title: Superparamagnetic gamma-Fe2O3@SiO2 nanoparticles: a novel support for the immobilization of [VO(acac)2].
abstract: This work reports a detailed investigation about the physicochemical properties of superparamagnetic gamma-Fe(2)O(3) 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, gamma-Fe(2)O(3), 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 gamma-Fe(2)O(3) nanoparticles are superparamagnetic and present an average size of approximately 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.
authors.affiliation: REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, s/n, 4169-007, Porto, Portugal.
authors.forename: Clara
authors.initials: C
authors.lastname: Pereira
authors.forename: André M
authors.initials: AM
authors.lastname: Pereira
authors.forename: Pedro
authors.initials: P
authors.lastname: Quaresma
authors.forename: Pedro B
authors.initials: PB
authors.lastname: Tavares
authors.forename: Eulália
authors.initials: E
authors.lastname: Pereira
authors.forename: João P
authors.initials: JP
authors.lastname: Araújo
authors.forename: Cristina
authors.initials: C
authors.lastname: Freire
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D008280:Magnetics; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D009942:Organometallic Compounds / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D009942:Organometallic Compounds; C507909:bis(acetylacetonato)oxovanadium(IV); C000499:ferric oxide; D012822:Silicon Dioxide