Observation of a promethium complex in solution.

Lanthanide rare-earth metals are ubiquitous in modern technologies1-5, but we know little about chemistry of the 61st element, promethium (Pm)6, a lanthanide that is highly radioactive and inaccessible. Despite its importance7,8, Pm has been conspicuously absent from the experimental studies of lanthanides, impeding our full comprehension of the so-called lanthanide contraction phenomenon: a fundamental aspect of the periodic table that is quoted in general chemistry textbooks. Here we demonstrate a stable chelation of the 147Pm radionuclide (half-life of 2.62 years) in aqueous solution by the newly synthesized organic diglycolamide ligand. The resulting homoleptic PmIII complex is studied using synchrotron X-ray absorption spectroscopy and quantum chemical calculations to establish the coordination structure and a bond distance of promethium. These fundamental insights allow a complete structural investigation of a full set of isostructural lanthanide complexes, ultimately capturing the lanthanide contraction in solution solely on the basis of experimental observations. Our results show accelerated shortening of bonds at the beginning of the lanthanide series, which can be correlated to the separation trends shown by diglycolamides9-11. The characterization of the radioactive PmIII complex in an aqueous environment deepens our understanding of intra-lanthanide behaviour12-15 and the chemistry and separation of the f-block elements16.

Siderophore-inspired chelator hijacks uranium from aqueous medium.

Over millennia, nature has evolved an ability to selectively recognize and sequester specific metal ions by employing a wide variety of supramolecular chelators. Iron-specific molecular carriers-siderophores-are noteworthy for their structural elegance, while exhibiting some of the strongest and most selective binding towards a specific metal ion. Development of simple uranyl (UO22+) recognition motifs possessing siderophore-like selectivity, however, presents a challenge. Herein we report a comprehensive theoretical, crystallographic and spectroscopic studies on the UO22+ binding with a non-toxic siderophore-inspired chelator, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2BHT). The optimal pKa values and structural preorganization endow H2BHT with one of the highest uranyl binding affinity and selectivity among molecular chelators. The results of small-molecule standards are validated by a proof-of-principle development of the H2BHT-functionalized polymeric adsorbent material that affords high uranium uptake capacity even in the presence of competing vanadium (V) ions in aqueous medium.

Enabling chloride salts for thermal energy storage: implications of salt purity.

Molten salts for use as heat transfer fluids in concentrated solar or nuclear power plants have experienced a resurgence over the past decade with a special focus on chloride-based salt mixtures, particularly for use in concentrating solar power and fast-spectrum nuclear reactors. Salt purification, specifically oxide removal, is required even for high purity commercial salts and can be achieved using many different methods. Carbochlorination, however, proves most effective according to thermodynamics and produces a gaseous byproduct easily removed from the salt. A variety of carbochlorinating reagents and reagent combinations were evaluated for thermodynamic favorability in the removal of common impurities in MgCl2-based feedstock or coverage gases used in industrial systems. Carbon tetrachloride exhibited superior purification thermodynamics above the melting point of common MgCl2-based salt compositions. Salt with composition of 68 : 32 mol% KCl : MgCl2 was purified on the kilogram scale by sparging with carbon tetrachloride, reducing dissolved oxide to trace levels (42 µmol MgO/kg salt). Interestingly, the lower purity salts exhibited magnesium and oxygen presence along grain boundaries in the corrosion layers while the purified salts did not, highlighting the need for decreased oxide content. The lessened corrosivity of the highly purified salt suggests a proper salt treatment may reduce dependence on specialized materials for use with molten salts.

Vacuum-Assisted Low-Temperature Synthesis of Reduced Graphene Oxide Thin-Film Electrodes for High-Performance Transparent and Flexible All-Solid-State Supercapacitors.

Simple and easily integrated design of flexible and transparent electrode materials affixed to polymer-based substrates hold great promise to have a revolutionary impact on the functionality and performance of energy storage devices for many future consumer electronics. Among these applications are touch sensors, roll-up displays, photovoltaic cells, health monitors, wireless sensors, and wearable communication devices. Here, we report an environmentally friendly, simple, and versatile approach to produce optically transparent and mechanically flexible all-solid-state supercapacitor devices. These supercapacitors were constructed on tin-doped indium oxide coated polyethylene terephthalate substrates by intercalation of a polymer-based gel electrolyte between two reduced graphene oxide (rGO) thin-film electrodes. The rGO electrodes were fabricated simply by drop-casting of graphene oxide (GO) films, followed by a novel low-temperature (≤250 °C) vacuum-assisted annealing approach for the in situ reduction of GO to rGO. A trade-off between the optical transparency and electrochemical performance is determined by the concentration of the GO in the initial dispersion, whereby the highest capacitance (∼650 µF cm-2) occurs at a relatively lower optical transmittance (24%). Notably, the all-solid-state supercapacitors demonstrated excellent mechanical flexibility with a capacity retention rate above 90% under various bending angles and cycles. These attributes underscore the potential of the present approach to provide a path toward the realization of thin-film-based supercapacitors as flexible and transparent energy storage devices for a variety of practical applications.

Fibers with Hyper-Crosslinked Functional Porous Frameworks.

The incorporation of robust porous frameworks into polymer fibers with handleable morphologies and flexible chemical compositions exhibits significant advantages for device fabrication in a wide range of applications. However, the soft linear polymeric chains of the fibers make the generation of nanopores extremely challenging. Herein, a facile synthetic strategy based on a combination of functional monomer grafting and hyper-crosslinking technology is developed for the porous engineering of polymeric fibers. In this methodology, the nanoporous framework originating from the hyper-crosslinking of aromatic monomers is covalently grafted onto fibers, which is beneficial to retaining their unique fiber morphology and to preserving their excellent mechanical properties. Moreover, this promising protocol can be further extended to the porous functionalization of polymeric matrices with diverse morphologies for target-specific applications.

Materials for the Recovery of Uranium from Seawater.

More than 1000× uranium exists in the oceans than exists in terrestrial ores. With nuclear power generation expected to increase over the coming decades, access to this unconventional reserve is a matter of energy security. With origins in the mid-1950s, materials have been developed for the selective recovery of seawater uranium for more than six decades, with a renewed interest in particular since 2010. This review comprehensively surveys materials developed from 2000-2016 for recovery of seawater uranium, in particular including recent developments in inorganic materials; polymer adsorbents and related research pertaining to amidoxime; and nanostructured materials such as metal-organic frameworks, porous-organic polymers, and mesoporous carbons. Challenges of performing reliable and reproducible uranium adsorption studies are also discussed, as well as the standardization of parameters necessary to ensure valid comparisons between different adsorbents.

Quantifying the binding strength of salicylaldoxime-uranyl complexes relative to competing salicylaldoxime-transition metal ion complexes in aqueous solution: a combined experimental and computational study.

The design of new ligands and investigation of UO2(2+) complexations are an essential aspect of reducing the cost of extracting uranium from seawater, improving the sorption efficiency for uranium and the selectivity for uranium over competing ions (such as the transition metal cations). The binding strengths of salicylaldoxime-UO2(2+) complexes were quantified for the first time and compared with the binding strengths of salicylic acid-UO2(2+) and representative amidoxime-UO2(2+) complexes. We found that the binding strengths of salicylaldoxime-UO2(2+) complexes are ∼2-4 log ß2 units greater in magnitude than their corresponding salicylic acid-UO2(2+) and representative amidoxime-UO2(2+) complexes; moreover, the selectivity of salicylaldoxime towards the UO2(2+) cation over competing Cu(2+) and Fe(3+) cations is far greater than those reported for salicylic acid and glutarimidedioxime in the literature. The higher UO2(2+) selectivity can likely be attributed to the different coordination modes observed for salicylaldoxime-UO2(2+) and salicylaldoxime-transition metal complexes. Density functional theory calculations indicate that salicylaldoxime can coordinate with UO2(2+) as a dianion species formed by η(2) coordination of the aldoximate and monodentate binding of the phenolate group. In contrast, salicylaldoxime coordinates with transition metal cations as a monoanion species via a chelate formed between phenolate and the oxime N; the complexes are stabilized via hydrogen bonding interactions between the oxime OH group and phenolate. By coupling the experimentally determined thermodynamic constants and the results of theoretical computations, we are able to derive a number of ligand design principles to further improve the UO2(2+) cation affinity, and thus further increase the selectivity of salicylaldoxime derivatives.

An efficient low-temperature route to nitrogen-doping and activation of mesoporous carbons for CO2 capture.

An innovative strategy for post-synthesis nitrogen-doping of mesoporous carbons (MCs) with high yields (>90%) at low temperatures (230-380 °C) by using a strong base, sodium amide (NaNH2), was developed. The as-prepared N-doped MCs exhibit a significantly enhanced CO2 adsorption performance in terms of capacity and selectivity when compared to their parent MCs.

Acid-functionalized mesoporous carbon: an efficient support for ruthenium-catalyzed γ-valerolactone production.

The hydrogenation of levulinic acid has been studied using Ru supported on ordered mesoporous carbons (OMCs) prepared by soft-templating. P- and S-containing acid groups were introduced by postsynthetic functionalization before the addition of 1 % Ru by incipient wetness impregnation. These functionalities and the reaction conditions mediate the activity and selectivity of the levulinic acid hydrogenation. The presence of S-containing groups (Ru/OMC-S and Ru/OMC-P/S) deactivates the Ru catalysts strongly, whereas the presence of P-containing groups (Ru/OMC-P) enhances the activity compared to that of pristine Ru/OMC. Under mild conditions (70 °C and 7 bar H2 ) the catalyst shows high selectivity to γ-valerolactone (GVL; >95 %) and high stability on recycling. However, under more severe conditions (200 °C and p H 2=40 bar) Ru/OMC-P is particularly able to promote GVL ring-opening and the consecutive hydrogenation to pentanoic acid.

Neutron imaging of ion transport in mesoporous carbon materials.

Neutron imaging is presented as a tool for quantifying the diffusion of ions inside porous materials, such as carbon electrodes used in the desalination process via capacitive deionization and in electrochemical energy-storage devices. Monolithic mesoporous carbon electrodes of ∼10 nm pore size were synthesized based on a soft-template method. The electrodes were used with an aqueous solution of gadolinium nitrate in an electrochemical flow-through cell designed for neutron imaging studies. Sequences of neutron images were obtained under various conditions of applied potential between the electrodes. The images revealed information on the direction and magnitude of ion transport within the electrodes. From the time-dependent concentration profiles inside the electrodes, the average value of the effective diffusion coefficient for gadolinium ions was estimated to be 2.09 ± 0.17 × 10(-11) m(2) s(-1) at 0 V and 1.42 ± 0.06 × 10(-10) m(2) s(-1) at 1.2 V. The values of the effective diffusion coefficient obtained from neutron imaging experiments can be used to evaluate model predictions of the ion transport rate in capacitive deionization and electrochemical energy-storage devices.

Lithium-sulfur batteries based on nitrogen-doped carbon and an ionic-liquid electrolyte.

Nitrogen-doped mesoporous carbon (NC) and sulfur were used to prepare an NC/S composite cathode, which was evaluated in an ionic-liquid electrolyte of 0.5 M lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in methylpropylpyrrolidinium bis(trifluoromethane sulfonyl)imide ([MPPY][TFSI]) by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and cycle testing. To facilitate the comparison, a C/S composite based on activated carbon (AC) without nitrogen doping was also fabricated under the same conditions. Compared with the AC/S composite, the NC/S composite showed enhanced activity toward sulfur reduction, as evidenced by the lower onset sulfur reduction potential, higher redox current density in the CV test, and faster charge-transfer kinetics, as indicated by EIS measurements. At room temperature under a current density of 84 mA g(-1) (C/20), the battery based on the NC/S composite exhibited a higher discharge potential and an initial capacity of 1420 mAh g(-1), whereas the battery based on the AC/S composite showed a lower discharge potential and an initial capacity of 1120 mAh g(-1). Both batteries showed similar capacity fading with cycling due to the intrinsic polysulfide solubility and the polysulfide shuttle mechanism; capacity fading can be improved by further cathode modification.

Carbon materials for chemical capacitive energy storage.

Carbon materials have attracted intense interests as electrode materials for electrochemical capacitors, because of their high surface area, electrical conductivity, chemical stability and low cost. Activated carbons produced by different activation processes from various precursors are the most widely used electrodes. Recently, with the rapid growth of nanotechnology, nanostructured electrode materials, such as carbon nanotubes and template-synthesized porous carbons have been developed. Their unique electrical properties and well controlled pore sizes and structures facilitate fast ion and electron transportation. In order to further improve the power and energy densities of the capacitors, carbon-based composites combining electrical double layer capacitors (EDLC)-capacitance and pseudo-capacitance have been explored. They show not only enhanced capacitance, but as well good cyclability. In this review, recent progresses on carbon-based electrode materials are summarized, including activated carbons, carbon nanotubes, and template-synthesized porous carbons, in particular mesoporous carbons. Their advantages and disadvantages as electrochemical capacitors are discussed. At the end of this review, the future trends of electrochemical capacitors with high energy and power are proposed.

Boron and nitrogen-rich carbons from ionic liquid precursors with tailorable surface properties.

A novel strategy for tailoring the adsorption and structural properties of ionic liquid derived carbons has been developed. By changing the carbonization temperature and ratios of ionic liquids (ILs) containing a cross-linkable anion, such as 1-butyl-3-methylimidazolium tricyanomethanide [BMIm][C(CN)(3)] and 1-ethyl-3-methylimidazolium tetracyanoborate [EMIm][B(CN)(4)], boron and nitrogen-rich carbons with slit-like pores and specific surface areas exceeding 500 m(2) g(-1) have been prepared. Furthermore, the nitrogen-rich carbons exhibit high adsorption capacity for CO(2) adsorption and selectivity for CO(2)/N(2) separation.

Phosphorylated mesoporous carbon as a solid acid catalyst.

Mesoporous carbon catalyst supports are attractive due to their wide chemical stability while potentially increasing mass-transport through and providing a path for larger molecules to access catalytic sites. Herein we report the synthesis of a phosphorylated mesoporous carbon solid-acid catalyst characterized by NH(3)-TPD and isopropanol dehydration.