National Institute Of Materials Physics - Romania

Hydrogen production from methanol decomposition to syngas (H2 + CO) is a promising alternative route for clean energy transition. One major challenge is related to the quest for stable, cost-effective, and selective catalysts operating below 400 degrees C. We illustrate an investigation of the surface reactivity of a Ni3Sn4 catalyst working at 250 degrees C, by combining density functional theory, operando X-ray absorption spectroscopy, and high-resolution transmission electron microscopy. We discovered that the catalytic reaction is driven by surface tin-oxide phases, which protects the underlying Ni atoms from irreversible chemical modifications, increasing the catalyst durability. Moreover, we found that Sn content plays a key role in enhancing the H2 selectivity, with respect to secondary products such as CO2. These findings open new perspectives for the engineering of scalable and low-cost catalysts for hydrogen production.

Green nanotechnology is a rapidly growing field linked to using the principles of green chemistry to design novel nanomaterials with great potential in environmental and health protection. In this work, metal and semiconducting particles (AuNPs, AgClNPs, ZnO, AuZnO, AgClZnO, and AuAgClZnO) were phytosynthesized through a "green" bottom-up approach, using burdock (Arctium lappa L.) aqueous extract. The morphological (SEM/TEM), structural (XRD, SAED), compositional (EDS), optical (UV-Vis absorption and FTIR spectroscopy), photocatalytic, and bio-properties of the prepared composites were analyzed. The particle size was determined by SEM/TEM and by DLS measurements. The phytoparticles presented high and moderate physical stability, evaluated by zeta potential measurements. The investigation of photocatalytic activity of these composites, using Rhodamine B solutions' degradation under solar light irradiation in the presence of prepared powders, showed different degradation efficiencies. Bioevaluation of the obtained composites revealed the antioxidant and antibacterial properties. The tricomponent system AuAgClZnO showed the best antioxidant activity for capturing ROS and ABTS center dot(+) radicals, and the best biocidal action against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The "green" developed composites can be considered potential adjuvants in biomedical (antioxidant or biocidal agents) or environmental (as antimicrobial agents and catalysts for degradation of water pollutants) applications.

In this study, we report on the synthesis of L-Cysteine (L-Cys)-coated magnetic iron oxide nanoparticles (NPs) loaded with doxorubicin (Dox). The Fe3O4-L-Cys-Dox NPs were extensively characterized for their compositional and morpho-structural features using EDS, SAED, XRD, FTIR and TEM. XPS, Mossbauer spectroscopy and SQUID measurements were also performed to determine the electronic and magnetic properties of the Fe3O4-L-Cys-Dox nanoparticles. Moreover, by means of a FO-SPR sensor, we evidenced and confirmed the binding of Dox to L-Cys. Biological tests on mouse (B16F10) and human (A375) metastatic melanoma cells evidenced the internalization of magnetic nanoparticles delivering Dox. Half maximum inhibitory concentration IC50 values of Fe3O4-L-Cys-Dox were determined for both cell lines: 4.26 mu g/mL for A375 and 2.74 mu g/mL for B16F10, as compared to 60.74 and 98.75 mu g/mL, respectively, for unloaded controls. Incubation of cells with Fe3O4-L-Cys-Dox modulated MAPK signaling pathway activity 3 h post-treatment and produced cell cycle arrest and increased apoptosis by 48 h. We show that within the first 2 h of incubation in physiological (pH = 7.4) media, similar to 10-15 mu M Dox/h was released from a 200 mu g/mL Fe3O4-L-Cys-Dox solution, as compared to double upon incubation in citrate solution (pH = 3), which resembles acidic environment conditions. Our results highlight the potential of Fe3O4-L-Cys-Dox NPs as efficient drug delivery vehicles in melanoma therapy.

In this study, we report the performance improvement of wound dressings by covering them with magnetite-based nanostructured coatings. The magnetite nanoparticles (Fe3O4 NPs) were functionalized with Nigella sativa (N. sativa) powder/essential oil and dicloxacillin and were synthesized as coatings by matrix assisted pulsed laser evaporation (MAPLE). The expected effects of this combination of materials are: (i) to reduce microbial contamination, and (ii) to promote rapid wound healing. The crystalline nature of core/shell Fe3O4 NPs and coatings was determined by X-ray diffraction (XRD). Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) have been coupled to investigate the stability and thermal degradation of core/shell nanoparticle components. The coatings' morphology was examined by scanning electron microscopy (SEM). The distribution of chemical elements and functional groups in the resulting coatings was evidenced by Fourier transform infrared (FTIR) spectrometry. In order to simulate the interaction between wound dressings and epithelial tissues and to evaluate the drug release in time, the samples were immersed in simulated body fluid (SBF) and investigated after different durations of time. The antimicrobial effect was evaluated in planktonic (free-floating) and attached (biofilms) bacteria models. The biocompatibility and regenerative properties of the nanostructured coatings were evaluated in vitro, at cellular, biochemical, and the molecular level. The obtained results show that magnetite-based nanostructured coatings functionalized with N. sativa and dicloxacillin are biocompatible and show an enhanced antimicrobial effect against Gram positive and Gram negative opportunistic bacteria.

The p-n junctions are the building blocks of nowadays electronic devices. The n- or p-type conductivity is obtained in classic semiconductors, like Si, by doping with atoms acting as donors or acceptors, respectively. Doping was used in ferroelectrics to influence the transition temperature, magnitude of some physical properties, but not necessarily conduction type. Therefore, comprehensive studies to obtain true ferroelectric p-n junctions by controlled doping are missing. Recently, it has been shown that Pb(Zr0.2Ti0.8)O-3 films doped with & AP;1% atomic Nb (n-type doping) or Fe (p-type doping) have different orientations of polarization in the as-grown state. Knowing that polarization orientation depends on doping type, the next step is to build ferroelectric p-n homojunctions and to study their properties in relation to ferroelectric polarization. p-n and n-p structures were grown for this purpose by successive deposition of Nb-doped and Fe-doped Pb(Zr,Ti)O-3 layers with different thicknesses. We find that these p-n homojunctions are ferroelectric, but the magnitude of the polarization and coercive field, as well as the dominant polarization orientation in the as-grown state, depend on the conduction type of the first grown layer. The I-V characteristics are quasi-linear, although the interfaces with the electrodes behaves as Schottky contacts. The resistance extracted from the I-V characteristics displays an exponential dependence on temperature, with an activation energy in the range of 0.14-0.17 eV. These results are explained assuming that the total current in the junction is the total of electron and hole injections at the electrode interfaces. It is shown that for relatively low doping concentrations, the current density contains a dominant term with a linear voltage dependence and an exponential temperature dependence, as observed experimentally, and a secondary (correction) term that is dependent on the free carrier density and can induce non-linear voltage dependence when this density is significant.

Glassy nanocomposites containing Yb3+/Er3+-doped GdF3 and LiGdF4 nanocrystals have been prepared by controlled crystallization of the xerogel and the structural, up-conversion luminescence, and magnetic properties were analyzed and discussed. Structural and morphological analysis showed uniform distribution of both GdF3 and LiGdF4 nanocrystals (tens of nm size), embedded in silica glass matrix as the result of thermal decomposition of the trifluoracetates, revealed as a strong exothermic peak at about 300 degrees C; the Li-ions co-doping showed a strong influence on the GdF3 and LiGdF4 nanocrystalline fraction. The energy dispersive spectrometry mapping showed Gd, F and Yb, Er within the nanocrystals but not in the silica glass matrix. X-ray diffraction pattern analysis indicated the crystalline lattice distortion consistent with the Yb/Er incorporation in both fluoride nanocrystals. The "green" ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and "red" (F-4(9/2)-> I-4(15/2)) up-conversion luminescences at 525, 545, and 660 nm observed under 980 nm laser light pumping were assigned to the Er3+ ions deexcitation through a two-photon process. The magnetic properties of the nanocomposite are strongly temperature dependent. The magnetization hysteresis loops show a ferromagnetic behavior at low temperatures (5K) related to the rare-earth ions contribution and the saturation magnetization of 39 emu/g. At 300 K a paramagnetic behavior was observed that was ascribed to the non-interacting localized nature of the magnetic moment of the rare-earth ions. Hence, such novel, multifunctional magnetic and optical materials can allow the intertwining between magnetism and photonics and might offer new opportunities for new magneto-optical device development.

The p-n junctions are the building blocks of nowadays electronic devices. The n- or p-type conductivity is obtained in classic semiconductors, like Si, by doping with atoms acting as donors or acceptors, respectively. Doping was used in ferroelectrics to influence the transition temperature, magnitude of some physical properties, but not necessarily conduction type. Therefore, comprehensive studies to obtain true ferroelectric p-n junctions by controlled doping are missing. Recently, it has been shown that Pb(Zr0.2Ti0.8)O-3 films doped with & AP;1% atomic Nb (n-type doping) or Fe (p-type doping) have different orientations of polarization in the as-grown state. Knowing that polarization orientation depends on doping type, the next step is to build ferroelectric p-n homojunctions and to study their properties in relation to ferroelectric polarization. p-n and n-p structures were grown for this purpose by successive deposition of Nb-doped and Fe-doped Pb(Zr,Ti)O-3 layers with different thicknesses. We find that these p-n homojunctions are ferroelectric, but the magnitude of the polarization and coercive field, as well as the dominant polarization orientation in the as-grown state, depend on the conduction type of the first grown layer. The I-V characteristics are quasi-linear, although the interfaces with the electrodes behaves as Schottky contacts. The resistance extracted from the I-V characteristics displays an exponential dependence on temperature, with an activation energy in the range of 0.14-0.17 eV. These results are explained assuming that the total current in the junction is the total of electron and hole injections at the electrode interfaces. It is shown that for relatively low doping concentrations, the current density contains a dominant term with a linear voltage dependence and an exponential temperature dependence, as observed experimentally, and a secondary (correction) term that is dependent on the free carrier density and can induce non-linear voltage dependence when this density is significant.

In this study, we report the performance improvement of wound dressings by covering them with magnetite-based nanostructured coatings. The magnetite nanoparticles (Fe3O4 NPs) were functionalized with Nigella sativa (N. sativa) powder/essential oil and dicloxacillin and were synthesized as coatings by matrix assisted pulsed laser evaporation (MAPLE). The expected effects of this combination of materials are: (i) to reduce microbial contamination, and (ii) to promote rapid wound healing. The crystalline nature of core/shell Fe3O4 NPs and coatings was determined by X-ray diffraction (XRD). Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) have been coupled to investigate the stability and thermal degradation of core/shell nanoparticle components. The coatings' morphology was examined by scanning electron microscopy (SEM). The distribution of chemical elements and functional groups in the resulting coatings was evidenced by Fourier transform infrared (FTIR) spectrometry. In order to simulate the interaction between wound dressings and epithelial tissues and to evaluate the drug release in time, the samples were immersed in simulated body fluid (SBF) and investigated after different durations of time. The antimicrobial effect was evaluated in planktonic (free-floating) and attached (biofilms) bacteria models. The biocompatibility and regenerative properties of the nanostructured coatings were evaluated in vitro, at cellular, biochemical, and the molecular level. The obtained results show that magnetite-based nanostructured coatings functionalized with N. sativa and dicloxacillin are biocompatible and show an enhanced antimicrobial effect against Gram positive and Gram negative opportunistic bacteria.

Glassy nanocomposites containing Yb3+/Er3+-doped GdF3 and LiGdF4 nanocrystals have been prepared by controlled crystallization of the xerogel and the structural, up-conversion luminescence, and magnetic properties were analyzed and discussed. Structural and morphological analysis showed uniform distribution of both GdF3 and LiGdF4 nanocrystals (tens of nm size), embedded in silica glass matrix as the result of thermal decomposition of the trifluoracetates, revealed as a strong exothermic peak at about 300 degrees C; the Li-ions co-doping showed a strong influence on the GdF3 and LiGdF4 nanocrystalline fraction. The energy dispersive spectrometry mapping showed Gd, F and Yb, Er within the nanocrystals but not in the silica glass matrix. X-ray diffraction pattern analysis indicated the crystalline lattice distortion consistent with the Yb/Er incorporation in both fluoride nanocrystals. The "green" ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and "red" (F-4(9/2)-> I-4(15/2)) up-conversion luminescences at 525, 545, and 660 nm observed under 980 nm laser light pumping were assigned to the Er3+ ions deexcitation through a two-photon process. The magnetic properties of the nanocomposite are strongly temperature dependent. The magnetization hysteresis loops show a ferromagnetic behavior at low temperatures (5K) related to the rare-earth ions contribution and the saturation magnetization of 39 emu/g. At 300 K a paramagnetic behavior was observed that was ascribed to the non-interacting localized nature of the magnetic moment of the rare-earth ions. Hence, such novel, multifunctional magnetic and optical materials can allow the intertwining between magnetism and photonics and might offer new opportunities for new magneto-optical device development.

Featuring a high hydrogen storage content of up to 20 wt%, complex metal borohydrides remain promising solid state hydrogen storage materials, with the real prospect of reversible behavior for a zero-emission economy. However, the thermodynamic barriers and sluggish kinetics are still barriers to overcome. In this context, nanoconfinement has provided a reliable method to improve the behavior of hydrogen storage materials. The present work describes the thermodynamic and kinetic enhancements of LiBH4 nanoconfined in MFe2O4 (M=Co, Ni) ferrite-catalyzed graphene host. Composites of LiBH4-catalysts were prepared by melt infiltration and investigated by X-ray diffraction, TEM, STEM-EDS and TPD. The role of ferrite additives, metal precursor treatment (Ar, Ar/H-2) and the effect on hydrogen storage parameters are discussed. The thermodynamic parameters for the most promising composite LiBH4-graphene-NiFe2O4 (Ar) were investigated by Kissinger plot method, revealing an E-A = 127 kJ/mol, significantly lower than that of neat LiBH4 (170 kJ/mol). The reversible H-2 content of LiBH4-graphene-NiFe2O4 (Ar) after 5 a/d cycles was similar to 6.14 wt%, in line with DOE's target of 5.5 wt% storage capacity, while exhibiting the lowest desorption temperature peak of 349 degrees C. The composites with catalysts treated in Ar have lower desorption temperature due to better catalyst dispersion than using H-2/Ar.