National Institute Of Materials Physics - Romania

This contribution concerns the effect of the chemical composition of the brucite-type layer of bi-cationic LDH materials ZnxAl and MgxAl (x = 2-5) and tri-cationic LDH MgyZnzAl (y + z = 4, y = 1, 2, 3) on their catalytic activity for olefin epoxidation with H2O2 in the presence of acetonitrile. LDH materials were prepared by the standard method of co-precipitation at constant pH 10, using an aqueous solution of the corresponding metal nitrates and a basic solution containing NaOH and Na2CO3. The fresh LDHs were calcined to yield the corresponding mixed oxides and then the recovery of the LDH structure by hydration of the mixed oxides was performed. The resulting samples were characterized by AAS, XRD, DRIFT, DR-UV-Vis, BET and determination of basic sites. The results of the catalytic tests for olefin epoxidation were well correlated with the basicity of the samples, which was in turn related to the M2+/Al3+ ratio and the electronegativity of different bivalent metals in the brucite-type layer.

This work reports on the influence of 5 MeV electron beam radiations on the morphological features and chemical structure of magnesium-doped hydroxyapatite/chitosan composite coatings generated by the magnetron sputtering technique. The exposure to ionizing radiation in a linear electron accelerator dedicated to medical use has been performed in a controllable manner by delivering up to 50 Gy radiation dose in fractions of 2 Gy radiation dose per 40 s. After the irradiation with electron beams, the surface of layers became nano-size structured. The partial detachment of irradiated layers from the substrates has been revealed only after visualizing their cross sections by scanning electron microscopy. The energy dispersive X-ray spectral analysis of layer cross-sections indicated that the distribution of chemical elements in the samples depends on the radiation dose. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction analysis have shown that the physicochemical processes induced by the ionizing radiation in the magnesium doped hydroxyapatite/chitosan composite coatings do not alter the apatite structure, and Mg remains bonded with the phosphate groups.

Palladium nanoparticles entrapped in porous aromatic frameworks (PAFs) or covalent organic frameworks may promote heterogeneous catalytic reactions. However, preparing such materials as active nanocatalysts usually requires additional steps for palladium entrapment and reduction. This paper reports as a new approach, a simple procedure leading to the self-entrapment of Pd nanoparticles within the PAF structure. Thus, the selected Sonogashira synthesis affords PAF-entrapped Pd nanoparticles that can catalyze the C-C Suzuki-Miyaura cross-coupling reactions. Following this new concept, PAFs were synthesized via Sonogashira cross-coupling of the tetraiodurated derivative of tetraphenyladamantane or spiro-9,9 '-bifluorene with 1,6-diethynylpyrene, then characterized them using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning transmission electron microscopy, and textural properties (i.e., adsorption-desorption isotherms). The PAF-entrapped Pd nanocatalysts showed high catalytic activity in Suzuki-Miyaura coupling reactions (demonstrated by preserving the turnover frequency values) and stability (demonstrated by palladium leaching and recycling experiments). This new approach presents a new class of PAFs with unique structural, topological, and compositional complexities as entrapped metal nanocatalysts or for other diverse applications.

Nanosized CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) ferrites were obtained through wet ferritization method. These ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), Fourier transform infrared spectroscopy (FTIR), Mossbauer spectroscopy and magnetic measurements. The XRD results revealed that the average crystallite size is 5.77 nm for CoFe1.8Tb0.2O4 and 6.42 nm for CoFe1.8Er0.2O4. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data showed that the Tb3+ and Er3+ ions occupy the octahedral sites. TEM images indicated the presence of polyhedral particles with average size 5.91 nm for CoFe1.8Tb0.2O4 and 6.80 nm for CoFe1.8Er0.2O4. Room temperature Mossbauer spectra exhibit typical nanoscaled cobalt ferrite spectra in good agreement with XRD and TEM data. The saturation magnetization value (M-s) is 60 emu/g for CoFe1.8Tb0.2O4 and 80 emu/g for CoFe1.8Er0.2O4. CoFe1.8RE0.2O4 nanoparticles showed similar antimicrobial efficacy against the five tested microbial strains, both in planktonic and biofilm state. The results highlight the promising potential of these types of nanoparticles for the development of novel anti-biofilm agents and materials.

In this paper, we present a theoretical perspective concerning the scattering of electrons on a twisted light (TL) driven graphene quantum dot (GQD). Relatively recently discovered, TL is a novel type of electromagnetic field which carries a finite orbital angular momentum oriented on the propagation direction, besides its spin. This striking property of TL is due to its spatial structure. It is well known that the localization of electrons in a GQD is forbidden by the Klein tunneling, an effect that manifests by the perfect transmission of electrons through a potential barrier, regardless of its magnitude. Here we demonstrate that, for a suitable choice of the scattering regimes, there emerge scattering resonances characterized by trapping states of the incident electron inside the GQD for finite periods of time. The most interesting result is the prediction regarding the possibility to control the trapping times using a TL irradiation. Also, we mention that the investigation was performed for a frequency of the TL within the infrared spectrum.

The present study brings developments in the area of tissue engineering of heart valves, with the design and application of a new 2D model for human heart valve. This model contains valvular interstitial cells (VIC) encapsulated in gold covered electrospun polycaprolactone (PCL/Au) fibers, the latter serving also as an electrochemical sensor that enables the monitoring of oxygen levels of cellular media. The biocompatibility of PCL and PCL/Au with VIC was evaluated after the encapsulation of VIC in both scaffolds using the lactate dehydrogenase assay. Fluorescence microscopy of the encapsulated cells was used for the investigation of cell morphology, by employing phalloidin labelled F-actin (red) and DAPI nuclear staining (blue). The electrochemical techniques allowed to investigate the effect of cell encapsulation within the PCL/Au 2D constructs and to quantify the dissolved oxygen levels in cell culture media at both PCL/Au and PCL/Au with encapsulated cells (PCL/ Au/cells). Experiments were performed in a hypoxistation, which allowed a fine control on the cellular media oxygenation. Electrochemical impedance spectroscopy (EIS) was used to evaluate the electrochemical behavior of the 2D constructs, PCL/Au and PCL/Au/cells, in cellular media at different O-2 concentration. Results were analyzed and both impedance values at a fixed frequency and values of the equivalent circuit elements were used to construct calibration curves for dissolved O-2 determination. The second electrochemical technique used to monitor the levels of O-2 at PCL/Au and PCL/Au/cells in the cellular media was square wave voltammetry with sensitivities of 1.5 and 2.5 mu A cm(-2) mu M-1, for PCL/Au and PCL/Au/cells, respectively.

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

A nanostructured samarium oxide electrode was constructed by electrodeposition onto the surface of a gold electrode on SiO2/Si wafer. The samarium oxides electrode's surface morphology was investigated by scanning electron microcopy showing a quasi-monodispersed nanoplatelets like structure. X-rays diffraction analysis demonstrated a mixture of monoclinic and hexagonal phases while the X-rays photoelectron spectroscopy indicated the co-existence of both Sm2+ and Sm3+ species in a 1:3 proportion. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the charge transfer processes at the surface of the samarium oxide electrode in the absence and in the presence of redox probes. A roughness factor of 2.5 was determined from the samarium oxide electrode while the charge transfer constant was almost double when compared to the planar gold electrode. Then, the samarium oxide electrode was used for the H2O2 detection by fixed potential amperometry at -0.20 V (vs. Ag/AgCl) with a linear region between 0.01 and 1.00 mM, a sensitivity of 153 mu A cm(-2) mM(-1) and a LoD = 2.70 mu M. Glucose oxidase was used as a model enzyme in order to test the capacity of the samarium oxides electrode for biosensing. The enzyme was immobilized by physical adsorption and the optimum conditions for glucose analysis investigated. The biosensor showed a linear range for glucose detection between 0.10 and 1.20 mM with a sensitivity of 8.40 mu A cm(-2) mM(-1) and a LoD = 8.00 mu M. Selectivity was tested toward common interfering species, and the results revealed the lack of biosensor response. The glucose biosensor on samarium oxides was tested for glucose detection in serum samples with a recovery factor of 90%, and the result validated with a commercial glucometer. (C) 2021 Elsevier Ltd. All rights reserved.

The reactions between [CuX(PPh3)](4) or [CuX(PPh3)(3)], X = Cl or Br, and N-benzoyl-N'-(4-methoxyphenyl)thio-urea (BTU-OMe), N-benzoyl-N'-(4-methylphenyl)thiourea (BTU-Me) in toluene gave new four-coordinated tetrahedral copper(I) complexes of two types: [CuX(BTU)(PPh3)(2)] (1, 2) and [CuX(BTU)(2)(PPh3)] (3,4) [BTU = N-benzoyl-N'-(4-methoxy/methyl phenyl)thiourea derivatives, X = Cl (a) and Br (b)]. These complexes were fully characterized by several analytical and spectroscopic (IR, UV/VIS, H-1, C-13 and P-31 NMR) techniques. The molecular structure of a representative complex, [Cu(BTU-OMe)(PPh3)(2)Cl] (3a), was determined by the single crystal X-ray diffraction method which reveals a distorted tetrahedral geometry where the Cu(I) ion is surrounded by one BTU ligand molecule, two PPh3 groups and one chloride anion. These eight heteroleptic complexes were found to emit in solid state with lifetimes in the 12-99 mu s range and with the highest quantum yield of 4.0% for 3b. The reaction between [CuBr(PPh3)](4) and N-benzoyl-N',N'-(di-n-butyl)thiourea (BTU-Bu-2) ligand gave the simple [CuBr(BTU-Bu-2)(3)] complex (5), when the PPh3 molecules were completely removed by the BTU derivative. The spectroscopic data indicated a distorted tetrahedral geometry produced by three BTU ligand molecules and one bromide anion. Complex 5 has the highest quantum yield (11%) with the lifetime of 29 mu s in solid-state.

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.