctionality into nano-enabled devices and processes. Nanohybrids are already at use in commercialized energy, electronics and medical products, which warrant immediate attention for their safety evaluation. These conjugated ensembles likely present a new set of physicochemical properties that are unique to their individual component attributes, hence increasing uncertainty in their risk evaluation. Established toxicological testing strategies and enumerated underlying mechanisms will thus need to be re-evaluated for the assessment of these horizon materials. This review will present a critical discussion on the altered physicochemical properties of nanohybrids and analyze the validity of existing nanotoxicology data against these unique properties. The article will also propose strategies to evaluate the conjugate materials' safety to help undertake future toxicological research on the nanohybrid material class.

Endohedral and exohedral hybrids involving fullerenes and carbon nanotubes

Since fullerenes and carbon nanotubes (CNTs) were discovered, these materials have attracted a great deal of attention in the scientific community due to their unique structures and properties. The properties of both carbon allotropes can be modulated by chemical functionalization, and merging fullerenes and CNTs combines the electronic and optical properties of CNTs with the excellent electron acceptor characteristic of fullerenes; moreover, a synergistic effect of these hybrids can be found, as the properties of both the nanotube and the fullerene are affected by the presence of the other. In these hybrids, the fullerene can be located inside (endohedral) or outside (exohedral) the CNT and both types of hybrid have specific features. CNT-fullerene hybrids have been studied for various applications, including photovoltaics, optical limiting and flame retardancy amongst others. This review outlines the progress in research on CNT-fullerene hybrids, including endohedral and exohedral combinations, their properties, functionalization, applications and outlook.

EPR characterisation of platinum nanoparticle functionalised carbon nanotube hybrid materials

The use of nanostructured carbon materials as electrodes for energy storage and conversion is an expanding area of research in recent years. Herein, platinum nanoparticles have been deposited onto both multi-walled and single-walled carbon nanotubes (CNTs) via a microwave assisted polyol reduction method. This interaction has been probed with electron paramagnetic resonance (EPR) and Raman spectroscopies to elucidate the charge/electron transfer interactions between the Pt nanoparticles and the CNTs. Observed shifts in the g factors of the CNTs are indicative of such an electronic interaction, strongly suggesting the covalent attachment of the nanoparticles to the carboxylic groups on the CNTs, formed during the microwave-assisted reduction process. The Pt decorated CNTs show a dramatic increase in electrochemical behaviour in terms of high reversible capacity and relatively stable cycle performance compared to unmodified CNTs increasing their applicability in energy storage devices. For instance, significant increases in the electrochemical double layer capacitance are observed for the CNT-NP composite electrode.

Fabrication of fullerene-decorated carbon nanotubes and their application in flame-retarding polypropylene

Multi-walled carbon nanotubes were decorated with fullerene (C(60)) via a three-step chemical functionalization, with the goal of combining their unique physical and chemical characteristics and simultaneously improving the solubility of CNTs in organic solvents. C(60) molecules, about 0.67% by molecule, were homogeneously bonded onto the surface of the CNTs. Electron microscopy clearly shows that C(60) molecules are introduced onto the surface of the CNTs, and this is also evidenced by their UV-VIS absorption spectra. Cone calorimetry measurements showed that compared with pristine CNTs, fullerene-decorated CNTs further reduced the flammability of polypropylene, which may be due to the free-radical-trapping effect of C(60) and the barrier effect of the CNT network.

[60]-fullerene and single-walled carbon nanotube-based ultrathin films stepwise grafted onto a self-assembled monolayer on ITO

A step-by-step method was used to prepare homogeneous ultrathin films composed of [60]-fullerene (C60) and single-walled carbon nanotubes (SWNTs), grafted onto the functional surface of an alkylsilane self-assembled monolayer (SAM) on an ITO substrate with an ITO-C60-SWNT sequence using amine addition across a double bond in C60 followed by amidation coupling with acid-functionalized SWNTs. Atomic force microscope and scanning electron microscope images of the resulting composite film showed two-component ball-tube microstructures with high-density coverage, where C60 was homogeneously distributed in the SWNT forest. The attachment of SWNTs to the residual amine units in the SAM on the ITO substrate (SAM-ITO) as well as on the C60 sphere results in the C60 molecules in the aggregated clusters being more separately dispersed, which forms a densely packed composite film as a result of the pi-pi interaction between the C60 buckyballs and the SWNT walls. It was found using ferrocene as an internal redox probe that the oxidative and reductive processes at the film-solution surface were effectively retarded because of obstruction from the densely packed film and the electronic effect of SWNT and C60. In addition, the electrochemical properties of C60 on SAM-ITO plates observed by cyclic voltammetry were significantly modified by chemical anchorage using SWNTs. X-ray photoelectron spectroscopy (XPS) analysis also indicated the successful grafting of C60 and SWNT. The XPS chemical shift of the binding energy showed the presence of electronic interactions between C60, SWNT, and ITO components. Such a uniformly distributed C60-SWNT film may be useful for future research in electrochemical and photoactive nanodevices.

Organic functionalisation and characterisation of single-walled carbon nanotubes

Since carbon nanotubes (CNTs) display unique structures and remarkable physical properties, a variety of applications have emerged in both materials and life sciences. In terms of applications, the functionalisation of nanotubes is extremely important, as it increases their solubility and processability, and combines the unique properties of single-walled carbon nanotubes (SWCNTs) with those of other classes of materials. A number of methods have been developed, which can be divided into two major approaches: (1) non-covalent supramolecular modifications, and (2) covalent functionalisation. In this tutorial review, we survey the covalent modification of SWCNTs with organic moieties, and illustrate the major analytical techniques routinely used to characterise the functionalised materials.