National Institute Of Materials Physics - Romania

Novel composite materials are being investigated for improving the energy storage performance of electrochemical capacitors. For this goal, synergistic effects via the combination of diverse types of materials are crucial. In this work, electrodes composed of reduced graphene oxide, multiwall carbon nanotubes, as well as cerium and manganese oxides were fabricated through reactive inverse matrix-assisted pulsed laser evaporation (RIMAPLE). UV-pulsed laser irradiation of frozen aqueous dispersions containing graphene oxide sheets, carbon nanotubes, and ceria nanoentities, besides manganese acetate precursor, led to the simultaneous chemical transformation and co-deposition of hybrid electrodes onto flexible metallic substrates via photothermal and photochemical processes. Thorough morphological and compositional studies of the electrodes demonstrated the laser-induced reduction of graphene oxide, besides the crystallization of a mixture of cerium and manganese oxide nanostructures decorating the carbon nanoentities during the deposition process. Electrochemical analyses revealed a remarkable improvement of performance with the combination of electrochemical double layer in the porous nanocarbon framework with pseudocapacitance from the oxide nanostructures, obtaining excellent volumetric capacitances of up to 140 F cm(-3) at 10 mV s(-1) with the combination of all four materials. The attained results are the best ones yet published regarding RIMAPLE of hybrid nanocarbon-based electrodes with micrometric thickness. Finally, symmetric electrochemical capacitors were fabricated using aqueous electrolyte, revealing excellent stability upon tens of thousands of charge-discharge cycles.

The 17th-19th century wooden and stone churches are an iconic symbol for the Romanian national heritage, raising urgent needs for the development of efficient and ecofriendly restoration and preservation solutions. Nanotechnology has a great but largely unexplored potential in this field, providing new tools and methods to achieve higher consolidation and protection efficiency, mainly due to the ability of nanoparticles to inhibit the growth and metabolic activity of different biodeteriorating agents, including fungi. The purpose of the present study was to report for the first time on the efficiency of MgB2 materials, mainly prized for their practical superconducting properties, against a large collection of filamentous fungal strains recently isolated from biodeteriorated wooden and stone heritage objects. Four types of MgB2 powders, with a crystallite size of 42-113 nm, were tested by qualitative (on 149 strains) and quantitative (on 87 strains) assays. The cytotoxicity was evaluated by the microscopic analysis of SiHa cells morphology and Hep2 cell cycle analysis and the ecotoxicity by the Allium test. The tested filamentous fungal strains belonged to 11 different genera, and those isolated from mural paintings and wooden objects exhibited the best capacity to colonize the inert substratum. All MgB2 powders exhibited similar and relatively low minimal inhibitory concentrations (MIC) values against the Aspergillus and Penicillium isolates, which were predominated among isolates. From the tested powders, PVZ and CERAC proved to be more efficient against the strains isolated from stone and wood materials, while LTS was active against the fungal strains colonizing the mural paintings and museum objects. The cytotoxicity results indicated that the tested powders are toxic for the human cells at concentrations higher than 50 mu g/ml, but, however, the very short lifetime of these NPs prevents their accumulation in the natural environment and, thus, the occurrence of toxic effects. The tested powders proved to be ecofriendly at the active antifungal concentrations, as suggested by the phytotoxicity test results. Taken together, our results suggest the potential of the MgB2 materials for the development of environmentally safe antifungal substances, which can be used in the control of the material cultural heritage biodeterioration process.

Doping SnO2 with trivalent lanthanide (Ln) metals aiming at optical applications faces several challenges. The elastic and electrostatic misfit between bulkier Ln activators and Sn host cation induces strain in the lattice as well as defects as a result of charge-compensation. These effects can be partially healed by thermal annealing. However, dopant segregation which occurs above a certain temperature drives quenching of Ln emission. In this work, we explore Li co-doping as a vehicle to improve the luminescence of lanthanide (Eu, Sm, Er, Dy and, Tb) doped SnO2 nanoparticles. In case of substitutional Ln dopants (Eu, Sm and Er), Li enhances significantly the Ln luminescence up to 40-46 times. The luminescence enhancement induced by Li co-doping is explained by an interplay of removal of nearby oxygen vacancies (Eu, Sm), improved Ln doping homogeneity (Er) and, improved crystallinity (Eu, Sm, Er). The improved crystallinity caused by Li co-doping accounts for less than 30% of the total enhancement. In the case of surface Ln dopants (Dy and Tb), Li co-doping does not alter the Ln emission, either in shape or intensity. Only a few Dy dopants succeed to substitute for Sn in the rutile lattice as shown by single-photon counting investigations. Collectively, our results show that the extent of luminescence enhancement induced by Li co-doping depend strongly on the Ln type. In SnO2, the common mechanisms that explain the Li induced enhancement of Ln luminescence in various hosts, either contribute partially (improved crystallization) or do not contribute at all (local structure distortion).

Addition of titanium dioxide nanoparticles (TiO2 NPs) in photocatalytic paints represents a promising alternative aiming to mineralize gaseous pollutants, such as volatile organic compounds (VOCs). However, the risks of release of nanoparticles to human health and the environmental impact have to be taken carefully into account for their development. To take into account these risks, we develop a new method of TiO2 NP synthesis. Here, we report the electrostatic stabilization in aqueous medium with pyrophosphate buffers of different pH ranges followed by coating with bio-inspired molecules (lysine, deferoxamine, dopamine) and polymers (polyacrylic acid, polyethylene glycol, polydopamine) of 4-5 nm spherical photocatalytic TiO2 NPs for the development of safer-by-design photocatalytic paint. Characterization of the so-formed TiO2 nanocomposites by dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the good grafting of the ligands on the TiO2 surface and an enhanced stability in water compared to the pristine TiO2 NPs. The photocatalytic activity of the TiO2 nanocomposites was investigated by following the degradation of methylene blue (MB) under irradiation. The results showed a modulation of the photocatalytic activity (decrease or increase of the MB degradation rate) as a function of the nature/binding strength of the bio-inspired coating on the oxide surface. Finally, the most promising nanocomposites were incorporated in paints on which preliminary chalking assays were performed after storage for one year in the dark or in interior daylight.

Gleditsia triacanthos is an aggressive invasive species in Eastern Europe, producing a significant number of pods that could represent an inexhaustible resource of raw material for various applications. The aim of this study was to extract cellulose from the Gleditsia triacanthos pods, characterize it by spectrophotometric and UHPLC-DAD-ESI/MS analysis, and use it to fabricate a wound dressing that is multi-functionalized with phenolic compounds extracted from the leaves of the same species. The obtained cellulose microfibers (CM) were functionalized, lyophilized, and characterized by ATR-FTIR and SEM. The water absorption and retention capacity as well as the controlled release of phenolic compounds with antioxidant properties evaluated in temporal dynamics were also determined. The antimicrobial activity against reference and clinical multi-drug-resistant Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae, Candida albicans, and Candida parapsilosis strains occurred immediately after the contact with the tested materials and was maintained for 24 h for all tested microbial strains. In conclusion, the multi-functionalized cellulose microfibers (MFCM) obtained from the reproductive organs of an invasive species can represent a promising alternative for the development of functional wound dressings with antioxidant and antimicrobial activity, as well as being a scalable example for designing cost-effective, circular bio-economy approaches to combat the accelerated spread of invasive species.

Multifunctional Bi- and Fe-modified carbon xerogel composites (CXBiFe), with different Fe concentrations, were obtained by a resorcinol-formaldehyde sol-gel method, followed by drying in ambient conditions and pyrolysis treatment. The morphological and structural characterization performed by X-ray diffraction (XRD), Raman spectroscopy, N-2 adsorption/desorption porosimetry, scanning electron microscopy (SEM) and scanning/transmission electron microscopy (STEM) analyses, indicates the formation of carbon-based nanocomposites with integrated Bi and Fe oxide nanoparticles. At higher Fe concentrations, Bi-Fe-O interactions lead to the formation of hybrid nanostructures and off-stoichiometric Bi2Fe4O9 mullite-like structures together with an excess of iron oxide nanoparticles. To examine the effect of the Fe content on the electrochemical performance of the CXBiFe composites, the obtained powders were initially dispersed in a chitosan solution and applied on the surface of glassy carbon electrodes. Then, the multifunctional character of the CXBiFe systems is assessed by involving the obtained modified electrodes for the detection of different analytes, such as biomarkers (hydrogen peroxide) and heavy metal ions (i.e., Pb2+). The achieved results indicate a drop in the detection limit for H2O2 as Fe content increases. Even though the current results suggest that the surface modifications of the Bi phase with Fe and O impurities lower Pb2+ detection efficiencies, Pb2+ sensing well below the admitted concentrations for drinkable water is also noticed.

Terahertz time-domain spectroscopy (THz-TDS) was employed for estimation of intrinsic dielectric loss of Zr0.8Sn0.2TiO4 (ZST) ceramics. Single-phase ZST dielectric resonators (DRs) with various synthesis parameters and, consequently, different extrinsic losses, were prepared by conventional ceramic technology. Even though the DRs exhibit a similar microstructure, their quality factor (Q is the inverse of dielectric loss tangent) measured in microwave (MW) domain at 6 GHz varies between 2500 and 8400. On the other hand, it was found that the THz dielectric loss is less sensitive to the sample preparation. The intrinsic losses (Q x f similar to 60 THz) of the ZST ceramics have been derived from THz data.

In this work, the effect of the single-walled carbon nanotubes (SWNTs) as the mixtures of metallic and semiconducting tubes (M + S-SWNTs) as well as highly separated semiconducting (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of poly(3-hexyl thiophene) (P3HT) was reported. Two methods were used to prepare such composites, that is, the chemical interaction of the two constituents and the electrochemical polymerization of the 3-hexyl thiophene onto the rough Au supports modified with carbon nanotubes (CNTs). The measurements of the anisotropic PL of these composites have highlighted a significant diminution of the angle of the binding of the P3HT films electrochemical synthetized onto Au electrodes covered with M + S-SWNTs. This change was attributed to metallic tubes, as was demonstrated using the anisotropic PL measurements carried out on the P3HT/M-SWNTs and P3HT/S-SWNTs composites. Small variations in the angle of the binding were reported in the case of the composites prepared by chemical interaction of the two constituents. The proposed mechanism to explain this behavior took into account the functionalization process of CNTs with P3HT. The experimental arguments of the functionalization process of CNTs with P3HT were shown by the UV-VIS-NIR and FTIR spectroscopy as well as surface-enhanced Raman scattering (SERS). A PL quenching process of P3HT induced both in the presence of S-SWNTs and M-SWNTs was reported, too. This process origins in the various de-excitation pathways which can be developed considering the energy levels diagram of the two constituents of each studied composite.

A novel series of Cu(II) complexes with formula M(HLn)(ClO4)(2)center dot mH(2)O [HLn: 13-membered pentaazamacrocyclic ligand resulted from condensation ofN,N '-bis(2-aminoethyl)ethane-1,2-diamine,l-tyrosine (HL1)/l-tryptophan (HL2)/l-phenylalanine (HL3) and formaldehyde] were synthesized by one-pot method. Techniques such as ESI-MS, IR, UV-Vis and EPR spectroscopy provided data characterizing the complexes as mononuclear species. The course of thermal decomposition was followed using TG/DSC-MS analysis in air atmosphere. The TG curves showed a gradual decomposition in several stages that comprise dehydration, decomposition of perchlorate ions as well as fragmentation and oxidative degradation of the organic part. The intermediates formed after first stage of water elimination are stable on 40, 15 and 80 degrees C interval for complexes (1), (2) and (3), respectively. The compounds were tested on the eukaryotic unicellular organismSaccharomyces cerevisiae, showing variable actions in terms of toxicity, cellular uptake and capacity to alleviate growth defects associated with Cu, Zn-superoxide dismutase (SOD1) depletion.

The present work reports the production and key properties of the CuCrFeTiV high entropy alloy synthetized mechanical alloying and spark plasma sintering. The milled powders and the as-sintered samples were analysed through scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy and particle induced X-ray emission. Magnetic properties together with electrical resistivity, thermal conductivity, specific heat differential thermal analysis were also evaluated on the consolidated samples. The powders reveal an increasing content in iron as the millings are prolonged up to 20 h. The elemental composition of the sintered alloy, determined through particle induced X-ray emission, confirms the final composition after mechanical alloying with an increase of iron and a decrease in the remaining elements. Furthermore, although the alloy presents electrical resistivity typical of a high entropy alloy, a ferromagnetic behaviour was found, consistently with major Fe content as detected in prior observations. Finally, thermal measurements show that this CuCrFeTiV entropy alloy possesses thermal properties suitable for its potential use as thermal barriers.