Publications

Short powder-in-tube tapes of MgB2 in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB2 core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB2 crystallite size, a weak contact between Fe and MgB2 core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB2 cores, the detected impurity phase is MgO, while at the interface with Fe, MgB4 also occurs. Impurity phases found at interface, MgO and MgB4, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB2 powder has an important contribution to observed differences, and its removal or control is recommended.

Contamination of water with heavy metals such as lead is a major worldwide problem because they affect the physiological functions of living organisms, cause cancer, and damage the immune system. Hydroxyapatite, (Ca-5(PO4)(3)OH) is considered one of the most effective materials for removing heavy metals from contaminated water. The hydroxyapatite nanopowders (N-HAp) obtained by a co-precipitation method were used in this research to determine the effectiveness in removing lead ions from contaminated solutions. In this study, we have investigated the structure and morphology of N-HAp nanopowders using X-ray diffraction (XRD), electronic transmission microscopy (TEM), and scanning electron microscopy (SEM). The structure information was also obtained by spectroscopy measurements. The Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy measurements revealed the presence of peaks corresponding to the phosphate and hydroxyl groups. The ability of N-HAp nanopowders to adsorb lead ions from aqueous solutions were established. The results of the kinetic and equilibrium studies on the removal of Pb (II) from aqueous solution revealed that the adsorption of lead (II) cations is due to the surface reaction with the hydroxyl terminal groups on the adsorbent and the combination of the positive charges of the metal cations with the negative charges on the adsorbent surfaces. These observations could validate the use of these ceramic nanopowders in ecological remediation strategies.

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

Ru@MNP-MWCNT catalysts were obtained via functionalization of nanostructured carbon-based carriers (ie, MWCNT) with base molecules (ie, 2-aminophenol and ethylenediamine) followed by the complexation with RuCl3. These structures demonstrated a highly efficient behavior for the selective wet oxidation of levulinic acid and glucose to succinic acid. However, to ensure an easy recovery and high recyclability the MWCNTs nanotubes were modified by incorporation of super-paramagnetic Fe3O4 nanoparticles into porous structure. Besides the catalytic performances the resulted composites showed a good mechanical resistance.

Using cyclic voltammetry, Raman scattering and infrared (IR) spectroscopy, new findings concerning the electrochemical synthesis of composites based on multi-wall carbon nanotubes (MWNTs) and polypyrrole (PPY) doped with H3PMo12O40 heteropolyanions are described in this report. To better understand the electrochemical mechanism behind the synthesis of these composites, the influence of the concentrations of pyrrole and the electrolytes of H3PMo12O40 and H2SO4 on the cyclic voltammogram profile is studied. The formation of PPY doped with H3PMo12O40 heteropolyanions onto the MWNT surface is demonstrated by complementary studies of Raman scattering and IR spectroscopy.

Zinc- (Zn) doped hydroxyapatite (HAp) were prepared by sol-gel method. Zinc-doped hydroxyapatite (ZnHAp) and HAp were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Rietveld analysis revealed that the HAp and 7ZnHAp powders obtained by sol-gel method have a monophasic hydroxyapatite structure belonging to the P6(3/m) spatial group. The results obtained from the ultrasound characterization of HAp and ZnHAp are also presented in this study. The effect of zinc concentration on properties that were deduced from ultrasonic measurements are studied in the case of a significant zinc concentration (x(Zn) = 0.07). From the values of the ultrasonic waves velocities were determined by the pairs of elastic coefficients of the suspensions (Young modulus E, Poisson coefficient nu), which have proven to be similar to those determined by other authors.

Porous reduced graphene oxide (rGO)/iron oxide nanohybrid thin films were grown through a laser-based technique onto flexible polymer, polydimethylsiloxane substrates. A frequency quadrupled pulsed Nd:YAG laser source (lambda = 266 nm, tau(FWHM) similar to 4 ns, upsilon = 10 Hz) was used for irradiation of dispersions containing the starting nano-materials, graphene oxide (GO) platelets and iron oxide nanoparticles (NPs), to be transferred to the substrates surface. The electrochemical response of the composite layers was investigated by cyclic voltammetry in dark and under UV/visible light illumination, as well as by electrochemical impedance spectroscopy. A comparative study was performed as a function of the nature of the GO base materials, monolayer or multilayer GO platelets, and relative concentration of GO/iron oxide NPs in the dispersions submitted to laser irradiation. The capacitance values of the nanohybrid materials which contain monolayer GO were found to be one order of magnitude higher as compared to their counterparts consisting of multilayer GO and iron oxide NPs. UV-visible light irradiation contributed to the significant enhancement of the electrochemical properties of the electrodes. These results indicate that the nanohybrid thin films are promising candidates as flexible electrodes in micro-supercapacitors and photoelectrochemical devices for simultaneous energy storage and solar energy conversion.

We report significant photoelectrochemical activity of Y-doped BiFeO3 (Y-BFO) epitaxial thin films deposited on Nb: SrTiO3 substrates. The Y-BFO photoanodes exhibit a strong dependence of the photocurrent values on the thickness of the films, and implicitly on the induced epitaxial strain. The peculiar crystalline structure of the Y-BFO thin films and the structural changes after the PEC experiments have been revealed by high resolution X-ray diffraction and transmission electron microscopy investigations. The crystalline coherence breaking due to the small ionic radius Y-addition was analyzed using Willliamson-Hall approach on the 2 theta-omega scans of the symmetric (00l) reflections and confirmed by high resolution TEM (HR-TEM) analysis. In the thinnest sample the lateral coherence length (L-parallel to) is preserved on larger nanoregions/ nanodomains. For higher thickness values L-parallel to is decreasing while domains tilt angles (alpha(tilt)) is increasing. The photocurrent value obtained for the thinnest sample was as high as J(ph) = 0.72 mA/cm(2), at 1.4 V(vs. RHE). The potentiostatic scans of the Y-BFO photoanodes show the stability of photoresponse, irrespective of the film's thickness. There is no clear cathodic photocurrent observation for the Y-BFO thin films confirming the n-type semiconductor behavior of the Y-BFO photoelectrodes.

We report on the successful laser transfer of biocompatible composite coatings based on polyaniline (PANI) embedded with magnetite (PANI-Fe3O4) and Lincomycin hydrochloride (PANI-Lincomycin) or Lincomycin-functionalized magnetite (PANI-Fe3O4@Lincomycin) by matrix assisted pulsed laser evaporation (MAPLE) technique. The physico-chemical investigations revealed relevant data regarding the stoichiometric deposition, morphology and topography of the as-deposited coatings. Regarding the MAPLE coatings, the FTIR studies evidenced the vibrational bands characteristic to pristine PANI material, while the SEM investigations unveiled a preferential particulate morphology (with aggregates shape and size depending on the deposited material). Additionally, the AFM measurements indicated variations of RMS value, following the Lincomycin and magnetite incorporation. The wettability measurements displayed a hydrophilic behavior of the synthesized coatings, while the electrochemical studies emphasized an enhanced resistance against corrosion in simulated body fluid when compared with bare Ti. Cellular viability, immunofluorescence and SEM results proved that the MAPLE coatings were suitable materials for beneficial adhesion, spreading and proliferation of osteoblast-like cells (MG-63). Moreover, an increased efficiency was evidenced against Staphylococcus aureus biofilm development. The multifunctional properties of the laser processed composite coatings - confirmed by cumulative biocompatible, antimicrobial and anticorrosive behaviors - recommend them as promising solutions for biomedical applications.

To avoid the deleterious effects of dopant segregation, synthesis methods that facilitate a homogenous dopant distribution in the ceria lattice were employed. Though doping ceria by wet impregnation was also credited to induce a homogeneous solid solution even in the heavy regime (concentration >= 20%, A. Corma, P. Atienzar, H. Garcia and J. Chane-Ching, Nat. Mater., 2004, 3, 394-397), no follow up investigation has been reported. Herein, we investigated ceria nanoparticles (1% Tm-CeO2 and 1% Eu-CeO2) wetimpregnated with trivalent rare-earth (Yb, 20%), bivalent (Ca, 20%) and isovalent (Zr, 30%) metals, followed by annealing in air. Homogeneity of the solid solutions of Yb-impregnated ceria was confirmed by a two-feature characterization toolbox that included X-ray diffraction, Raman spectroscopy, transmission electron microscopy, as well as up-conversion emission as a probe tool. Since the up-conversion emission of Tm was not detectable in the absence of Yb while its efficiency depends on the average distance between Yb and Tm ions, the Yb incorporation and its migration from the surface to the lattice bulk sites in wet-impregnated ceria can be "visualized" and compared with that of the Yb bulk-doped counterpart. The use of Eu luminescence as a local probe confirmed the homogeneity of solid solutions of Ca and Zr-impregnated ceria and also sustained the opposite roles of Ca and Zr as the repeller and the scavenger of oxygen vacancies, respectively. All these results suggested that heavy doping of ceria by wet impregnation with metals with +2, +3 and +4 valencies represent a facile alternative to conventional doping approaches. Therefore, the effects of the amount and the type of metal dopant on the structural properties of CeO2 could be investigated in a more systematic and probably a more reproducible manner, which would significantly increase the potential of ceria in catalysis and other applications.