Uranium accumulation in environmentally relevant microplastics and agricultural soil at acidic and circumneutral pH.

The co-occurrence of microplastics (MPs) with potentially toxic metals in the environment stresses the need to address their physicochemical interactions and the potential ecological and human health implications. Here, we investigated the reaction of aqueous U with agricultural soil and high-density polyethylene (HDPE) through the integration of batch experiments, microscopy, and spectroscopy. The aqueous initial concentration of U (100 µM) decreased between 98.6 and 99.2 % at pH 5 and between 86.2 and 98.9 % at pH 7.5 following the first half hour of reaction with 10 g of soil. In similar experimental conditions but with added HDPE, aqueous U decreased between 98.6 and 99.7 % at pH 5 and between 76.1 and 95.2 % at pH 7.5, suggesting that HDPE modified the accumulation of U in soil as a function of pH. Uranium-bearing precipitates on the cracked surface of HDPE were identified by SEM/EDS after two weeks of agitation in water at both pH 5 and 7.5. Accumulation of U on the near-surface region of reacted HDPE was confirmed by XPS. Our findings suggest that the precipitation of U was facilitated by the weathering of the surface of HDPE. These results provide insights about surface-mediated reactions of aqueous metals with MPs, contributing relevant information about the mobility of metals and MPs at co-contaminated agricultural sites.

Impact of Surface Functionalization and Deposition Method on Cu-BDC surMOF Formation, Morphology, Crystallinity, and Stability.

For direct integration into device architectures, surface-anchored metal-organic framework (surMOF) thin films are attractive systems for a wide variety of electronic, photonic, sensing, and gas storage applications. This research systematically investigates the effect of deposition method and surface functionalization on the film formation of a copper paddle-wheel-based surMOF. Solution-phase layer-by-layer (LBL) immersion and LBL spray deposition methods are employed to deposit copper benzene-1,4-dicarboxylate (Cu-BDC) on gold substrates functionalized with carboxyl- and hydroxyl-terminated alkanethiol self-assembled monolayers (SAMs). A difference in crystal orientation is observed by atomic force microscopy and X-ray diffractometry based on surface functionalization for films deposited by the LBL immersion method but not for spray-deposited films. Cu-BDC crystallites with a strong preferred orientation perpendicular to the substrate were observed for the films deposited by the LBL immersion method on carboxyl-terminated SAMs. These crystals could be removed upon testing adhesive properties, whereas all other Cu-BDC surMOF film structures demonstrated excellent adhesive properties. Additionally, film stability upon exposure to water or heat was investigated. Ellipsometric data provide insight into film formation elucidating 7 and 14 Å average thicknesses per deposition cycle for films deposited by the immersion method on 11-mercapto-1-undecanol (MUD) and 16-mercaptohexadecanoic acid (MHDA), respectively. In contrast, the films deposited by the spray method are thicker with the same average thickness per deposition cycle (21 Å) for both SAMs. While the spray method takes less time to grow thicker films, it produces similar crystallite structures, regardless of the surface functionalization. This research is fundamental to understanding the impact of deposition method and surface functionalization on surMOF film growth and to provide strategies for the preparation of high-quality surMOFs.

Expanding the synthetic toolbox to access pristine and rare-earth-doped BaFBr nanocrystals.

A new synthetic route to access pristine and rare-earth-doped BaFBr nanocrystals is described. Central to this route is an organic-inorganic hybrid precursor of formula Ba5(CF2BrCOO)10(H2O)7 that serves as a dual-halogen source. Thermolysis of this precursor in a mixture of high-boiling point organic solvents yields spherical BaFBr nanocrystals (≈20 nm in diameter). Yb:Er:BaFBr nanocuboids (≈26 nm in length) are obtained following the same route. Rare-earth-doped nanocrystals display NIR-to-visible photon upconversion under 980 nm excitation. The temperature-dependence of the green emission from Er3+ may be exploited for optical temperature sensing between 150 and 450 K, achieving a sensitivity of 1.1 × 10-2 K-1 and a mean calculated temperature of 300.9 ± 1.5 K at 300 K. The synthetic route presented herein not only enables access to unexplored upconverting materials but also, and more importantly, creates the opportunity to develop solution-processable photostimulable phosphors based on BaFBr.

Bimetallic Trifluoroacetates as Precursors to Layered Perovskites A2MnF4 (A = K, Rb, and Cs).

Four novel alkali-manganese(II) trifluoroacetates were synthesized, and their potential as self-fluorinating precursors to layered perovskites A2MnF4 (A = K, Rb, and Cs) was demonstrated. Na2Mn(tfa)4, K4Mn2(tfa)8, Rb4Mn2(tfa)8·0.23H2O, and Cs3Mn2(tfa)7(tfaH) (tfa = CF3COO- and tfaH = CF3COOH) were grown as single crystals, and their crystal structures solved using X-ray diffraction. Chemically pure K4Mn2(tfa)8, Rb4Mn2(tfa)8·0.23H2O, and Cs3Mn2(tfa)7(tfaH) were also prepared in polycrystalline form as confirmed by thermal analysis and powder X-ray diffraction. Thermolysis of these powders yielded the isostructural series K2MnF4, Rb2MnF4, and Cs2MnF4 at low temperatures (≈200-300 °C). Trifluoromethyl groups belonging to the trifluoroacetato ligands served as the fluorine source, thereby eliminating the need for external fluorinating agents. K2MnF4 and Rb2MnF4 were obtained as single-phase powders, whereas Cs2MnF4 crystallized along with CsMnF3. Access to polycrystalline Cs2MnF4 coupled to Rietveld analysis enabled elucidation of the crystal structure of this ternary fluoride, which had remained elusive. Findings presented in this article expand the synthetic accessibility of polycrystalline A2MnF4 fluorides, for which a scarce number of routes is available in the literature.

Rubidium-Alkaline-Earth Trifluoroacetate Hybrids as Self-Fluorinating Single-Source Precursors to Mixed-Metal Fluorides.

Three novel bimetallic hybrid crystals featuring rubidium-alkaline-earth metal pairs and trifluoroacetato ligands were synthesized, and their utility as self-fluorinating single-source precursors to the corresponding mixed-metal fluorides was demonstrated. Rb2Mg2(tfa)6(tfaH)2·3H2O, RbCa(tfa)3, and RbSr2(tfa)5 (tfa = CF3COO-; tfaH = CF3COOH) were synthesized in both single-crystal and polycrystalline forms via solvent evaporation. Their crystal structures were solved using single-crystal X-ray diffraction (XRD), and chemical purity was confirmed using thermal analysis (TGA/DTA). Metal-oxygen-metal connectivity in Rb2Mg2(tfa)6(tfaH)2·3H2O was restricted to four-metal building blocks. In contrast, RbCa(tfa)3 and RbSr2(tfa)5 were found to be extended inorganic hybrids ( Cheetham et al. Chem. Commun. 2006 , 0 , 4780 - 4795 ) exhibiting infinite metal connectivity in three and two dimensions, respectively. Systematic analysis of the coordination modes of the trifluoroacetato ligand revealed its ability to bridge alkali and alkaline-earth metals. Rietveld analysis of powder X-ray diffraction data (PXRD) showed that thermal decomposition of Rb2Mg2(tfa)6(tfaH)2·3H2O and RbCa(tfa)3 under inert atmosphere yielded crystalline RbMgF3 and RbCaF3, respectively. This solid-state transformation occurred without the need for an external fluorinating agent because the trifluoromethyl group acted as a built-in fluorine source. Solid-state and solution thermolysis of Rb2Mg2(tfa)6(tfaH)2·3H2O provided access to the hexagonal and cubic polymorphs of the fluoroperovskite RbMgF3, respectively. Findings reported in this article highlight that bimetallic trifluoroacetates offer unique features from the standpoint of both crystal lattice topology and reactivity.

Bimetallic Trifluoroacetates as Single-Source Precursors for Alkali-Manganese Fluoroperovskites.

Alkali-manganese(II) trifluoroacetates were synthesized, and their potential as single-source precursors for the solid-state and solution-phase synthesis of AMnF3 fluoroperovskites (A = Na, K, Rb, Cs) was demonstrated. Crystals of Na2Mn2(tfa)6(tfaH), K2Mn2(tfa)6(tfaH)2·H2O, Rb2Mn2(tfa)6·H2O, and CsMn(tfa)3 (tfa = trifluoroacetato) were grown via solvent evaporation and their crystal structures solved using single-crystal X-ray diffraction (XRD). Chemical purity was confirmed using thermal analyses (TGA/DTA) and Rietveld analysis of powder XRD patterns. Thermal decomposition of Na2Mn2(tfa)6(tfaH), K2Mn2(tfa)6(tfaH)2·H2O, Rb2Mn2(tfa)6·H2O, and CsMn(tfa)3 in both the solid state and solution phase yielded crystalline, single-phase NaMnF3, KMnF3, RbMnF3, and CsMnF3 fluoroperovskites, respectively. Nanocrystals (<100 nm) and submicrocrystals (<500 nm) were obtained in a mixture of high-boiling-point organic solvents. Crystal structures of bimetallic trifluoroacetates displayed a variety of building blocks, coordination environments of the alkali atoms, and coordination modes of the trifluoroacetato ligand. Alkali-fluorine interactions ranging from chemical bonds to short contacts were observed throughout the series. The coordination flexibility of the trifluoroacetato ligand was attributed to the ability of the -CF3 groups to interact with alkali atoms over a broad range of distances. The synthetic approach described in this investigation provides a starting point to expand the library of fluorinated single-source precursors suitable for solution-phase routes to mixed-metal fluorides.