Publications

Fabrication and extensive characterization of hard-soft nanocomposites composed of hard magnetic low-temperature phase LTP-MnBi and amorphous Fe70Si10B20 soft magnetic phase for bulk magnets are reported. Samples with compositions Mn55Bi45 + x center dot(Fe70Si10B20) (x = 0, 3, 5, 10, 20 wt.%) were prepared by spark plasma sintering of powder mixtures. Characterization has been performed by X-ray diffraction, scanning and transmission electron microscopy, magnetometry and Fe-57 Mossbauer spectroscopy. It was shown that samples contain crystallized and nanometric LTP-MnBi phases with various elemental compositions depending on the degree of Bi clustering. Complex correlations between starting compositions, processes during fabrication, and functional magnetic characteristics were observed. Unexpected special situations of the relation between microstructure and magnetic coupling mechanisms are discovered. Exchange spring effects of different strengths occur, being very sensitive to morpho-structural and compositional features, which in turn are controlled by processing conditions. An in-depth analysis of related microscopic characteristics is provided. Results of this work suggest that fabrication by powder metallurgy routes, such as spark plasma sintering of hard and soft magnetic powder mixtures, of MnBi-based composites with exchange spring phenomena have a high potential in designing and optimization of suitable materials with tunable magnetic properties towards rare-earth-free permanent magnet applications.

CuFeS2 is a prominent chalcogenide that possesses similar optical properties and a significantly lower cost, compared to gold. Additionally, covalent organic frameworks are a class of materials at the forefront of current research, mainly used as photoactive components and porous absorbers. Hence, in this work, hydrophilic CuFeS2 particles are coupled with multi-functional covalent organic frameworks through ionic bonding to produce a hybrid material with unique and optimized properties. To render the CuFeS2 particles negatively charged and dispersible in water, we coated them with sodium dodecyl sulfonate, shifting the surface plasmon resonance of the nanoparticles from 472 to 492 nm. When they are electrostatically assembled with the positively charged COFs, an S-scheme is formed and the fluorescence of the hybrid materials is highly quenched, with the electron transfer happening from the networks to the nanoparticles and a simultaneous energy exchange which is dependent on the emission wavelength. Through detailed fluorescence spectroscopy, time-resolved measurements and Stern-Volmer analysis, we identified an efficient emission quenching that differs from the bulk to the exfoliated hybrid system, while detailed electron microscopy studies demonstrated the strong interaction between the two components. The quenching mechanisms and the on or off surface resonance dependent lifetime could be applied to photocatalytic and photovoltaic applications.

Willows from engineered wetland systems (EWS) offer a sustainable approach to wastewater treatment and biomass production. Our study assesses their potential for nutrient recovery and carbon sequestration using slow pyrolysis (600 degrees C) and hydrothermal carbonization (250 degrees C). Here, we propose EWS-pyrochars as a ready-to integrate opportunity for soil amendment, as they exhibit a predominant CO2 2 release and the absence of harmful compounds in pyrolysis-chromatograms, indicating higher stability than hydrochars. Using sequential Pextractions, we observed a high bioavailability in the willow-woodchips and a significant P-retention in EWSchars-up to 92 % in pyrochars and near-complete retention in hydrochars, along with a higher labile-P fraction of 21 % in hydrochars than 5 % in pyrochars. Utilizing X-ray-based techniques, Raman spectroscopy, scanning electron microscopy, and gas physisorption, we characterized the EWS-chars' structures. We revealed innovative 3D-visualizations, which transcend previous literature by providing insights into the chars' internal porosity and quantifying, for the first time, their carbonaceous structural thickness via a meshing algorithm and the mean Feret diameter. EWS-pyrochars exhibit remarkable aromaticity with a higher concentration of overall sp2 2 Catoms at 63 % vs. 43 % in hydrochars. Moreover, unlike hydrochars, which depict occluded porosity, EWSpyrochars exhibited 92 % water storage-like pores. Although hydrochars indicated lower carbonization and thermal stability than pyrochars, their higher carbon retention (55 vs. 41 % in pyrochar) suggest superior annual benefits-on a 10 ha EWS scale-of 80-tons of carbon sequestration and 334 kg of phosphorus recovery versus 60-tons of carbon and 298 kg of phosphorus with pyrochars. Our findings suggest innovative materials for resource recovery, advancing the engineered wetland systems field, shifting their traditional use, and opening the opportunity for future integration into biorefineries.

Carbon monoxide (CO) is reversibly adsorbed on and desorbed from ferroelectric (001) oriented, BaO-terminated barium titanate. All processes are characterized in real time via photoelectron spectroscopy. Adsorption proceeds on different sites/geometries as a function of substrate temperature. Below room temperature, CO is adsorbed on surface Ba. At room temperature, adsorption proceeds on surface oxygen, whereas at high temperatures, "hollow" site adsorption occurs with carbon coordinated with three oxygens, one oxygen initially belonging to CO and two oxygens from the substrate. The amount of CO adsorbed is about one molecule for 10 surface unit cells, which is slightly increased at low temperatures. CO is desorbed if the substrate is heated above the Curie temperature, which is a sign of the definitory role of ferroelectric polarization. The BaTiO3(001) surface is unaffected by repeated cycles of adsorption-desorption.

Plastics are omnipresent in the environment and degrade into smaller fragments in time. This study shows how plastics could reach nanometer sizes under specific conditions and the interaction of the nanofragments with prokaryotic cells. Imaging and spectroscopy techniques were employed to determine the modifications induced in artificially aged low-density polyethylene (LDPE). Scanning electron microscopy indicated that nanometer-scale LDPE could be obtained after ultraviolet-C (UVC) exposure for 10 days. Raman and Fourier-transformed infrared spectroscopy confirmed the chemical changes within the UVC-exposed LDPE are consistent with the increase of crystallinity. Moreover, the interaction between the degraded LDPE and chemo- and photosynthetic organisms was observed through fluorescence, confocal, electron microscopy techniques, and electron paramagnetic resonance spectroscopy. The results showed how micro/nano-LDPE could influence the development of Escherichia coli and Arthrospira platensis after only 72 h of interaction. This fundamental study indicates the environmental presence and effects of nanometer-sized LDPE resulting from light exposure.

A novel scaffold for in situ electrochemical detection of cell biomarkers was developed using electrospun nanofibers and commercial adhesive polymeric membranes. The electrochemical sensing of cell biomarkers requires the cultivation of the cells on/near the (bio)sensor surface in a manner to preserve an appropriate electroactive available surface and to avoid the surface passivation and sensor damage. This can be achieved by employing biocompatible nanofiber meshes that allow the cells to have a normal behavior and do not alter the electrochemical detection. For a better mechanical stability and ease of handling, nylon 6/6 nanofibers were collected on commercial polymeric membranes, at an optimal fiber density, obtaining a double-layered platform. To demonstrate the functionality of the fabricated scaffold, the screening of cellular stress has been achieved integrating melanoma B16-F10 cells and the (bio)sensor components on the transducer whereas the melanin exocytosis was successfully quantified using a commercial electrode. Either directly on the surface of the (bio)sensor or spatially detached from it, the integration of cell cultures in biosensing platforms based on electrospun nanofibers represents a powerful bioanalytical tool able to provide real-time information about the biomarker release, enzyme activity or inhibition, and monitoring of various cellular events.

Infections related to orthopedic/stomatology surgery are widely recognized as a significant health concern. Therefore, the development of new materials with superior biological properties and good stability could represent a valuable alternative to the classical treatments. In this paper, the fluorine-substituted hydroxyapatite (FHAp) suspension, with the chemical formula Ca10(PO4)6(OH)2-2xF2x (where x = 0.05), was prepared using a modified coprecipitation technique. Stability studies were conducted by zeta potential and ultrasound measurements for the first time. The X-ray diffraction (XRD) patterns of FHAp powders displayed a hexagonal structure akin to that of pure hydroxyapatite (HAp). The XPS general spectrum revealed peaks corresponding to the constituent elements of fluorine-substituted hydroxyapatite such as calcium, phosphorus, oxygen, and fluorine. The purity of the obtained FHAp samples was confirmed by energy-dispersive X-ray spectroscopy (EDS) studies. The FHAp morphology was evaluated by scanning electron microscopy (SEM) measurements. Fourier-transform infrared spectroscopy (FTIR) studies were performed in order to study the vibrational properties of the FHAp samples. The FHAp suspensions were tested for antibacterial activity against reference strains such as Staphylococcus aureus 25923 ATCC, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. Additionally, the biocompatibility of the FHAp suspensions was assessed using human fetal osteoblastic cells (hFOB 1.19 cell line). The results of our biological tests suggest that FHAp suspensions are promising candidates for the future development of new biocompatible and antimicrobial agents for use in the biomedical field.

We model the equilibrium properties of a two-dimensional electron gas in a square lateral superlattice of quantum dots in a GaAs heterostructure subject to an external homogeneous perpendicular magnetic field and a far-infrared circular cylindrical photon cavity with one quantized mode, the TE011 mode. In a truncated linear basis constructed by a tensor product of the single-electron states of the noninteracting system and the eigenstates of the photon number operator, a local spin density approximation of density functional theory is used to compute the electron-photon states of the two-dimensional electron gas in the cavity. The common spatial symmetry of the vector fields for the external magnetic field and the cavity photon field in the long wavelength approximation enhances higher order magnetic single- and multiphoton processes for both the para- and the diamagnetic electron-photon interactions. The electron-photon coupling introduces explicit photon replicas into the band structure and all subbands gain a photon content, constant for each subband, that can deviate from an integer value as the coupling is increased or the photon energy is varied. The subbands show a complex Rabi anticrossing behavior when the photon energy and the coupling bring subbands into resonances. The complicated energy subband structure leads to photon density variations in reciprocal space when resonances occur in the spectrum. The electron-photon coupling polarizes the charge density and tends to reduce the Coulomb exchange effects as the coupling strength increases.

Tri-layered heterojunction devices based on oxide thin films are attracting significant attention for ultra-fast visible photodetection. However, the responsivity of these devices is still low. In this work, high performance photodetectors based on a tri-layered heterojunction of n-Si/p-Co3O4/n-ZnO were fabricated. Under no applied bias, a maximum responsivity and detectivity of 14.2 mA W-1 and 1.34 x 10(12) Jones were achieved respectively, for a power density of 9.35 mW cm(-2). Remarkably, a significant increase in the responsivity of approximately 864% was found when the device was biased at -2 V. This effect is understood based on the coupling of the photovoltaic and pyroelectric effects. Also, upon applying an external bias of -2 V, at a laser power density of 9.35 mW cm(-2) and at a chopper frequency of 10 Hz, the device exhibits a detectivity and sensitivity of 3.4 x 10(11) Jones and 2.2, respectively, together with a rise and fall time of 4 and 2 mu s, respectively. Compared to high performance Al/Si/SnO/ZnO/ITO and Au/pCuI/ZnO devices, our voltage-biased Al/Si/Co3O4/ZnO/ITO devices exhibit a >40% increase in R and >10x higher D*. Furthermore, an important advantage of our PDs is the p-type component, Co3O4, which is more stable and stoichiometric than CuI and SnO, ensuring PD performance that is stable with time. Therefore, n-Si/p-Co3O4/n-ZnO heterojunction devices shows great promise for ultrafast visible photodetection.