Using Diglycolamide Extractants in an Imidazolium-Based Ionic Liquid for Rare Earth Element Extraction and Recovery
Not Available
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Engineering topics
Jing, Dapeng
Publications and source records attributed to Jing, Dapeng.
The nontrivial effects of annealing on superconducting properties of Nb single crystals
The effect of annealing on the superconducting properties of niobium single crystals was studied using optical, magnetic, and scanning tunneling microscopy (STM) methods. Pieces of the same crystal boule were studied before and after the annealing at 800 ${^\circ}\textrm{C}$, 1400 ${^\circ}\textrm{C}$, and near the melting point of niobium (2477 ${^\circ}\textrm{C}$). The initial samples had a high hydrogen content and low-temperature imaging revealed large hydrides (hundreds of micrometers) appearing below 190 K. The formation of these large precipitates is already completely suppressed by annealing at 800 ${^\circ}\textrm{C}$. However, the overall superconducting properties of the annealed samples did not improve and, in fact, worsened. In particular, the superconducting transition temperature decreased, the upper critical field increased, and the pinning strength increased. In the STM study, the sample was annealed initially at 400 ${^\circ}\textrm{C}$, measured, annealed at 1700 ${^\circ}\textrm{C}$, and measured again. The STM revealed a ‘dirty’ superconducting gap with a significant spatial variation in tunneling conductance after annealing at 400 ${^\circ}\textrm{C}$. The clean gap was recovered after annealing at 1700 ${^\circ}\textrm{C}$. This is likely due to oxygen redistribution near the surface, which is always covered by oxide layers in as-grown crystals. Our results indicate that vacuum annealing at least up to 1400 ${^\circ}\textrm{C}$, while removing a large percentage of hydrogen, introduces additional nanosized defects, likely hydride precipitates, that act as efficient pair-breaking and pinning centers. The dimensionless scattering rate is estimated to have increased from $\Gamma = 0.2$ to about $\Gamma = 0.4$ after annealing at 1400 ${^\circ}\textrm{C}$. These results on single crystals differ drastically from those obtained in polycrystalline bulk niobium (i.e. cut from superconducting radio-frequency cavities), where annealing is known to have a significant positive effect that is attributed to the improvement of the crystalline structure masking the more subtle influence of the hydrides.
43 PARTICLE ACCELERATORS↗
Structure and Formation Mechanisms in Tantalum and Niobium Oxides in Superconducting Quantum Circuits
Not Available
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Crystal structure and shape selection in the growth of 3D metallic crystallites on layered materials: Fe on MoS 2
Nucleation and growth of supported 3D metal clusters or crystallites during deposition on MoS 2 , or on other weakly-adhering layered materials, can potentially produce diverse growth shapes, and even crystal structures differing from the bulk metal. For Fe deposition on MoS 2 , SEM and AFM observations reveal three distinct crystallite shapes. By comparison with atomistic structure models incorporating realistic Fe-MoS 2 interface structures, here we conclude that these are: triangular fcc(111) pyramids with sloped {100} side facets; bcc(110) A-frame tents with sloped {100} side facets; and bcc(110) mesas with vertical {100} and {110} side facets. The following picture is proposed for the competitive formation of clusters and crystallites with different structures: (i) small nanoclusters formed at the onset of deposition exhibit facile fluxional dynamics allowing sampling of different crystal structures and shapes; (ii) sufficient fluxionality implies a Boltzmann distribution of sampled structures, and thus coexistence of different structures follows from the demonstrated similar energies for those structures; (iii) growing clusters reach a threshold size above which the characteristic time scale for restructuring exceeds that for cluster growth. Thereafter, clusters are locked-in to a specific crystal structure and shape as revealed by imaging of larger crystallites. Despite a penalty for fcc(111) over bcc(111) pyramids based on bulk energetics, favorable surface and interface energies makes them preferable for smaller sizes.
36 MATERIALS SCIENCE↗
Balancing elementary steps enables coke-free dry reforming of methane
Balancing kinetics, a crucial priority in catalysis, is frequently achieved by sacrificing activity of elementary steps to suppress side reactions and enhance catalyst stability. Dry reforming of methane (DRM), a process operated at high temperature, usually involves fast C-H activation but sluggish carbon removal, resulting in coke deposition and catalyst deactivation. Studies focused solely on catalyst innovation are insufficient in addressing coke formation efficiently. Herein, we develop coke-free catalysts that balance kinetics of elementary steps for overall thermodynamics optimization. Beginning from a highly active cobalt aluminum oxide (CoAl 2 O 4 ) catalyst that is susceptible to severe coke formation, we substitute aluminum (Al) with gallium (Ga), reporting a CoAl 0.5 Ga 1.5 O 4 -R catalyst that performs DRM stably over 1000 hours without observable coke deposition. We find that Ga enhances DRM stability by suppressing C-H activation to balance carbon removal. A series of coke-free DRM catalysts are developed herein by partially substituting Al from CoAl 2 O 4 with other metals.
36 MATERIALS SCIENCE↗
Probing of the Noninnocent Role of P in Transition-Metal Phosphide Hydrogen Evolution Reaction Electrocatalysts via Replacement with Electropositive Si
Transition-metal phosphides (TMP) have been identified as promising electrocatalysts for the hydrogen evolution reaction (HER). Despite recent computational investigations identifying P sites as being crucial for hydrogen adsorption, the main mode of optimization for TMPs has been focused on changing the metal sites. Here, to experimentally verify computational hypotheses and provide a route for HER electrocatalyst optimization via ternary compounds, we performed systematic experimental studies of structurally related NiSi 1–x P x phases, namely, Ni 2 SiP, Ni 5 Si 2 P 3 , Ni 3 SiP 2 , and Ni 7 Si 2 P 5 , which are ordered derivatives of the NiSi structure (Pnma, oP-8, MnP structure type). We found that P played a significant role in modulating HER activity in an acidic electrolyte because the incorporation of P in NiSi reduced the overpotential at current density j = 10 mA/cm 2 from η 10 = 529 mV (NiSi) to η 10 = 97 mV (Ni 2 SiP). Ni 2 SiP outperformed the current state-of-the-art Ni5P4 electrocatalyst prepared and studied in identical conditions both in terms of activity and stability, which is attributed to the presence of covalent Ni–Si bonding in the structure. Within the family of ternary Ni–Si–P compounds, electrocatalytic activity correlates with the number of Ni-3d states at the Fermi energy.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The Structure of Boron Monoxide
Boron monoxide (BO), prepared by the thermal condensation of tetrahydroxydiboron, was first reported in 1955; however, its structure could not be determined. With the recent attention on boron-based two-dimensional materials, such as borophene and hexagonal boron nitride, there is renewed interest in BO. A large number of stable BO structures have been computationally identified, but none are supported by experiments. The consensus is that the material likely forms a boroxine-based two-dimensional material. Herein, we apply advanced 11 B NMR experiments to determine the relative orientations of B(B)O 2 centers in BO. We find that the material is composed of D 2h -symmetric O 2 B–BO 2 units that organize to form larger B 4 O 2 rings. Further, powder diffraction experiments additionally reveal that these units organize to form two-dimensional layers with a random stacking pattern. This observation is in agreement with earlier density functional theory (DFT) studies that showed B 4 O 2 -based structures to be the most stable.
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General Strategy for Incorporation of Functional Group Handles into Covalent Organic Frameworks via the Ugi Reaction
The library of imine-linked covalent organic frameworks (COFs) has grown significantly over the last two decades, featuring a variety of morphologies, pore sizes, and applications. An array of synthetic methods has been developed to expand the scope of the COF functionalities; however, most of these methods were designed to introduce functional scaffolds tailored to a specific application. Having a general approach to diversify COFs via late-stage incorporation of functional group handles would greatly facilitate the transformation of these materials into platforms for a variety of useful applications. In this paper, we report a general strategy to introduce functional group handles in COFs via the Ugi multicomponent reaction. To demonstrate the versatility of this approach, we have synthesized two COFs with hexagonal and kagome morphologies. We then introduced azide, alkyne, and vinyl functional groups, which could be readily utilized for a variety of post-synthetic modifications. This facile approach enables the functionalization of any COFs containing imine linkages.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Unusual flat and extended morphology of intercalated Cu under MoS 2
We report a general method was developed to intercalate metals under layered materials through a controlled density of sputtered defects. The method has already been applied to study a range of metals intercalated under graphite, and different types of morphologies were realized. In the current work, we extend the method to the study of intercalation under MoS 2 , noting that work on this system is rather limited. We use Cu as the prototype metal for comparison with Cu intercalation under graphite. Although the growth conditions needed for intercalation under graphite and MoS 2 are similar, the type of intercalated phases is very different. Each Cu island that nucleates on top of MoS 2 during Cu deposition provides material that is transferred below MoS 2 through sputtered defects under the island base; this transfer results in a uniform intercalated Cu “carpet” morphology that extends over the mesoscale. On the contrary, Cu intercalation under graphite results in well separated, compact islands formed by monomer detachment from small Cu islands on top and transfer below through defects far from the islands. The structural techniques (scanning electron microscopy and atomic force microscopy) and spectroscopic techniques (x-ray photoelectron spectroscopy and energy-dispersive spectroscopy) are used for the characterization of the intercalated Cu layer.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Thermodynamically Driven Formation of Intercalated Cu Carpets from Supported Cu Pyramids on MoS 2
Thermodynamic and kinetic analyses based on our first-principles density functional theory calculations are used to interpret the experimentally observed formation of Cu carpets intercalated under the top layer of a 2H-MoS 2 substrate. Spontaneous Cu transport from Cu pyramids on top of the MoS 2 substrate through surface point defects to the growing Cu carpet is shown to be driven by a slightly lower chemical potential for the Cu carpet. We demonstrate that the competition between a preference for a thicker Cu carpet and the cost of elastic stretching of the top MoS 2 layer results in a selected Cu carpet thickness. Furthermore, we also propose that Cu transport occurs primarily via vacancy-mediated diffusion through constricting point defect portals.
36 MATERIALS SCIENCE↗
Synthesis of SrTiO 3 and Al-doped SrTiO 3 via the deep eutectic solvent route
SrTiO 3 and aluminum-doped SrTiO 3 are synthesized by calcination of metal salts dissolved in a deep eutectic solvent (DES) without any post-synthesis treatment.
36 MATERIALS SCIENCE↗
Direct methane activation by atomically thin platinum nanolayers on two-dimensional metal carbides
We report efficient and direct conversion of methane to value-added products has been a long-term challenge in shale gas applications. Here, we show that atomically thin nanolayers of Pt with a single or double atomic layer thickness, supported on a two-dimensional molybdenum titanium carbide (MXene), catalyse non-oxidative coupling of methane to ethane/ethylene (C 2 ). Kinetic and theoretical studies, combined with in-situ spectroscopic and microscopic characterizations, demonstrate that Pt nanolayers anchored at the hexagonal close-packed sites of the MXene support can activate the first C–H bond of methane to form methyl radicals that favour desorption over further dehydrogenation and thus suppress coke deposition. At 750 °C and 7% methane conversion, the catalyst runs for 72 hours of continuous operation without deactivation and exhibits >98% selectivity towards C 2 products, with a turnover frequency of 0.2–0.6 s -1 . Our findings provide insights into the design of highly active and stable catalysts for methane activation and create a platform for developing atomically thin supported metal catalysts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity
Abstract Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd‐based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure‐phase PdSn nanocatalyst. PdSn shows an >96 % selectivity toward hydrogenating C=O bonds of various α,β‐unsaturated aldehydes, highest in reported Pd‐based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn‐ to Pd 3 Sn 2 ‐structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.
Chen, Minda↗
Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity
Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd-based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure-phase PdSn nanocatalyst. Furthermore, PdSn shows an >96% selectivity toward hydrogenating C=O bonds of various α,β-unsaturated aldehydes, highest in reported Pd-based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn- to Pd 3 Sn 2 -structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cover Feature: New Noncentrosymmetric Tetrel Pnictides Composed of Square-Planar Gold(I) with Peculiar Bonding (Chem. Eur. J. 26/2021)
Compared to common types of Au(I) coordination, such as linear, trigonal planar, and tetrahedral units observed in extended solids, the square planar coordination is rare. Au(I)relia, shown in the cover image, exhibits the 3-centered bonding of Au-Tt-Au and Au-Pn-Au (on her feathers), square planar cis-[AuTt2Pn2] units (her pendant), and linear …-Au-Au-Au-… chains (her legs) that are characteristic of the novel equiatomic AuSiAs, AuGeP, and AuGeAs compounds. The image was created by designer Grant Luhmann.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Crystal Structure and Properties of Layered Pnictides BaCuSi2Pn3 (Pn = P, As)
Two novel layered compounds BaCuSi 2 Pn 3 (Pn = P, As) adopting new structure types are reported. As revealed by single-crystal X-ray diffraction, both compounds are composed of unique Cu–Si–Pn layers featuring CuPn 3 and Si 2 Pn 6 structural motifs found in other archetypal pnictide materials. The stacking of the isostructural Cu–Si–Pn layers is different for phosphide and arsenide compounds. Synthesis from elements aided by in situ synchrotron powder X-ray diffraction resulted in the obtainment of bulk powders with a minimized amount of admixtures. Experimentally measured physical properties of BaCuSi 2 As 3 unexpectedly showed metal-like behavior at temperatures above 15 K, despite the fact that density functional theory calculations predict a small band gap of 0.4 eV. BaCuSi 2 As 3 exhibits ultralow thermal conductivity, which can be explained by the combination of a layered crystal structure with alternating covalent and ionic bonding, which feature rattling of Cu atoms similar to that in tetrahedrites.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
New Noncentrosymmetric Tetrel Pnictides Composed of Square‐Planar Gold(I) with Peculiar Bonding
Abstract Three novel isostructural equiatomic gold tetrel pnictides, AuSiAs, AuGeP, and AuGeAs, were synthesized and characterized. These phases crystallize in the noncentrosymmetric (NCS) monoclinic space group Cc (no. 9), featuring square‐planar Au within cis ‐[AuTt 2 Pn 2 ] units (Tt=tetrel, Si, Ge; Pn=pnictogen, P, As). This is in drastic contrast to the structure of previously reported AuSiP, which exhibits typical linear coordination of Au with Si and P. Chemical bonding analysis through the electron localization function suggests covalent two‐center two‐electron Tt−Pn bonds, and three‐center Au−Tt−Au and Au−Pn−Au bonds with 1.6 e − per bond. X‐ray photoelectron spectroscopy studies support the covalent and nonionic nature of Au−Pn and Au−Tt bonds. The title materials were found to be n ‐type narrow‐gap semiconductors or semimetals, with nearly temperature‐independent electrical resistivities and low thermal conductivities. A combination of the semimetallic properties with tunable NCS structure provides opportunities for the development of materials based on gold tetrel pnictides.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Structure evolution of single-site Pt in a metal–organic framework
Heterogeneous single-metal-site catalyst or single-atom catalyst research has grown rapidly due to the accessibility of modern characterization techniques that can provide invaluable information at the atomic-scale. Herein, we study the structural evolution of isolated single Pt sites incorporated in a metal–organic framework containing bipyridine functional groups using in situ diffuse reflectance infrared Fourier transform spectroscopy with CO as the probe molecule. The structure and electronic properties of the isolated Pt sites are further corroborated by x-ray photoelectron spectroscopy and aberration-corrected scanning transmission electron microscopy. Here, we find the prerequisite of high temperature He treatment for Pt activation and CO insertion and inquire into the structural transformation of Pt site process by dynamic nuclear polarization-enhanced solid-state nuclear magnetic resonance spectroscopy.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗