Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy

Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.Junta de Andalucía Feder PE2009-FQM-4554 TEP-217EU FP7 AL-NANOFUNC CT-REGPOT2011-1-28589

AC Magnetic Heating of Superparamagnetic Fe and Co Nanoparticles

AC magnetic heating of superparamagnetic Co and Fe nanoparticles for application in hyperthermia was measured to find a size of nanoparticles that would result in an optimal heating for given amplitude and frequency of ac externally applied magnetic field. To measure it, a custom-made power supply connected to a 20-turn insulated copper coil in the shape of a spiral solenoid cooled with water was used. A fiber-optic temperature sensor has been used to measure the temperature with an accuracy of 0.0001 K. The magnetic field with magnitude of 20.6 μT and a frequency of oscillation equal to 348 kHz was generated inside the coil to heat magnetic nanoparticles. The maximum specific power loss or the highest heating rate for Co magnetic nanoparticles was achieved for nanoparticles of 8.2 nm in diameter. The maximum heating rate for coated Fe was found for nanoparticles with diameter of 18.61 nm.</jats:p

New routes to Cu(l)/Cu nanocatalysts for the multicomponent click synthesis of 1,2,3-triazoles

An array of copper and copper–zinc based nanoparticles (NPs) have been fabricated employing a variety of polymeric capping agents. Analysis by TEM, XRPD and XPS suggests that by manipulating reagent, reductant and solvent conditions it is possible to achieve materials that are mono-/narrow disperse with mean particle sizes in the ≤10 nm regime. Oxidative stability in air is achieved for monometallic NPs using poly(methyl methacrylate) (PMMA) anti-agglomerant in conjunction with a variety of reducing conditions. In contrast, those encapsulated by either poly(1-vinylpyrrolidin-2-one) (PVP) or poly(4-vinylpyridine) (PVPy) rapidly show Cu2O formation, with all data suggesting progressive oxidation from Cu to Cu@Cu2O core–shell structure and finally Cu2O. Bimetallic copper–zinc systems, reveal metal segregation and the formation of Cu2O and ZnO. Catalysts have been screened in the synthesis of 1,2,3-triazoles through multicomponent azide–alkyne 1,3-dipolar cycloaddition. Whereas PMMA- and PVPy-coating results in reduced catalytic activity, those protected by PVP are highly active, with quantitative triazole syntheses achieved at room temperature and with catalyst loadings of 0.03 mol% metal for Cu and CuZn systems prepared using NaH2PO2, N2H4 or NaBH4 reductants.This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN; CTQ2007-65218 and Consolider Ingenio 2010-CSD2007-00006), the Generalitat Valenciana (GV; PROMETEO/2009/039), and FEDER. Y. M. and B. R. K. thank the ISO of the Universidad de Alicante, the UK EPSRC and the University of Cambridge for grants

Size-Effect of Pd-(Poly(N-vinyl-2-pyrrolidone)) Nanocatalysts on Selective Hydrogenation of Alkynols with Different Alkyl Chains

We have studied the effect of unsupported Pd nanoparticle (NP) size in the selective C C semi-hydrogenation of alkynols with different alkyl chains, i.e., C-16 in dehydroisophytol (DIP) (to isophytol (IP)) vs C-1 in 2-methyl-3-butyn-2-ol (MBY) (to 2-methyl-3-buten-2-ol (MBE)). The Pd NPs were synthesized via colloidal technique with poly(N-vinyl-2-pyrrolidone) (PVP) as stabilizing agent where a range of crystal sizes (2.1-9.8 nm; confirmed by HRTEM) was generated. Both reactions show antipathetic structure sensitivity consistent with higher specific activity (TOF) over larger Pd NPs where the structure sensitivity effect is more pronounced for NPs = 88%) selectivity to the target alkenol product at almost complete (98%) conversion. Increased IP selectivity (S-IP; (XDIP=98%) ca. 95%) was observed over smaller (2.1-3.0 nm) Pd NPs while ca. 98% selectivity to MBE (S-MBE; XDIP=98%) is obtained irrespective of particle size. The kinetic results were consistent with a Langmuir-Hinshelwood model. The observed Pd NPs size effect on catalytic response is ascribed to a contribution of Pd electronic surface modifications, fraction of Pd-plane active sites and the steric effects which impact akynol/alkenol adsorption constants. The results obtained in this work provide a powerful tool for catalyst design for industrial applications