Over 60 years of nuclear activities have resulted in a global legacy of radioactive wastes, with uranium considered a key radionuclide in both disposal and contaminated land scenarios. With the understanding that U has been incorporated into a range of iron (oxyhydr)oxides, these minerals may be considered a secondary barrier to the migration of radionuclides in the environment. However, the long-term stability of U-incorporated iron (oxyhydr)oxides is largely unknown, with the end-fate of incorporated species potentially impacted by biogeochemical processes. In particular, studies show that significant electron transfer may occur between stable iron (oxyhydr)oxides such as goethite and adsorbed Fe(II). These interactions can also induce varying degrees of iron (oxyhydr)oxide recrystallization (<4% to >90%). Here, the fate of U(VI)-incorporated goethite during exposure to Fe(II) was investigated using geochemical analysis and X-ray absorption spectroscopy (XAS). Analysis of XAS spectra revealed that incorporated U(VI) was reduced to U(V) as the reaction with Fe(II) progressed, with minimal recrystallization (approximately 2%) of the goethite phase. These results therefore indicate that U may remain incorporated within goethite as U(V) even under iron-reducing conditions. This develops the concept of iron (oxyhydr)oxides acting as a secondary barrier to radionuclide migration in the environment.

Hematite nanoparticles were synthesized with U(VI) in circumneutral water through a coprecipitation and hydrothermal treatment process. XRD, TEM, and EXAFS analyses reveal that uranium may aggregate along grain boundaries and occupy Fe sites within hematite. The described synthesis method produces crystalline, single-phase iron oxide nanoparticles absent of surface-bound uranyl complexes. EXAFS data were comparable to spectra from existing studies whose syntheses were more representative of natu-rally occurring, extended aging processes. This work provides and validates an accelerated method of synthesizing uranium-immobilized iron oxide nanoparticles for further mechanistic studies. High tem-perature oxide melt solution calorimetry measurements were performed to calculate the thermodynamic stability of uranium-incorporated iron oxide nanoparticles. Increasing uranium content within hematite resulted in more positive formation enthalpies. Standard formation enthalpies of UxFe(2-2x)O(3) were as high as 76.88 +/- 2.83 kJ/mol relative to their binary oxides, or -764.04 +/- 3.74 kJ/mol relative to their con-stituent elements, at x = 0.037. Data on the thermodynamic stability of uranium retention pathways may assist in predicting waste uranyl remobilization, as well as in developing more effective methods to retain uranium captured from aqueous environments. (C) 2021 Elsevier B.V. All rights reserved.

Over 60 years of nuclear activities have resulted in a global legacy of radioactive waste and contaminated land. Higher activity wastes are destined for disposal in a deep underground geological facility (GDF), with iron (oxyhydr)oxide phases expected to be ubiquitous in and around the repository. Additionally, uranium will be a significant radionuclide in many of these wastes. Given that a range of uranium-incorporated iron (oxyhydr)oxides have been reported in the literature, these mineral phases may be considered a secondary barrier to the migration of uranium in the environment. However, the long-term stability of these phases under fluctuating geochemical conditions is unknown. Stable iron oxyhydroxides (e.g. goethite) have undergone extensive recrystallisation (>90%) during Fe-atom exchange, with incorporated species released and/or reduced during the recrystallisation process. Here, the stability and fate of uranium-incorporated goethite during Fe-atom exchange was investigated. A U(VI)-goethite species was hydrothermally synthesized and reacted with aqueous Fe(II). The system was monitored using geochemical analysis and X-ray absorption spectroscopy (XAS), with an aqueous 57 Fe(II) tracer used to track the extent of Fe-atom exchange. This revealed that only ~2% of structural Fe(III) was exchanged with aqueous Fe(II), with the retention of incorporated U confirmed by acid digestions. Despite this, M IV -edge HR XANES and L III -edge EXAFS revealed an ingress of near-surface U(V) as the Fe-atom

State-of-the-art high temperature oxide melt solution calorimetry and density functional theory were employed to produce the first systematic study of thermodynamic stability in a series of binary and ternary Chevrel phases. Rapid microwave-assisted solid-state heating methods facilitated the nucleation of pure-phase polycrystalline MyMo6S8 (M = Fe, Ni, Cu; y = 0, 1, 2) Chevrel phases, and a stability trend was observed wherein intercalation of M y species engenders stability that depends on both the electropositivity and ionic radii of the intercalant species. Ab initio calculations indicate that this stability trend results from competing ionic and covalent contributions, where transition metal intercalation stabilizes the Chevrel structure through increased ionicity but destabilizes the structure through reduced covalency of the Mo6S8 clusters. Our calculations predicted that over intercalation of high-valent M-y, species leads to slight destabilization of the Mo-6 octahedral cores, which we confirm using calorimetry and X-ray absorption spectroscopy. Our combined computational and calorimetric analysis reveals the interplay of the foundational principles of ionic and covalent bonding characteristics that govern the thermodynamic stability of Chevrel and other inorganic phases.

Recently, the causative agents of Maternal Autoantibody-Related (MAR) autism, pathological autoantibodies and their epitopic targets (e.g. lactate dehydrogenase B [LDH B] peptide), have been identified. Herein, we report on the development of Systems for Nanoparticle-based Autoantibody Reception and Entrapment (SNAREs), which we hypothesized could scavenge disease-propagating MAR autoantibodies from the maternal blood. To demonstrate this functionality, we synthesized 15 nm dextran iron oxide nanoparticles surface-modified with citric acid, methoxy PEG(10 kDa) amine, and LDH B peptide (33.8 μg peptide/cm2). In vitro, we demonstrated significantly lower macrophage uptake for SNAREs compared to control NPs. The hallmark result of this study was the efficacy of the SNAREs to remove 90% of LDH B autoantibody from patient-derived serum. Further, in vitro cytotoxicity testing and a maximal tolerated dose study in mice demonstrated the safety of the SNARE formulation. This work establishes the feasibility of SNAREs as the first-ever prophylactic against MAR autism.