Separation of molecules based on molecular size in zeolites with appropriate pore aperture dimensions has given rise to the definition of "molecular sieves" and has been the basis for a variety of separation applications. We show here that for a class of chabazite zeolites, what appears to be "molecular sieving" based on dimension is actually separation based on a difference in ability of a guest molecule to induce temporary and reversible cation deviation from the center of pore apertures, allowing for exclusive admission of certain molecules. This new mechanism of discrimination permits "size-inverse" separation: we illustrate the case of admission of a larger molecule (CO) in preference to a smaller molecule (N(2)). Through a combination of experimental and computational approaches, we have uncovered the underlying mechanism and show that it is similar to a "molecular trapdoor". Our materials show the highest selectivity of CO(2) over CH(4) reported to date with important application to natural gas purification.

Aging in super glassy polymers such as poly(trimethylsilylpropyne) (PTMSP), poly(4‐methyl‐2‐pentyne) (PMP), and polymers with intrinsic microporosity (PIM‐1) reduces gas permeabilities and limits their application as gas‐separation membranes. While super glassy polymers are initially very porous, and ultra‐permeable, they quickly pack into a denser phase becoming less porous and permeable. This age‐old problem has been solved by adding an ultraporous additive that maintains the low density, porous, initial stage of super glassy polymers through absorbing a portion of the polymer chains within its pores thereby holding the chains in their open position. This result is the first time that aging in super glassy polymers is inhibited whilst maintaining enhanced CO2 permeability for one year and improving CO2/N2 selectivity. This approach could allow super glassy polymers to be revisited for commercial application in gas separations.

Poly(vinyl alcohol), PVOH, films have been studied as a function of water content. The states of water present in the polymer (bound or free) have been characterized and are a function of water content. The effects of water content (and hence state) on the free volume, chain mobility, and glass transition (T g) behavior have been studied by positron annihilation lifetime spectroscopy, 13C solid state nuclear magnetic resonance, and dynamic mechanical analysis. The addition of approximately 30 wt % water results in a marked increase in free volume cavity size and polymer chain mobility and a corresponding decrease in T g. The water is in a molecular, nonfreezable state for water additions up to approximately 30 wt %, hence it is postulated that nonfreezing water is responsible for the majority of the plasticization in this system. The plasticization is attributed to the increasing free volume and lubrication provided as the water swells the polymer and disrupts polymer−polymer hydrogen bonding. A limited equivalence between the action of water on the polymer and the action of temperature (thermal energy) is proposed.

With controlled nanometre-sized pores and surface areas of thousands of square metres per gram, metal-organic frameworks (MOFs) may have an integral role in future catalysis, filtration and sensing applications. In general, for MOF-based device fabrication, well-organized or patterned MOF growth is required, and thus conventional synthetic routes are not suitable. Moreover, to expand their applicability, the introduction of additional functionality into MOFs is desirable. Here, we explore the use of nanostructured poly-hydrate zinc phosphate (α-hopeite) microparticles as nucleation seeds for MOFs that simultaneously address all these issues. Affording spatial control of nucleation and significantly accelerating MOF growth, these α-hopeite microparticles are found to act as nucleation agents both in solution and on solid surfaces. In addition, the introduction of functional nanoparticles (metallic, semiconducting, polymeric) into these nucleating seeds translates directly to the fabrication of functional MOFs suitable for molecular size-selective applications.

A porous treasure: Porous aromatic framework PAF‐1 (see picture, blue structure) has been lithiated, giving a reduced framework with an increased gas storage capacity compared to native PAF‐1 (by 22, 71, and 320 % for H2, CH4, and CO2, respectively). The reduced framework was examined spectroscopically, and the potential hydrogen storage capacity was calculated.

The reaction of '70-labelled water with titanium n-propoxide [T~(OPT")~] proceeds rapidly to produce OTi, and OTi, environments that can be clearly identified from 1 7 0 magic-angle spinning NMR spectra. The gel structure is highly disordered but the quadrupolar interaction is shown to be small throughout (quadrupolar coupling constant, C,< 1.5 MHz). Organic fragments, which can be monitored by 13C NMR, remain right up until crystallisation of anatase at 300 "C. Crystallisation is confirmed by electron diffraction, and electron microscopy determines the crystallite size to be ca. 3 nm. 170 NMR and electron diffraction are also used to follow the conversion of anatase to rutile. Keywords Sol-gel processing ; Titania ; 1 7 0 MAS NMR ; Electron diffraction Sol-gel processing is becoming increasingly important in the formation of oxide precursors for the manufacture of dense ceramics' and high-surface-area samples.2 Hydrolysis of metal alkoxides can be controlled carefully to produce very fine Paper 3/01282D;

A wide range of 17O-enriched phases ABO3 and A2BO3 (A = Li, Na, Ca, Sr, Ba, and La; B = Ti, Zr, Sn, Nb, and Al) and related compounds has been synthesized and studied using 17O magic angle spinning (MAS) NMR spectroscopy. In these highly ionic phases, the 17O electric field gradients are small, and as a result highly resolved NMR spectra that reveal subtle structural inequivalences are observed. For titanates and zirconates the 17O chemical shifts fall in distinct, well-defined regions (372−564 and 280−376 ppm, respectively). The ratio of isotropic 17O chemical shifts from isostructural titanates and zirconates with the same A cation is constant, and this ratio is close to the ratio of the polarizing powers of titanium and zirconium. The B cation appears to be the dominant influence in determining the 17O chemical shift in these compounds. Additionally the number of oxygen resonances and the shift difference between them increases as the symmetry of the structure decreases. 119Sn MAS NMR has been applied to a variety of stannates and shows a large shift difference (68.2 ppm) between CaSnO3 phases with the ilmenite and GdFeO3 perovskite type crystal structures. 27Al and 17O MAS NMR have been used to study the conversion of lanthanum and aluminum sol−gel precursors to crystalline LaAlO3 perovskite. 17O NMR proves to be more informative than 27Al NMR and shows that the formation of LaAlO3 proceeds via the reaction of separate lanthanum and aluminum oxides initially formed.

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