Showing papers by "Gaetano Granozzi published in 2011"
TL;DR: A new method for the synthesis in water of FeOx–MNPs via a top-down physical technique consisting in Laser Ablation Synthesis in Solution (LASiS), which shows excellent biocompatibility.
Abstract: Multifunctional iron oxide (FeOx) magnetic nanoparticles (MNPs) are promising items for biomedical applications. They are studied as theranostic agents for cancer treatment, selective probes for bioanalytical assays, controllable carriers for drug delivery and biocompatible tools for cell sorting or tissue repair. Here we report a new method for the synthesis in water of FeOx–MNPsvia a top-down physical technique consisting in Laser Ablation Synthesis in Solution (LASiS). LASiS is a green method that does not require chemicals or stabilizers, because nanoparticles are directly obtained in water as a stable colloidal system. A gamut of characterization techniques was used for investigating the structure of FeOx–MNPs that have a polycrystalline structure prevalently composed of magnetite (ca. 75%) and hematite (ca. 22%). The FeOx–MNPs exhibit very good magnetic properties if compared to what is usually reported for iron oxide nanoparticles, with saturation magnetization close to the bulk value (ca. 80 emu g−1) and typical signatures of the coexistence of ferrimagnetic and antiferromagnetic phases in the same particle. The functionalization of FeOx–MNPs after the synthesis was possible with a variety of ligands. In particular, we succeeded in the functionalization of FeOx–MNPs with carboxylated phosphonates, fluorescent alkylamines, fluorescent isothiocyanates and bovine serum albumin. Our FeOx–MNPs showed excellent biocompatibility. Multifunctional FeOx–MNPs were exploited for macrophage cell labelling with fluorescent probes as well as for cell sorting and manipulation by external magnetic fields.
83 citations
TL;DR: In this paper, the authors reported a new method for large-scale facile synthesis of micron-sized partially oxidized graphene (POG) sheets with dramatically improved electronic properties compared to other solution-phase exfoliated graphene.
Abstract: Solution exfoliation of graphite holds promise for large-scale bulk synthesis of graphene. Non-covalent exfoliation is attractive because the electronic structure of graphene is preserved but the yield is low and the lateral dimensions of the sheets are small. Chemical exfoliation via formation of graphite oxide is a highly versatile and scalable route but the covalent functionalization of graphene with oxygen significantly alters the properties. Here, we report a new method for large-scale facile synthesis of micron-sized partially oxidized graphene (POG) sheets with dramatically improved electronic properties compared to other solution-phase exfoliated graphene. Due to low initial oxygen content (∼12%), POG requires only mild annealing (<300 °C) to achieve a sheet resistance of 28 kΩ sq−1 at the neutrality point, only a factor of ∼4 larger than the intrinsic sheet resistance of pristine graphene (∼6 kΩ sq−1) and substantially lower than graphene exfoliated by other methods. Such a partial oxidation approach opens up new promising routes to solution based high-performance, low temperature, transparent and conducting graphene-based flexible electronics.
82 citations
TL;DR: In this paper, the surface-enhanced Raman scattering (SERS) properties of these substrates have been studied in terms of the enhancement factor (EF), point-to-point reproducibility and sample to sample repeatability.
Abstract: Commercially available digital versatile discs (DVDs) contain a silver-coated spiral distribution of rectangular-shaped grooves (AgDVD): for the first time, they have been used to produce surface-enhanced Raman scattering (SERS) substrates by electrochemical deposition of silver nanoparticles (AgNPs@AgDVD). The overall procedure only requires cheap and widely available materials and can be easily accomplished. Scanning electron microscopy images of AgNPs@AgDVD revealed that small AgNPs (average diameter about 15 nm) are present within the valleys of AgDVD, whereas over the ridges, the AgNPs are bigger, more densely packed and with a dendrite-like morphology somewhere. The SERS properties of these substrates have been studied in terms of the enhancement factor (EF), point-to-point reproducibility and sample-to-sample repeatability. It turned out that high SERS EF and good reproducibility requirements are both fulfilled. As for repeatability, remarkably better results than typical literature values have been achieved. Such an easy&cheap preparation along with efficient SERS properties make DVD-derived SERS substrates very good candidates for the development of convenient and disposable sensing platforms.
42 citations
TL;DR: In this paper, three paradigmatic examples of directed self-assembling and self-organisation of transition metal nanoparticles (NPs) on oxide ultrathin layers grown on single crystal metal surfaces are analyzed.
35 citations
TL;DR: The locations of the valence band maximum and the leading peak in the O 1s XAS spectrum indicate a band gap similar to anatase but with the Fermi level closer to mid-gap than found for bulk, n-type TiO(2).
Abstract: The electronic structure of TiO(2) nanosheets on the Pt(110)-(1 x 2) surface has been investigated by using high resolution photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The T ...
14 citations
TL;DR: In this article, the geometric and electronic structure of a (4×1) termination over a Pt3Sn near-surface ordered alloy obtained by depositing Sn on the Pt(110) and subsequent annealing was investigated.
Abstract: Pt–Sn alloys play an important role as oxygen reduction reaction (ORR) catalysts in fuel cell technology both for their role in rationalizing the mechanism responsible for the better performances of bimetallic catalysts and for their practical applications. Here we present a complete experimental and theoretical study on the geometric and electronic structure of a (4×1) termination over a Pt3Sn near-surface ordered alloy obtained by depositing Sn on the Pt(110) and subsequent annealing. LEED and STM measurements combined with DFT simulations allow us to determine the atomistic structure of this phase, and to rationalize the peculiar dependence of its STM pattern on the applied bias and the compositional order in deep layers. Both photoemission experiments and density functional calculations indicate that in this phase the Sn–Pt alloying process determines important changes in the electronic properties, and in particular a relevant shift of the Pt 5d band centroid with respect to clean Pt.
13 citations
TL;DR: In this paper, a complete surface science investigation of a model system obtained depositing different amounts of Fe on the z′-TiOx/Pt(111) ultrathin (UT) film, whose structure is known in great detail, is presented.
Abstract: This work presents a complete surface science investigation of a model system obtained depositing different amounts of Fe on the z′-TiOx/Pt(111) ultrathin (UT) film, whose structure is known in great detail. The system has been investigated both at room temperature (RT) and after thermal treatments in an ultrahigh vacuum at temperatures in the room temperature to 900 K range. In contrast with standard thermodynamic predictions, we show that Fe nanoparticles (NPs) strongly compete with Ti to bind oxygen, i.e., a redox reaction where Fe oxidizes and Ti is further reduced to an extent proportional to the amount of deposited Fe is observed. The z′-TiOx UT film is first destabilized by the presence of Fe, but as soon as the temperature is raised, so activating an interdiffusion of Fe into the Pt substrate, a rather ordered UT TiOx film is formed again. However, a new hexagonal (h-TiOx) phase replaces the z′-TiOx one in the room temperature to 800 K range, which progressively transforms into the most stable z′-...
10 citations
TL;DR: In this article, the role of Au nanoparticles inside TiO2-NiO sol-gel thin films for hydrogen sulfide optical detection has been assessed by combining optical spectroscopy, X-ray diffraction (XRD), reaction products analysis and XPS data.
Abstract: The role of Au nanoparticles inside TiO2-NiO sol-gel thin films for hydrogen sulfide optical detection has been assessed by combining optical spectroscopy, X-ray diffraction (XRD), reaction products analysis and X-ray photoemission spectroscopy (XPS) data. Sulfur oxides (i.e., SO2 and SO3, hereafter SOx) are clearly distinguished as reaction products and SOx species are detected on the surface of the samples by XPS. After exposure to H2S, no metal sulfide species can be detected, neither by XRD nor XPS, so we propose that the reaction mechanism does not involve the formation of Ni, Ti or Au sulfides, but a direct catalytic oxidation of H2S to SOx. The role of Au is to provide an optical probe sensitive to the H2S presence, while the oxide matrix is responsible for the conversion of H2Sto SOx.
7 citations
TL;DR: Experimental and theoretical evidence of sequential redox processes and structural transformations occurring by increasing temperature in a metal/oxide/metal system obtained via deposition of Fe atoms onto a z'-TiO(1.25)/Pt(111) ultrathin film in UHV is presented.
Abstract: We present experimental and theoretical evidence of sequential redox processes and structural transformations occurring by increasing temperature in a metal/oxide/metal system obtained via deposition of Fe atoms onto a z′-TiO1.25/Pt(111) ultrathin film in UHV. The initial reduction of the z′-TiOx phase by Fe at room temperature is followed by Fe diffusion and partial penetration into the substrate at intermediate temperatures. This triggers the formation of a bi-component material in which mixed FeO/TiO2 nanoislands coexist on a h-TiO1.14 ultrathin film, notably restructured (from rectangular to hexagonal) and reduced (from Ti:O = 1:1.25 to 1:1.14) with respect to the original TiO1.25 phase. Further heating recovers the pristine z′-TiOx phase while Fe completely dissolves into the substrate.
6 citations
01 Jan 2011
TL;DR: In this article, two major driving factors are considered in the description of the self-assembling process on these systems, giving rise to ordered arrays of metal nanoparticles (NPs): the presence of defects in the oxide layer and the metal-oxide interaction.
Abstract: In this work we present some significant paradigmatic examples of directed self-assembling of transition metals deposited on ultrathin oxide layers grown on single crystal metal surfaces. Two major driving factors are considered in the description of the self-assembling process on these systems, giving rise to ordered arrays of metal nanoparticles (NPs): the presence of defects in the oxide layer and the metal–oxide interaction. We first summarize the structure of different oxide layers, and we discuss the role of geometric and electronic factors in the formation of ordered Au and Fe NP arrays on the selected systems. The discussion suggests that the defective oxide template can drive the self-organization of NPs, if the defects are accessible through the diffusion of metal adatoms on the surface, which in turn, is determined by the metal–oxide interaction.