Explore the vast range of titles available.

Upconversion nanoparticles (UCNPs) are under consideration for their use as bioimaging probes with enhanced optical performance for real time follow-up under non-invasive conditions. Photostable and core-shell NaYF4:Yb3+, Er3+-SiO2 UCNPs obtained by a novel and simple co-precipitation method from lanthanide nitrates or oxides were herein synthesized for the first time. The sol–gel Stöber method followed by oven or supercritical gel drying was used to confer biocompatible surface properties to UCNPs by the formation of an ultrathin silica coating. Upconversion (UC) spectra were studied to evaluate the fluorescence of UCNPs upon red/near infrared (NIR) irradiation. ζ-potential measurements, TEM analyses, XRD patterns and long-term physicochemical stability were also assessed and confirmed that the UCNPs co-precipitation synthesis is a shape- and phase-controlling approach. The bio- and hemocompatibility of the UCNPs formulation with the highest fluorescence intensity was evaluated with murine fibroblasts and human blood, respectively, and provided excellent results that endorse the efficacy of the silica gel coating. The herein synthesized UCNPs can be regarded as efficient fluorescent probes for bioimaging purposes with the high luminescence, physicochemical stability and biocompatibility required for biomedical applications.

ZnO nanocrystals with three different morphologies have been synthesized via a simple sol-gel-based method using Brosimum parinarioides (bitter Amapá) and Parahancornia amapa (sweet Amapá) latex as chelating agents. X-ray diffraction (XRD) and electron diffraction patterns (SAED) patterns showed the ZnO nanocrystals were a pure hexagonal wurtzite phase of ZnO. XRD-based spherical harmonics predictions and HRTEM images depicted that the nanocrystallites constitute pitanga-like (~15.8 nm), teetotum-like (~16.8 nm), and cambuci-like (~22.2 nm) shapes for the samples synthesized using bitter Amapá, sweet Amapá, and bitter/sweet Amapá chelating agent, respectively. The band gap luminescence was observed at ~2.67–2.79 eV along with several structural defect-related, blue emissions at 468–474 nm (VO, VZn, Zni), green emissions positioned at 513.89–515.89 (h-VO+), and orange emission at 600.78 nm (VO+–VO++). The best MB dye removal efficiency (85%) was mainly ascribed to the unique shape and oxygen vacancy defects found in the teetotum-like ZnO nanocrystals. Thus, the bitter Amapá and sweet Amapá latex are effective chelating agents for synthesizing distinctive-shaped ZnO nanocrystals with highly defective and remarkable photocatalytic activity.

The use of scaffolds, three-dimensional porous, biodegradable and biocompatible structures, that can be produced from natural polymers, synthetics, ceramics and metals is crucial in the tissue engineering field. Chitosan is a polysaccharide of natural origin, found in the exoskeleton of marine arthropods and in the cell wall of fungi, with enormous popularity in the production of three-dimensional materials for Tissue Engineering, in particular bone repair. This polymer has several advantages in the production of these structures in bone regeneration and repair: biodegradability, biocompatibility, non-toxicity and antimicrobial properties. This study aimed to prepare porous scaffolds, for bone repair of degenerative diseases in the spine with better performance and less secondary effects, based on chitosan and another biopolymer (sodium alginate) with the incorporation of calcium phosphates (hydroxyapatite and β-tricalcium phosphate), for tissue engineering application. The obtained scaffolds were object of a detailed characterization, namely with regard to their porosity through the ethanol method, degradation, positron annihilation spectroscopy (PAS), mechanical properties, scanning electronic microscope (SEM), thermal stability through thermogravimetric analysis (TGA), chemical composition through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results obtained showed that the different scaffolds presented pores able to support osteoid matrix growth. The crosslinking of scaffolds was also evaluated and resulted in pores with smaller dimensions and higher regularity in the chitosan-sodium alginate polymer without calcium phosphate scaffold. It was also possible to observe the effect of inorganics on mixed-matrix scaffolds, both morphologically and chemically. These scaffolds showed promising results in terms of mechanical and chemical properties, along with promising porosity for tissue regeneration applications.

Ba1−xSrxFe12O19 (x = 0.0, 0.5 and 1.0) hard-magnetic nanohexaferrites prepared by autocombustion were primarily investigated using Mössbauer spectroscopy and optical studies. Morphological examination by electron scanning microscopy revealed that the particles agglomerated into grains with a hexagonal shape. The grain size increases with the amount of Sr content, from ca. 490 nm (x = 0.0) to ca. 700 nm (x = 1.0). Room-temperature Mössbauer spectroscopy showed that the mean hyperfine field increased with the substitution of Ba2+ by Sr2+, consistent with magnetization results. The preferential sites occupied by Fe ions in the hexaferrite structure were determined. Optical studies revealed that all compounds absorb up to ca. 1000 nm, and that the bandgap energy decreases with increasing Sr content.

Haltern 70 amphorae sherds from Castro do Vieito, a Roman settlement from the NW of Portugal occupied during the early imperial period, were studied by Mössbauer spectroscopy at room temperature and 4.2 K, XRD, and XRF, aiming to understand the firing conditions of their production. Firing in air at 750 and 800 °C were performed in a sherd that was carefully studied. Also, a handle with part of the neck attached and with the potter’s stamp “LH …” was studied. In general, it can be deduced that the amphorae were fired under reducing conditions between 800 and 950 °C, having been subjected to an oxidation process only when already cooling. It was also inferred that the provenance of all the Haltern 70 amphorae found in Castro do Vieito is probably the same and that the stamped amphora also seems to come from the same locality.

In this work, we synthesized the Co0.85Bi0.15Fe1.9X0.1O4 (X = Ce3+, Sm3+, Ho3+, and Er3+) nanoparticles via the auto-combustion method. The cell viability against two breast cancer cells (MDA-MB-231 and T-47D cells) and the PC3 prostate cancer cells were carefully analyzed and correlated with the structural parameters and particle size values as well as the chemical composition. The produced compounds’ morphological and structural characteristics were performed using scanning transmission microscopy (TEM) and X-ray Diffraction (XRD). For all compounds, the analyses of the XRD experimental data revealed a structurally reversed cubic spinel with space group Fd-3m. All of the compounds had crystallites smaller than 45 nm which concorded well with the particle size values deduced from TEM images. Co0.85Bi0.15Fe1.9Ho0.1O4 nanoparticles induced a high mortality of breast and prostate cancer cells (MDA-MB-231, T-47D, and PC3) while the Co0.85Bi0.15Fe1.9Sm0.1O4 compound (higher particle size) reduced almost 35% of MDA-MB-231 cancer cells. With very low cytotoxicity against normal human cells, the Co0.85Bi0.15Fe1.9Ho0.1O4 nanoparticles play a significant role in the elimination of cancer cells.

The impact of Co-addition (x = 0, 2, 4, and 6 at. %) in the as-cast and annealed Ni50Mn37.5Sn12.5 Heusler alloy at 900 °C for 24 h on the microstructure, magnetic properties, and the martensitic transition was studied using X-ray diffraction (XRD), scanning electron microscopy, vibrating sample magnetometry, and differential scanning calorimetry. The crystal structure of as-cast samples consists of a 14M modulated martensite structure, a face-centered (FCC) γ phase, and a face-centered tetragonal (FCT) MnNi-type phase L10. The as-cast samples show a dendritic microstructure with different contrasts and non-uniform distribution. The annealed samples exhibit dual 14M and γ phases for the Co0 and Co2, but 14M + γ + MnNi for the Co4 and Co6. The appearance of the martensitic transformation in the annealed Co0 and Co2 samples can be due to the disappearance of the dendritic microstructure. The characteristic temperatures (martensite start, Ms; martensite finish, Mf; austenite start, As; and austenite finish, Af) decrease with Co addition. A ferromagnetic-like order exists at a lower temperature of 1.8 K for the as-cast and annealed samples and decreases at 300 K. The annealing increases the fraction of the AFM contributions at 300 K. The exchange bias values of the Co0, An-Co2, and An-Co6 are 146.7 Oe, 24 O2, and 32.6 Oe, respectively, at 300 K.

About 100 sherds from Haltern 70 amphorae recovered from Castro do Vieito (NW Portugal) and from kiln sites located at Guadalquivir valley, Rio Tinto valley, bay of Cadix and Algarve coast, were analyzed by X-ray fluorescence spectroscopy (XRF) and X-ray diffraction (XRD). The study aimed mainly to verify the provenance of Castro do Vieito (CV) Haltern 70 amphorae. Principal components analysis (PCA) and cluster analysis (CA) were performed. A CV sherd with a potter’s stamp “LH…” was studied among other CV sherds and it was found that they have the same origin, and probably a unique provenance. The most considered area of Haltern 70 type, Guadalquivir valley, is not likely to be the origin of CV Haltern 70 amphorae. Moreover, it is quite possible that these amphorae were produced in a region with Nb rich soils.

Novel promising thermal insulator materials based on alumina-silica aerogel composites reinforced with Kevlar® pulp were prepared using less hazardous base catalysts and ambient pressure drying procedures. The base formulation included tetraethoxysilane (TEOS) and vinyltrimethoxysilane (VTMS) as silica precursors and hexamethyldisilazane (HMDZ) was used for the silylation of the composites. The incorporation of alumina phase in the aerogels was performed through aluminium chloride (AlCl 3 ) or aluminium trisec-butoxide (ATSB) precursors, replacing a small part of Si (up to 15 mol%) by Al. For system optimisation, several parameters that could influence the key properties (bulk density, thermal conductivity and thermal stability) of the aerogel were investigated, namely the base catalysts, the washing and the heat treatment conditions. All the composites prepared were highly hydrophobic and their properties depended on the aluminium precursor used and its content. The most promising composites were those based on AlCl 3 , which achieved low bulk density and thermal conductivity values, down to 120 kg m −3 and 28 mW m −1  K −1 (Hot Disk ® ), and they were thermally stable up to 550 °C, indicating their suitability for thermal insulation applications in more harsh environments. Highlights Novel Kevlar pulp-reinforced alumina-silica aerogels with different precursors. Nanocomposites´ properties are dependent on the alumina precursor and amount. Optimization of post-processing of the gels different catalysts and solvents. Heat treatment improves the thermal stability and mechanical resistance of aerogels.

The report attempts to study some spinel such as cobalt (Co–F), nickel (Ni–F), copper (Cu–F) and magnesium (Mg–F) nanoferrites, which are synthesized by coprecipitation route and annealed at 850 °C for 2 h. Powder X-ray diffraction patterns depict the formation of single cubic spinel structure ( Fd-3m ). Thereby, lattice parameter is ranging between 8.3420 and 8.4009 Å, while average crystallite size is found in 20–38 nm. Transmission electron and scanning electron microscopies exhibit that the nanoparticles are agglomerated and revealing mixture of spherical and irregular shapes. The fit of Co–F, Ni–F and Cu–F room 57 Fe Mössbauer spectra was established with two sextets, which reflects that the Fe 3+ is occupied two sub-lattices of spinel system. A weak percentage of quadruple doublet, 2%, was observed in both Ni–F and Cu–F spectra. Exceptionally, the Mg–F room 57 Fe Mössbauer spectrum indicates broadening lines due to disordering of iron magnetic moments because of small nanoparticle size (20 nm), it was fitted with hyperfine field distribution, Mg–F spectrum was also collected at 6 K reflecting a ferrimagnetic ordering according to Néel’s theory. M(T) curves indicate that the blocking temperature is higher than 300 K, except the Mg–F sample shows a T B of ~226 K. Besides, the M(H) loops at 5 K exhibit a soft behavior and the magnetic parameters like M s , M r , µ e , M r /M s ration, H c and K a have determined for the studied spinel ferrites.