Fe-substituted mullite powders for the in situ synthesis of carbon nanotubes by catalytic chemical vapor deposition

Powders of iron-substituted mullite were prepared by combustion and further calcination in air at different temperatures. A detailed study involving notably Mo¨ssbauer spectroscopy showed that the Fe3+ ions are distributed between the mullite phase and a corundum phase that progressively dissolves into mullite upon the increase in calcination temperature. Carbon nanotube-Fe-mullite nanocomposites were prepared for the first time by a direct method involving a reduction of these powders in H2-CH4 and without any mechanical mixing step. The carbon nanotubes formed by the catalytic decomposition of CH4 on the smallest metal particles are mostly double-walled and multiwalled, although some carbon nanofibers are also observed

Carbon nanostructures derived through hypergolic reaction of conductive polymers with fuming nitric acid at ambient conditions

Hypergolic systems rely on organic fuel and a powerful oxidizer that spontaneously ignites upon contact without any external ignition source. Although their main utilization pertains to rocket fuels and propellants, it is only recently that hypergolics has been established from our group as a new general method for the synthesis of different morphologies of carbon nanostructures depending on the hypergolic pair (organic fuel-oxidizer). In search of new pairs, the hypergolic mixture described here contains polyaniline as the organic source of carbon and fuming nitric acid as strong oxidizer. Specifically, the two reagents react rapidly and spontaneously upon contact at ambient conditions to afford carbon nanosheets. Further liquid-phase exfoliation of the nanosheets in dimethylformamide results in dispersed single layers exhibiting strong Tyndall effect. The method can be extended to other conductive polymers, such as polythiophene and polypyrrole, leading to the formation of different type carbon nanostructures (e.g., photolumincent carbon dots). Apart from being a new synthesis pathway towards carbon nanomaterials and a new type of reaction for conductive polymers, the present hypergolic pairs also provide a novel set of rocket bipropellants based on conductive polymers.Web of Science266art. no. 159

Microwave synthesis, characterization and perspectives of wood pencil-derived carbon

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil's graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70-75 mg/g within 24 h at 23 degrees C, pH = 3.Web of Science121art. no. 41

DNA-Functionalized Gold Nanoparticles in Macromolecularly Crowded Polymer Solutions

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry B, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp310662mDNA-functionalized gold nanoparticles (AuNPs) are one of the most commonly used reagents in nanobiotechnology. They are important not only for practical applications in analytical chemistry and drug delivery, but also for fundamental understanding of nanoscience. For biological samples such as blood serum or for intracellular applications, the effects of crowded cellular proteins and nucleic acids need to be considered. The thermodynamic effect of crowding is to induce nanoparticle aggregation. But before such aggregation can take place, there might also be a depletion repulsive barrier. Polyethylene glycol (PEG) is one of the most frequently used polymers to mimic the crowded cellular environment. We show herein that while DNA-functionalized AuNPs are very stable in buffer (e.g., no PEG) and citrate-capped AuNPs are very stable in PEG, DNA-functionalized AuNPs are unstable in PEG and are easily aggregated. Although such aggregation in PEG is mediated by DNA, no sharp melting transition typical for DNA-linked AuNPs is observed. We attribute this broad melting to depletion force instead of DNA base pairing. The effects of PEG molecular weight, concentration and temperature have been studied in detail and we also find an interesting PEG phase separation and AuNP partition into the water-rich phase at high temperature.University of Waterloo || Canadian Foundation for Innovation || Natural Sciences and Engineering Research Council || Ontario Ministry of Research and Innovation |

Surface Composition of Carbon Nanotubes-Fe-Alumina Nanocomposite Powders: An Integral Low-Energy Electron Mo1ssbauer Spectroscopic Study

The surface state of carbon nanotubes-Fe-alumina nanocomposite powders was studied by transmission and integral low-energy electron Mo¨ssbauer spectroscopy. Several samples, prepared under reduction of the R-Al1.8-Fe0.2O3 precursor in a H2-CH4 atmosphere applying the same heating and cooling rate and changing only the maximum temperature (800-1070 °C) were investigated, demonstrating that integral low-energy electron Mo¨ssbauer spectroscopy is a promising tool complementing transmission Mössbauer spectroscopy for the investigation of the location of the metal Fe and iron-carbide particles in the different carbon nanotubenanocomposite systems containing iron. The nature of the iron species (Fe3+, Fe3C, R-Fe, ç-Fe-C) is correlated to their location in the material. In particular, much information was derived for the powders prepared by using a moderate reduction temperature (800, 850, and 910 °C), for which the transmission and integral low-energy electron Mössbauer spectra are markedly different. Indeed, R-Fe and Fe3C were not observed as surface species, while ç-Fe-C is present at the surface and in the bulk in the same proportion independent of the temperature of preparation. This could show that most of the nanoparticles (detected as Fe3C and/or ç-Fe-C) that contribute to the formation of carbon nanotubes are located in the outer porosity of the material, as opposed to the topmost (ca. 5 nm) surface. For the higher reduction temperatures Tr of 990 °C and 1070 °C, all Fe and Fe-carbide particles formed during the reduction are distributed evenly in the bulk and the surface of the matrix grains. The integral low-energy electron Mo¨ssbauer spectroscopic study of a powder oxidized in air at 600 °C suggests that all Fe3C particles oxidize to R-Fe2O3, while the R-Fe and/or ç-Fe-C are partly transformed to Fe1-xO and R-Fe2O3, the latter phase forming a protecting layer that prevents total oxidation

Probing the perturbation of lecithin bilayers by unmodified C60 fullerenes using experimental methods and computational simulations

In this study, we aimed to use physicochemical and theoretical tools to understand fundamental problems of the interaction between lipid bilayers (Egg-PC liposomes) and unmodified C60 fullerenes. The morphology, the size, and the electrokinetic properties of plain and C60-loaded liposomes were investigated by means of atomic force microscopy, dynamic light scattering, and ?-potential studies, respectively. The incorporation of C60 molecules into the liposomes increases their size; however, there was no effect on their electrokinetic properties. Visualization studies revealed that the presence of C60 in the membranes induced distortion in vesicle morphology, resulting in nonspherical vesicles. To elucidate further the impact of C60 molecules on lipid bilayers, we assessed their miscibility by fluorescence spectroscopy measurements. Fluorescence measurements showed that the presence of C60 in liposomes causes a pronounced effect on the Nile red emission spectrum due to alterations to the packing of the lipid membrane. The release of vesicle-encapsulated calcein was used as a measure of the integrity of the liposomes. Plain liposomes were found to be more stable compared with C60-loaded (PC) liposomes, suggesting that C60 ruptures the liposome membrane. Toxicity studies of C60 in liposomes were carried out on cultured cells [rodent fibroblasts (3T3)] to assess further their toxicity. The results suggest that fullerene cytotoxic effect was reduced significantly after its incorporation into the liposomal bilayer after 24 h of incubation with the rodent fibroblasts (3T3). Finally, energy minimization studies were employed to underpin the experimental observations. The theoretical calculations show that low concentration of fullerene molecules present in the membrane had no effect on the membrane integrity; however, at high concentrations of fullerenes significant enlargement of the surface area is observed, supporting the experimental finding

Editorial for the Special Issue on “Graphene-Related Materials: Synthesis and Applications”

Since the groundbreaking discovery of graphene by Geim and Novoselov in 2004, there has been continuous research focused on the utilization of graphene (GR) and graphene-related materials (GRms) in technologically high-impact applications, spanning from electronics, sensing, and spintronics, to catalysis, energy storage, and environmental remediation [...

Selective Functionalization Blended with Scaffold Conductivity in Graphene Acid Promotes H2O2 Electrochemical Sensing

The widespread industrial use of H2O2 has provoked great interest in the development of new and more efficient materials for its detection. Enzymatic electrochemical sensors have drawn particular attention, primarily because of their excellent selectivity. However, their high cost, instability, complex immobilization, and inherent tendency toward denaturation of the enzyme significantly limit their practical usefulness. Inspired by the powerful proton-catalyzed H2O2 reduction mechanism of peroxidases, we have developed a well-defined and densely functionalized carboxylic graphene derivative (graphene acid, GA) that serves as a proton source and conductive electrode for binding and detecting H2O2. An unprecedented H2O2 sensitivity of 525 \u3bcA cm\u20132 mM\u20131 is achieved by optimizing the balance between the carboxyl group content and scaffold conductivity of GA. Importantly, the GA sensor greatly outperforms all reported carbon-based H2O2 sensors and is superior to enzymatic ones because of its simple immobilization, low cost, and uncompromised sensitivity even after continuous operation for 7 days. In addition, GA-based sensing electrodes remain highly selective in the presence of interferents such as ascorbic acid, paracetamol, and glucose, as well as complex matrices such as milk. GA-based sensors thus have considerable potential for use in practical industrial sensing technologies