National Institute Of Materials Physics - Romania

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101. Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones
Authors: Dumitru, I; Chiriac, FL; Ilis, M; Pasuk, I; Manaila-Maximean, D; Micutz, M; Staicu, T; Circu, V

Published: MAY 2022, CRYSTALS, 12, 715, DOI: 10.3390/cryst12050715

The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br- and PF6- counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C-6, C-8 and C-10 do not show mesomorphic properties, while longer chain analogues with C-12 and C-14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6- counterion do not exhibit liquid crystal properties.
102. Electrochemical and In Vitro Biological Evaluation of Bio-Active Coatings Deposited by Magnetron Sputtering onto Biocompatible Mg-0 .8Ca Alloy
Authors: Bita, AI; Antoniac, I; Miculescu, M; Stan, GE; Leonat, L; Antoniac, A; Constantin, B; Forna, N

Published: MAY 2022, MATERIALS, 15, 3100, DOI: 10.3390/ma15093100

The use of resorbable magnesium alloys in the design of implants represents a new direction in the healthcare domain. Two main research avenues are currently explored for developing or improving metallic biomaterials: (i) increase of their corrosion resistance by designed compositional and structural modifications, and (ii) functionalization of their surfaces by coating with ceramic or polymeric layers. The main objective of this work was to comparatively assess bio-functional coatings (i.e., highly-crystallized hydroxyapatite and silica-rich glass) deposited by radio-frequency magnetron sputtering (RF-MS) on a biodegradable Mg-0.8Ca alloy (0.8 wt.% of Ca). After probing their morphology (by scanning electron microscopy) and structure (by Fourier transform infrared spectroscopy and grazing incidence X-ray diffraction), the corrosion resistance of the RF-MS coated Mg-0.8Ca substrates was electrochemically tested (in synthetic biological media with different degrees of biomimicry), and their cytocompatibility was assessed in osteoblast and fibroblast cell cultures. By collective assessment, the most promising performances, in terms of mass loss (similar to 7% after 12 days), hydrogen release rate (similar to 6 mL/cm(2) after 12 days), electrochemical corrosion parameters and cytocompatibility, were obtained for the crystalline HA coating.
103. Electrocatalytic Properties of Mixed-Oxide-Containing Composite-Supported Platinum for Polymer Electrolyte Membrane (PEM) Fuel Cells
Authors: Ayyubov, I; Talas, E; Salmanzade, K; Kuncser, A; Paszti, Z; Neatu, S; Mirea, AG; Florea, M; Tompos, A; Borbath, I

Published: MAY 2022, MATERIALS, 15, 3671, DOI: 10.3390/ma15103671

TiO2-based mixed oxide-carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti1-xMoxO2-C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky-Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H2O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability.
104. Magnetic Core-Shell Iron Oxides-Based Nanophotocatalysts and Nanoadsorbents for Multifunctional Thin Films
Authors: Musat, V; Stanica, N; Anghel, EM; Atkinson, I; Culita, DC; Polosan, S; Crintea, L; Ceoromila, AC; Buruiana, CT; Carp, O

Published: MAY 2022, MEMBRANES, 12, 466, DOI: 10.3390/membranes12050466

In recent years, iron oxides-based nanostructured composite materials are of particular interest for the preparation of multifunctional thin films and membranes to be used in sustainable magnetic field adsorption and photocatalysis processes, intelligent coatings, and packing or bio-medical applications. In this paper, superparamagnetic iron oxide (core)-silica (shell) nanoparticles suitable for thin films and membrane functionalization were obtained by co-precipitation and ultrasonic-assisted sol-gel methods. The comparative/combined effect of the magnetic core co-precipitation temperature (80 and 95 degrees C) and ZnO-doping of the silica shell on the photocatalytic and nano-sorption properties of the resulted composite nanoparticles were investigated by ultraviolet-visible (UV-VIS) spectroscopy monitoring the discoloration of methylene blue (MB) solution under ultraviolet (UV) irradiation and darkness, respectively. The morphology, structure, textural, and magnetic parameters of the investigated powders were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) measurements, and saturation magnetization (vibrating sample magnetometry, VSM). The intraparticle diffusion model controlled the MB adsorption. The pseudo- and second-order kinetics described the MB photodegradation. When using SiO2-shell functionalized nanoparticles, the adsorption and photodegradation constant rates are three-four times higher than for using starting core iron oxide nanoparticles. The obtained magnetic nanoparticles (MNPs) were tested for films deposition.
105. Effects of Calcination Temperature on CO-Sensing Mechanism for NiO-Based Gas Sensors
Authors: Stanoiu, A; Ghica, C; Mihalcea, CG; Ghica, D; Somacescu, S; Florea, OG; Simion, CE

Published: MAY 2022, CHEMOSENSORS, 10, 191, DOI: 10.3390/chemosensors10050191

NiO-sensitive materials have been synthesized via the hydrothermal synthesis route and calcined in air at 400 degrees C and, alternatively, at 500 degrees C. Structural, morphological, and spectroscopic investigations were involved. As such, the XRD patterns showed a higher crystallinity degree for the NiO calcined at 500 degrees C. Such an aspect is in line with the XPS data indicating a lower surface hydroxylation relative to NiO calcined at 400 degrees C. An HRTEM microstructural investigation revealed that the two samples differ essentially at the morphological level, having different sizes of the crystalline nanoparticles, different density of the surface defects, and preferential faceting according to the main crystallographic planes. In order to identify their specific gas-sensing mechanism towards CO exposure under the in-field atmosphere, the simultaneous evaluation of the electrical resistance and contact potential difference was carried out. The results allowed the decoupling of the water physisorption from the chemisorption of the ambient oxygen species. Thus, the specific CO interaction mechanism induced by the calcination temperature of NiO has been highlighted.
106. A curcumin-loaded silica carrier with NH3 sensitivity and antimicrobial properties
Authors: Todan, L; Voicescu, M; Culita, DC; Lincu, D; Ion, RM; Calin, M; Raut, I; Kuncser, AC

Published: MAY 2022, CHEMICAL PAPERS, 76, DOI: 10.1007/s11696-022-02090-7

In this study curcumin was immobilized in a silica matrix to overcome its poor aqueous solubility and rapid degradation profile. Two kinds of sol-gel powders based on colloidal silica were synthesized and characterized, one prepared with an ethanolic solution of curcumin and the other using cethyltrimethylammonium bromide (CTAB) to solubilize the dye. The successful integration of curcumin in the matrix as well as the interaction with the components of the composite powders was validated by different analysis methods (DSC, FTIR). The samples morphology was evaluated by SEM. UV-Vis and fluorescence studies showed that curcumin was stable, in its enol configuration in both matrices. The sensitivity to ammonia was proved by exposing the powders to NH3 vapors in a sealed vessel. Color changes were measured with a colorimeter. UV-Vis spectra showed that the enol form of the dye in EtOH/CTAB based SiO2 matrices was energetically stable under NH3 atmosphere, even after being kept a few days at low temperature. A fluorescence quenching of both samples was noticed due to interaction curcumin-ammonia. Both samples have antimicrobial properties, the CTAB containing one being more efficient. The EtOH/CTAB based SiO2 powders may represent a novel signaling and antimicrobial system, useful for food or pharmaceutical applications. [GRAPHICS] .
107. Pinning Potential of the Self-Assembled Artificial Pinning Centers in Nanostructured YBa2Cu3O7-x Superconducting Films
Authors: Ivan, I; Ionescu, AM; Crisan, DN; Andrei, A; Galluzzi, A; Polichetti, M; Mosqueira, J; Crisan, A

Published: MAY 2022, NANOMATERIALS, 12, 1713, DOI: 10.3390/nano12101713

For high-field power applications of high-temperature superconductors, it became obvious in recent years that nano-engineered artificial pinning centers are needed for increasing the critical current and pinning potential. As opposed to the artificial pinning centers obtained by irradiation with various particles, which is a quite expensive approach, we have studied superconducting samples having self-assembled defects, created during the sample fabrication, that act as effective pinning centers. We introduced a simple, straight-forward method of estimating the frequency-dependent critical current density by using frequency-dependent AC susceptibility measurements, in fixed temperatures and DC magnetic fields, from the positions of the maxima in the dependence of the out-of-phase susceptibility on the amplitude of AC excitation magnetic field. The results are compatible with a model that stipulates a logarithmic dependence of the pinning potential on the probing current. A mathematical derivation allowed us to estimate from the experimental data the pinning potentials in various samples, and in various DC magnetic fields. The resulted values indicate large pinning potentials, leading to very small probability of magnetic flux escaping the pinning wells, hence, leading to very high critical currents in high magnetic fields.
108. Physicochemical and Biological Evaluation of Chitosan-Coated Magnesium-Doped Hydroxyapatite Composite Layers Obtained by Vacuum Deposition
Authors: Predoi, D; Ciobanu, CS; Iconaru, SL; Raaen, S; Badea, ML; Rokosz, K

Published: MAY 2022, COATINGS, 12, 702, DOI: 10.3390/coatings12050702

In the present work, the effectiveness of vacuum deposition technique for obtaining composite thin films based on chitosan-coated magnesium-doped hydroxyapatite Ca10-xMgx(PO4)(6) (OH)(2) with x(Mg) = 0.025 (MgHApCh) was proved for the first time. The prepared samples were exposed to three doses (0, 3, and 6 Gy) of gamma irradiation. The MgHApCh composite thin films nonirradiated and irradiated were evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) studies. The biological evaluation of the samples was also presented. All the results obtained from this study showed that the vacuum deposition method allowed for obtaining uniform and homogeneous layers. Fine cracks were observed on the MgHApCh composite thin films' surface after exposure to a 6 Gy irradiation dose. Additionally, after gamma irradiation, a decrease in Ca, P, and Mg content was noticed. The MgHApCh composite thin films with doses of 0 and 3 Gy of gamma irradiation showed a cellular viability similar to that of the control. Samples with 6 Gy doses of gamma irradiation did not cause significantly higher fibroblast cell death than the control (p > 0.05). On the other hand, the homogeneous distribution of pores that appeared on the surface of coatings after 6 Gy doses of gamma irradiation did not prevent the adhesion of fibroblast cells and their spread on the coatings. In conclusion, we could say that the thin films could be suitable both for use in bone implants and for other orthopedic and dentistry applications.
109. Iron-Oxide-Nanoparticles-Doped Polyaniline Composite Thin Films
Authors: Butoi, B; Ciobanu, CS; Iconaru, SL; Negrila, CC; Badea, MA; Balas, M; Dinischiotu, A; Predoi, G; Bita, B; Groza, A; Predoi, D

Published: MAY 2022, POLYMERS, 14, 1821, DOI: 10.3390/polym14091821

Iron-oxide-doped polyaniline (PANI-IO) thin films were obtained by the polymerization of aniline monomers and iron oxide solutions in direct current glow discharge plasma in the absence of a buffer gas for the first time. The PANI-IO thin films were deposited on optical polished Si wafers in order to study surface morphology and evaluate their in vitro biocompatibility. The characterization of the coatings was accomplished using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), metallographic microscopy (MM), and X-ray photoelectron spectroscopy (XPS). In vitro biocompatibility assessments were also conducted on the PANI-IO thin films. It was observed that a uniform distribution of iron oxide particles inside the PANI layers was obtained. The constituent elements of the coatings were uniformly distributed. The Fe-O bonds were associated with magnetite in the XPS studies. The surface morphology of the PANI-IO thin films was assessed by atomic force microscopy (AFM). The AFM topographies revealed that PANI-IO exhibited the morphology of a uniformly distributed and continuous layer. The viability of Caco-2 cells cultured on the Si substrate and PANI-IO coating was not significantly modified compared to control cells. Moreover, after 24 h of incubation, we observed no increase in LDH activity in media in comparison to the control. In addition, our results revealed that the NO levels for the Si substrate and PANI-IO coating were similar to those found in the control sample.
110. Self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors
Authors: Costas, A; Florica, C; Preda, N; Besleaga, C; Kuncser, A; Enculescu, I

Published: APR 27 2022, SCIENTIFIC REPORTS, 12, 6834, DOI: 10.1038/s41598-022-10879-5

An original photodetector system based on self-connected CuO-ZnO radial core-shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO-ZnO core-shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO-ZnO core-shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p-n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron-hole pairs at the CuO-ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO-ZnO core-shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.

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