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“Straining” to Separate the Rare Earths: How the Lanthanide Contraction Impacts Chelation by Diglycolamide Ligands
The subtle energetic differences underpinning adjacent lanthanide discrimination are explored with diglycolamide ligands. Our approach converges liquid–liquid extraction experiments with solution-phase X-ray absorption spectroscopy (XAS) and density functional theory (DFT) simulations, spanning the lanthanide series. The homoleptic [(DGA)3Ln]3+ complex was confirmed in the organic extractive solution by XAS, and this was modeled using DFT. An interplay between steric strain and coordination energies apparently gives rise to a nonlinear trend in discriminatory lanthanide ion complexation across the series. Our results highlight the importance of optimizing chelate molecular geometry to account for both coordination interactions and strain energies when designing new ligands for efficient adjacent lanthanide separation for rare-earth refining.
Tailored CO 2 -philic Gas Separation Membranes via One-Pot Thiol–ene Chemistry
Recently, thiol–ene chemistry attracts much attention in the construction of functional polymer materials due to its versatility and fast reaction kinetics, though only a few studies have been reported on its utilization in the fabrication of elastic polymer materials. Herein, a series of elastic, poly(dimethylsiloxane)–poly(ethylene glycol) methyl ether acrylate (PDMS–PEGMEA)-based co-polymer membranes are synthesized via a one-pot thiol–ene reaction. These membranes are highly stable and exhibit tunable thermal/mechanical properties by tailoring the cross-linker and side-chain functionality. When used for gas separation application, all grafted elastomer membranes show excellent gas permeability and selectivity, and the membrane with an optimal composition (PDMS–PEGMEA 30 –EOPDMS 10 ) has reached the Robeson upper bound (CO 2 permeability ~800 barrer and α[CO 2 /N 2 ] ~39). The high permeability originates from the extremely fast chain mobility of PDMS molecules at the ambient temperature. Tailoring the PEGMEA content allows control of the α[CO 2 /N 2 ] ranging from 21 to 39 by enhancing gas solubility within the membrane matrix. This study provides a promising strategy to be utilized for the gutter layer, selective layer, or their combination in the industrial gas separation modules.
Kinetics of Ion Exchange of Zr/Sn(IV) Phosphonate–Phosphate Hybrid Materials for Separation of Lanthanides from Oxidized Actinides
The kinetics of ion exchange of Zr/Sn(IV) phosphonate-phosphate hybrid ion exchange materials have been studied with several types of ions of specific interest to nuclear fuel recycling including Nd 3+ at 4.5 and 43 mM and NpO 2 + at 2.9 mM spanning multiple HNO 3 concentrations. In most cases the equilibrium was reached in less than 12 h. The ion exchange behavior followed that of pseudo first-order adsorption with rates ranging from 0.430–4.10 h -1 and 0.290–0.435 h -1 for Nd 3+ and NpO 2 + , respectively. A separation with both Nd 3+ and NpO 2 + present was performed, resulting in separation factors of 1.9–12, 1.7–6.6, and 2.0–5.7 at 1×10 -1 , 1×10 -2 , and 1×10 -3 M HNO 3 , respectively.
Redox-Active Metal-Organic Composites for Highly Selective Oxygen Separation Applications
A redox-active metal-organic composite material shows improved and selective O-2 adsorption over N-2 with respect to individual components (MIL-101 and ferrocene). The O-2 sensitivity of the composite material arises due to the formation of maghemite nanoparticles with the pore of the metal-organic framework material.
Continuous Redirection and Separation of Microbeads by Faradaic Ion Concentration Polarization
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Synthesis Strategies for Ultrastable Zeolite GIS Polymorphs as Sorbents for Selective Separations
Abstract Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure‐directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities. Herein, we present organic‐free syntheses of two polymorphs of the small‐pore zeolite P (GIS), P1 and P2. Using a combination of adsorption measurements and density functional theory calculations, we show that GIS polymorphs are selective adsorbents for H 2 O relative to other light gases (e.g., H 2 , N 2 , CO 2 ). Our findings refute prior theoretical studies postulating that GIS‐type zeolites are excellent materials for CO 2 separation/sequestration. We also show that P2 is significantly more thermally stable than P1, which broadens the operating conditions for GIS‐type zeolites in commercial applications and opens new avenues for exploring their potential use in processes such as catalysis.
Leveraging Actinide Hydrolysis Chemistry for Targeted Th and U Separations using Amidoxime-Functionalized Poly(HIPE)s
Polymerized high internal phase emulsions (poly(HIPE)s) are porous polymer monoliths whose synthesis can easily be tailored to allow incorporation of functional units. In this work, nitrile containing poly(HIPE)s have been prepared with either acrylonitrile (AN) or 4-cyanostyrene (4CS) comonomers. Post-synthetic modification of these nitrile-containing poly(HIPE)s yields their corresponding amidoximated analogues, which were studied for actinide uptake. These amidoxime-functionalized, porous polymers were shown to adsorb 95 % Th4+ species from aqueous solution within 30 minutes. In contrast to other amidoxime containing polymers the uptake of UO22+ in these poly(HIPE)s is lower under similar conditions. A critical analysis of actinide separations and high-energy X-ray scattering data provides insight into the polymers’ selectivity, enabled by the uptake of multinuclear Th clusters.
CaCo x Zr 1− x O 3− δ Perovskites as Oxygen‐Selective Sorbents for Air Separation
Abstract ABO 3− δ perovskites are ideal for high‐temperature thermochemical air separation for oxygen production because their oxygen nonstoichiometry δ can be varied in response to changes in temperature and oxygen partial pressure [ ]. Herein, the outstanding oxygen‐sorption performance of CaCo x Zr 1− x O 3− δ perovskites and their potential application as oxygen‐selective sorbents for air separation is reported. In situ thermal X‐ray diffraction was used to study the materials’ structural changes in response to temperature variations in air and inert atmosphere. Temperature‐programmed reduction was employed to elucidate the relationship between perovskite composition and redox property. O 2 sorption performance was evaluated by isothermal analyses at various temperature and along with long‐term absorption–desorption cycle tests. The high oxygen‐sorption capacity was mainly attributed to Co at B‐site, whereas partial substitution of Co by Zr enhanced the structural crystallinity and thermal stability of the perovskite. A stable oxygen production of 2.87 wt % was observed at 900 °C during 5 min‐sorption cycles for 100 cycles.
Optimizing multi-step B-side charge separation in photosynthetic reaction centers from Rhodobacter capsulatus
Using high-throughput methods for mutagenesis, protein isolation and charge-separation functionality, we have assayed 40 Rhodobacter capsulatus reaction center (RC) mutants for their P+ QB- yield (P is a dimer of bacteriochlorophylls and Q is a ubiquinone) as produced using the normally inactive B-side cofactors BB and HB (where B is a bacteriochlorophyll and H is a bacteriopheophytin). Two sets of mutants explore all possible residues at M131 (M polypeptide, native residue Val near HB) in tandem with either a fixed His or a fixed Asn at L181 (L polypeptide, native residue Phe near BB). A third set of mutants explores all possible residues at L181 with a fixed Glu at M131 that can form a hydrogen bond to HB. For each set of mutants, the results of a rapid millisecond screening assay that probes the yield of P+ QB- are compared among that set and to the other mutants reported here or previously. For a subset of eight mutants, the rate constants and yields of the individual B-side electron transfer processes are determined via transient absorption measurements spanning 100 fs to 50 μs. The resulting ranking of mutants for their yield of P+ QB- from ultrafast experiments is in good agreement with that obtained from the millisecond screening assay, further validating the efficient, high-throughput screen for B-side transmembrane charge separation. Results from mutants that individually show progress toward optimization of P+ HB- → P+ QB- electron transfer or initial P* → P+ HB- conversion highlight unmet challenges of optimizing both processes simultaneously.
Selective Crystallization for Green Separations of Lanthanides Using 5-(Pyrimidyl)Tetrazolate
In an effort to develop facile, low-cost, and environmentally benign separations of lanthanides, the coordination chemistry and selective crystallization of Ln 3+ cations with the water-soluble ligand 5-(pyrimidyl)tetrazolate (pmtz) have been investigated. The wide range of coordination modes of pmtz allows for discrimination between these cations, and five distinct compound types can be prepared that are dependent on the lanthanide employed. La 3+ leads to the formation of [La(pmtz) 2 (H 2 O) 6 ]Cl (S1). [Ln(pmtz) 3 (H 2 O) 3 ]·(3+n)H 2 O is obtained with Ce 3+ and Pr 3+ (S2). Ce 3+ can also form [(Ce(pmtz) 2 (H 2 O) 3 ) 2 (μ-pmtz)](pmtz)·11H 2 O (S3). [(Ln(pmtz) 2 (H 2 O) 3 ) 2 (μ-pmtz)] 2 (pmtz) 2 ·14H 2 O (S4) is formed with Nd 3+ and Sm 3+ . Here, the smaller Ln 3+ cations, Dy 3+ to Lu 3+ , all yield [Ln(H 2 O) 8 ](pmtz) 3 ·3H 2 O (S5). This selective crystallization of Ln 3+ cations based primarily on ionic radii provides a simple method for achieving group separations.
Surface-Enhanced Separation of Water from Hydrocarbons: Potential Dewatering Membranes for the Catalytic Fast Pyrolysis of Pine Biomass
The impact of surface-selective coatings on water permeation through a membrane when exposed to catalytic fast pyrolysis (CFP) vapor products was studied by tailoring the surface properties of the membrane coating from superhydrophilic to superhydrophobic. Our approach used high-performance architectured surface-selective (HiPAS) membranes that were inserted after a CFP reactor. At this insertion point, the inner wall surface of a tubular membrane was exposed to a mixture of water and upgraded product vapors, including light gases and deoxygenated hydrocarbons. Under proper membrane operating conditions, a high selectivity for water over one-ring upgraded biomass pyrolysis hydrocarbons was observed as a result of a surface-enhanced capillary condensation process. Owing to this surface-enhanced effect, HiPAS membranes have the potential to enable high flux separations, suggesting that water can be selectively removed from the CFP product vapors.
Salt-Induced Liquid?Liquid Phase Separation and Interfacial Crystal Formation in Poly(N-isopropylacr
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Improving Solar Cell Performance Using Quantum Dot Triad Charge-Separation Engines
Here, we use kinetic modeling to explore the current–voltage, power–voltage, and power conversion efficiency characteristics of quantum dot dyads and triads as possible light absorption and charge separation engines in quantum dot, bulk heterojunction solar cells. The external and internal power conversion quantum efficiencies are significantly enhanced by introducing a third quantum dot between the donor and acceptor quantum dots. Given the constraint of comparable charge-recombination and charge-separation rates, open-circuit voltages for triads are predicted to be about 10%–17% larger than those for dyads, and short-circuit currents for triads are about 400% larger than those for dyads. These improvements in the efficiencies can be further enhanced by tuning the band-edge energy offset of the middle-position quantum dot from its neighbors. The band-edge energies of the middle quantum dot should be tuned so that they form a cascading band-edge energy alignment from the band-edge energies of the left CdTe QD to the right CdSe QD. To produce the most favorable solar cell performance, the middle quantum dot’s conduction (valence) band edge should be closer to the right quantum dot’s band edge when the charge recombination rates are low (high) and near the conduction (valence) band edge of the left quantum dot when the charge recombination rates are high (low). This analysis identifies prime strategies to design multi-QD assemblies for solar energy harvesting and conversion.