Maria F. Casula

Università degli studi di Cagliari, Cagliari, Sardinia, Italy

Are you Maria F. Casula?

Claim your profile

Publications (112)484.63 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Cu-based nanoparticles, supported on either a silica aerogel or cubic mesostructured silicas obtained using two different synthetic protocols, were used as catalysts for the Water Gas Shift reaction. The obtained nanocomposites were thoroughly characterized before and after catalysis using N2 adsorption-desorption measurements at -196 °C, transmission electron microscopy, wide-angle and low-angle X-ray diffraction. It was found that the samples before catalysis contain nanoparticles of copper oxides - either CuO or Cu2O - while the formation of metallic copper nanoparticles, constituting the active catalytic phase, is observed either using a pretreatment in reducing atmosphere or directly during the catalytic reaction due to the presence of CO. A key role in determining the catalytic performances of the samples is played by the ability of the different matrices in promoting a high dispersion of Cu metal nanoparticles. The best catalytic performances are obtained with the aerogel sample, which also exhibits constant CO conversion values at constant temperature and quite a reproducible behaviour after subsequent catalytic runs. On the other hand, in the catalysts based on cubic mesostructured silica the detrimental effects related to sintering of Cu nanoparticles are avoided only on the silica support which is able to produce a reasonable dispersion of the copper nanophase.
    No preview · Article · Feb 2016 · ChemPlusChem
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the theranostic properties of magnetosomes (MNs) extracted from magnetotactic bacteria, promising for nanomedicine applications. Besides a physico-chemical characterization, their potentiality as mediators for magnetic fluid hyperthermia and contrast agents for magnetic resonance imaging, both in vitro and in vivo, are here singled out. The MNs, constituted by magnetite nanocrystals arranged in chains, show a superparamagnetic behaviour and a clear evidence of Verwey transition, as signature of magnetite presence. The phospholipid membrane provides a good protection against oxidation and the MNs oxidation state is stable over months. Using an alternate magnetic field, the specific absorption rate was measured, resulting among the highest reported in literature. The MRI contrast efficiency was evaluated by means of the acquisition of complete NMRD profiles. The transverse relaxivity resulted as high as the one of a former commercial contrast agent. The MNs were inoculated into an animal model of tumour and their presence was detected by magnetic resonance images two weeks after the injection in the tumour mass. Copyright © 2015 John Wiley & Sons, Ltd.
    Full-text · Article · Nov 2015 · Contrast Media & Molecular Imaging
  • [Show abstract] [Hide abstract]
    ABSTRACT: Graphene sheets increase the Raman signal through a chemical enhancement mechanism which gives rise to graphene-mediated enhanced Raman scattering (GERS). The low enhancement factor and the surface available for analysis are, however, a limitation on the application of graphene-mediated enhanced Raman scattering (ERS). We have, therefore, developed a new GERS platform, which is based on mesoporous ordered films made of titania anatase containing dispersed sheets of exfoliated graphene. The analytical enhancement factor has revealed that the combination of titania and graphene produces a significant increase in GERS response using Rhodamine 6G as molecular probe. This is a new effect, which we have defined as Ti-GERS (Titania-induced Graphene-mediated ERS) and is attributed to synergic interfacial interactions between graphene sheets and titania at the nanocrystals edges within the nanocomposite. In the future, the Ti-GERS effect is expected to foster a development of better performing Raman based analytical devices avoiding use of expensive noble metals.
    No preview · Article · Jul 2015 · Journal of Physical Chemistry Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: CdSe@CdS dot@rods with diameter around 6 nm and length of either 20, 27, or 30 nm and dot@octapods with pod diameters of ∼15 nm and lengths of ∼50 nm were investigated by X-ray absorption spectroscopy. These heterostructures are prepared by seed-mediated routes, where the structure, composition, and morphology of the CdSe nanocrystals used as a seed play key roles in directing the growth of the second semiconducting domain. The local structural environment of all the elements in the CdSe@CdS heterostructures was investigated at the Cd, S, and Se K-edges by taking advantage of the selectivity of X-ray absorption spectroscopy, and was compared to pure reference compounds. We found that the structural features of dot@rods are independent of the size of the rods. These structures can be described as made of a CdSe dot and a CdS rod, both in the wurtzite phase with a high crystallinity of both the core and the rod. This result supports the effectiveness of high temperature colloidal synthesis in promoting the formation of core@shell nanocrystals with very low defectivity. On the other hand, data on the CdSe@CdS with octapod morphology suggest the occurrence of a core composed of a CdSe cubic sphalerite phase with eight pods made of CdS wurtzite phase. Our findings are compared to current models proposed for the design of functional heterostructures with controlled nanoarchitecture.
    Full-text · Article · Jun 2015 · The Journal of Physical Chemistry C
  • Matteo Sestu · Daniela Carta · Maria Francesca Casula · Anna Corrias · Gabriele Navarra
    [Show abstract] [Hide abstract]
    ABSTRACT: The structure of the iron oxyhydroxide called feroxyhyte (δ-FeOOH), which shows an elusive X-ray powder diffraction pattern, has been represented so far using models describing a mean structure based on the crystalline network of the iron(III) oxide hematite (α-Fe2O3). In this paper, a novel description of the mean structure of feroxyhyte is presented, which is based on the structure of the thermodynamically stable iron oxyhydroxide goethite. Starting from different local arrangements present in the goethite network, a mean structural model is determined which shows an X-ray powder diffraction pattern almost coincident with previous studies. This outcome enables to integrate the structure of feroxyhyte among those of other well characterized iron oxyhydroxides.
    No preview · Article · May 2015 · Journal of Solid State Chemistry
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A new type of mesostructured hybrid organic-inorganic film has been synthesised by evaporation-induced self-assembly using 3-glycidoxypropyltrimethoxysilane as precursor and a tri-block copolymer, Pluronic F127, as template. The chemistry has been tuned to form in the sol bridged polysilsesquioxanes that self-organize into ordered lamellar structures. Controlled aging in highly basic conditions, which has been monitored by Raman and infrared spectroscopy, has been used to obtain the layered ordered hybrid structures in the precursor sol. The pH of the sol has been adjusted to form the micelles that act as templates during solvent evaporation. Self-assembly of the system has been studied in situ by small and wide angle X-ray scattering using a synchrotron light source, which have confirmed both the formation of hybrid layered structures and the organization of a rombohedral mesophase in the hybrid films. The present approach allows ordering the hybrid film in two different length scales; at the end of film processing, hybrid crystals are retained into the pore walls and the micelles are arranged within the films with a long range order.
    Full-text · Article · Mar 2015 · Physical Chemistry Chemical Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A one-pot approach making use of a zinc oxide sol precursor and 14 carbon quantum dots, together with a partially fluorinated block copolymer as 15 templating agent, has been used to synthesize a porous matrix characterized by 16 interesting energy transfer properties. The choice of the fluorinated surfactant for 17 inducing the porosity into the inorganic matrix has allowed an easy removal of the 18 templating agent at low temperature, preserving at the same time the functional 19 properties of the carbon quantum dots. The resulting nanocomposite films have 20 been characterized by steady-state 3D mapping that has evidenced a complex 21 behavior as a function of the carbon quantum dots concentration. In particular, 22 the luminescence bands of the zinc oxide matrix appear to be modulated by the 23 broad emission of the carbon quantum dots, which depends on their aggregation 24 state. These results can be thus considered as a step further toward the fine-tuning 25 of the luminescence properties provided by zinc oxide-based nanocomposites as a 26 result of a doping effect due to the presence of carbon quantum dots.
    Full-text · Article · Jan 2015 · The Journal of Physical Chemistry C
  • D. Carta · F. Boi · A. Corrias · S. Bullita · Z. Kónya · M.F. Casula
    [Show abstract] [Hide abstract]
    ABSTRACT: A series of catalysts containing iron and cobalt nanoparticles supported on a highly ordered mesoporous cubic Im3m silica (SBA-16) were prepared by wet impregnation and used for the production of multi-walled carbon nanotubes (MWCNTs) by catalytic chemical vapor deposition (CCVD) of acetylene. The catalysts were characterized by low- and wide-angle X-ray diffraction, N2 physisorption analysis at 77 K and transmission electron microscopy to study the influence of different metal loading and impregnation time on the CCVD process. Quality and morphology of the MWCNTs was assessed by transmission and scanning electron microscopy, whereas thermal analysis was used to estimate the amount of CNTs produced. It was found that the nanocomposites are catalytically active with particular reference to samples with relatively high metal loading, and are stable under the conditions adopted for the CNT production by the CCVD process.
    No preview · Conference Paper · Dec 2014
  • Claudia Marras · Danilo Loche · Anna Corrias · Zoltan Konya · Maria Francesca Casula
    [Show abstract] [Hide abstract]
    ABSTRACT: Highly porous nanocomposite aerogels based on bimetallic Fe and Mo nanoparticles with a variable Fe:Mo weight ratio ranging from 5:1; 3:1; and 0.7:1 dispersed on amorphous silica were obtained. N2 physisorption, X-ray diffraction, and transmission electron microscopy indicate that the Fe/Mo-SiO2 nanocomposite aerogels as obtained by a co-gelation sol-gel route followed by supercritical drying and reduction treatment under H2 exhibit Fe and Mo nanocrystals with size in the range 4-10 and 15 nm, respectively, supported on highly porous silica. The catalytic performance of the Fe/Mo-SiO2 aerogels for the synthesis of multi wall carbon nanotubes (MWCNT) by catalytic chemical vapour deposition (CCVD) was evaluated in terms of amount and quality of the produced CNTs as assessed by gravimetric results, thermal analysis, and TEM. The effect of catalyst composition and CCVD temperature was investigated, pointing out that high reaction temperatures (800 °C) favor the formation of MWCNTs with high quality in elevated yield, the highest C uptake value being >400 %. Catalyst composition and CCVD temperature were also found to affect the homogeneity of CNT morphology, the best MWCNT quality (with outer diameter 23-25 nm) being achieved at 800 °C with the catalyst having the largest Mo content.
    No preview · Article · Oct 2014 · Journal of Sol-Gel Science and Technology
  • Source
    Luca Medda · Maria F Casula · Maura Monduzzi · Andrea Salis
    [Show abstract] [Hide abstract]
    ABSTRACT: Silica-based ordered mesoporous materials are very attractive matrices to prepare smart depot systems for several kinds of therapeutic agents. This work focuses on the well known SBA-15 mesoporous silica and lysozyme, an antimicrobial protein. In order to improve the bioadhesion properties of SBA-15 particles, the effect of hyaluronic acid functionalization on lysozyme adsorption was investigated. SBA-15 samples having high (H-SBA) and low (L-SBA) levels of functionalization were analyzed during the three steps of the preparations: 1. introduction of the -NH2 groups to obtain the SBA-NH2 samples; 2. functionalization with hyaluronic acid to obtain the SBA-HA matrices; 3. adsorption of lysozyme. All silica matrices were characterized through N2-adsorption/desorption isotherms, SAXS, TEM, thermogravimetric analysis, and FTIR spectroscopy. The whole of the experimental data suggests that a high level of functionalization of the silica surface allows for a negligible lysozyme adsorption mainly due to unfavorable electrostatic interactions (H-SBA-NH2) or steric hindrance (H-SBA-HA). A low degree of functionalization of the silica surface brings about a very good performance towards lysozyme adsorption, being 71 % (L-SBA-NH2) and 63 % (L-SBA-HA) respectively, compared to that observed for original SBA-15. Finally, two different kinetic - a 'pseudo-second order' and a 'intraparticle diffusion' - models were compared to fit lysozyme adsorption data, the latter resulting more reliable than the former.
    Full-text · Article · Oct 2014 · Langmuir
  • Daniela Carta · Danilo Loche · Maria Francesca Casula · Nikolett Olàh · Dominika Olasz · Anna Corrias
    [Show abstract] [Hide abstract]
    ABSTRACT: Porous monoliths of nanocomposites containing Ni (5 wt.%) and FeNi (5 wt.%) nanoparticles dispersed on an SBA-16 type matrix were prepared following a templated-gelation method based on the sol-gel process. The nanocomposites were characterized by energy dispersive X-ray spectroscopy, N-2 physisorption at 77 K, X-ray diffraction and transmission and scanning electron microscopy. In particular, N-2 physisorption and transmission electron microscopy analysis show that the ordered mesoporous structure and the high surface area of all the samples are preserved after calcination in air at 500 degrees C and also after reduction in H-2 flux at 800 degrees C, indicating a very high thermal stability of the samples. As a result of the effective dispersion of the nanophase within the porous texture, nanocomposites containing Ni nanocrystals with an average size of 6 nm homogeneously dispersed within the pores of the amorphous silica matrix were obtained.
    No preview · Article · Oct 2014 · Journal of Non-Crystalline Solids
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Silica mesoporous nanocomposite films containing graphene nanosheets and gold nanoparticles have been prepared via a one-pot synthesis using silicon tetrachloride, gold(III) chloride tetrahydrate, a 1-N-vinyl-2-pyrrolidone dispersion of exfoliated graphene and Pluronic F127 as a structuring agent. The composite films have shown Graphene-mediated Surface-Enhanced Raman Scattering (G-SERS). Graphene has been introduced as dispersed bilayer sheets while gold has been thermally reduced in situ to form nanoparticles of around 6 nm which preferentially nucleate on the surface of the graphene nanosheets. The presence of graphene and gold nanoparticles does not interfere with the self-assembly process and silica mesoporous films ordered as 2D hexagonal structures. The material has shown a remarkable analytical enhancement factor ranging from 80 up to 136 using Rhodamine 6G as a Raman probe. The films have been characterised by grazing incidence X-ray diffraction, FTIR and UV-Vis spectroscopies; transmission electron microscopy and spectroscopic ellipsometry have been used to study the morphology, thickness and porosities of the samples. Raman spectroscopy has been employed to characterise the graphene nanosheets embedded into the mesoporous films and the Enhanced Raman Scattering.
    Full-text · Article · Sep 2014 · Physical Chemistry Chemical Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Camptothecin (CPT; (S)-(+)-4-ethyl-4-hydroxy-1H-pyrano[3',4':6,7]indolizino[1,2- b]quinoline-3,14-(4H,12H)-dione) is a highly cytotoxic natural alkaloid that has not yet found use as chemotherapeutic agent due to its poor water-solubility and chemical instability and, as a consequence, no effective administration means have been designed. In this work, camptothecin has been successfully loaded into iron oxide superparamagnetic nanoparticles with average size 14 nm. It was found that surface modification of the nanoparticles by polyethylene glycol enables loading a large amount of camptothecin. While the unloaded nanoparticles do not induce apoptosis in H460 lung cancer cell line, the camptothecin-loaded nanoparticle formulations exhibit remarkable pro-apoptotic activity. These results indicate that camptothecin retains its biological activity after loading onto the magnetic nanoparticles. The proposed materials represent novel materials based on naturally occurring bioactive molecules loaded onto nanoparticles to be used as chemotherapeutic formulations. The procedure seems apt to be extended to other active molecules extracted from natural products. In addition, these materials offer the potential of being further implemented for combined imaging and therapeutics, as magnetic nanoparticles are known to be multifunctional tools for biomedicine.
    Full-text · Article · Aug 2014 · Beilstein Journal of Nanotechnology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Debye scattering equation is known since 1915 [1]. Altought this formula can, in principle, describe scattering from any multiple particle systems, its application is normally limited to small domains as clusters or low-sized nanoparticles. This is mostly due to the very high computational effort needed. Indeed, computing time strongly depends on the number of atoms. In recent years, the availability of highly performant graphics processing units (GPU) allowed their use for general purposes including strongly demanding scientific applications. This feature was exploited in the Debye Function Analysis to study more complex systems with several thousand of atoms [2]. Here, we present a refinement code using both the Debye scattering equation implemented on a commercial GPU and the Reverse Monte Carlo algorithm [3] to study the structure of two disordered nano-sized iron oxy-hydroxides, feroxyhite and ferrihydrite. The determination of their structure appears rather complex. Different interpretations of the X-ray diffraction pattern have been put forward and debates remain about the exact nature of their crystalline structure. The proposed models show some structural features that are not in accordance with the known structures of other iron oxy-hydroxides: goethite, akaganeite and lepidocrocite. To evaluate their validity, these models are used as starting atom sets in the refinement procedure. To reach a quantitative agreement between the experimental diffraction pattern and the calculated one, the atom positions are randomly modified. X-ray diffraction pattern is calculed using Debye scattering equation; to speed up calculation time, a parallelized version of the equation is optimized to run on Nvidia GeForce 690 GPU.
    No preview · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
  • [Show abstract] [Hide abstract]
    ABSTRACT: Porous monoliths of a 3D cubic cage mesostructured silica (SBA-16 type) and of composites containing Co (5% wt.) and FeCo (5% wt.) nanophases dispersed in the SBA-16 type matrix were prepared following a templated-gelation method. Optically clear disk-shaped monoliths with diameter around 10 cm were obtained whose absorption spectra are tunable based on the composition. Low-angle X-ray diffraction, N-2 physisorption and transmission electron microscopy show that the ordered mesoporous structure and high surface area are preserved after calcination at 500 degrees C and after reduction at 800 degrees C, indicating a very high thermal stability. X-ray absorption spectroscopy at the Fe and Co K-edges allowed us to identify the intermediate products before and after reduction. In particular, the formation of a nanophase of layered cobalt silicate hydroxide was determined in the Co containing sample calcined at 500 degrees C. This compound is easily reducible giving rise to a superparamagnetic nanocomposite containing pure fcc Co nanoparticles dispersed within the 3D mesoporous silica structure. Extensive characterization points out that the proposed procedure is promising in the preparation of functional nanocomposites with adjustable magnetic and optical properties.
    No preview · Article · Aug 2014 · Microporous and Mesoporous Materials
  • Source
    [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.
    Full-text · Article · Jul 2014 · New Journal of Chemistry
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · May 2014 · The Journal of Physical Chemistry C
  • Source
    S Bullita · A Casu · M F Casula · G Concas · F Congiu · A Corrias · A Falqui · D Loche · C Marras
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Jan 2014 · Physical Chemistry Chemical Physics
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jan 2014 · Nanoscale
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Nov 2013 · ACS Applied Materials & Interfaces