Addressing the Effect of Magnetic Particle Hyperthermia Application on the Composition and Spatial Distribution of Iron Oxide Nanoparticles Using X‑ray Spectroscopic Techniques

Iron oxide magnetic nanoparticles (MNPs) are promising candidates in magnetic particle hyperthermia (MPH) applications. However, MPH often initiates the oxidation process of magnetite to maghemite, thus modifying the magnetic properties and heating efficiency of the MNPs. Here, we report on the degree of oxidation of iron-oxide MNPs in parallel to their spatial distribution in order to understand the oxidation behavior and extent of aggregation upon MPH application. The micrometric spatial distribution of the MNPs in an agarose gel matrix was addressed using two-dimensional μ-X-ray fluorescence (XRF) elemental mapping. It is demonstrated that both the size and MPH application disturb their homogenous distribution. The most pronounced changes are detected in the smallest (10 mn) MNPs, where MPH prompts the creation of extended aggregates. Surface and bulk properties of the MNPs are addressed using X-ray absorption fine structure (XAFS) spectroscopies. XAFS measurements using soft X-rays reveal the complete transformation of the MNP surface from magnetite to maghemite to a depth of ca. 4.5 nm, independently of their size. The implemented hard X-ray spectroscopic methods reveal a core/shell Fe3O4/γ-Fe2O3 structure. The surface shell becomes progressively thicker as the diameter of the MNP increases, yet the extent of surface oxidation is less pronounced in the larger MNPs. The degree of oxidation of the MNPs is also a function of the MPH applications and is enhanced due to the thermal load suffered during the MPH treatment

Tin Oxide Nanoparticles via Solar Vapor Deposition for Hexavalent Chromium Remediation

Tin oxide nanoparticles optimized to capture low concentrations of hexavalent chromium from water were developed through a facile, scalable, and low-cost one-step solar vapor deposition methodology. Considering the preservation of high electron donation capacity as the key to support the reduction of mobile Cr(VI) into insoluble forms, the growth of SnO nanoparticles was favored by the co-evaporation of SnO2 with Fe powders at various mass ratios. Characterization techniques indicated that the percentage and the stability of SnO is proportional to the Fe content in the target with a requirement of at least 50% wt to inhibit the formation of a passive SnO2 surface layer. The produced particles were evaluated regarding their efficiency to capture Cr(VI) under conditions similar to water treatment for drinking purposes (pH 7). It was revealed that passivation-free SnO nanoparticles deliver significant improvement in the adsorption capacity corresponding to the residual concentration of 25 μg/L, reaching a value of 1.74 mg/g for the sample prepared with 50% wt Fe in the target. The increase of water acidity was found responsible for the activation of more reduction sites on the particle surface, as reflected through the elevation of efficiency by more than 20% at pH 6

Multiplying Magnetic Hyperthermia Response by Nanoparticle Assembling

The oriented attachment of magnetic nanoparticles is recognized as an important pathway in the magnetic-hyperthermia cancer treatment roadmap, thus, understanding the physical origin of their enhanced heating properties is a crucial task for the development of optimized application schemes. Here, we present a detailed theoretical analysis of the hysteresis losses in dipolar-coupled magnetic nanoparticle assemblies as a function of both the geometry and length of the array, and of the orientation of the particles’ magnetic anisotropy. Our results suggest that the chain-like arrangement biomimicking magnetotactic bacteria has the superior heating performance, increasing more than 5 times in comparison with the randomly distributed system when aligned with the magnetic field. The size of the chains and the anisotropy of the particles can be correlated with the applied magnetic field in order to have optimum conditions for heat dissipation. Our experimental calorimetrical measurements performed in aqueous and agar gel suspensions of 44 nm magnetite nanoparticles at different densities, and oriented in a magnetic field, unambiguously demonstrate the important role of chain alignment on the heating efficiency. In low agar viscosity, similar to those of common biological media, the initial orientation of the chains plays a minor role in the enhanced heating capacity while at high agar viscosity, chains aligned along the applied magnetic field show the maximum heating. This knowledge opens new perspectives for improved handling of magnetic hyperthermia agents, an alternative to conventional cancer therapies

Tetravalent Manganese Feroxyhyte: A Novel Nanoadsorbent Equally Selective for As(III) and As(V) Removal from Drinking Water

The development of a single-phase Fe/Mn oxy-hydroxide (δ-Fe_0.76Mn_0.24OOH), highly efficient at adsorbing both As­(III) and As­(V), is reported. Its synthesis involves the coprecipitation of FeSO₄ and KMnO₄ in a kilogram-scale continuous process, in acidic and strongly oxidizing environments. The produced material was identified as a manganese feroxyhyte in which tetravalent manganese is homogeneously distributed into the crystal unit, whereas a second-order hollow spherical morphology is favored. According to this structuration, the oxy-hydroxide maintains the high adsorption capacity for As­(V) of a single Fe oxy-hydroxide combined with enhanced As­(III) removal based on the oxidizing mediation of Mn­(IV). Ion-exchange between arsenic species and sulfates as well as the strongly positive surface charge further facilitate arsenic adsorption. Batch adsorption tests performed in natural-like water indicate that Mn­(IV)-feroxyhyte can remove 11.7 μg As­(V)/mg and 6.7 μg As­(III)/mg at equilibrium pH 7, before residual concentration overcomes the regulation limit of 10 μg As/L for drinking water. The improved efficiency of this material, its low cost, and the possibility for scaling-up its production to industry indicate the high practical impact and environmental importance of this novel adsorbent

Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> Nanoparticles with Enhanced Electrocatalytic Properties for Oxygen Evolution in Carbonate Electrolyte

The design and engineering of earth-abundant catalysts that are both cost-effective and highly active for water splitting are crucial challenges in a number of energy conversion and storage technologies. In this direction, herein we report the synthesis of Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> core–shell nanoheterostructures and the characterization of their electrocatalytic performance toward the oxygen evolution reaction (OER). Such nanoparticles (NPs) were produced by a two-step synthesis procedure involving the colloidal synthesis of Fe₃O₄ nanocubes with a defective shell and the posterior diffusion of nickel cations within this defective shell. Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> NPs were subsequently spin-coated over ITO-covered glass and their electrocatalytic activity toward water oxidation in carbonate electrolyte was characterized. Fe₃O₄@NiFe_<i>x</i>O_<i>y</i> catalysts reached current densities above 1 mA/cm² with a 410 mV overpotential and Tafel slopes of 48 mV/dec, which is among the best electrocatalytic performances reported in carbonate electrolyte