From caged compounds with isolated U atoms to frustrated magnets with 2- or 3-atom clusters: a review of Al-rich uranium aluminides with transition metals.

Crystal structures and physical properties of four families of Al-rich ternary uranium compounds with transition metals () are reviewed, namely UAl, UAl, UAl, and UAl. The compounds can be described as consisting of 1 (isolated), 2 (dumbbells) or 3 (triangles) uranium atom clusters, surrounded (1-2-20, 1-2-10 and 6-4-43) or not (3-4-12) by large cages, which strongly influence their magnetic and related properties. Indeed, the ground states of the described systems evolve from Curie-like paramagnetism in the case of the phases with well-isolated, single U-atoms, to complex magnetic order or possible frustrated magnetism in the case of the systems with uranium triangles forming a breathing kagome lattice.

Aging and reactivity assessment of nanoscale zerovalent iron in groundwater systems.

In this study, changes in the reactivity of nanoscale zerovalent iron (NZVI) in five different groundwater (GW) systems under anoxic and oxic conditions were examined over a wide range of aging time (0 - 60 d). p-nitrophenol (p-NP) was used as a redox-sensitive probe, whereas nalidixic acid (NA), a typical antibiotic found in the natural environment, was used as a sorbing compound. Investigation of the p-NP reduction in pure water systems showed that NZVI lost 41% and 98% of its reductive activity under anoxic and oxic conditions after 60 d, while enhancement of its reactivity was observed after short-term aging in GW (1 - 5 d), followed by a further decline.

Alteration of birnessite reactivity in dynamic anoxic/oxic environments.

Although the oxidative capacity of manganese oxides has been widely investigated, potential changes of the surface reactivity in dynamic anoxic/oxic environments have been often overlooked. In this study, we showed that the reactivity of layer structured manganese oxide (birnessite) was highly sensitive to variable redox conditions within environmentally relevant ranges of pH (4.0 - 8.

A Tunable Structural Family with Ultralow Thermal Conductivity: Copper-Deficient Cu□PbBiS.

Understanding the mechanism that connects heat transport with crystal structures and order/disorder phenomena is crucial to develop materials with ultralow thermal conductivity (κ), for thermoelectric and thermal barrier applications, and requires the study of highly pure materials. We synthesized the n-type sulfide CuPbBiS with an ultralow κ value of 0.6-0.

Mineralization Enhancement of Pharmaceutical Contaminants by Radical-Based Oxidation Promoted by Oxide-Bound Metal Ions.

While the use of transition metal oxides in catalyzing advanced oxidation reactions has been widely investigated, very few reports have focused on how the preliminary contact of oxides with target compounds may affect the succession of reaction. In this study, we examined the adsorption and electron transfer reactions of two fluoroquinolones, flumequine (FLU), and norfloxacin (NOR), with goethite (α-FeOOH) or manganese (Mn) oxide, and their impact on the subsequent mineralization of target compounds using HO or SO under UVA irradiation. Intriguingly, higher total organic carbon (TOC) removal was achieved when antibiotics and metal oxides were allowed for preequilibration before starting the oxidation reaction.

Importance of the Mixing and High-Temperature Heating Steps in the Controlled Thermal Coprecipitation Synthesis of Sub-5-nm Na(Gd-Yb)F:Tm.

In order to achieve a significant size reduction to get ultrasmall upconverting nanoparticles (UCNPs) following a thermal coprecipitation pathway, we identified two critical points: the UCNP precursor mixing and high-temperature heating steps. Significant differences could be observed according to the way the inorganic sodium and fluoride sources were mixed to the rare-earth oleate before the high-temperature heating step. More interestingly, accurate monitoring of the high-temperature heating step using microwave (MW) dielectric heating yielded major improvement toward ultrasmall UCNPs.

Unexpected Magnetic Ordering on the Cr Substructure in UCrSiC and Structural Relationships in Quaternary U-Cr-Si-C Compounds.

Previous experimental and theoretical studies revealed that carbon insertion into the RCrSi compounds drastically affects the magnetic behavior, since chromium does not carry any magnetic moment in RCrSiC (R = Y, La-Sm, Gd-Er) compounds in contrast to RCrSi (R = Y, Sm, Gd-Lu, Th) compounds. In this study, we report on the unexpected magnetic ordering of chromium atoms in the isotype quaternary UCrSiC compound. While specific heat and magnetic measurements suggest a Pauli paramagnetic behavior, neutron powder diffraction reveals an antiferromagnetic ordering of the chromium substructure at high temperature ( T > 300 K), while that of uranium remains nonmagnetically ordered down to 2 K.

Synthesis and structural/physical properties of U3Fe2Ge7: a single-crystal study.

A single crystal of U3Fe2Ge7 was synthesized by the tin-flux method, and its structural and electronic properties were studied. The compound crystallizes in the orthorhombic crystal structure of La3Co2Sn7 type with two Wyckoff sites for the U atoms. U3Fe2Ge7 displays a ferromagnetic order below TC = 62 K.