Preparation of MIL100/MIL101-alginate composite beads for selective phosphate removal from aqueous solution

Numerous studies have reported various approaches for synthesizing phosphate-capturing adsorbents to mitigate eutrophication. Despite the efforts, concerns about production cost, the complexity of synthesis steps, environmental friendliness, and applicability in industrial settings continue to be a problem. Herein, phosphate-selective composite adsorbents were prepared by incorporating alginate (Alg) with MIL100 and MIL101 to produce the MIL100/Alg and MIL101/Alg beads, where Fe³⁺ served as the crosslinker. The unsaturated coordination bond of MIL100 and MIL101 serves as a Lewis acid that can attract phosphate. The adsorption equilibrium isotherm, uptake kinetics, and effects of operating parameters were studied. The phosphate adsorption capacity of MIL100/Alg (103.3 mg P/g) and MIL101/Alg (109.5 mg P/g) outperformed their constituting components at pH 6 and 30 °C. Detailed evaluation of the adsorbent porosity using N₂ sorption reveals the formation of mesoporous structures on the Alg network upon incorporation of MIL100 and MIL101. The composite adsorbents have excellent selectivity toward anionic phosphate and can be easily regenerated. Phosphate adsorption by MIL100/Alg and MIL101/Alg was driven by electrostatic attraction and ligand exchange. Preliminary economic analysis on the synthesis of the adsorbents indicates that the composites, MIL100/Alg and MIL101/Alg, are economically viable adsorbents.

State-of-the-art progress for the selective crystallization of actinides, synthesis of actinide compounds and their functionalization

Crystallization and immobilization of actinides to form actinide compounds are of significant importance for the extraction and reutilization of nuclear waste in the nuclear industry. In this paper, the state-of-art progress in the crystallization of actinides are summarized, as well as the main functionalization of the actinide compounds, i.e., as adsorbents for heavy metal ions and organic pollutant in waste management, as (photo)catalysts for organic degradation and conversion, including degradation of organic dyes and antibiotics, dehydrogenation of N-heterocycles, CO₂ cycloaddition, selective alcohol oxidation and selective oxidation of sulfides. This review will give a comprehensive summary about the synthesis and application exploration of solid actinide crystalline salts and actinide-based metal organic frameworks in the past decades. Finally, the future perspectives and challenges are proposed in the end to give a promising direction for future investigation.

Influence of the First Coordination of Uranyl on Its Luminescence Properties: A Study of Uranyl Binitrate with N,N-Dialkyl Amide DEHiBA and Water

Uranyl binitrate complexes have a particular interest in the nuclear industry, especially in the reprocessing of spent nuclear fuel. The modified PUREX extraction process is designed to extract U(VI) in the form of UO₂(NO₃)₂(L)₂ as has been confirmed by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD), and time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements. In this study, the L ligands are two molecules of N,N-di-(ethyl-2-hexyl)isobutyramide (DEHiBA) monoamide used to bind uranyl in its first coordination sphere. DEHiBA ligands can coordinate uranyl in either trans- or cis-position with respect to the nitrate ligands, and these two conformers may coexist in solution. To use luminescence spectroscopy as a speciation technique, it is important to determine whether or not these conformers can be discriminated by their spectroscopic properties. To answer this question, the spectra of trans- and cis-UO₂(NO₃)₂(DEiBA)₂ conformers were modeled with ab initio methods and compared to the experimental time-resolved luminescence spectra on UO₂(NO₃)₂(DEHiBA)₂ systems. Moreover, the hydrated uranyl binitrate UO₂(NO₃)₂(H₂O)₂ complexes in the same trans and cis configurations were modeled to quantify the impact of organic DEHiBA on the luminescence properties.

Hydrothermal Synthesis and Structural Investigation of a Crystalline Uranyl Borosilicate

The relevance of multidimensional and porous crystalline materials to nuclear waste remediation and storage applications has motivated exploratory research focused on materials discovery of compounds, such as actinide mixed-oxoanion phases, which exhibit rich structural chemistry. The novel phase K1.8Na1.2[(UO2)BSi4O12] has been synthesized using hydrothermal methods, representing the first example of a uranyl borosilicate. The three-dimensional structure crystallizes in the orthorhombic space group Cmce with lattice parameters a = 15.5471(19) Å, b = 14.3403(17) Å, c = 11.7315(15) Å, and V = 2615.5(6) Å3, and is composed of UO6 octahedra linked by [BSi4O12]5− chains to form a [(UO2)BSi4O12]3− framework. The synthesis method, structure, results of Raman, IR, and X-ray absorption spectroscopy, and thermal stability are discussed.

A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany

Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1–2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite–metatorbernite (Cu(UO₂)₂(AsO₄)_2−x(PO₄)_x·8H₂O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO₂)₂(SiO₃OH)₂·6H₂O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO₂)₂(PO₄)₂·8H₂O) were identified. The Cu(UO₂)₂(AsO₄)_2−x(PO₄)_x·8H₂O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed.

A multi-technique elemental and microphase analysis of altered granitic rock from the Krunkelbach Valley uranium deposit, Black Forest, Southern Germany.

A quencher-free DNAzyme beacon for fluorescently sensing uranyl ions via embedding 2-aminopurine

DNAzyme-based fluorescent probes have provided valuable protocols for detecting uranium, one of the most common radioactive contaminants in the environment, with ultra-high selectivity and sensitivity. Designing novel DNAzyme beacons to update the mode of fluorescence reporting and/or quenching will continuously enhance "turn-on" sensing performance as well as promote actual application of the biological probes. In this work, we developed a novel quencher-free DNAzyme beacon by embedding fluorescent 2-aminopurine for rapid detection of uranyl ion. 2-aminopurine is able to substitute adenine and keep strong fluorescence in single-stranded DNA whereas being quenched in the hybridized double-stranded DNA by the base-stacking interaction. The combination of such trait of 2-aminopurine and cleavage reaction of DNAzyme in the presence of target co-factors possesses two main advantages for ion sensing: simplicity for avoidance of extra quencher groups and high performance because of superiority of DNAzyme essence. The experimental conditions including embedding site, pH and salt concentration of buffer solutions, and the amount ratio of enzyme strand to substrate strand used to form DNAzymes were systematically optimized to inspire the highest performance of the biological beacon. Thus, a detection limit of 9.6 nM, a wide linear range from 5 nM to 400 nM (R² = 0.997), and selectivity of more than 400 000-fold over other metal ions were achieved by the novel DNAzyme probes. The highly sensitive, selective and quencher-free DNAzyme probes accommodated a simple and cost-efficient alternative to current fluorescent counterparts, holding a great potential for further application in practical ion assay.

Detection and identification of solids, surfaces, and solutions of uranium using vibrational spectroscopy

The purpose of this review is to provide an overview of uranium speciation using vibrational spectroscopy methods including Raman and IR. Uranium is a naturally occurring, radioactive element that is utilized in the nuclear energy and national security sectors. Fundamental uranium chemistry is also an active area of investigation due to ongoing questions regarding the participation of 5f orbitals in bonding, variation in oxidation states and coordination environments, and unique chemical and physical properties. Importantly, uranium speciation affects fate and transportation in the environment, influences bioavailability and toxicity to human health, controls separation processes for nuclear waste, and impacts isotopic partitioning and geochronological dating. This review article provides a thorough discussion of the vibrational modes for U(IV), U(V), and U(VI) and applications of infrared absorption and Raman scattering spectroscopies in the identification and detection of both naturally occurring and synthetic uranium species in solid and solution states. The vibrational frequencies of the uranyl moiety, including both symmetric and asymmetric stretches are sensitive to the coordinating ligands and used to identify individual species in water, organic solvents, and ionic liquids or on the surface of materials. Additionally, vibrational spectroscopy allows for the in situ detection and real-time monitoring of chemical reactions involving uranium. Finally, techniques to enhance uranium species signals with vibrational modes are discussed to expand the application of vibrational spectroscopy to biological, environmental, inorganic, and materials scientists and engineers.

Optical and Chemical Characterization of Uranium Dioxide (UO2) and Uraninite Mineral: Calculation of the Fundamental Optical Constants

Uranium dioxide (UO₂) is a material with historical and emerging applications in numerous areas such as photonics, nuclear energy, and aerospace electronics. While often grown synthetically as single-crystal UO₂, the mineralogical form of UO₂ called uraninite is of interest as a precursor to various chemical processes involving uranium-bearing chemicals. Here, we investigate the optical and chemical properties of a series of three UO₂ specimens: synthetic single-crystal UO₂, uraninite ore of relatively high purity, and massive uraninite mineral containing numerous impurities. An optical technique called single-angle reflectance spectroscopy was used to derive the optical constants n and k of these uranium specimens by measuring the specular reflectance spectra of a polished surface across the mid- and far-infrared spectral domains (ca. 7000-50 cm^-1). X-ray diffractometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were further used to analyze the surface composition of the mineralogical forms of UO₂. Most notably, the massive uraninite mineral was observed to contain significant deposits of calcite and quartz in addition to UO₂ (as well as other metal oxides and radioactive decay products). Knowledge of the infrared optical constants for this series of uranium chemicals facilitates nondestructive, noncontact detection of UO₂ under a variety of conditions.

Identification of Uranium Minerals in Natural U-Bearing Rocks Using Infrared Reflectance Spectroscopy

The identification of minerals, including uranium-bearing species, is often a labor-intensive process using X-ray diffraction (XRD), fluorescence, or other solid-phase or wet chemical techniques. While handheld XRD and fluorescence instruments can aid in field applications, handheld infrared (IR) reflectance spectrometers can now also be used in industrial or field environments, with rapid, nondestructive identification possible via analysis of the solid's reflectance spectrum providing information not found in other techniques. In this paper, we report the use of laboratory methods that measure the IR hemispherical reflectance of solids using an integrating sphere and have applied it to the identification of mineral mixtures (i.e., rocks), with widely varying percentages of uranium mineral content. We then apply classical least squares (CLS) and multivariate curve resolution (MCR) methods to better discriminate the minerals (along with two pure uranium chemicals U₃O₈ and UO₂) against many common natural and anthropogenic background materials (e.g., silica sand, asphalt, calcite, K-feldspar) with good success. Ground truth as to mineral content was attained primarily by XRD. Identification is facile and specific, both for samples that are pure or are partially composed of uranium (e.g., boltwoodite, tyuyamunite, etc.) or non-uranium minerals. The characteristic IR bands generate unique (or class-specific) bands, typically arising from similar chemical moieties or functional groups in the minerals: uranyls, phosphates, silicates, etc. In some cases, the chemical groups that provide spectral discrimination in the longwave IR reflectance by generating upward-going (reststrahlen) bands can provide discrimination in the midwave and shortwave IR via downward-going absorption features, i.e., weaker overtone or combination bands arising from the same chemical moieties.

Spectroscopic markers for uranium(vi) phosphates. Part II: the use of time-resolved photoluminescence

3D time-resolved luminescence imaging by means of a streak camera can detect and discriminate low amounts of various uranyl minerals via concomitant analysis of spectral properties and photoluminescence lifetimes.

The crystalline α,ω-dicarboxylate metal complex with the longest aliphatic chain to date: uranyl 1,15-pentadecanedioate

A bilayer 2D network is formed in uranyl 1,15-pentadecanedioate, different from the species obtained with related ligands and bulkier counterions.