Maria F. Casula

Università degli studi di Cagliari, Cagliari, Sardinia, Italy

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Publications (88)265.35 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fabrication of graphene nanocomposite films via sol–gel chemistry is still a challenging task because of the low solubility of graphene in common solvents. In the present work we have successfully developed a suitable synthesis method employing a solution of exfoliated graphene in 1-vinyl-2-pyrrolidone that is added to an anhydrous sol of silicon tetrachloride in ethanol. Thin graphene–silica films with high optical transparency have been obtained; the graphene sheets are composed of two layers and do not aggregate at a large range of concentrations upon incorporation into the matrix. Thermal processing of the silica films allows complete removal of 1-vinyl-2-pyrrolidone without oxidation or degradation of the graphene sheets which are embedded in the oxide.
    New Journal of Chemistry 07/2014; 38(8). · 2.97 Impact Factor
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    ABSTRACT: The possibility of extending the technological applications of photocatalytic mesoporous titania films relies upon the capability of lowering the processing temperature while maintaining its functional properties. Here we present a synthesis of mesoporous titania films, which makes use of a partially fluorinated surfactant Zonyl FS300 as a mesostructur-ing agent. The photoinduced degradation activity has been followed by FTIR spectroscopy as a function of the films' thermal annealing, ranging from 150 up to 400 °C, by using stearic acid as a model compound. The results have been compared with the benchmark templating agent Pluronic F127 and highlighted a constantly higher activity of the Zonyl-templated films, up to 50%, throughout the range of the temperatures analyzed. Raman spectroscopy indicates that Zonyl FS300 is capable of producing nanosized titania crystals at temperatures lower than Pluronic F127. This explains the different photocatalytic response of the corresponding mesoporous thin films processed at low temperatures.
    The Journal of Physical Chemistry C. 05/2014; 118(22).
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    ABSTRACT: We report the detailed structural characterization and magnetic investigation of nanocrystalline zinc ferrite nanoparticles supported on a silica aerogel porous matrix which differ in size (in the range 4-11 nm) and the inversion degree (from 0.4 to 0.2) as compared to bulk zinc ferrite which has a normal spinel structure. The samples were investigated by zero-field-cooling-field-cooling, thermo-remnant DC magnetization measurements, AC magnetization investigation and Mössbauer spectroscopy. The nanocomposites are superparamagnetic at room temperature; the temperature of the superparamagnetic transition in the samples decreases with the particle size and therefore it is mainly determined by the inversion degree rather than by the particle size, which would give an opposite effect on the blocking temperature. The contribution of particle interaction to the magnetic behavior of the nanocomposites decreases significantly in the sample with the largest particle size. The values of the anisotropy constant give evidence that the anisotropy constant decreases upon increasing the particle size of the samples. All these results clearly indicate that, even when dispersed with low concentration in a non-magnetic and highly porous and insulating matrix, the zinc ferrite nanoparticles show a magnetic behavior similar to that displayed when they are unsupported or dispersed in a similar but denser matrix, and with higher loading. The effective anisotropy measured for our samples appears to be systematically higher than that measured for supported zinc ferrite nanoparticles of similar size, indicating that this effect probably occurs as a consequence of the high inversion degree.
    Physical Chemistry Chemical Physics 01/2014; · 3.83 Impact Factor
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    ABSTRACT: We synthesize colloidal CdSe@CdS octapod nanocrystals decorated with Pt domains, resulting in a metal-semiconductor heterostructure. We devise a protocol to control the growth of Pt on the CdS surface, realizing both a selective tipping and a non-selective coverage. Ultrafast optical spectroscopy, particularly femtosecond transient absorption, is employed to correlate the dynamics of optical excitations with the nanocrystal morphology. We find two regimes for capture of photoexcited electrons by Pt domains: a slow capture after energy relaxation in the semiconductor, occurring in tipped nanocrystals and resulting in large spatial separation of charges, and an ultrafast capture of hot electrons occurring in nanocrystals covered in Pt, where charge separation happens faster than energy relaxation and Auger recombination. Besides the relevance for fundamental materials science and control at the nanoscale, our nanocrystals may be employed in solar photocatalysis.
    Nanoscale 01/2014; · 6.23 Impact Factor
  • Journal of Non-Crystalline Solids 01/2014; · 1.60 Impact Factor
  • Microporous and Mesoporous Materials 01/2014; 194:157–166. · 3.37 Impact Factor
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    ABSTRACT: To fully exploit the potential of self-assembly in a single step, we have designed an inte-grated process to get mesoporous graphene nanocomposite films. The synthesis allows in-corporating graphene sheets with a small number of defects into highly ordered and trans-parent mesoporous titania films. The careful design of the porous matrix at the mesoscale ensures the highest diffusivity in the films which exhibit an enhanced photocatalytic effi-ciency while the high order of the mesoporosity is not affected by the insertion of the gra-phene sheets and it is well preserved after controlled thermal treatment. The nanocomposite films can be easily processed by deep X-ray lithography to produce functional arrays.
    ACS Applied Materials & Interfaces 11/2013; · 5.01 Impact Factor
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    ABSTRACT: Magnetic and superparamagnetic colloids represent a versatile platform for the design of functional nanostructures which may act as effective tools for biomedicine, being active in cancer therapy, tissue imaging and magnetic separation. The structural, morphological and hence magnetic features of the magnetic nanoparticles must be tuned for optimal perfomance in a given application. In this work, iron oxide nanocrystals have been prepared as prospective heat mediators in magnetic fluid hyperthermia therapy. A procedure based on the partial oxidation of iron (II) precursors in water based media has been adopted and the synthesis outcome has been investigated by X-Ray diffraction and Transmission electron microscopy. It was found that by adjusting the synthetic parameters (mainly the oxidation rate) magnetic iron oxide nanocrystals with cubic and cuboctahedral shape and average size 50 nm were obtained. The nanocrystals were tested as hyperthermic mediators through Specific Absorption Rate (SAR) measurements. The samples act as heat mediators, being able to increase the temperature from physiological temperature to the temperatures used for magnetic hyperthermia by short exposure to an alternative magnetic field and exhibit a reproducible temperature kinetic behavior.
    Proc SPIE 02/2013;
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    ABSTRACT: We present a systematic experimental comparison of the superparamagnetic relaxation time constants obtained by means of dynamic magnetic measurements and (1)H-NMR relaxometry, on ferrite-based nanosystems with different composition, various core sizes and dispersed in different solvents. The application of a heuristic model for the relaxivity allowed a comparison between the reversal time of magnetization as seen by NMR and the results from the AC susceptibility experiments, and an estimation of fundamental microscopic properties. A good agreement between the NMR and AC results was found when fitting the AC data to a Vogel-Fulcher law. Key parameters obtained from the model have been exploited to evaluate the impact of the contribution from magnetic anisotropy to the relaxivity curves and estimate the minimum approach distance of the bulk solvent.
    Journal of Physics Condensed Matter 01/2013; 25(6):066008. · 2.22 Impact Factor
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    ABSTRACT: A mesoporous ordered cubic Im3m silica (SBA-16) characterized by a three dimensional cage-like structure of pores was used as a host matrix for the preparation of a series of FeCo-SiO2 nanocomposites with different alloy loading and composition by the wet impregnation method. The mesoporous structure of the SBA-16-type support, prepared according to a versatile sol-gel templated synthetic method, which makes use of n-butanol as a co-surfactant, is stable during the treatments necessary to obtain the final nanocomposites, as pointed out by low-angle X-Ray diffraction, transmission electron microscopy, and N2 physisorption at 77 K. Wide-angle X-ray diffraction shows that upon reduction at 800 °C, FeCo nanocrystals (6–7 nm) with the typical bcc structure are formed and energy-dispersive X-ray spectroscopy analysis, performed by scanning transmission electron microscopy on one of the samples, shows that the Fe/Co atomic ratio in the alloy nanoparticles is very close to the expected value of two. Electron tomography was used for the first time to gain evidence on the highly interconnected mesoporous structure of SBA-16 and the arrangement of the nanoparticles within the matrix. It was found that spherical alloy nanocrystals with narrow size distribution are homogeneously distributed throughout the mesoporous matrix and that the resulting FeCo-SiO2 nanocomposite material displays superparamagnetic behavior with high strength dipolar interactions, as expected for particles with a large magnetic moment.
    ChemPlusChem 01/2013; 78(4):364.
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    ABSTRACT: Hybrid materials obtained through a Microwave-assisted grafting of organic functional groups on mesoporous silica (MCM-41 type) have been characterized by X-ray powder diffraction, TG-DSC, N2 adsorption, solid state 13C- and 29Si-NMR, TEM and SEM. The studied grafting procedure is effective in the preparation of hybrid organosilicas under solvent-free conditions. Microwaves allows an ultra-fast and clean functionalization of the mesoporous materials and the method has been applied to produce a wide series of functional materials. The hybrid materials maintain the original mesoporous structure when the loading of linked organic groups does not exceed 10 %. In this cases, the slight pore volume reduction is linearly correlated to the organic amount in the product. If functional groups able to interact among them through hydrogen bond are used, hybrid materials exhibit high Organic/SiO2 ratios and low pore volumes due to the formation of a network occluding the pores, where functional groups of free organosilane molecules interacts with the functional groups of molecules linked to the matrix. NMR data confirm that the network is composed by organosilane molecules linked or not to the framework. Acid washing is able to labilize hydrogen bond and open the network. In the case of bulky but chemically inert functionalising agents the network is not produced.
    Journal of Porous Materials 01/2013; 20(4). · 1.35 Impact Factor
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    ABSTRACT: The optical properties of 7-hydroxy-4-methyl coumarin immobilized on polyethylene glycol support and dissolved in distilled water solution are compared to the optical properties of the dye dissolved in ethanol and discussed on the basis of the formation of different chemical species of the dye molecule. The presence of the polymeric support affects both the absorption and emission features of the coumarin by changing the chemical equilibrium among the different species typically observed at the ground and excited states. The optical properties of synthesized PEG-supported coumarins are able to warrant bio-medical applications in water-based environment and enable to gain insights on the photophysical activity of coumarins, in particular the steric hindrance of the polymeric support inhibits the formation of the tautomeric form of the compound in the excited state, a further proof of the single step neutral to tautomer reaction in coumarins.
    The Journal of Physical Chemistry A 10/2012; · 2.77 Impact Factor
  • ChemInform 08/2012; 43(35).
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    ABSTRACT: In this work, nanocomposites constituted of FeCo alloy nanoparticles dispersed on a highly porous silica aerogel have been designed as catalysts for low temperature Fischer–Tropsch synthesis. The catalysts were characterized by XRD, TEM, N2 physisorption and SEM analysis. A high catalytic activity with CO conversions up to 95 % has been obtained, with enhanced selectivity for the C2–C4 hydrocarbons. Graphical Abstract
    Catalysis Letters 07/2012; 142:1061. · 2.24 Impact Factor
  • Physical review. B, Condensed matter 05/2012; 85(17). · 3.77 Impact Factor
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    ABSTRACT: We report a broadband 1H-NMR study of the temperature spin dynamics of nearly monodisperse dextran-coated γ-Fe2O3 magnetic nanoparticles. We observed a maximum in T1−1(T) that decreases in amplitude and shifts toward higher temperatures with increasing field. We suggest that this is related to the progressive superparamagnetic spin blocking of the ferrite core. The data can be explained by assuming a single electronic spin-spin correlation time and introducing a field-dependent distribution of anisotropy energy barriers.
    Physical review. B, Condensed matter 05/2012; 85(17). · 3.77 Impact Factor
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    ABSTRACT: In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.
    Chemical Society Reviews 04/2012; 41(11):4306-34. · 24.89 Impact Factor
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    ABSTRACT: Stoichiometric magnetic nanosized ferrites MFe2O4 (M = Mn, Co, Ni) were prepared in form of nearly spherical nanocrystals supported on a highly porous silica aerogel matrix, by a sol-gel procedure. X-ray diffraction and transmission electron microscopy indicate that these materials are made out of non-agglomerated ferrite nanocrystals having size in the 5-10 nm range. Investigation by Mössbauer Spectroscopy was used to gain insights on the superparamagnetic relaxation and on the inversion degree. Magnetic ordering at room temperature varies from superparamagnetic in the NiFe2O4 sample, highly blocked (approximately 70%) in the MnFe2O4 sample and nearly fully blocked in the CoFe2O4 sample. A fitting procedure of the Mössbauer data has been used in order to resolve the spectrum into the tetrahedral and octahedral components; in this way, an inversion degree of 0.68 (very close to bulk values) was obtained for 6 nm silica-supported CoFe2O4 nanocrystals.
    Journal of Nanoscience and Nanotechnology 11/2011; 11(11):10136-41. · 1.15 Impact Factor
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    ABSTRACT: The creation of novel engineered multimodal nanoparticles (NPs) is a key focus in bionanotechnology and can lead to deep understanding of biological processes at the molecular level. Here, we present a multi-component system made of gold-coupled core-shell SPIONs, as a new nanoprobe with signal enhancement in surface Raman spectroscopy, due to its jagged-shaped gold shell coating.
    Chemical Communications 08/2011; 47(37):10404-6. · 6.38 Impact Factor
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    ABSTRACT: Porous organic–inorganic hybrid films with well defined pore shape and dimension have been obtained via a salt-template route. Sodium chloride precipitates during film deposition as templating for cubic shape pores; combining this salt-template route with controlled phase separation, pores of spherical shape in the same film have been also obtained. The dimensions of the nanocubes and nanospheres are in the 20–200 nm range and can be modulated through the film processing conditions. We have systematically investigated the effect of precursor solution aging and surfactant concentration on the porous film structure using infrared spectroscopy, spectroscopic ellipsometry, X-ray diffraction, Raman imaging, atomic force microscopy and transmission electron microscopy. Only a very specific combination of different synthesis parameters, such as surfactant concentration and aging of the precursor solution, allows the formation of the pore templates.
    New Journal of Chemistry 08/2011; 35(8):1624-1629. · 2.97 Impact Factor

Publication Stats

586 Citations
265.35 Total Impact Points

Institutions

  • 2000–2014
    • Università degli studi di Cagliari
      • • Department of Chemical and Geological Science
      • • Department of Surgical Science
      Cagliari, Sardinia, Italy
  • 2013
    • University of Pavia
      • Department of Physics
      Ticinum, Lombardy, Italy
  • 2009
    • Philipps University of Marburg
      Marburg, Hesse, Germany
  • 2006
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, MO, United States
  • 2005
    • Universität Ulm
      Ulm, Baden-Württemberg, Germany