A novel multiwalled carbon nanotube-cyclodextrin nanocomposite for solid-phase microextraction-gas chromatography-mass spectrometry determination of polycyclic aromatic hydrocarbons in snow samples.

Novel solid-phase microextraction coatings based on the use of multiwalled carbon nanotube-cyclodextrin (MWCNT-CD) nanocomposites were developed for the determination of 16-priority polycyclic aromatic hydrocarbons at ultratrace levels in snow samples. The performance of both ß- and γ-CD was tested to increase the detection capabilities towards the heaviest and most lipophilic compounds, i.e., five- and six-ring PAHs. To facilitate the interactions of MWCNTs with CDs, an oxidation procedure using both HNO3 and H2O2 was applied, obtaining superior results using MWCNTs-H2O2-γ-CD fiber. Detection and quantitation limits below 0.7 and 2.3 ng/L, RSD lower than 21%, and recoveries of 88(± 2)-119.8(± 0.4)% proved the reliability of the developed method for the determination of PAHs at ultratrace levels. The complexation capability of the γ-CD was also demonstrated in solution by NMR and fluorescence spectroscopy studies and at solid state by XRD analysis. Finally, snow samples collected in the ski area of Dolomiti di Brenta were analyzed, showing a different distribution of the 16 priority PAHs, being naphthalene, phenanthrene, fluoranthene, and pyrene the only compounds detected in all the analyzed samples.

Structural and morphological modifications of thermally reduced cerium oxide ultrathin epitaxial films on Pt(111).

The modifications of the stoichiometry, morphology and surface structure of cerium oxide ultrathin films induced by thermal treatments under vacuum and oxygen partial pressure were studied using in situ X-ray photoemission spectroscopy, scanning tunnelling microscopy and low energy electron diffraction. The effect of the film nominal thickness, heating temperature and heating time on the degree of reduction of the film was investigated. The reduction is more relevant on the film surface, where different ordered surface structures were observed at different degrees of reduction for very thin films. The obtained results are discussed taking into account the dimensionality of the oxide and the effects of the proximity of the Pt substrate. After reduction it was always possible to re-oxidize the films back to their original oxidation state by thermal treatment under oxygen-rich conditions.

Controlled co-deposition of FePt nanoparticles embedded in MgO: a detailed investigation of structure and electronic and magnetic properties.

Films of FePt nanoparticles (NPs) embedded in MgO were obtained by controlled co-deposition of FePt NPs pre-formed by a gas aggregation source and of Mg evaporated in an oxygen atmosphere. Assemblies of core-shell FePt@MgO NPs and films of FePt NPs embedded in MgO matrix could be obtained by varying FePt and Mg deposition rates. Transmission electron microscopy (TEM) and high resolution-TEM revealed the core-shell structure of the NPs, with an FePt core (of average diameter (d) = 4.75 nm) presenting a multitwinned icosahedral structure, and MgO partially in crystalline form. The functional effect of the MgO shell in shielding the FePt core from external oxidation was shown with XPS. Upon controlled annealing, a transition from A1 to L10 ordering could be obtained, with structural and morphological re-arrangement. The magnetic hysteresis loops obtained from alternating gradient field magnetometry at room temperature show a 'wasp-waist' shape, with small values of coercive field (Hc = 300-1400 Oe), decreasing at increasing amounts of co-deposited MgO.

Magnetic solid-phase extraction based on diphenyl functionalization of Fe3O4 magnetic nanoparticles for the determination of polycyclic aromatic hydrocarbons in urine samples.

Superparamagnetic Fe(3)O(4) diphenyl nanoparticles were prepared according to a solvothernal procedure and characterized by X-ray diffraction, infrared spectroscopy, surface area measurements, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The magnetic phases present in the nanoparticle samples were analyzed by thermomagnetic analysis and the samples' magnetic properties were studied by vibrating sample magnetometry. The resulting nanoparticles having an average diameter of 200 nm were then used as solid-phase extraction sorbent for the determination of polycyclic aromatic hydrocarbons in urine samples. Method validation proved the feasibility of the developed beads for the quantitation of the investigated analytes at trace levels obtaining lower limit of quantitation values in the ng/l range. A good precision with coefficients of variations always lower than 15% was obtained. Finally, the superior extraction performance of the synthesized nanoparticles with respect to commercially available beads was proved.

Iron oxidation, interfacial expansion, and buckling at the Fe/NiO(001) interface.

In order to provide a structural basis for a physical understanding of exchange bias in metal/magnetic-oxide interfaces, we have determined the structure of the Fe/NiO(001) interface by means of x-ray absorption spectroscopy and ab initio density functional theory calculations. A Fe-Ni alloyed phase on top of an interfacial FeO planar layer is formed. The FeO layer exhibits a 7% expanded interlayer distance and a 0.3 A buckling; its presence is predicted to increase the spin magnetic moment of the interface Fe atoms by 0.6 mu(B), compared to the ideally abrupt interface.