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.

New routes to Cu(I)/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 Cu(2)O formation, with all data suggesting progressive oxidation from Cu to Cu@Cu(2)O core-shell structure and finally Cu(2)O. Bimetallic copper-zinc systems, reveal metal segregation and the formation of Cu(2)O 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 NaH(2)PO(2), N(2)H(4) or NaBH(4) reductants.

Selective oxidation with dioxygen by gold nanoparticle catalysts derived from 55-atom clusters.

Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic properties, but the origin of the catalytic activity is still not fully understood. Experimental work on gold particles supported on a titanium dioxide (110) single-crystal surface has established a striking size threshold effect associated with a metal-to-insulator transition, with gold particles catalytically active only if their diameters fall below approximately 3.5 nm. However, the remarkable catalytic behaviour might also in part arise from strong electronic interaction between the gold and the titanium dioxide support. In the case of industrially important selective oxidation reactions, explanation of the effectiveness of gold nanoparticle catalysts is complicated by the need for additives to drive the reaction, and/or the presence of strong support interactions and incomplete understanding of their possible catalytic role. Here we show that very small gold entities ( approximately 1.4 nm) derived from 55-atom gold clusters and supported on inert materials are efficient and robust catalysts for the selective oxidation of styrene by dioxygen. We find a sharp size threshold in catalytic activity, in that particles with diameters of approximately 2 nm and above are completely inactive. Our observations suggest that catalytic activity arises from the altered electronic structure intrinsic to small gold nanoparticles, and that the use of 55-atom gold clusters may prove a viable route to the synthesis of robust gold catalysts suited to practical application.