Airborne magnetic nanoparticles may contribute to COVID-19 outbreak: Relationships in Greece and Iran.

This work attempts to shed light on whether the COVID-19 pandemic rides on airborne pollution. In particular, a two-city study provides evidence that PM2.5 contributes to the timing and severity of the epidemic, without adjustment for confounders. The publicly available data of deaths between March and October 2020, updated it on May 30, 2021, and the average seasonal concentrations of PM2.5 pollution over the previous years in Thessaloniki, the second-largest city of Greece, were investigated. It was found that changes in coronavirus-related deaths follow changes in air pollution and that the correlation between the two data sets is maximized at the lag time of one month. Similar data from Tehran were gathered for comparison. The results of this study underscore that it is possible, if not likely, that pollution nanoparticles are related to COVID-19 fatalities (Granger causality, p < 0.05), contributing to the understanding of the environmental impact on pandemics.

How size, shape and assembly of magnetic nanoparticles give rise to different hyperthermia scenarios.

The use of magnetic nanoparticles (MNPs) to locally increase the temperature at the nanoscale under the remote application of alternating magnetic fields (magnetic particle hyperthermia, MHT) has become an important subject of nanomedicine multidisciplinary research, focusing among other topics on the optimization of the heating performance of MNPs and their assemblies under the effect of the magnetic field. We report experimental data of heat released by MNPs using a wide range of anisometric shapes and their assemblies in different media. We outline a basic theoretical investigation, which assists the interpretation of the experimental data, including the effect of the size, shape and assembly of MNPs on the MNPs' hysteresis loops and the maximum heat delivered. We report heat release data of anisometric MNPs, including nanodisks, spindles (elongated nanoparticles) and nanocubes, analysing, for a given shape, the size dependence. We study the MNPs either acting as individuals or assembled through a magnetic-field-assisted method. Thus, the physical geometrical arrangement of these anisometric particles, the magnetization switching and the heat release (by means of the determination of the specific adsorption rate, SAR values) under the application of AC fields have been analysed and compared in aqueous suspensions and after immobilization in agar matrix mimicking the tumour environment. The different nano-systems were analysed when dispersed at random or in assembled configurations. We report a systematic fall in the SAR for all anisometric MNPs randomly embedded in a viscous environment. However, certain anisometric shapes will have a less marked, an almost total preservation or even an increase in SAR when embedded in a viscous environment with certain orientation, in contrast to the measurements in water solution. Discrepancies between theoretical and experimental values reflect the complexity of the systems due to the interplay of different factors such as size, shape and nanoparticle assembly due to magnetic interactions. We demonstrate that magnetic assembly holds great potential for producing materials with high functional and structural diversity, as we transform our nanoscale building blocks (anisometric MNPs) into a material displaying enhanced SAR properties.

Magnetic nanoparticles: An indicator of health risks related to anthropogenic airborne particulate matter.

Due to their small dimensions, airborne particles are able to penetrate through inhalation into many human organs, from the lungs to the cardiovascular system and the brain, which can threaten our health. This work establishes a novel approach of collecting quantitative data regarding the fraction, the composition and the size distribution of combustion-emitted particulate matter through the magnetic characterization and analysis of samples received by common air pollution monitoring. To this end, SQUID magnetometry measurements were carried out for samples from urban and suburban areas in Thessaloniki, the second largest city of Greece, taking into consideration the seasonal and weekly variation of airborne particles levels as determined by occurring traffic and meteorological conditions. The level of estimated magnetically-responding atmospheric particulate matter was at least 0.5 % wt. of the collected samples, mostly being present in the form of ultrafine particles with nuclei sizes of approximately 14 nm and their aggregates. The estimated quantities of magnetic particulate matter show maximum values during autumn months (0.8 % wt.) when increased commuting takes place, appearing higher in the city center by up to 50% than those in suburban areas. In combination with high-resolution transmission electron imaging and elemental analysis, it was found that Fe3O4 and similar ferrites, some of them attached to heavy metals (Co, Cr), are the dominant magnetic contributors arising from anthropogenic high-temperature processes, e.g. due to traffic emissions. Importantly, nasal cytologic samples collected from residents of both central and suburban areas showed same pattern in what concerns magnetic behavior, thus verifying the critical role of nanosized magnetic particles in the assessment of air pollution threats. Despite the inherent statistical limitations of our study, such findings also indicate the potential transmission of infectious pathogens by means of pollution-derived nanoparticles into the respiratory system of the human body.

Controlling Magnetization Reversal and Hyperthermia Efficiency in Core-Shell Iron-Iron Oxide Magnetic Nanoparticles by Tuning the Interphase Coupling.

Magnetic particle hyperthermia, in which colloidal nanostructures are exposed to an alternating magnetic field, is a promising approach to cancer therapy. Unfortunately, the clinical efficacy of hyperthermia has not yet been optimized. Consequently, routes to improve magnetic particle hyperthermia, such as designing hybrid structures comprised of different phase materials, are actively pursued. Here, we demonstrate enhanced hyperthermia efficiency in relatively large spherical Fe/Fe-oxide core-shell nanoparticles through the manipulation of interactions between the core and shell phases. Experimental results on representative samples with diameters in the range 30-80 nm indicate a direct correlation of hysteresis losses to the observed heating with a maximum efficiency of around 0.9 kW/g. The absolute particle size, the core-shell ratio, and the interposition of a thin wüstite interlayer are shown to have powerful effects on the specific absorption rate. By comparing our measurements to micromagnetic calculations, we have unveiled the occurrence of topologically nontrivial magnetization reversal modes under which interparticle interactions become negligible, aggregates formation is minimized and the energy that is converted into heat is increased. This information has been overlooked until date and is in stark contrast to the existing knowledge on homogeneous particles.

Optimization of tetravalent manganese feroxyhyte's negative charge density: A high-performing mercury adsorbent from drinking water.

This study demonstrates an optimization procedure for the development of an Hg-specified adsorbent able to comply with the regulation limit for drinking water of 1µg/L. On this purpose, the synthesis of Mn(IV)-feroxyhyte was modified to achieve high negative charge density by combining alkaline and extreme oxidizing conditions. In particular, precipitation of FeSO4 at pH9 and excess of KMnO4 follows a very fast nucleation step providing a product with very small nanocrystal size (1-2nm), high specific surface area (300m2/g) and maximum negative charge density (1.8mmol H+/g). The adsorbent was validated for Hg removal in batch experiments and column tests using natural-like water indicating an adsorption capacity as high as 2.5µg/mg at equilibrium concentration 1µg/L under reliable conditions of application. Importantly, the adsorption is an exothermic spontaneous process, resulting in the formation of inner sphere complexes by sharing both A-type and B-type oxygen atoms with the metal surface octahedral as revealed by the X-ray absorption fine structure results.

Arrangement at the nanoscale: Effect on magnetic particle hyperthermia.

In this work, we present the arrangement of Fe3O4 magnetic nanoparticles into 3D linear chains and its effect on magnetic particle hyperthermia efficiency. The alignment has been performed under a 40 mT magnetic field in an agarose gel matrix. Two different sizes of magnetite nanoparticles, 10 and 40 nm, have been examined, exhibiting room temperature superparamagnetic and ferromagnetic behavior, in terms of DC magnetic field, respectively. The chain formation is experimentally visualized by scanning electron microscopy images. A molecular Dynamics anisotropic diffusion model that outlines the role of intrinsic particle properties and inter-particle distances on dipolar interactions has been used to simulate the chain formation process. The anisotropic character of the aligned samples is also reflected to ferromagnetic resonance and static magnetometry measurements. Compared to the non-aligned samples, magnetically aligned ones present enhanced heating efficiency increasing specific loss power value by a factor of two. Dipolar interactions are responsible for the chain formation of controllable density and thickness inducing shape anisotropy, which in turn enhances magnetic particle hyperthermia efficiency.

Monitoring the role of Mn and Fe in the As-removal efficiency of tetravalent manganese feroxyhyte nanoparticles from drinking water: An X-ray absorption spectroscopy study.

The implementation of amorphous tetravalent manganese feroxyhyte (TMFx) nanoparticles, prepared via co-precipitation synthesis, as an efficient As(V)-removal material is investigated using X-ray absorption fine structure (XAFS) spectroscopy at the Fe-, Mn- and As-K-edges. The optimum synthesis conditions and chemical composition of the TMFx adsorbent were determined by the degree of polymerization in the adsorbents' microstructure. Under synthesis into mildly acidic conditions, the change in the polymerization of the metal-oxyhydroxyl chains (metal=Fe, Mn) provides more adsorption sites at edges and corner sites in the bonding environment of Fe and Mn, respectively, thereby enhancing As uptake. After exposure to As-polluted water, similar microstructural changes related to As-bidentate and monodentate geometries are generated: As(V) preferentially occupies the high energy adsorption sites ((2)C complexes) available in the Mn-oxyhydroxyl groups and the low energy edge sites offered by Fe ((2)E complexes). It is revealed that optimum arsenic-removal by TMFx occurs into mildly acidic synthesis pH and for iron to manganese molar ratio equal to 3.

Ferrimagnetic nanocrystal assemblies as versatile magnetic particle hyperthermia mediators.

Colloidal nanocrystal assemblies (nanoclusters), consisting of 13 nm iron oxide nanocrystals, were synthesized in various sizes (45-98 nm), and were investigated as heating mediators for magnetic particle hyperthermia. The colloidal nanocrystal clusters show enhanced heating efficiency in comparison with their constituent primary iron oxide nanocrystals due to collective magnetic features. The fine tuning of intra-cluster magnetic interactions results to the domination of the hysteresis losses mechanism over the relaxation loss heating contributions and eventually to a versatile magnetic particle hyperthermia mediator.

Kinetic modeling of AS(III) and AS(V) adsorption by a novel tetravalent manganese feroxyhyte.

HYPOTHESIS: The purpose of the present work is the development of a kinetic model for the adsorption of As(III) and As(V) onto tetravalent manganese feroxyhyte (δ-Fe0.75Mn0.25OOH), which have been recently proved to be very efficient adsorbent for the particular species. EXPERIMENTS: In this respect equilibrium and adsorption kinetic experiments onto this type of adsorbent for As(III) and As(V) were performed. Two sizes of adsorbate particles are tested in order to acquire better insight to the adsorption process. RESULTS: The adsorption kinetic curves cannot be described by the well-known adsorption kinetic models so a detailed model that takes into account the structure of the adsorbent particle is developed. The model parameters were extracted by the requirement of agreement between model and experimental results. The batch model developed here is necessary for the development of models for fixed bed adsorption devices in order to exploit the commercial prospects of the particular adsorbent. This work constitutes the first attempt of kinetic study and adsorption model development for the specific very promising adsorbent.

An X-ray absorption study of synthesis- and As adsorption-induced microstructural modifications in Fe oxy-hydroxides.

Synthetic adsorbents based on Fe oxy-hydroxides (FeOOH) prepared under a wide range of pH-values via intense oxidation conditions of FeSO4 as well as the As(III) and As(V) adsorption mechanism are investigated using X-ray absorption fine structure (XAFS) spectroscopies at the Fe- and As-K-edges. Synthesis in an alkaline environment promotes the face-connectivity of the Fe(O,OH)6 chains at the expense of edge- and corner-sharing linkage, which is consistent with the lower surface charge density and in turn with the lower arsenic adsorption capacity. Microstructural changes are also detected after As(V) adsorption onto FeOOH synthesized at pH 5.5: the ratio of face-/edge-sharing sites increases from approximately 0.4-0.7 as a function of the As(V)-loading. This modification of the polymeric Fe(O,OH)6 structure at higher As/Fe ratios is attributed to strong As(V) bidentate mononuclear ((2)E) and binuclear ((2)C) adsorption. In contrast, no alterations in the FeOOH microstructure were observed, possibly due to the weaker (2)E linkage of As(III).

Optimizing magnetic nanoparticles for drinking water technology: The case of Cr(VI).

The potential of magnetite nanoparticles to be applied in drinking water treatment for the removal of hexavalent chromium is discussed. In this study, a method for their preparation which combines the use of low-cost iron sources (FeSO4 and Fe2(SO4)3) and a continuous flow mode, was developed. The produced magnetite nanoparticles with a size of around 20 nm, appeared relatively stable to passivation providing a removal capacity of 1.8 µg Cr(VI)/mg for a residual concentration of 50 µg/L when tested in natural water at pH7. Such efficiency is explained by the reducing ability of magnetite which turns Cr(VI) to an insoluble Cr(OH)3 form. The successful operation of a small-scale system consisting of a contact reactor and a magnetic separator demonstrates a way for the practical introduction and recovery of magnetite nanoparticles in water treatment technology.

Occurrence of Cr(VI) in drinking water of Greece and relation to the geological background.

This study provides a survey on potential Cr(VI) exposure attributed to drinking water in Greece. For this reason, a wide sampling and chemical analysis of tap waters from around 600 sites, supplied by groundwater resources, was conducted focusing on areas in which the geological substrate is predominated by ultramafic minerals. Results indicate that although violations of the current chromium regulation limit in tap water are very rare, 25% of cases showed Cr(VI) concentrations above 10 µg/L, whereas Cr(VI) was detectable in 70% of the samples (>2 µg/L). Mineralogy and conditions of groundwater reservoirs were correlated to suggest a possible Cr(VI) leaching mechanism. Higher Cr(VI) values are observed in aquifers in alluvial and neogene sediments of serpentine and amphibolite, originating from the erosion of ophiolithic and metamorphic rocks. In contrast, Cr(VI) concentration in samples from ophiolithic and metamorphic rocks was always below 10 µg/L due to both low contact time and surface area, as verified by low conductivity and salt concentration values. These findings indicate that under specific conditions, pollution of water by Cr(VI) is favorable by a slow MnO2-catalyzed oxidation of soluble Cr(III) to Cr(VI) in which manganese products [Mn(III)/Mn(II)] are probably re-oxidized by oxygen.

Evaluation of nickel ferrite nanoparticles coated with oleylamine by NMR relaxation measurements and magnetic hyperthermia.

Nickel ferrite nanoparticles were synthesized via a facile solvothermal approach. Oleylamine (OAm) was used in all synthetic procedures as a stabilizing agent and solvent. By varying the polarity of the solvents, hydrophobic NiFe2O4 nanoparticles coated with OAm of relatively similar sizes (9-11.7 nm) and in a range of magnetization values (32.0-53.5 emu g(-1)) were obtained. The as-prepared hydrophobic nanoparticles were characterized by XRD, TEM, SEM, TGA and VSM and converted to hydrophilic by two different approaches. The addition of a positively charged ligand (cetyltrimethyl ammonium bromide, CTAB) and the ligand exchange procedure (2,3-dimercaptosuccinic acid, DMSA) have been successfully applied. The aqueous suspensions of NiFe2O4@CTAB and NiFe2O4@DMSA showed good colloidal stability after a long period of time. The different surface modification affected both the NMR relaxometric measurements and the hyperthermia effects. In both techniques CTAB modification demonstrated higher r2 relaxivity (278.9 s(-1) mM(-1) in an NMR spectrometer at 11.7 T) and SAR values (423.4 W g(-1) at an applied AC field with a particle concentration of 0.5 mg mL(-1)). The results indicate that a coating with a larger molecule as CTAB under the same size, shape and magnetization of NiFe2O4 NPs gave rise to NMR relaxometric properties and heating efficacy.

Cu-Zn powders as potential Cr(VI) adsorbents for drinking water.

This work examines the possibility of applying CuZn alloys as a reducing medium for the efficient removal of hexavalent chromium from drinking water. In an effort to develop a route for producing powders of CuZn alloys under mild conditions and investigate the optimum composition for such application, a series of alloys in the form of powders were prepared, by a sequence of Cu and Zn ball-milling and low temperature annealing. Batch Cr(VI) removal tests, performed to evaluate and compare the efficiency of the products under typical natural water parameters (pH 7 and natural-like water), indicated that the best performing material have a composition around 50 wt% Cu. The dominant reduction mechanisms are both the corrosion of the alloy surface and the electron transfer to the solution. The behavior of granulated CuZn media was tested in rapid-scale column tests using the commercial KDF which verified the high potential of CuZn alloys in Cr(VI) removal. Nevertheless, Cu and Zn leaching problems should be also considered.

The effect of composition and structural ordering on the magnetism of FePt nanoparticles.

Spherical 4 nm FePt nanoparticles were synthesized by the simultaneous decomposition of Fe(CO)5 and the polyol reduction of Pt(acac)2. The final Fe-to-Pt composition was tuned between 15-55 at.% by varying the ingredient precursor ratios. The effect of composition and structural ordering on the macroscopic magnetic features of final FePt nanoparticles was examined via post-synthetic annealing stages at different conditions. Structural ordering is promoted in all cases, though samples approximating equiatomic Fe/Pt ratios eventually transform to fct-FePt phase while the FePt3-phase is favored for the Pt-richer samples. Consequently, the magnetic features of the annealed nanoparticles may be categorized; the hard magnetic FePt region dominating for Fe content between 40-55 at.% and the soft magnetic FePt3 region dominating in the region 20-30 at.% while Fe content less than 20 at.% results in Pt-richer phases with diminishing ferromagnetic behavior.

Size-induced effects in wet-chemically synthesized CoPt3 nanoparticles.

CoPt3 alloy spherical nanoparticles with sizes tuned between 3-7 nm were produced by the simultaneous thermal treatment of proper platinum and cobalt precursors in the presence of surfactants. The final size and composition of the particles are determined by the precursors' ratio, the chemical behavior of Co precursors and the stabilizing efficiency of the surfactants. By employing higher reaction temperatures (approximately 350 degrees C) better alloying is achieved leading to enhancement of macroscopic magnetic features and decrease of the superparamagnetic limit down to 7 nm.

Three-dimensional momentum imaging of electron wave packet interference in few-cycle laser pulses.

Using a reaction microscope, three-dimensional (3D) electron (and ion) momentum (P) spectra have been recorded for carrier-envelope-phase (CEP) stabilized few-cycle ( approximately 5 fs), intense ( approximately 4 x 10(14) W/cm2) laser pulses (740 nm) impinging on He. Preferential emission of low-energy electrons (E(e)<15 eV) to either hemisphere is observed as a function of the CEP. Clear interference patterns emerge in P space at CEPs with maximum asymmetry, interpreted as attosecond interferences of rescattered and directly emitted electron wave packets by means of a simple model.

Ultrafast superheating and melting of bulk ice.

The superheating of a solid to a temperature beyond its melting point, without the solid actually melting, is a well-known phenomenon. It occurs with many substances, particularly those that can readily be produced as high-quality crystals. In principle, ice should also be amenable to superheating. But the complex three-dimensional network of hydrogen bonds that holds water molecules together and gives rise to unusual solid and liquid properties strongly affects the melting behaviour of ice; in particular, ice usually contains many defects owing to the directionality of its hydrogen bonds. However, simulations are readily able to 'create' defect-free ice that can be superheated. Here we show that by exciting the OH stretching mode of water, it is possible to superheat ice. When using an ice sample at an initial temperature of 270 K, we observe an average temperature rise of 20 +/- 2 K that persists over the monitored time interval of 250 ps without melting.