Revealing the interparticle magnetic interactions of iron oxide nanoparticles-carbon nanotubes hybrid materials

Spinel iron oxide nanoparticles capped with organic molecules have been successfully prepared and used to produce iron oxide nanoparticles-single wall carbon nanotubes hybrid materials, which were characterized by a number of experimental techniques. The nanoparticles in both samples have an average particle size of about 10 nm and acquire a chemical composition of the type Fe3-xO4, with 0<x<1/3. 57Fe Mössbauer spectroscopy and magnetization measurements suggest that the free capped nanoparticles experience stronger superparamagnetic effects with respect to the nanoparticles of the hybrid sample, which show stronger magnetic interparticle interactions. The mutual proximity of the magnetic nanoparticles of the hybrid sample is proposed to be the origin for this behaviour, which is triggered by their denser anchoring to the outer surface of the singe wall carbon nanotubes due to the reduced dimensions of the latter.

Modified Carbon Nanostructures As Catalysts For Oxygen Reduction Reaction

This work is oriented to take advantage of graphene and nanotubes features in electrocatalysis. At present, a main challenge in this context deals with obtaining inexpensive, energetically efficient and durable catalysts for oxygen reduction in Polymer Electrolyte Membrane Fuel Cells (PEMFC). Platinum and Pt-alloys are currently the best cathode catalysts for this reaction. However, since the metal is scarce and expensive, there is a strong effort to find alternative catalysts. Nitrogen-doped carbon catalysts, also containing iron and cobalt centres, appear to be good and promising platinum alternatives1. For outstanding electronic, mechanical and structural properties graphene oxide and nanotubes could be extremely interesting substitutes either as a catalyst itself or as catalyst support. In this work, we will present some preliminary electrochemical results on Oxygen Reduction Reaction about a series of graphene oxide intercalated with polyethyleneimine of different molecular weight2 and doped with iron, and iron doped nitrogen modified nanotubes, prepared using different nitrogen insertion methods. Physico-chemical characterisation will be also presented. 1 F. Jaouen, V. Goellner, M. Lefevre, J. Herranz, E. Proietti, J.P. Dodelet, Electrochim. Acta 87 (2013) 619. 2 T. Tsoufis, F. Katsaros, Z. Sideratou, B.J. Kooi, M.A. Karakassides, A. Siozios, Chem. A Eur. J., In Press, DOI: 10.1002/chem.201304599

Effect of [Fe(CN) <inf>6</inf>] ^4- substitutions on the spin-flop transition of a layered nickel phyllosilicate

A 3 to 1 Ni/Si antiferromagnetic layered phyllosilicate, Ni 3Si(C 3H 6NH 3)F 0.65O 1.9(OH) 4.45(CH 3COO) 1.1•xH 2O, was modified with K 4[Fe(CN) 6]•3H 2O. This compound retained its ordering as proved by X-ray diffraction, while infrared spectra revealed the presence of [Fe(CN) 6] 4- groups and X-ray photoelectron spectroscopy showed that the latter partially substitute the acetate groups. Both the parent and the modified compound are canted antiferromagnets with an anisotropy perpendicular to the layers and show spin-flop transitions. For the parent compound, a single step spin-flop occurs at H = 24 kOe. The modified compound shows increased antiferromagnetic canting and a two-step transition (H 1 = 24 kOe, H 2 = 48 kOe). These results testify to the existence of competing interactions that depend sensitively on the grafted species. © 2012 American Chemical Society

Novel Nanohybrids Derived from the Attachment of FePt Nanoparticles on Carbon Nanotubes

Multiwalled carbon nanotubes (MWCNTs) were used as nanotemplates for the dispersion and stabilization of FePt nanoparticles (NPs). Pre-formed capped FePt NPs were connected to the MWCNTs external surface via covalent binding through organic linkers. Free FePt NPs and MWCNTs-FePt hybrids were annealed in vacuum at 700 degrees C in order to achieve the L1(0) ordering of the FePt phase. Both as prepared and annealed samples were characterized and studied using a combination of experimental techniques, such as Raman and Mossbauer spectroscopies, powder X-ray Diffraction (XRD), magnetization and transmittion electron microscopy (TEM) measurements. TEM measurements of the hybrid sample before annealing show that a fine dispersion of NPs along the MWCNTs surface is achieved, while a certain amount of free particles attached to each other in well connected dense assemblies of periodical or non-periodical particle arrangements is also observed. XRD measurements reveal that the FePt phase has the face-centered cubic (fcc) disordered crystal structure in the as prepared samples, which is transformed to the face-centered tetragonal (fct) L1(0) ordered crystal structure after annealing. An increase in the average particle size is observed after annealing, which is higher for the free NPs sample. Superparamagnetic phenomena due to the small FePt particle size are observed in the Mossbauer spectra of the as prepared samples. Mossbauer and magnetization measurements of the MWCNTs-FePt hybrids sample reveal that the part of the FePt particles attached to the MWCNTs surface shows superparamagnetic phenomena at RT even after the annealing process. The hard magnetic L1(0) phase characteristics are evident in the magnetization measurements of both samples after annealing, with the coercivity of the hybrid sample over-scaling that of the free NPs sample by a factor of 1.25

Halloysite nanotube-magnetic iron oxide nanoparticle hybrids for the rapid catalytic decomposition of pentachlorophenol

Halloysite clay are a very attractive class of alumino-silicate based, natural nanotubes possessing high aspect ratio, significant thermal and mechanical stability, as well as tunable surface chemistry. We report a novel, facile, synthetic approach involving a modified wet-impregnation method for the in situ synthesis of small, magnetite nanoparticles at the surface of natural halloysite nanotubes. In addition to their magnetic properties, the synthesized magnetite-halloysite hybrids are evaluated for the first time against the catalytic decomposition of pentachlorophenol from reaction solutions at room temperature. Their performance was found superior compared to free, self-supported NPs synthesized with previously reported methods. Very interestingly, after their first catalytic evaluation cycle and because of their magnetic properties the hybrids could be easily recovered from their corresponding reaction solution. The halloysite-nanoparticle hybrids are also very promising in terms of sustainability, since we demonstrate that they can be re-collected, cleaned and re-used for multiple catalytic cycles without any significant loss in their catalytic activity. (C) 2016 Elsevier B.V. All rights reserved

Development of effective nanobiocatalytic systems through the immobilization of hydrolases on functionalized carbon-based nanomaterials

In this study we report the use of functionalized carbon-based nanomaterials, such as amine-functionalized graphene oxide (GO) and multi-walled carbon nanotubes (CNTs), as effective immobilization supports for various lipases and esterases of industrial interest. Structural and biochemical characterization have revealed that the curvature of the nanomaterial affect the immobilization yield, the catalytic behavior and the secondary structure of enzymes. Infrared spectroscopy study indicates that the catalytic behavior of the immobilized enzymes is correlated with their α-helical content. Hydrolases exhibit higher esterification activity (up to 20-fold) when immobilized on CNTs compared to GO. The covalently immobilized enzymes exhibited comparable or even higher activity compared to the physically adsorbed ones, while they presented higher operational stability. The enhanced catalytic behavior observed for most of the hydrolases covalently immobilized on amine-functionalized CNTs indicate that these functionalized nanomaterials are suitable for the development of efficient nanobiocatalytic systems.

In situ growth of capping-free magnetic iron oxide nanoparticles on liquid-phase exfoliated graphene

We report a facile approach for the in situ synthesis of very small iron oxide nanoparticles on the surface of high-quality graphene sheets. Our synthetic strategy involved the direct, liquid-phase exfoliation of highly crystalline graphite (avoiding any oxidation treatment) and the subsequent chemical functionalization of the graphene sheets via the well-established 1,3-dipolar cycloaddition reaction. The resulting graphene derivatives were employed for the immobilization of the nanoparticle precursor (Fe cations) at the introduced organic groups by a modified wet-impregnation method, followed by interaction with acetic acid vapours. The final graphene-iron oxide hybrid material was achieved by heating (calcination) in an inert atmosphere. Characterization by X-ray diffraction, transmission electron and atomic force microscopy, Raman and X-ray photoelectron spectroscopy gave evidence for the formation of rather small (<12 nm), spherical, magnetite-rich nanoparticles which were evenly distributed on the surface of few-layer (<1.2 nm thick) graphene. Due to the presence of the iron oxide nanoparticles, the hybrid material showed a superparamagnetic behaviour at room temperature