Structural and spectroscopic characterization of an einsteinium complex.

The transplutonium elements (atomic numbers 95-103) are a group of metals that lie at the edge of the periodic table. As a result, the patterns and trends used to predict and control the physics and chemistry for transition metals, main-group elements and lanthanides are less applicable to transplutonium elements. Furthermore, understanding the properties of these heavy elements has been restricted by their scarcity and radioactivity. This is especially true for einsteinium (Es), the heaviest element on the periodic table that can currently be generated in quantities sufficient to enable classical macroscale studies1. Here we characterize a coordination complex of einsteinium, using less than 200 nanograms of 254Es (with half-life of 275.7(5) days), with an organic hydroxypyridinone-based chelating ligand. X-ray absorption spectroscopic and structural studies are used to determine the energy of the L3-edge and a bond distance of einsteinium. Photophysical measurements show antenna sensitization of EsIII luminescence; they also reveal a hypsochromic shift on metal complexation, which had not previously been observed in lower-atomic-number actinide elements. These findings are indicative of an intermediate spin-orbit coupling scheme in which j-j coupling (whereby single-electron orbital angular momentum and spin are first coupled to form a total angular momentum, j) prevails over Russell-Saunders coupling. Together with previous actinide complexation studies2, our results highlight the need to continue studying the unusual behaviour of the actinide elements, especially those that are scarce and short-lived.

Additive Destabilization of Porous Magnesium Borohydride Framework with Core-Shell Structure.

Design of interfaces with thermodynamic and kinetic specificity is of great importance for hydrogen storage from both an applied and fundamental perspective. Here, in order to destabilize the metal hydride and protect the dehydrogenated products from oxidizing, a unique core-shell structure of porous Mg(BH4 )2 -based framework with a thin layer (no more than 5 nm) of MgCl2 additives on the surface, has been proposed and synthesized via a wet-chemical method. The local structure and electronic state of the present complex system are systematically investigated to understand the correlation between the distribution of additives and dehydrogenation property of Mg(BH4 )2 . A significant improvement is achieved for hydrogen desorption with chlorides: initial hydrogen release from MgCl2 decorated γ-phase Mg(BH4 )2 particles commences at 100 °C and reaches a maximum of 9.4 wt% at 385 °C. Besides the decreased decomposition temperature, an activation barrier of about 76.4 kJ mol-1 lower than that of Mg(BH4 )2 without MgCl2 is obtained. Moreover, MgCl2 decoration can also prevent the whole decomposed system (both Mg- and B- elements) from oxidizing, which is a necessary condition to reversibility.

Design Rules for Self-Assembly of 2D Nanocrystal/Metal-Organic Framework Superstructures.

We demonstrate the guiding principles behind simple two dimensional self-assembly of MOF nanoparticles (NPs) and oleic acid capped iron oxide (Fe3 O4 ) NCs into a uniform two-dimensional bi-layered superstructure. This self-assembly process can be controlled by the energy of ligand-ligand interactions between surface ligands on Fe3 O4 NCs and Zr6 O4 (OH)4 (fumarate)6 MOF NPs. Scanning transmission electron microscopy (TEM)/energy-dispersive X-ray spectroscopy and TEM tomography confirm the hierarchical co-assembly of Fe3 O4 NCs with MOF NPs as ligand energies are manipulated to promote facile diffusion of the smaller NCs. First-principles calculations and event-driven molecular dynamics simulations indicate that the observed patterns are dictated by combination of ligand-surface and ligand-ligand interactions. This study opens a new avenue for design and self-assembly of MOFs and NCs into high surface area assemblies, mimicking the structure of supported catalyst architectures, and provides a thorough fundamental understanding of the self-assembly process, which could be a guide for designing functional materials with desired structure.

Assembly and Photocarrier Dynamics of Heterostructured Nanocomposite Photoanodes from Multicomponent Colloidal Nanocrystals.

Multicomponent oxides and their heterostructures are rapidly emerging as promising light absorbers to drive oxidative chemistry. To fully exploit their functionality, precise tuning of their composition and structure is crucial. Here, we report a novel solution-based route to nanostructured bismuth vanadate (BiVO4) that facilitates the assembly of BiVO4/metal oxide (TiO2, WO3, and Al2O3) nanocomposites in which the morphology of the metal oxide building blocks is finely tailored. The combination of transient absorption spectroscopy-spanning from picoseconds to second time scales-and photoelectrochemical measurements reveals that the achieved structural tunability is key to understanding and directing charge separation, transport, and efficiency in these complex oxide heterostructured films.

Nanocomposite Architecture for Rapid, Spectrally-Selective Electrochromic Modulation of Solar Transmittance.

Two active electrochromic materials, vacancy-doped tungsten oxide (WO(3-x)) nanocrystals and amorphous niobium oxide (NbOx) glass are arranged into a mesostructured architecture. In a strategy applicable across electrochemical applications, the critical dimensions and interfacial connections in the nanocomposite are designed to optimize pathways for electrochemical charging and discharging. The result is an unprecedented optical range for modulation of visible and near-infrared solar radiation with rapid switching kinetics that indicate the WO(3-x) nanocrystal framework effectively pumps charge out of the normally sluggish NbOx glass. The material is durable for at least 2000 electrochemical cycles.

Monodisperse Sn nanocrystals as a platform for the study of mechanical damage during electrochemical reactions with Li.

Monodisperse Sn spherical nanocrystals of 10.0 ± 0.2 nm were prepared in dispersible colloidal form. They were used as a model platform to study the impact of size on the accommodation of colossal volume changes during electrochemical lithiation using ex situ transmission electron microscopy (TEM). Significant mechanical damage was observed after full lithiation, indicating that even crystals at these very small dimensions are not sufficient to prevent particle pulverization that compromises electrode durability.

A nature-inspired hydrogen-bonded supramolecular complex for selective copper ion removal from water.

Herein, we present a scalable approach for the synthesis of a hydrogen-bonded organic-inorganic framework via coordination-driven supramolecular chemistry, for efficient remediation of trace heavy metal ions from water. In particular, using copper as our model ion of interest and inspired by nature's use of histidine residues within the active sites of various copper binding proteins, we design a framework featuring pendant imidazole rings and copper-chelating salicylaldoxime, known as zinc imidazole salicylaldoxime supramolecule. This material is water-stable and exhibits unprecedented adsorption kinetics, up to 50 times faster than state-of-the-art materials for selective copper ion capture from water. Furthermore, selective copper removal is achieved using this material in a pH range that was proven ineffective with previously reported metal-organic frameworks. Molecular dynamics simulations show that this supramolecule can reversibly breathe water through lattice expansion and contraction, and that water is initially transported into the lattice through hopping between hydrogen-bond sites.

Impact of Source Position and Obstructions on Fume Hood Releases.

A fume hood is the most central piece of safety equipment available to researchers in a laboratory environment. While it is understood that the face velocity and sash height can drastically influence airflow patterns, few specific recommendations can be given to the researcher to guide them to maximize the safety of their particular hood. This stems from the issue that fundamentally little is known regarding how obstructions within the hood can push potentially harmful particles or chemicals out of the fume hood and into the breathing zone. In this work, we demonstrate how the position of a typical nanoparticle synthesis setup, including a Schlenk line and stir plate on an adjustable stand, influences airflow in a constant velocity fume hood. Using a combination of smoke evolution experiments and the aid of computational fluid dynamics simulations, we show how the location and height of the reaction components impact airflow. This work offers a highly visual display intended especially for new or inexperienced fume hood users. Based upon our studies and simulations, we provide detailed guidance to researchers and lab technicians on how to optimally modify reaction placement in order to protect the breathing zone while working.

Tuning the Surface Plasmon Resonance of Lanthanum Hexaboride to Absorb Solar Heat: A Review.

While traditional noble metal (Ag, Au, and Cu) nanoparticles are well known for their plasmonic properties, they typically only absorb in the ultraviolet and visible regions. The study of metal hexaborides, lanthanum hexaboride (LaB6) in particular, expands the available absorbance range of these metals well into the near-infrared. As a result, LaB6 has become a material of interest for its energy and heat absorption properties, most notably to those trying to absorb solar heat. Given the growing popularity of LaB6, this review focuses on the advances made in the past decade with respect to controlling the plasmonic properties of LaB6 nanoparticles. This review discusses the fundamental structure of LaB6 and explains how decreasing the nanoparticle size changes the atomic vibrations on the surface and thus the plasmonic absorbance band. We explain how doping LaB6 nanoparticles with lanthanide metals (Y, Sm, and Eu) red-shifts the absorbance band and describe research focusing on the correlation between size dependent and morphological effects on the surface plasmon resonance. This work also describes successes that have been made in dispersing LaB6 nanoparticles for various optical applications, highlighting the most difficult challenges encountered in this field of study.

Moving the Plasmon of LaB6 from IR to Near-IR via Eu-Doping.

Lanthanum hexaboride (LaB6) has become a material of intense interest in recent years due to its low work function, thermal stability and intriguing optical properties. LaB6 is also a semiconductor plasmonic material with the ability to support strong plasmon modes. Some of these modes uniquely stretch into the infrared, allowing the material to absorb around 1000 nm, which is of great interest to the window industry. It is well known that the plasmon of LaB6 can be tuned by controlling particle size and shape. In this work, we explore the options available to further tune the optical properties by describing how metal vacancies and Eu doping concentrations are additional knobs for tuning the absorbance from the near-IR to far-IR in La1-xEuxB6 (x = 0, 0.2, 0.5, 0.8, and 1.0). We also report that there is a direct correlation between Eu concentration and metal vacancies within the Eu1-xLaxB6.

Effects of Size and Structural Defects on the Vibrational Properties of Lanthanum Hexaboride Nanocrystals.

Lanthanum hexaboride (LaB6) is notable for its thermionic emission and mechanical strength and is being explored for its potential applications in IR-absorbing photovoltaic cells and thermally insulating window coatings. Previous studies have not investigated how the properties of LaB6 change on the nanoscale. Despite interest in the tunable plasmonic properties of nanocrystalline LaB6, studies have been limited due to challenges in the synthesis of phase-pure, size-controlled, high-purity nanocrystals without high temperatures or pressures. Here, we report, for the first time, the ability to control particle size and boron content through reaction temperature and heating ramp rate, which allows the effects of size and defects on the vibrational modes of the nanocrystals to be studied independently. Understanding these effects is important to develop methods to fully control the properties of nanocrystalline LaB6, such as IR absorbance. In contrast to previous studies on stoichiometric LaB6 nanocrystals, we report here that boron content and lanthanum vacancies have a greater influence on their vibrational properties than their particle size.

Temperature-dependent supramolecular stereoisomerism in porous copper coordination networks based on a designed carboxylate ligand.

Two novel temperature-controlled supramolecular stereoisomers of porous copper coordination networks have been synthesized and characterized.

Chemical Control of Plasmons in Metal Chalcogenide and Metal Oxide Nanostructures.

The field of plasmonics has grown to impact a diverse set of scientific disciplines ranging from quantum optics and photovoltaics to metamaterials and medicine. Plasmonics research has traditionally focused on noble metals; however, any material with a sufficiently high carrier density can support surface plasmon modes. Recently, researchers have made great gains in the synthetic (both intrinsic and extrinsic) control over the morphology and doping of nanoscale oxides, pnictides, sulfides, and selenides. These synthetic advances have, collectively, blossomed into a new, emerging class of plasmonic metal chalcogenides that complement traditional metallic materials. Chalcogenide and oxide nanostructures expand plasmonic properties into new spectral domains and also provide a rich suite of chemical controls available to manipulate plasmons, such as particle doping, shape, and composition. New opportunities in plasmonic chalcogenide nanomaterials are highlighted in this article, showing how they may be used to fundamentally tune the interaction and localization of electromagnetic fields on semiconductor surfaces in a way that enables new horizons in basic research and energy-relevant applications.

Bandgap Tunability in Sb-Alloyed BiVO4 Quaternary Oxides as Visible Light Absorbers for Solar Fuel Applications.

The challenge of fine compositional tuning and microstructure control in complex oxides is overcome by developing a general two-step synthetic approach. Antimony-alloyed bismuth vanadate, which is identified as a novel light absorber for solar fuel applications, is prepared in a wide compositional range. The bandgap of this quaternary oxide linearly decreases with the Sb content, in agreement with first-principles calculations.

Stability and porosity enhancement through concurrent ligand extension and secondary building unit stabilization.

A trigonal nanosized carboxylate ligand, 1,3,5-tris[4'-carboxy(1,1'-biphenyl-4-yl)]benzene (TCBPB), has been synthesized and applied in the construction of porous metal-organic frameworks (MOFs). A solvothermal reaction of TCBPB and a zinc salt in the presence of pyridine produces 1, an unstable MOF consisting of a tetrazinc secondary building unit (SBU) with labile terminal ligands. Changing pyridine to a noncoordinating base in the assembly procedure affords 2, a stable MOF with permanent porosity containing an octazinc SBU without labile terminal ligands.