Clara Pereira - Superparamagnetic γ-Fe2O3@SiO2 nanoparticles: a novel support for the immobilization of [VO(acac)2] catalyst

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  Superparamagnetic    γ-Fe2O3@SiO2  nanoparticles: a novel support for the immobilization of   [VO(acac)2] catalyst,   Clara Pereira,   André M. Pereira, Pedro Quaresma, Pedro B. Tavares, Eulália   Pereira, João P. Araújo, Cristina Freire, Dalton Transactions  2010,   39,   2842–2854.   DOI:   10.1039/b920853d


  This work reports a detailed investigation about the   physicochemical properties of superparamagnetic   γ-Fe2O3  nanomaterial synthesized by the co-precipitation method and   coated with two silica shells, and its application as support for   the immobilization of oxovanadium(IV)   acetylacetonate ([VO(acac)2]). The   influence of the silica coatings on the surface composition and   physicochemical interactions of the core-shell nanocomposites is   discussed based on the combination of several techniques:   electron microscopy techniques (SEM and TEM with EDS), DLS,   powder XRD, XPS, FTIR and magnetic characterization. The identity   of the iron oxide,   γ-Fe2O3, was   confirmed by XPS, FTIR and by the Rietveld refinement of the PXRD   pattern. The results obtained by electron microscopy techniques,   XRD and magnetization indicated that the   γ-Fe2O3  nanoparticles are superparamagnetic and present an average size   of [similar]6.5 nm. The first silica coating leads   to a core-shell nanomaterial with an average particle size of 21   nm and upon the second coating, the average size increases to 240   nm. Magnetic measurements revealed that the silica-coated   nanomaterials maintain the superparamagnetic state at room   temperature, although with an expected reduction of the   magnetization saturation due to the increase of the silica shell   thickness. Furthermore, a numerical fit of the temperature   dependence of magnetization was performed to determine the core   size distribution and the effect of the silica coatings on the   dipolar magnetic interactions.   [VO(acac)2] was covalently immobilized   on the surface of the silica-coated magnetic nanoparticles   functionalized with amine groups, as confirmed by chemical   analysis and XPS. In a proof-of-principle experiment, we   demonstrated the catalytic performance of the novel magnetic   hybrid nanomaterial in the epoxidation of geraniol, which   presented high selectivity towards the 2,3-epoxygeraniol product   and easy recovery by magnetic separation.

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