National Institute Of Materials Physics - Romania

High density samples (92-94.5 %) of MgB2 were prepared by Spark Plasma Sintering (SPS). The on-off pulsed current patterns of SPS processing were 8-4, 12-2, 24-2, 99-1. Patterns with more on pulses favor formation of a higher amount of the secondary MgB4 phase through the decomposition of MgB2. They also promote enhancement of larger MgO crystallites without a strong increase in the amount of this phase. Densification rate and pressure in the SPS chamber show a similar behavior, but their amplitude varies and the temperatures defining different stages present some shifts. As-revealed differences induced by pulsed patterns impact superconducting properties in a complex manner. An attempt to assess correlations between the pattern and different superconducting parameters is presented.

Among various "families" of iron-based superconductors, the quite recently discovered AeAFe(4)As(4) (where Ae is an alkali-earth metal and A is an alkali metal) has high critical current density, a very high upper critical field, and a low anisotropy, and has recently received much interest for the possibility of high magnetic field applications at the liquid hydrogen temperature. We have performed DC magnetization relaxation and frequency-dependent AC susceptibility measurements on high-quality single crystals of CaKFe4As4 with the aim of determining the pinning potential U*. The temperature dependence of U* displays a clear crossover between elastic creep and plastic creep. At temperatures around 27-28 K, U* has a very high value, up to 1200 K, resulting in an infinitesimally small probability of thermally activated flux jumps. From the dependence of the normalized pinning potential on irreversible magnetization, we have determined the creep exponents in the two creep regimes, which are in complete agreement with theoretical models. The estimation of the pinning potential from multifrequency AC susceptibility measurements was possible only near the critical temperature due to equipment limitations, and the resulting value is very close to the one that resulted from the magnetization relaxation data. Magnetic hysteresis loops revealed a second magnetization peak and very high values of the critical current density.

Flexible porous materials have gained a high interest due to their impact on the development of electrochemical point-ofcare devices for monitoring the state of health of individuals. Among the porous materials, paper and textiles are most commonly used due to their innate capillary action on fluids. In this article, attention is paid to the retention of analytes in paper and textile porous substrates, and possible procedures to overcome this effect are discussed. The patterning of hydrophilic and hydrophobic regions for sample flow manipulation, and the folding properties of the flexible substrates for 3D architectures capable of transfer of analytes, are considered in relation to current electrode materials and detection methodologies.

Technological progress has led to the development of analytical tools that promise a huge socio-economic impact on our daily lives and an improved quality of life for all. The use of plant extract synthesized nanoparticles in the development and fabrication of optical or electrochemical (bio)sensors presents major advantages. Besides their low-cost fabrication and scalability, these nanoparticles may have a dual role, serving as a transducer component and as a recognition element, the latter requiring their functionalization with specific components. Different approaches, such as surface modification techniques to facilitate precise biomolecule attachment, thereby augmenting recognition capabilities, or fine tuning functional groups on nanoparticle surfaces are preferred for ensuring stable biomolecule conjugation while preserving bioactivity. Size optimization, maximizing surface area, and tailored nanoparticle shapes increase the potential for robust interactions and enhance the transduction. This article specifically aims to illustrate the adaptability and effectiveness of these biosensing platforms in identifying precise biological targets along with their far-reaching implications across various domains, spanning healthcare diagnostics, environmental monitoring, and diverse bioanalytical fields. By exploring these applications, the article highlights the significance of prioritizing the use of natural resources for nanoparticle synthesis. This emphasis aligns with the worldwide goal of envisioning sustainable and customized biosensing solutions, emphasizing heightened sensitivity and selectivity.

This study aimed to exploit two invasive plant species to develop a novel, multifunctional, bioactive wound dressing based on a microporous cellulosic sponge (CS) from Gleditsia triacanthos pods and functionalizing them with Phytolacca americana fruit extract. The CS was functionalized, lyophilized, and characterized by Attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, contact angle, water absorption, and retention capacity. In addition, two parameters were evaluated in temporal dynamics: controlled release of phenolic compounds and antioxidant activities. The hemolytic index, blood clotting kinetics, lactate dehydrogenase release, and wound scratch assays proved their hemo- and bio-compatibility, as well as their ability to promote cell proliferation and migration promoting-activity and to inhibit microbial growth. Furthermore, the obtained spongious material exhibited an anti-inflammatory effect by modulating the macrophages' secretion profile of IL-6 and IL-10. In conclusion, the microporous cellulosic sponge obtained from G. triacanthos could be used as a vehicle to ensure the controlled release of bioactive principles with pro-wound healing activities extracted from invasive plants. [GRAPHICS] .

A magnesium-doped hydroxyapatite in chitosan matrix (MgHApC) sample was developed as a potential platform for numerous applications in the pharmaceutical, medical, and food industries. Magnesium-doped hydroxyapatite suspensions in the chitosan matrix were obtained by the coprecipitation technique. The surface shape and morphological features were determined by scanning electron microscopy (SEM). The hydrodynamic diameter of the suspended particles was determined by Dynamic light scattering (DLS) measurements. The stability of MgHApC suspensions was evaluated by ultrasonic measurements. The hydrodynamic diameter of the MgHApC particles in suspension was 29.5 nm. The diameter of MgHApC particles calculated from SEM was 12.5 +/- 2 nm. Following the SEM observations, it was seen that the MgHApC particles have a spherical shape. The Fourier-transform infrared spectroscopy (FTIR) studies conducted on MgHApC proved the presence of chitosan and hydroxyapatite in the studied specimens. In vitro antimicrobial assays were performed on Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231 microbial strains. The antimicrobial experiments showed that MgHApC exhibited very good antimicrobial properties against all the tested microorganisms. More than that, the results of the in vitro studies revealed that the antimicrobial properties of the samples depend on the incubation time. The evaluation of the sample's cytotoxicity was performed using the human colon cancer (HCT-8) cell line. Our results suggested the great potential of MgHApC to be used in future applications in the field of biomedical applications (e.g., dentistry, orthopedics, etc.).

Herewith, we investigated the capacitive properties of hybrid nanometric architectures consisting of tungsten oxide nanoparticles deposited on graphite (WOx/G) and graphite coated with highly-porous carbon nanowall layers (WOx/CNW/G). The deposition of the nanostructured oxide was performed by a plasma-assisted sublimation, vapor transport and condensation technique. The samples containing the CNW interlayer show superior areal capacitances making this architecture and its fabrication route promising approaches for supercapacitor applications. Thus, areal capacitances of WOx/CNW/G and WOx/G, estimated from galvanostatic chargedischarge tests (GCD) at an applied density current of 1 mA cm-2, are 1247.2 mF cm-2 and 527.3 mF cm-2, respectively. From SEM and XPS investigations, it was observed that CNW promotes the formation of a high amount of small tungsten oxide particles, homogeneously distributed on electrode surface, and facilitates the formation of highly conductive tungsten nitride species, resulting in electrodes with remarkable charge-storage capacity.

In this study, a sol-gel film based on lead sulfide (PbS) quantum dots incorporated into a host network was synthesized as a special nanostructured composite material with potential applications in temperature sensor systems. This work dealt with the optical, structural, and morphological properties of a representative PbS quantum dot (QD)-containing thin film belonging to the Al2O3-SiO2-P2O5 system. The film was prepared using the sol-gel method combined with the spin coating technique, starting from a precursor solution containing a suspension of PbS QDs in toluene with a narrow size distribution and coated on a glass substrate in a multilayer process, followed by annealing of each deposited layer. The size (approximately 10 nm) of the lead sulfide nanocrystallites was validated by XRD and by the quantum confinement effect based on the band gap value and by TEM results. The photoluminescence peak of 1505 nm was very close to that of the precursor PbS QD solution, which demonstrated that the synthesis route of the film preserved the optical emission characteristic of the PbS QDs. The photoluminescence of the lead sulfide QD-containing film in the near infrared domain demonstrates that this material is a promising candidate for future sensing applications in temperature monitoring.

Photocatalysis is one of the approaches for solving environmental issues derived from extremely harmful pollution caused by industrial dyes, medicine, and heavy metals. Titanium dioxide is among the most promising photocatalytic semiconductors; thus, in this work, TiO2 powders were prepared by a hydrothermal synthesis using titanium tetrachloride TiCl4 as a Ti source. The effect of the hydrochloric acid (HCl) concentration on TiO2 formation was analyzed, in which a thorough morpho-structural analysis was performed employing different analysis methods like XRD, Raman spectroscopy, SEM/TEM, and N-2 physisorption. EPR spectroscopy was employed to characterize the paramagnetic defect centers and the photogeneration of reactive oxygen species. Photocatalytic properties were tested by photocatalytic degradation of the rhodamine B (RhB) dye under UV light irradiation and using a solar simulator. The pH value directly influenced the formation of the TiO2 phases; for less acidic conditions, the anatase phase of TiO2 crystallized, with a crystallite size of approximate to 9 nm. Promising results were observed for TiO2, which contained 76% rutile, showing a 96% degradation of RhB under the solar simulator and 91% under UV light after 90 min irradiation, and the best result showed that the sample with 67% of the anatase phase after 60 min irradiation under the solar simulator had a 99% degradation efficiency.

Bulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high tem-perature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic mea-surements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86-97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best le-vitation results were recorded when using boron with a purity of 95-97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 super-conducting magnets for levitation applications and enhances the applicability potential of MgB2 super-conductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.& COPY; 2023 Elsevier B.V. All rights reserved.