New materials capable of separating mixtures of saturated, unsaturated, and aromatic hydrocarbons can enable more efficient industrial processes and cleaner energy. Outstanding challenges in ...hydrocarbon separations stem from the similar structures, properties, and reactivities of the molecules comprising many of these mixtures. With high surface areas, tunable pore geometries, and adjustable surface functionality, metal–organic frameworks hold tremendous promise for effecting previously difficult or impossible separations. In this review, we provide a comprehensive account of the metal–organic frameworks that have been investigated for hydrocarbon separations within the context of their potential relevance for separating various industrial alkane-, alkene-, and aromatic-containing mixtures.
The structures and magnetic properties of K(18-crown-6)+ (1) and K(18-crown-6)(THF)2+ (2) salts of the η8-cyclooctatetraenide sandwich complex Er(COT)2− (COT2– = cyclooctatetraene dianion) are ...reported. Despite slight differences in symmetry, both compounds exhibit slow magnetic relaxation under zero applied dc field with relaxation barriers of ∼150 cm–1 and waist-restricted magnetic hysteresis. Dc relaxation and dilution studies suggest that the drop in the magnetic hysteresis near zero field is influenced by a bulk magnetic avalanche effect coupled with tunneling of the magnetization. Through dilution with K(18-crown-6)(THF)2Y(COT)2 (3), these phenomena are substantially quenched, resulting in an open hysteresis loop to 10 K. Importantly, this represents the highest blocking temperature yet observed for a mononuclear complex and the second highest for any single-molecule magnet. A comprehensive comparative analysis of the magnetism of K(18-crown-6)Ln(COT)2 (Ln = Sm, Tb, Dy, Ho, Yb) reveals slow relaxation only for K(18-crown-6)Dy(COT)2 (4) with weak temperature dependence. Collectively, these results highlight the utility of an equatorial ligand field for facilitating slow magnetic relaxation in the prolate ErIII ion.
Two representative metal-organic frameworks, Zn4O(BTB)2 (BTB3- = 1,3,5-benzenetribenzoate; MOF-177) and Mg2(dobdc) (dobdc4- = 1,4-dioxido-2,5-benzenedicarboxylate; Mg-MOF-74, CPO-27-Mg), are ...evaluated in detail for their potential use in post-combustion CO2 capture via temperature swing adsorption (TSA). Low-pressure single-component CO2 and N2 adsorption isotherms were measured every 10 degreeC from 20 to 200 degreeC, allowing the performance of each material to be analyzed precisely. In order to gain a more complete understanding of the separation phenomena and the thermodynamics of CO2 adsorption, the isotherms were analyzed using a variety of methods. With regard to the isosteric heat of CO2 adsorption, Mg2(dobdc) exhibits an abrupt drop at loadings approaching the saturation of the Mg2+ sites, which has significant implications for regeneration in different industrial applications. The CO2/N2 selectivities were calculated using ideal adsorbed solution theory (IAST) for MOF-177, Mg2(dobdc), and zeolite NaX, and working capacities were estimated using a simplified TSA model. Significantly, MOF-177 fails to exhibit a positive working capacity even at regeneration temperatures as high as 200 degreeC, while Mg2(dobdc) reaches a working capacity of 17.6 wt % at this temperature. Breakthrough simulations were also performed for the three materials, demonstrating the superior performance of Mg2(dobdc) over MOF-177 and zeolite NaX. These results show that the presence of strong CO2 adsorption sites is essential for a metal-organic framework to be of utility in post-combustion CO2 capture via a TSA process, and present a methodology for the evaluation of new metal-organic frameworks via analysis of single-component gas adsorption isotherms.
A redox−active metal–organic framework, Fe2(dobpdc) (dobpdc4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate), is shown to undergo a topotactic oxidative insertion reaction with a variety of weakly ...coordinating anions, including BF4 – and PF6 –. The reaction results in just a minor lattice contraction, and a broad intervalence charge-transfer band emerges, indicative of charge mobility. Although both metal- and ligand-based oxidations can be accessed, only the former were found to be fully reversible and, importantly, proceed stoichiometrically under both chemical and electrochemical conditions. Electrochemical measurements probing the effects of nanoconfinement on the insertion reaction revealed strong anion size and solvent dependences. Significantly, the anion insertion behavior of Fe2(dobpdc) enabled its use in the construction of a dual-ion battery prototype incorporating a sodium anode. As a cathode, the material displays a particularly high initial reduction potential and is further stable for at least 50 charge/discharge cycles, exhibiting a maximum specific energy of 316 Wh/kg.
The escalating level of atmospheric carbon dioxide is one of the most pressing environmental concerns of our age. Carbon capture and storage (CCS) from large point sources such as power plants is one ...option for reducing anthropogenic CO₂ emissions; however, currently the capture alone will increase the energy requirements of a plant by 25-40 %. This Review highlights the challenges for capture technologies which have the greatest likelihood of reducing CO₂ emissions to the atmosphere, namely postcombustion (predominantly CO₂/N₂ separation), precombustion (CO₂/H₂) capture, and natural gas sweetening (CO₂/CH₄). The key factor which underlies significant advancements lies in improved materials that perform the separations. In this regard, the most recent developments and emerging concepts in CO₂ separations by solvent absorption, chemical and physical adsorption, and membranes, amongst others, will be discussed, with particular attention on progress in the burgeoning field of metal-organic frameworks.
During development, both cells and tissues must acquire the correct shape to allow their proper function. This is especially relevant in the nervous system, where the shape of individual cell ...processes, such as the axons and dendrites, and the shape of entire tissues, such as the folding of the neocortex, are highly specialized. While many aspects of neural development have been uncovered, there are still several open questions concerning the mechanisms governing cell and tissue shape. In this review, we discuss the role of the extracellular matrix (ECM) in these processes. In particular, we consider how the ECM regulates cell shape, proliferation, differentiation and migration, and more recent work highlighting a key role of ECM in the morphogenesis of neural tissues.
The identification of properties that contribute to the persistence and resilience of ecosystems despite climate change constitutes a research priority of global relevance. Here we present a novel, ...empirical approach to assess the relative sensitivity of ecosystems to climate variability, one property of resilience that builds on theoretical modelling work recognizing that systems closer to critical thresholds respond more sensitively to external perturbations. We develop a new metric, the vegetation sensitivity index, that identifies areas sensitive to climate variability over the past 14 years. The metric uses time series data derived from the moderate-resolution imaging spectroradiometer (MODIS) enhanced vegetation index, and three climatic variables that drive vegetation productivity (air temperature, water availability and cloud cover). Underlying the analysis is an autoregressive modelling approach used to identify climate drivers of vegetation productivity on monthly timescales, in addition to regions with memory effects and reduced response rates to external forcing. We find ecologically sensitive regions with amplified responses to climate variability in the Arctic tundra, parts of the boreal forest belt, the tropical rainforest, alpine regions worldwide, steppe and prairie regions of central Asia and North and South America, the Caatinga deciduous forest in eastern South America, and eastern areas of Australia. Our study provides a quantitative methodology for assessing the relative response rate of ecosystems--be they natural or with a strong anthropogenic signature--to environmental variability, which is the first step towards addressing why some regions appear to be more sensitive than others, and what impact this has on the resilience of ecosystem service provision and human well-being.
Scientists have long employed lanthanide elements in the design of materials with extraordinary magnetic properties, including the strongest magnets known, SmCo5 and Nd2Fe14B. The properties of these ...materials are largely a product of fine-tuning the interaction between the lanthanide ion and the crystal lattice. Recently, synthetic chemists have begun to utilize f-elements-both lanthanides and actinides-for the construction of single-molecule magnets, resulting in a rapid expansion of the field. The desirable magnetic characteristics of the f-elements are contingent upon the interaction between the single-ion electron density and the crystal field environment in which it is placed. This interaction leads to the single-ion anisotropies requisite for strong single-molecule magnets. Therefore, it is of vital importance to understand the particular crystal field environments that could lead to maximization of the anisotropy for individual f-elements. Here, we summarize a qualitative method for predicting the ligand architectures that will generate magnetic anisotropy for a variety of f-element ions. It is hoped that this simple model will serve to guide the design of stronger single-molecule magnets incorporating the f-elements.
Abstract Plant-soil feedbacks are shaped by microbial legacies that plants leave in the soil. We tested the persistence of these legacies after subsequent colonization by the same or other plant ...species using 6 typical grassland plant species. Soil fungal legacies were detectable for months, but the current plant effect on fungi amplified in time. By contrast, in bacterial communities, legacies faded away rapidly and bacteria communities were influenced strongly by the current plant. However, both fungal and bacterial legacies were conserved inside the roots of the current plant species and their composition significantly correlated with plant growth. Hence, microbial soil legacies present at the time of plant establishment play a vital role in shaping plant growth even when these legacies have faded away in the soil due the growth of the current plant species. We conclude that soil microbiome legacies are reversible and versatile, but that they can create plant-soil feedbacks via altering the endophytic community acquired during early ontogeny.
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