Search

High permeance membranes were produced by addition of highly permeable nanoparticulate fillers (hypercrosslinked polystyrene, HCP, and its carbonized form, C-HCP) to a high free volume polymer (polymer of intrinsic microporosity PIM-1) in a thin film (typically 2 µm) on a porous polyacrylonitrile support. Self-standing mixed matrix membranes (MMMs) of thicknesses in the range 40–90 µm were also prepared with the same polymer and fillers. While robust MMMs could only be formed for moderate filler loadings, thin film nanocomposite (TFN) membranes could be produced from dispersions with filler loadings up to 60 wt%. On increasing the filler loading, CO2 permeance increased in line with the predictions of the Maxwell model for a highly permeable filler. Physical ageing led to some loss of permeance coupled with an increase in CO2/N2 selectivity. However, for TFN membranes the greatest effects of ageing were seen within 90 days. After ageing, TFN membranes showed high permeance with reasonable selectivity; for example, with 60 wt% C-HCP, CO2 permeance > 9300 GPU, CO2/N2 selectivity ~ 11.

The binding domains within a mixed matrix membrane (MMM) that is selective for CO2 comprising MFM-300(Al) and the polymer 6FDA-Durene-DABA have been established via in situ synchrotron IR microspectroscopy. The MOF crystals are fully accessible and play a critical role in the binding of CO2, creating a selective pathway to promote permeation of CO2 within and through the MMM. This study reveals directly the molecular mechanism for the overall enhanced performance of this MMM in terms of permeability, solubility and selectivity for CO2.

Charging programs giving rise to desired burden and gas distributions in the ironmaking blast furnace were detected through an evolutionary multi-objective optimization strategy. The Pareto optimal...

A steel plant flow sheet containing a top gas recycling blast furnace is simulated and subjected to multi-objective optimization through an evolutionary approach. A recently proposed k-optimality criterion is used, which allows optimizing a large number of objectives in an evolutionary way, which is difficult to do by other methods. A number of promising optimum results, showing the optimum tradeoffs between several cost factors are identified and analyzed. The results appear to be very significant in the context of CO2 reduction challenges faced by the steel industries today.

The burden distribution in the ironmaking blast furnace plays an important role for the operation as it affects the gas flow distribution, heat and mass transfer, and chemical reactions in the shaft. This work studies certain aspects of burden distribution by small-scale experiments and numerical simulation by the discrete element method (DEM). Particular attention is focused on the complex layer-formation process and the problems associated with estimating the burden layer distribution by burden profile measurements. The formation of mixed layers is studied, and a computational method for estimating the extent of the mixed layer, as well as its voidage, is proposed and applied on the results of the DEM simulations. In studying a charging program and its resulting burden distribution, the mixed layers of coke and pellets were found to show lower voidage than the individual burden layers. The dynamic evolution of the mixed layer during the charging process is also analyzed. The results of the study can be used to gain deeper insight into the complex charging process of the blast furnace, which is useful in the design of new charging programs and for mathematical models that do not consider the full behavior of the particles in the burden layers.

The changing of solid particulate matter in the ironmaking blast furnace is studied in the paper using modeling and experiments in small scale. A small-scale charging rig is used to study the layer formation when coke and pellets are charged using a bell-less charging equipment. The modeling involved the use of a simplified geometric model as well as discrete element modeling (DEM). In DEM, both spherical and non-spherical (clumped particles) models were used to describe the coke, while for pellets a spherical model was used. The results from the different models are compared to the experimental findings, and conclusions concerning the appropriateness of the models are drawn. Finally, a challenging phenomenon, i.e., the coke push effect, where lighter coke on the burden surface is shifted by charging of the heavier pellets is discussed and some simulation results for the full-scale problem are presented.

The identification of preferred binding domains within a host structure provides important insights into the function of materials. State-of-the-art reports mostly focus on crystallographic studies of empty and single component guest-loaded host structures to determine the location of guests. However, measurements of material properties (e.g., adsorption and breakthrough of substrates) are usually performed for a wide range of pressure (guest coverage) and/or using multi-component gas mixtures. Here we report the development of a multifunctional gas dosing system for use in X-ray powder diffraction studies on Beamline I11 at Diamond Light Source. This facility is fully automated and enables in situ crystallographic studies of host structures under (i) unlimited target gas loadings and (ii) loading of multi-component gas mixtures. A proof-of-concept study was conducted on a hydroxyl-decorated porous material MFM-300(VIII) under (i) five different CO2 pressures covering the isotherm range and (ii) the loading of equimolar mixtures of CO2/N2. The study has successfully captured the structural dynamics underpinning CO2 uptake as a function of surface coverage. Moreover, MFM-300(VIII) was incorporated in a mixed matrix membrane (MMM) with PIM-1 in order to evaluate the CO2/N2 separation potential of this material. Gas permeation measurements on the MMM show a great improvement over the bare PIM-1 polymer for CO2/N2 separation based on the ideal selectivity.

This paper presents an approach by which charging programs in the blast furnace can be evolved. The core of the method is a mathematical model, which on the basis of a given charging program estimates the two-dimensional distribution of burden layers in the shaft. A gas flow model uses this information to estimate the gas distribution, applying a simplified treatment of the conditions in the upper shaft. The aim is to find the charging program that gives a state of the furnace shaft matching a target for the radial temperature profile at the level of an in-burden probe. This is accomplished by applying a genetic algorithm that makes an efficient search among the huge number of potential charging programs, executing the burden and gas flow models in the function evaluations. The method is illustrated by six cases, where targets for the gas temperature distribution are given and the genetic algorithm evolves the charging sequence and the chute settings for the dumps. It is demonstrated that the algorithm ef...

A mathematical model for fast evaluation of charging programs in bell-less top blast furnaces is presented. The model describes the burden formation and descent procedures in the blast furnace, and can be used for designing charging programs. Experimental results in small scale were used to validate the model. The model was applied to a real charging program from a reference blast furnace. Through comparison between the estimated burden distribution and gas temperatures from an above-burden probe it was concluded that the model has captured the main features of the distribution of coke and pellets. The potential of using the model for the design of new charging programs was finally illustrated by analyzing the effect of small changes in the positions of the rings on the arising burden distribution.

An amide-functionalized metal organic framework (MOF) material, MFM-136, shows a high CO2 uptake of 12.6 mmol g–1 at 20 bar and 298 K. MFM-136 is the first example of an acylamide pyrimidyl isophthalate MOF without open metal sites and, thus, provides a unique platform to study guest binding, particularly the role of free amides. Neutron diffraction reveals that, surprisingly, there is no direct binding between the adsorbed CO2/CH4 molecules and the pendant amide group in the pore. This observation has been confirmed unambiguously by inelastic neutron spectroscopy. This suggests that introduction of functional groups solely may not necessarily induce specific guest–host binding in porous materials, but it is a combination of pore size, geometry, and functional group that leads to enhanced gas adsorption properties.

High-free-volume glassy polymers, such as polymers of intrinsic microporosity (PIMs) and poly(trimethylsilylpropyne), have attracted attention as membrane materials due to their high permeability. However, loss of free volume over time, or aging, limits their applicability. Introduction of a secondary filler phase can reduce this aging but either cost or instability rules out scale up for many fillers. Here, we report a cheap, acid-tolerant, nanoparticulate hypercrosslinked polymer ‘sponge’ as an alternative filler. On adding the filler, permeability is enhanced and aging is strongly retarded. This is accompanied by a CO2/N2 selectivity that increases over time, surpassing the Robeson upper bound.

The method of choice for in-depth investigation of the magnetic anisotropy in molecular nanomagnets is high-frequency electron spin resonance (HFESR) spectroscopy. It has the benefits of high resolution and facile access to large energy splittings. However, the sensitivity is limited to about 107 spins for a reasonable data acquisition time. In contrast, methods based on the measurement of the deflection of a cantilever were shown to enable single spin magnetic resonance sensitivity. In the area of molecular nanomagnets, the technique of torque detected electron spin resonance (TDESR) has been used sporadically. Here, we explore the applicability of that technique by investigating molecular nanomagnets with different types of magnetic anisotropy. We also assess different methods for the detection of the magnetic torque. We find that all types of samples are amenable to these studies, but that sensitivities do not yet rival those of HFESR.

Big softy! A soft porous molecular crystal composed of organic cages exhibits complex multistep gas sorption isotherms (see figure), analogous to those observed in soft porous metal–organic frameworks. Softness is induced by frustrated packing of the cages and structural flexibility leads to kinetic guest trapping.

Limited natural resources and a growing concern about the potential effect of carbon dioxide emissions on the world's climate have triggered a search of ways to suppressing the emissions of CO2 in primary steelmaking. A possible future solution is to strip CO2 from the blast furnace top gas, feeding back the gas to the tuyere level. The work reported in this article explores states of an integrated steel plant that arise if both production costs and emissions are simultaneously minimized. This multiobjective problem is tackled by genetic algorithms using a predator–prey strategy for constructing the Pareto-frontier of nondominating solutions. Four alternative ways of treating the top gas recycling problem are explored, and the resulting solutions are analyzed with respect to the two objectives and to the internal states of the plant they correspond to. Conclusions are drawn concerning the solutions in terms of technical feasibility and complexity.

The measured Rabi oscillations of an ensemble of spins (here the spins 3/2 of the V15 single molecular magnet) are strongly damped by the excitation ac-field. The corresponding decoherence mechanism is attributed to an electromagnetic noise created by the dipolar spin-bath, inhomogeneously driven by the microwave field. Decoherence by electronic and nuclear spin-baths express themselves very differently vs microwave power. This decoherence mechanism should apply to all types of weakly interacting ensembles of qubits, beyond magnetism.

Pulling the old switcheroo: Microporosity can be switched “on” and “off” in a crystalline molecular organic solid composed of cage molecules (see scheme). The switch is facilitated by conformational flexibility in the soft organic crystal state.

Interlocked molecules comprise two or more separate components that are joined by 'mechanical' rather than covalent bonds. In other words, these molecular assemblies cannot be dissociated without the cleavage of one or more chemical bonds. Although recent progress has enabled the preparation of such topologies through coordination or templating interactions, three-dimensional interlocked covalent architectures remain difficult to prepare. Here, we present a template-free one-pot synthesis of triply interlocked organic cages. These 20-component dimers consist of two tetrahedral monomeric cages each built from four nodes and six linkers. The monomers exhibit axial chirality, which is recognized by their partner cage during the template-free interlocking assembly process. The dimeric cages also include two well-defined cavities per assembly, which for one of the systems studied led to the formation of a supramolecular host-guest chain. These interlocked organic molecules may prove useful as part of a toolkit for the modular construction of complex porous solids and other supramolecular assemblies.

The effect of confinement and energy transfer on the dynamics of a molecular magnet, known as a model system to study quantum coherence, is investigated. For this purpose the well-known polyoxovanadate [V(15)As(6)O(42)(H(2)O)](6-) (V(15)) is incorporated into a protein (human serum albumin, HSA) cavity. Due to a huge overlap of the optical absorption spectrum of V(15) with the emission spectrum of a fluorescence center of HSA (containing a single tryptophan residue), energy transfer is induced and probed by steady-state and time-resolved fluorescence. The geometrical coordination and the distance of the confined V(15) to the tryptophan moiety of HSA are investigated at various temperatures. This effect is used as a local probe for the thermal denaturation of the protein at elevated temperatures.

Spherical capsules of the type [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-) exhibiting 20 {Mo(9)O(9)} pores with crown ether functions allowed us to perform a sophisticated study of the title phenomenon based on synthetic work as well as NMR spectroscopy. The pores of the host system interact in solution specifically with guests that can be noncovalently bonded, such as formamidinium and acetamidinium cations, while having different affinities to the pores. The exchange between the guest species present in solution and in the pores was investigated, including, besides the extreme scenarios of complete pore closing and complete opening, that of stepwise pore plugging. Because of this option it was possible to model for the first time passive transmembrane cation transport based on gated pores/channels. These have the appropriate dimensions and can even adopt different structure flexibilities in response to different cations. The present investigation is based on related syntheses as well as on numerous detailed (7)Li NMR studies of Li(+) transport/exchange equilibria in dependence of the pore environment/guest situations. One compound containing capsules with sulfate ligands (2) could be obtained in which all the pores are plugged with formamidinium cations and another corresponding one was obtained with additionally encapsulated Ca(2+) ions (3); these were taken up after temporary release of some of the formamidinium plugs/guests upon short heating of the related solution.

We performed electron spin-resonance measurements on single crystals of the molecular nanomagnet ${\mathrm{V}}_{15}$ using a novel broadband spectrometer, both in parallel and in perpendicular modes, we see $({B}_{1}\ensuremath{\parallel}{B}_{0},{B}_{1}\ensuremath{\perp}{B}_{0})$. Measurements were carried out in proximity of the spin level crossing at ${B}_{0}=2.75\phantom{\rule{0.28em}{0ex}}\mathrm{T}$. We observed spin-forbidden transitions from the $S=1/2$ zero-field ground state to the $S=3/2$ excited state in parallel mode spectra. Spin-forbidden transitions are employed for switching of coherent interactions between qubits in recent quantum simulator proposals. Our theoretical investigations showed that the mixing of spin states can result from either an antisymmetric exchange interaction or a combination of static distortion and hyperfine interaction.

The energy-efficient separation of chemical feedstocks is a major sustainability challenge. Porous extended frameworks such as zeolites or metal-organic frameworks are one potential solution to this problem. Here, we show that organic molecules, rather than frameworks, can separate other organic molecules by size and shape. A molecular organic cage is shown to separate a common aromatic feedstock (mesitylene) from its structural isomer (4-ethyltoluene) with an unprecedented perfect specificity for the latter. This specificity stems from the structure of the intrinsically porous cage molecule, which is itself synthesized from a derivative of mesitylene. In other words, crystalline organic molecules are used to separate other organic molecules. The specificity is defined by the cage structure alone, so this solid-state 'shape sorting' is, uniquely, mirrored for cage molecules in solution. The behaviour can be understood from a combination of atomistic simulations for individual cage molecules and solid-state molecular dynamics simulations.

Three-dimensional (3D) technology offers greater device integration, reduced signal delay and reduced interconnect power. It also provides greater design flexibility by allowing heterogeneous integration. In this work, a 3D thermal model of a multicore system is developed to investigate the effects of hotspot, and placement of silicon die layers, on the thermal performance of a modern flip-chip package. In this regard, both the steady-state and transient heat transfer analysis has been performed on the 3D flip-chip package. Two different thermal models were evaluated under different operating conditions. Through experimental simulations, we have found a model which has better thermal performance. The optimal placement solution is also provided based on the maximum temperature attained by the individual silicon dies. We have also provided the improvement that is required in the heat sink thermal resistance of a 3D system when compared to the single-die system.

By the deliberate choice of the internal ligands of the porous nanocapsules [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-), the respective cavities' shells can be differently sized/functionalized. This allows one to trap the same large number of water molecules, that is, 100 in a capsule cavity with formate ligands having a larger space available, as well as in a cavity containing sulfates and hypophosphites, that is, with less space. Whereas the 100 molecules fill the space completely in the second case in which they are organized in three shells, a four-shell system with underoccupation and broken hydrogen bonds is observed in the other case. This is an unprecedented result in terms of the structurally well defined special forms of "higher and lower density" water molecule assemblies. Precisely, by replacing the larger ligands in the mentioned nanocapsule type by formates, voids in the capsule cavity of (HC(NH(2))(2))(22)[{(HC(NH(2))(2))(20)+(H(2)O)(100)} subset{(Mo)Mo(5)O(21)(H(2)O)(6)}(12){Mo(2)O(4)(HCO(2))}(30)]ca. 200 H(2)O are generated that get filled with water molecules concomitant with an expansion of the three to four shell {H(2)O}(100) cluster. The water shells in both capsules containing different ligands are organized in the form of dodecahedra (partly with underoccupation) and a strongly distorted rhombicosidodecahedron spanned by a {H(2)O}(60)={(H(2)O)(5)}(12) aggregate. The well-defined water shells only emerge if cations cannot enter into the capsules, which is achieved by closing the pores with plugs/guests such as formamidinium cations. The work is based on the syntheses of two new compounds, related single-crystal X-ray diffraction studies, and molecular dynamics simulations, which show remarkably that water molecule shell structuring occurs in the capsules due to the confined conditions even in the case of open pores and at room temperature if cation uptake is prevented.

Molecular magnets are a type of molecule containing multiple magnetic ions whose spins are tightly coupled to give a single 'collective' spin. The quantum mechanical properties of this collective spin are attracting attention as a possible basis for the functional unit of a quantum computer. Until now it has not been clear whether the quantum spin states of these molecular entities are sufficiently long-lived to permit useful computation, but new work suggests that they are. Bertaina et al. observed pronounced quantum oscillations between the spin states of one such molecular magnet, consistent with long-lived quantum coherence, in this system at least. They also outline a scheme by which, through careful material design, these properties could be harnessed in a practical context. Molecular magnets are a class of molecule containing multiple magnetic ions whose spins are tightly coupled to give a single 'collective' spin. But it has remained an open question whether the quantum spin states of these molecular entities are sufficiently long-lived to permit useful computation. Pronounced quantum oscillations between the spin states of one such molecular magnet have been observed, indicating that quantum coherence is long-lived. The term ‘molecular magnet’ generally refers to a molecular entity containing several magnetic ions whose coupled spins generate a collective spin, S (ref. 1). Such complex multi-spin systems provide attractive targets for the study of quantum effects at the mesoscopic scale. In these molecules, the large energy barriers between collective spin states can be crossed by thermal activation or quantum tunnelling, depending on the temperature or an applied magnetic field2,3,4. There is the hope that these mesoscopic spin states can be harnessed for the realization of quantum bits—‘qubits’, the basic building blocks of a quantum computer—based on molecular magnets5,6,7,8. But strong decoherence9 must be overcome if the envisaged applications are to become practical. Here we report the observation and analysis of Rabi oscillations (quantum oscillations resulting from the coherent absorption and emission of photons driven by an electromagnetic wave10) of a molecular magnet in a hybrid system, in which discrete and well-separated magnetic clusters are embedded in a self-organized non-magnetic environment. Each cluster contains 15 antiferromagnetically coupled S = 1/2 spins, leading to an S = 1/2 collective ground state11,12,13. When this system is placed into a resonant cavity, the microwave field induces oscillatory transitions between the ground and excited collective spin states, indicative of long-lived quantum coherence. The present observation of quantum oscillations suggests that low-dimension self-organized qubit networks having coherence times of the order of 100 μs (at liquid helium temperatures) are a realistic prospect.

Nature 453, 203–206 (2008) The authors report that in a recent extension of this Letter, considering different concentrations, they were not able to reproduce the very weak signal of the ground-state EPR transition (the red curves termed ‘1/2’ in Figs 3 and 4). The authors report that the signal is hardly observable (with intensity lower than that of the cavity background); but the more important S = 3/2 transitions (blue curves in Figs 3 and 4), which give rise to well-defined oscillations with several periods and high signal intensity, are reproducible.

Ubiquitous water is apart from its anomalies, for several reasons the most mysterious compound. According to its basic role in life processes it has even been considered as a biomolecule especially in context of the important role of confined “high and low density water”. C. Bo, A. Muller et al. report on page 1844 ff., confined higher and lower density water assemblies encapsulated in the same type of porous capsule that exhibit differently functionalized internal shells (see picture).

Based on a combined theoretical-experimental study, we propose that substituted m-phenylene ligands (m-N-Phi-N) can act as tuneable strong ferromagnetic couplers connecting Cu(II) ions; a new complex presenting that bridge with J close to +15 cm(-1) has been suggested and synthesized.

Two different SURMOF films have been grown on a transparent conducting surface for spectro-electrochemical characterisation of radical species., The application of metal–organic framework (MOF) materials in electrochemical and electrochromic devices remains rare. One of the main reasons for this is the inability to readily access their detailed electrochemistry. The inherent insolubility of these materials does not allow interrogation by traditional solution-based electrochemical or spectroscopic methods. In this study, we report a straightforward alternative approach to the spectroelectrochemical study of MOFs. We have used two systems as exemplars in this study, MFM-186 and MFM-180. The method involves chemical modification of a working electrode to attach MOF materials without using corrosive reagents such as inorganic acids or bases which otherwise could limit their application in device development. MFM-186 demonstrates the formation of a stable radical species [MFM-186]˙+ on electrochemical oxidation, and this has been characterised by electrochemical, spectroelectrochemical and EPR spectroscopic techniques coupled to DFT analysis.