Exploring actinide materials through synchrotron radiation techniques

Repurposing of steel rolling sludge: Solvent-free preparation of α-Fe2O3 nanoparticles and its application for As(III/V)-containing wastewater treatment

Steel rolling sludge (SRS) is the by-product of metallurgical industry with abundant iron content, which needs to be utilized for producing high value-added products. Herein, cost-effective and highly adsorbent α-Fe₂O₃ nanoparticles were prepared from SRS via a novel solvent-free method and applied to treat As(III/V)-containing wastewater. The structure of the prepared nanoparticles was observed to be spherical with a small crystal size (12.58 nm) and high specific surface area (145.03 m²/g). The nucleation mechanism of α-Fe₂O₃ nanoparticles and the effect of crystal water were investigated. More importantly, compared with the traditional methods of preparation cost and yield, this study was found to have excellent economic benefits. The adsorption results indicated that the adsorbent could effectively remove arsenic over a wide pH range, and the optimal performance of nano adsorbent for As(III) and As(V) removal was observed at pH 4.0-9.0 and 2.0-4.0, respectively. The adsorption process was consistent with pseudo-second-order kinetic and Langmuir isothermal model. The maximum adsorption capacity (q_m) of adsorbent for As(III) and As(V) was 75.67 mg/g and 56.07 mg/g, respectively. Furthermore, α-Fe₂O₃ nanoparticles exhibited great stability, and q_m remained at 64.43 mg/g and 42.39 mg/g after five cycles. Particularly, the As(III) was removed by forming inner-sphere complexes with the adsorbent, and it partially oxidized to As(V) during this process. In contrast, the As(V) was removed by electrostatic adsorption and reaction with -OH on the adsorbent surface. Overall, resource utilization of SRS and the treatment of As(III)/(V)-containing wastewater in this study are in line with the current developments in the environmental and waste-to-value research.

Synthesis and multi-scale properties of PuO2 nanoparticles: recent advances and open questions

Due to the increased attention given to actinide nanomaterials, the question of their structure-property relationship is on the spotlight of recent publications. Plutonium oxide (PuO₂) particularly plays a central role in nuclear energetics and a comprehensive knowledge about its properties when nanosizing is of paramount interest to understand its behaviour in environmental migration schemes but also for the development of advanced nuclear energy systems underway. The element plutonium further stimulates the curiosity of scientists due to the unique physical and chemical properties it exhibits around the periodic table. PuO₂ crystallizes in the fluorite structure of the face-centered cubic system for which the properties can be significantly affected when shrinking. Identifying the formation mechanism of PuO₂ nanoparticles, their related atomic, electronic and crystalline structures, and their reactivity in addition to their nanoscale properties, appears to be a fascinating and challenging ongoing topic, whose recent advances are discussed in this review.

Induced Ferromagnetism in Epitaxial Uranium Dioxide Thin Films

Actinide materials have various applications that range from nuclear energy to quantum computing. Most current efforts have focused on bulk actinide materials. Tuning functional properties by using strain engineering in epitaxial thin films is largely lacking. Using uranium dioxide (UO₂ ) as a model system, in this work, the authors explore strain engineering in actinide epitaxial thin films and investigate the origin of induced ferromagnetism in an antiferromagnet UO₂ . It is found that UO_{2+ x} thin films are hypostoichiometric (x<0) with in-plane tensile strain, while they are hyperstoichiometric (x>0) with in-plane compressive strain. Different from strain engineering in non-actinide oxide thin films, the epitaxial strain in UO₂ is accommodated by point defects such as vacancies and interstitials due to the low formation energy. Both epitaxial strain and strain relaxation induced point defects such as oxygen/uranium vacancies and oxygen/uranium interstitials can distort magnetic structure and result in magnetic moments. This work reveals the correlation among strain, point defects and ferromagnetism in strain engineered UO_{2+ x} thin films and the results offer new opportunities to understand the influence of coupled order parameters on the emergent properties of many other actinide thin films.

Thermal Energy Transport in Oxide Nuclear Fuel

To efficiently capture the energy of the nuclear bond, advanced nuclear reactor concepts seek solid fuels that must withstand unprecedented temperature and radiation extremes. In these advanced fuels, thermal energy transport under irradiation is directly related to reactor performance as well as reactor safety. The science of thermal transport in nuclear fuel is a grand challenge as a result of both computational and experimental complexities. Here we provide a comprehensive review of thermal transport research on two actinide oxides: one currently in use in commercial nuclear reactors, uranium dioxide (UO₂), and one advanced fuel candidate material, thorium dioxide (ThO₂). In both materials, heat is carried by lattice waves or phonons. Crystalline defects caused by fission events effectively scatter phonons and lead to a degradation in fuel performance over time. Bolstered by new computational and experimental tools, researchers are now developing the foundational work necessary to accurately model and ultimately control thermal transport in advanced nuclear fuels. We begin by reviewing research aimed at understanding thermal transport in perfect single crystals. The absence of defects enables studies that focus on the fundamental aspects of phonon transport. Next, we review research that targets defect generation and evolution. Here the focus is on ion irradiation studies used as surrogates for damage caused by fission products. We end this review with a discussion of modeling and experimental efforts directed at predicting and validating mesoscale thermal transport in the presence of irradiation defects. While efforts in these research areas have been robust, challenging work remains in developing holistic tools to capture and predict thermal energy transport across widely varying environmental conditions.

Experimental and first-principle computational exploration on biomass cellulose/magnesium hydroxide composite: Local structure, interfacial interaction and antibacterial property

The specification of the local structure and clarification of interfacial interactions of biomass composites is of tremendous significance in synthesizing novel materials and advancing their performance in various demanding applications. However, it remains challenging due to the limitations of experimental techniques, particularly for the manner that biomass composites commonly have hydrogen bonds involved in the vicinity of active sites and interfaces. Herein, the cellulose/Mg(OH)₂ nanocomposite has been synthesized via a simple hydrothermal approach and examined by density functional theory (DFT) calculations. The composite exhibits a layered morphology; Mg(OH)₂ flakes are around 50 nm in size and well-dispersed. They either anchor onto the cellulose surface or intercalate between layers. The specific composite structure was confirmed theoretically, in line with XRD, SEM and TEM observations. The interfacial interactions were found to be hydrogen bonding. The average adsorption energy per hydroxyl group was computed to be within -0.47 and -0.26 eV for a composite model comprising three cellulose chains and a two-layered Mg(OH)₂ cluster. The combined computational/experimental results allow to postulate the antibacterial mechanism of the nanocomposite.

Thorium(IV) adsorption onto multilayered Ti3C2Tx MXene: a batch, X-ray diffraction and EXAFS combined study

The interlayer regulation of layered environmental adsorption materials such as two-dimensional early transition metal carbides and carbonitrides (MXenes) plays an important role in their purification performance for specific pollutants. Here the enhanced uptake of Th^IV by multilayered titanium carbides (Ti₃C₂T_x) through a hydrated intercalation strategy is reported. Th^IV adsorption behaviors of three Ti₃C₂T_x samples with different c lattice parameters were studied as a function of contact time, pH, initial concentration, temperature and ion strength in batch experiments. The results indicated that the Th^IV uptake was pH and ionic strength dependent, and the adsorption process followed the pseudo-second-order kinetics and the heterogeneous isotherm (Freundlich) model. Thermodynamic data suggested that the adsorption process of all MXene samples was a spontaneous endothermic reaction. The dimethyl sulfoxide intercalated hydrated Ti₃C₂T_x featured the largest interlayer space and exhibited the highest Th^IV adsorption capacity (162 mg g^-1 at pH 3.4 or 112 mg g^-1 at pH 3.0), reflecting the significant increase in available adsorption sites from Ti₃C₂T_x interlayers. The adsorption mechanism has been clarified based on adsorption experiments and spectroscopic characterizations. An ion exchange process was proposed for the interaction between hydrated MXenes and Th^IV, where H⁺ from surface [Ti-O]^-H⁺ groups were the primary active sites on Ti₃C₂T_x. Extended X-ray absorption fine structure (EXAFS) fitting results, in combination with X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses, clearly indicated that Th^IV mainly formed the outer-sphere complexes on Ti₃C₂T_x surface through electrostatic interaction under strong acid conditions, while at pH > 3.0 the adsorption mechanism was determined by inner-sphere coordination and electrostatic interaction together.

A spectroscopic hike in the U-O phase diagram

The U-O phase diagram is of paramount interest for nuclear-related applications and has therefore been extensively studied. Experimental data have been gathered to feed the thermodynamic calculations and achieve an optimization of the U-O system modelling. Although considered as well established, a critical assessment of this large body of experimental data is necessary, especially in light of the recent development of new techniques applicable to actinide materials. Here we show how in situ X-ray absorption near-edge structure (XANES) is suitable and relevant for phase diagram determination. New experimental data points have been collected using this method and discussed in regard to the available data. Comparing our experimental data with thermodynamic calculations, we observe that the current version of the U-O phase diagram misses some experimental data in specific domains. This lack of experimental data generates inaccuracy in the model, which can be overcome using in situ XANES. Indeed, as shown in the paper, this method is suitable for collecting experimental data in non-ambient conditions and for multiphasic systems.

2D-layered Mg(OH)2 material adsorbing cellobiose via interfacial chemical coupling and its applications in handling toxic Cd2+ and UO22+ ions

The interfacial chemistry of nanocomposite materials is of overarching importance in the separation and purification science; moreover, its understanding helps to guide synthesis, clarify structure-property relationship and unearth novel applications. However, the composites feature rather complicated local structures and hydrogen bonds are often involved in the interface and the vicinity of active sites. In this regard, density functional theory first-principle calculations associated with experimental study have synergistically examined two-dimensional (2D) magnesium hydroxide material with different layers and their adsorption toward cellobiose. Hydrogen bonds are found responsible for the interfacial coupling, which make it vital to cover the dispersion correction in the calculation. The average adsorption energy ranges from -0.29 to -0.35 eV, falling well within the range of reported hydrogen-bonding strength. On the basis of calculated structural/interfacial properties and experimental findings, the 2D Mg(OH)₂ in terms of three-layer model was unraveled to substitute toxic Cd²⁺ ion and sorb radioactive UO₂²⁺ that is coordinated by water and hydroxyl groups. These reactions are thermodynamically feasible. The ion-exchanging mechanism was proposed for cadmium removal and the outer-sphere adsorption one for uranium extraction.

Facile fabrication of metakaolin/slag-based zeolite microspheres (M/SZMs) geopolymer for the efficient remediation of Cs+ and Sr2+ from aqueous media

Herein we report the fabrication of metakaolin/slag-based geopolymer microspheres by dispersion-suspension-solidification technology, and were then transformed into zeolite microspheres by in-situ thermal curing. The rheological properties and mechanical strength of metakaolin/slag-based zeolite microspheres (M/SZMs) were improved by adding slag. The zeolite microspheres were texturally and morphologically characterized by BET, SEM-EDX and XRD techniques. At 20% slag contents of the total mass of M/SZMs, the specific surface area was significantly increased without changing the structure of the zeolite. Rheological properties analysis of slurry revealed pseudoplastic fluid phase and fitted well to Herschel-Bulkley model. The adsorptive removal data of M/SZMs for Cs⁺ and Sr²⁺ from wastewater followed pseudo-second-order kinetics. The maximum adsorption capacity of M/SZMs for Cs⁺ and Sr²⁺ was 103.74 mg/g and 54.90 mg/g and were best explained by Freundlich and Langmuir isotherm models, respectively. M/SZMs exhibited excellent dynamic separation effect in column-based experimental set up. In addition, M/SZMs also realized outstanding adsorptive removal performance for Cs⁺ and Sr²⁺ from different real wastewater samples. Owing to the simplistic fabrication approach, low cost and highly efficacious nature, M/SZMs can be ranked as alternative candidates for the abatement of Cs⁺ and Sr²⁺ from wastewater.

Probing electronic structure in berkelium and californium via an electron microscopy nanosampling approach

Due to their rarity and radioactive nature, comparatively little is known about the actinides, particularly those with atomic numbers higher than that of plutonium, and their compounds. In this work, we describe how transmission electron microscopy can provide comprehensive, safe, and cost-effective characterization using only single nanogram amounts of highly-radioactive, solid compounds. Chlorides of the rare elements berkelium and californium are dropcast and then converted in situ to oxides using the electron beam. The f-band occupancies are probed using electron energy loss spectroscopy and an unexpectedly weak spin-orbit-coupling is identified for berkelium. In contrast, californium follows a jj coupling scheme. These results have important implications for the chemistries of these elements and solidify the status of californium as a transitional element in the actinide series.

The obtention and study of actinide elements is challenging due to various factors including their radioactivity and scarcity. Herein, the authors characterize the atomic and electronic structure of Am, Cm, Bk, and Cf compounds using a transmission electron microscopy-based workflow that only requires nanogram amounts of the actinide element.

The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO2

The structural characterisation of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non-homogeneous samples with NPs less than 3 nm. By combining high-energy X-ray scattering (HEXS) and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD XANES) analysis, we have characterised for the first time both the short- and medium-range order of ThO2 NPs obtained by chemical precipitation. By using this methodology, a novel insight into the structures of NPs at different stages of their formation has been achieved. The pair distribution function revealed a high concentration of ThO2 small units similar to thorium hexamer clusters mixed with 1 nm ThO2 NPs in the initial steps of formation. Drying the precipitates at around 150 °C promoted the recrystallisation of the smallest units into more thermodynamically stable ThO2 NPs. HERFD XANES analysis at the thorium M4 edge, a direct probe for f states, showed variations that we have correlated with the breakdown of the local symmetry around the thorium atoms, which most likely concerns surface atoms. Together, HEXS and HERFD XANES are a powerful methodology for investigating actinide NPs and their formation mechanism.

Mussel-inspired anti-biofouling and robust hybrid nanocomposite hydrogel for uranium extraction from seawater

A major challenge of uranium extraction from seawater (UES) is to effectively block the biofouling without destroying the ecological balance, especially prevent the attachment of macroalgae on the surface of the adsorbent. Herein, a robust montmorillonite-polydopamine/polyacrylamide nanocomposite hydrogel is reported by a two-step method, including PDA intercalation MMT and further free radical polymerization with AM monomers. The interpenetrating structure of hydrogel lead to high water permeability with the swelling ratio of 51, which could fully facilitate the internal accessible sites exposure and increase the uranium diffusion. As a result, a high adsorption capacity of 44 mg g^-1 was achieved in lab-scale dynamic adsorption. Most importantly, the prepared anti-biofouling hydrogel adsorbents display excellent anti-adhesion ability towards Nitzschia after 8 days contact. The adsorption capacity of uranium can reach 2130 μg g^-1 in algae-contained simulated seawater. This hydrogel also exhibited a long service life of acceptable mechanical strength and adsorption capacity after at least 6 adsorption-desorption cycles. This new anti-biofouling nanocomposite hydrogel shows great potential as a new generation adsorbent for UES.

Redox and structural properties of accessible actinide(ii) metallocalixarenes (Ac to Pu): a relativistic DFT study

The redox properties of actinides play a significant role in manipulating organometallic chemistry and energy/environment science, for being involved in fundamental concepts (oxidation state, bonding and reactivity), nuclear fuel cycles and contamination remediation. Herein, a series of trans-calix[2]pyrrole[2]benzene (H₂L²) actinide complexes (An = Ac–Pu, and oxidation states of +II and +III) have been studied by relativistic density functional theory. Reduction potentials (E⁰) of [AnL²]⁺/[AnL²] were computed within −2.45 and −1.64 V versus Fc⁺/Fc in THF, comparable to experimental values of −2.50 V for [UL^1e]/[UL^1e]⁻ (H₃L^1e = (^Ad,MeArOH)₃mesitylene and Ad = adamantyl) and −2.35 V for [U(Cp^iPr)₂]⁺/[U(Cp^iPr)₂] (Cp^iPr = C₅ⁱPr₅). The E⁰ values show an overall increasing trend from Ac to Pu but a break point at Np being lower than adjacent elements. The arene/actinide mixed reduction mechanism is proposed, showing arenes predominant in Ac–Pa complexes but diverting to metal-centered domination in U–Pu ones. Besides being consistent with previously reported those of An^III/An^II couples, the changing trend of our reduction potentials is corroborated by geometric data, topological analysis of bonds and electronic structures as well as additional calculations on actinide complexes ligated by tris(alkyloxide)arene, silyl-cyclopentadiene and octadentate Schiff-base polypyrrole in terms of electron affinity. The regularity would help to explore synthesis and property of novel actinide(ii) complex.

DFT study reveals the trend of reduction potential of [AnL²]⁺/[AnL²] (An = Ac ∼ Pu), comparable to previously reported ones of An^III/An^II and corroborated by calculations of relevant complexes and structural/bonding properties of [AnL²]^+/0.

A mail-in and user facility for X-ray absorption near-edge structure: the CEI-XANES laboratory X-ray spectrometer at the University of Washington

There are more than 100 beamlines or endstations worldwide that frequently support X-ray absorption fine-structure (XAFS) measurements, thus providing critical enabling capability for research across numerous scientific disciplines. However, the absence of a supporting tier of more readily accessible, lower-performing options has caused systemic inefficiencies, resulting in high oversubscription and the omission of many scientifically and socially valuable XAFS applications that are incompatible with the synchrotron facility access model. To this end, this work describes the design, performance and uses of the Clean Energy Institute X-ray absorption near-edge structure (CEI-XANES) laboratory spectrometer and its use as both a user-present and mail-in facility. Such new additions to the XAFS infrastructure landscape raise important questions about the most productive interactions between synchrotron radiation and laboratory-based capabilities; this can be discussed in the framework of five categories, only one of which is competitive. The categories include independent operation on independent problems, use dictated by convenience, pre-synchrotron preparatory use of laboratory capability, post-synchrotron follow-up use of laboratory capability, and parallel use of both synchrotron radiation and laboratory systems.

Inverse Trans Influence in Low-Valence Actinide-Group 10 Metal Complexes of Phosphinoaryl Oxides: A Theoretical Study via Tuning Metals and Donor Ligands

The recognition and in-depth understanding of inverse trans influence (ITI) have successfully guided the synthesis of novel actinide complexes and enriched actinide chemistry. Those complexes, however, are mainly limited to the involvement of high-valence actinide and/or metal-ligand multiple bonds. Examples containing both low oxidation state actinide and metal-metal single bond remain rare. Herein, more than 20 actinide-transition metal (An-TM) complexes of phosphinoaryl oxide ligands have been designed in accordance with several experimentally known analogs, by changing the metal atoms (An = Th, Pa, U, Np, and Pu; and TM = Ni, Pd, and Pt), actinide oxidation states (IV and III) and metal-metal axial donor ligands (X = Me₃SiO, F, Cl, Br, and I). The relativistic density functional theory study of structural (trans-An-X and cis-An-O toward An-TM), bonding (topological electron/energy density), and electronic properties reveals the order of the ITI stabilizing actinide-metal bond. Computed electron affinity (EA) values, related to the electrochemical reduction, linearly correlate with experimentally measured reduction potentials. Although the same ITI order for the ligand donors was shown as in a previous study, the correlation between electrochemical reduction and the ITI was found to be weak when the actinide atoms were changed. For most complexes, the reduction is primarily of an actinide-based mechanism with minor participation of transition metal and phosphinoaryl oxide, whereas that of thorium-nickel complexes is different.

Adsorption of Eu(III) and Th(IV) on three-dimensional graphene-based macrostructure studied by spectroscopic investigation

One of the most important reasons for the controversy over the development of nuclear energy is the proper disposal of spent fuel. Separation of actinide and lanthanide ions is an important part of safe long-term storage of radioactive waste. Herein, a three-dimensional (3D) graphene-based macrostructure (GOCS) was utilized to remove actinide thorium and lanthanide europium ions from aqueous solutions. The adsorption of Eu(III) and Th(IV) on the GOCS was evaluated as a function of adsorption time, solution pH, initial ion concentrations, and ionic strength. The experimentally determined maximum adsorption capacities of this GOCS for Eu(III) (pH 6.0) and Th(IV) (pH 3.0) are as high as 150 and 220 mg/g, respectively. By using Fourier transformation infrared (FT-IR), X-ray photoelectron (XPS), and extended X-ray absorption fine structure (EXAFS) spectroscopy, we concluded that the Eu(III) and Th(IV) adsorption was predominantly attributed to the inner-sphere coordination with various oxygen- and nitrogen-containing functional groups on GOCS surfaces. Our selective adsorption results demonstrate that the actinide and lanthanide ions can be effectively separated from transition metal ions. This study provides new clues to the overall recycling of actinide and lanthanide ions in radioactive environmental pollution treatments.

Removal of U(VI) from aqueous solution using phosphate functionalized bacterial cellulose as efficient adsorbent

In this study, phosphate functionalized bacterial cellulose with micro-fibrous structure was prepared, characterized and applied for U(VI) adsorption. The successful grafting of phosphoric functional groups was proved by the FTIR spectra and EDS analysis (P~4.15 wt%), and the porous structure was confirmed by SEM and BET analyses. Furthermore, the effect of initial pH, contact time, initial concentration, and temperature were studied. The as-prepared adsorbent showed a high adsorption capacity at wide pH range (4.0–8.0) and its maximum adsorption capacity was calculated to be 50.65 mg/g. This endothermic adsorption process conformed to the pseudo second-order kinetic model and the Elovich kinetic models and the Langmuir isothermal models. According to the FTIR and XPS analysis, an adsorption mechanism was tentatively proposed, mainly due to the interaction between U(VI) and phosphoric groups.

Hollow cobalt sulfide for highly efficient uranium adsorption from aqueous solutions

The preparation of hollow Co₃S₄nanostructures by ZIF-67 guarantees high uranium adsorption performance in aqueous solutions.

Rational design of carbonaceous nanofiber/Ni-Al layered double hydroxide nanocomposites for high-efficiency removal of heavy metals from aqueous solutions

Heavy metal pollution of water sources has raised global environmental sustainability concerns, calling for the development of high-performance materials for effective pollution treatment. Herein, we report a facile approach to synthesize carbonaceous nanofiber/NiAl layered double hydroxide (CNF/LDH) nanocomposites for high-efficiency elimination of heavy metals from aqueous solutions. The CNF/LDH nanocomposites were characterized by three-dimensional architectures formed by the gradual self-assembly of flower-like LDH on CNF. The nanocomposites exhibited excellent hydrophilicity and high structural stability in aqueous solutions, guaranteeing the high availability of active sites in these environments. High-efficiency elimination of heavy metal ions by the CNF/LDH nanocomposites was demonstrated by the high uptake capacities of Cu(II) (219.6 mg/g) and Cr(VI) (341.2 mg/g). The sorption isotherms coincided with the Freundlich model, most likely because of the presence of heterogeneous binding sites. The dominant interaction mechanisms consisted of surface complexation and electrostatic interaction, as verified by a combination of X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy analyses and density functional theory calculations. The results presented herein confirm the importance of CNF/LDH nanocomposites as emerging and promising materials for the efficient removal of heavy metal ions and other environmental pollutants.

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.

A novel magnetite nanorod-decorated Si-Schiff base complex for efficient immobilization of U(vi) and Pb(ii) from water solutions

A novel silicon Schiff base complex (Si-SBC) and magnetite nanorod-decorated Si-SBC (M/SiO2-Si-SBC) were synthesized and well characterized in detail. The synthesized materials were applied for the removal of U(vi) and Pb(ii) from water solutions under various experimental conditions. The monolayer maximum adsorption capacities of M/SiO2-Si-SBC (6.45 × 10-4 mol g-1 for Pb(ii) and 4.82 × 10-4 mol g-1 for U(vi)) obtained from the Langmuir model at 25 °C and pH = 5.00 ± 0.05 were higher than those of Si-SBC (5.18 × 10-4 mol g-1 for Pb(ii) and 3.70 × 10-4 mol g-1 for U(vi)). Moreover, DFT calculations showed that the high adsorption energies (Ead) of 7.61 kcal mol-1 for Pb2+-(Si-SBC) and 2.72 kcal mol-1 for UO22+-(Si-SBC) are mainly attributed to stronger electrostatic interactions. The results revealed that the Si-SBC and M/SiO2-Si-SBC could be used as efficient adsorbents for the effective elimination of U(vi) and Pb(ii) from contaminated wastewater. High sorption capacity and reusability indicated the practical applications of the synthesized materials in environmental pollution cleanup.

Rationally designed core-shell and yolk-shell magnetic titanate nanosheets for efficient U(VI) adsorption performance

The hierarchical core-shell and yolk-shell magnetic titanate nanosheets (Fe₃O₄@TNS) were successfully synthesized by employing magnetic nanoparticles (NPs) as interior core and intercrossed titanate nanostructures (NSs) as exterior shell. The as-prepared magnetic Fe₃O₄@TNS nanosheets had high specific areas (114.9 m² g^-1 for core-shell Fe₃O₄@TNS and 130.1 m² g^-1 for yolk-shell Fe₃O₄@TNS). Taking advantage of the unique multilayer structure, the nanosheets were suitable for eliminating U(VI) from polluted water environment. The sorption was strongly affected by pH values and weakly influenced by ionic strength, suggesting that the sorption of U(VI) on Fe₃O₄@TNS was mainly dominated by ion exchange and outer-sphere surface complexion. The maximum sorption capacities (Q_max) calculated from the Langmuir model were 68.59, 121.36 and 264.55 mg g^-1 for core-shell Fe₃O₄@TNS and 82.85, 173.01 and 283.29 mg g^-1 for yolk-shell Fe₃O₄@TNS, at 298 K, 313 K and 328 K, respectively. Thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) demonstrated that the sorption process was endothermic and spontaneous. Based on X-ray photoelectron spectroscopy (XPS) analyses, the sorption mechanism was confirmed to be cation-exchange between interlayered Na⁺ and UO₂²⁺. The yolk-shell Fe₃O₄@TNS had more extraordinary sorption efficiency than core-shell Fe₃O₄@TNS since the yolk-shell structure provided internal void space inside the titanate shell to accommodate more exchangeable active sites. The flexible recollection and high efficient sorption capacity made core-shell and yolk-shell Fe₃O₄@TNS nanosheets promising materials to eliminate U(VI) or other actinides in wastewater cleanup applications.

Macroscopic and microscopic investigation of uranium elimination by Ca–Mg–Al-layered double hydroxide supported nanoscale zero valent iron

Ca–Mg–Al-LDH/nZVI nanocomposites showed excellent U(vi) removal performance from aqueous solutions through the coordination of reduction and adsorption reactions.

Highly efficient Pb(ii) and Cu(ii) removal using hollow Fe3O4@PDA nanoparticles with excellent application capability and reusability

The easily synthesized Fe₃O₄@PDA material showed excellent performance for Pb(ii) and Cu(ii) elimination from wastewater, and its adsorption mechanism was revealed.

Abnormal Pressure-Induced Photoluminescence Enhancement and Phase Decomposition in Pyrochlore La2 Sn2 O7

La₂ Sn₂ O₇ is a transparent conducting oxide (TCO) material and shows a strong near-infrared fluorescent at ambient pressure and room temperature. By in situ high-pressure research, pressure-induced visible photoluminescence (PL) above 2 GPa near 2 eV is observed. The emergence of unusual visible PL behavior is associated with the seriously trigonal lattice distortion of the SnO₆ octehedra, under which the Sn-O1-Sn exchange angle θ is decreased below 22.1 GPa, thus enhancing the PL quantum yield leading to Sn ³ P₁ → ¹ S₀ photons transition. Besides, bandgap closing followed by bandgap opening and the visible PL appearing at the point of the gap reversal, which is consistent with high-pressure phase decomposition, are discovered. The high-pressure PL results demonstrate a well-defined pressure window (7-17 GPa) with flat maximum PL yielding and sharp edges at both ends, which may provide a great calibration tool for pressure sensors for operation in the deep sea or at extreme conditions.

Extraction of local coordination structure in a low-concentration uranyl system by XANES

Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoretical L3-edge X-ray absorption near-edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE1 = 168.3/R(U-Oax)(2) - 38.5 (for the axial plane) and ΔE2 = 428.4/R(U-Oeq)(2) - 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the U L3-edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X-ray absorption fine-structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl-ligand complexes, such as the uranyl-carbonate complex. Most importantly, the XANES research method could be extended to low-concentration uranyl systems, as indicated by the results of the uranyl-amidoximate complex (∼40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides.

Synthesis of a novel organic-inorganic hybrid of polyaniline/titanium phosphate for Re(VII) removal

The organic-inorganic hybrid material of polyaniline/titanium(IV) (PANI/Ti(HPO4)2) was synthesized by an oxidative polymerization reaction. The PANI/Ti(HPO4)2 was applied to remove Re(VII). The size of Ti(HPO4)2 nanoplates has no obvious effect on the sorption capacity. The effects of various environmental factors (such as pH, extra anions (NO3(-) and MO4(2-)) and temperature) on Re(VII) sorption to PANI/Ti(HPO4)2 were investigated by batch experiments. The sorption kinetics followed a pseudo-second-order model. The nitrogen-containing functional groups of PANI promoted Re(VII) sorption. The PANI/Ti(HPO4)2 exhibited excellent maximum sorption capacity to Re(VII) (47.62 mg g(-1)), which was superior to that of PANI (10.75 mg g(-1)) and much higher than that of many other sorbents. The sorption isotherms of Re(VII) can be well fitted with the Langmuir model. Re(VII) sorption decreased with increasing solution pH at pH > 4.0, which implied that Re(VII) sorption on PANI/Ti(HPO4)2 might be attributed to the outer-sphere complexation between amine and imine groups on the surface of PANI/Ti(HPO4)2 and Re(VII). This study implies that the hybrid material of PANI/Ti(HPO4)2 can be regarded as a potential sorbent to remove Re(VII) and its analogues from large volumes of aqueous solutions.

Comparison of U(VI) adsorption onto nanoscale zero-valent iron and red soil in the presence of U(VI)-CO3/Ca-U(VI)-CO3 complexes

The influence of U(VI)-CO3 and Ca-U(VI)-CO3 complexes on U(VI) adsorption onto red soil and nanoscale zero-valent iron (NZVI) was investigated using batch adsorption and fixed-bed column experiments to simulate the feasibility of NZVI as the reactive medium in permeable- reactive barriers (PRB) for in situ remediation of uranium-contaminated red soils. The adsorption capacity (qe) and distribution constant (Kd) of NZVI and red soil decreased with increasing pH, dissolved carbonate and calcium concentrations, but the qe and Kd values of NZVI were 5-10 times higher than those of red soil. The breakthrough pore volume (PV) values increased with the decrease of pH, dissolved carbonate and calcium concentration; however, the breakthrough PV values of the PRB column filled with 5% NZVI were 2.0-3.5 times higher than the 100% red soil column. The U(VI)-CO3 complexes adsorbed onto the surface of red soil/NZVI (≡SOH) to form SO-UO2CO3(-) or SO-UO2 (CO3)2(3-). XPS and XRD analysis further confirmed the reduction of U(VI) to U(IV) and the formation of FeOOH on NZVI surfaces. The findings of this study are significant to the remediation of uranium-contaminated red soils and the consideration of practical U(VI) species in the natural environment.

Efficient removal of uranium from aqueous solution by zero-valent iron nanoparticle and its graphene composite

Zero-valent iron nanoparticle (ZVI-np) and its graphene composites were prepared and applied in the removal of uranium under anoxic conditions. It was found that solutions containing 24 ppm U(VI) could be completely cleaned up by ZVI-nps, regardless of the presence of NaHCO3, humic acid, mimic groundwater constituents or the change of solution pH from 5 to 9, manifesting the promising potential of this reactive material in permeable reactive barrier (PRB) to remediate uranium-contaminated groundwater. In the measurement of maximum sorption capacity, removal efficiency of uranium kept at 100% until C0(U) = 643 ppm, and the saturation sorption of 8173 mg U/g ZVI-nps was achieved at C0(U) = 714 ppm. In addition, reaction mechanisms were clarified based on the results of SEM, XRD, XANES, and chemical leaching in (NH4)2CO3 solution. Partially reductive precipitation of U(VI) as U3O7 was prevalent when sufficient iron was available; nevertheless, hydrolysis precipitation of U(VI) on surface would be predominant as iron got insufficient, characterized by releases of Fe(2+) ions. The dissolution of Fe(0) cores was assigned to be the driving force of continuous formation of U(VI) (hydr)oxide. The incorporation of graphene supporting matrix was found to facilitate faster removal rate and higher U(VI) reduction ratio, thus benefitting the long-term immobilization of uranium in geochemical environment.