Stepwise Observation and Quantification and Mixed Matrix Membrane Separation of CO2 within a Hydroxy-Decorated Porous Host

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(V-III) under (i) five different CO2 pressures covering the isotherm range and (ii) the loading of equimolar mixtures of CO2/N-2. The study has successfully captured the structural dynamics underpinning CO2 uptake as a function of surface coverage. Moreover, MFM-300(V-III) was incorporated in a mixed matrix membrane (MMM) with PIM-1 in order to evaluate the CO2/N-2 separation potential of this material. Gas permeation measurements on the MMM show a great improvement over the bare PIM-1 polymer for CO2/N-2 separation based on the ideal selectivity

Free volume and intrinsic microporosity in polymers

The concept of free volume is useful for explaining aspects of the chain mobility and permeability of polymers, even though its precise definition is subject to debate. Polymers that trap a large amount of interconnected free volume in the glassy state behave in many respects like microporous materials and potentially find application in membrane separations and heterogeneous catalysis. The development is outlined of a new type of polymer, for which the molecular structure contains sites of contortion (e.g. spiro-centres) within a rigid backbone (e.g. ladder polymer). These polymers of intrinsic microporosity (PIMs) include both insoluble network polymers and soluble non-network polymers that may be processed into membranes or other useful forms. Experimental methods are discussed for elucidating the free volume or micropore distribution, and the behaviour of PIMs is compared with that of the ultrapermeable polymer poly(1-trimethylsilyl-1-propyne)

Synthesis and Gas Permeation Properties of Spirobischromane-Based Polymers of Intrinsic Microporosity

Polymers of intrinsic microporosity (PIMs) possess molecular structures composed of fused rings with linear units linked together by a site of contortion so that the macromolecular structure is both rigid and highly non-linear. For PIM-1, which has previously demonstrated encouraging gas permeability data, the site of contortion is provided by the monomer 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane. Here we describe the synthesis and properties of a PIM derived from the structurally related 6,6′,7,7′-tetrahydroxy-4,4,4′,4′-tetramethyl-2,2′-spirobischromane and copolymers prepared from combination of this monomer with other PIM-forming biscatechol monomers, including the highly rigid monomer 9,10-dimethyl-9,10-ethano-9,10-dihydro-2,3,6,7-tetrahydroxyanthracene. Generally, the polymers display good solubility in organic solvents and have high average molecular masses () in the range 80 000–200 000 g · mol−1 and, therefore, are able to form robust, solvent-cast films. Gas permeability and selectivity for He, H2, N2, O2, CO2, and CH4 were measured for the polymers and compared to the values previously obtained for PIM-1. The spirobischromane-based polymers demonstrate enhanced selectivity for a number of gas pairs but with significantly lower values for permeability. The solubility coefficient for CO2 of two of the copolymers exceed even that of PIM-1, which previously demonstrated the highest value for a membrane-forming polymer. Therefore, these polymers might be useful for gas or vapor separations relying on solubility selectivity

Hydrogen absorption in 3.1 nanometre sized palladium samples: does structure matter?

In this work the hydrogen absorption behaviour of two types of Pd-clusters, different in structure but similar in size (3.1 nm), will be presented. First, icosahedral Pd clusters stabilised in surfactants; second, cubic Pd clusters stabilised in a Teflon-AF matrix. The phase transition in these samples was monitored by in-situ X-ray diffraction. It will be shown that the hydrogen uptake ability depends strongly on the lattice structure, which is affected by the type of stabiliser. Teflon AF stabilised clusters (cubic clusters) show the phase transition which is common for bulk Pd, whereas the surfactant stabilised clusters (icosahedral clusters) show only weak lattice dilatation upon hydrogen absorption. Pressure-lattice parameter isotherms show that the cubic clusters absorb large amounts of hydrogen in comparison to the icosahedral clusters. The measured lattice expansion is 0.130 angstrom at 10(5) Pa and 300 K, which is about 320% the amount measured for icosahedral clusters (0.04 angstrom). This suggests that surface sites are available for hydrogen in the Pd-Teflon-AF samples which are not accessible for Pd-surfactant-clusters, and that the icosahedral lattice absorbs less hydrogen for similar external pressures

Polymers of intrinsic microporosity derived from bis(phenazyl) monomers

Novel polymers of intrinsic microporosity (PIMs) are prepared from bis(phenazyl) monomers derived from readily available bis(catechol)s. One of the polymers (termed PIM-7) has an excellent combination of properties with high internal surface area, good film-forming characteristics, and gas transport properties that make it a suitable candidate for gas separation membranes. The high gas permeability and good ideal selectivity of PIM-7 place it above Robeson's upper-bound for a number of commercially important gas pairs (e.g., O2/N2, CO2/CH4, and CO2/N2)