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Membranes are particularly attractive for lowering the energy intensity of separations as they eliminate phase changes. While many tantalizing polymers are known, limitations in selectivity and stability slightly preclude further development. Mixed-matrix membranes may address these shortcomings. Key to their realization is the intimate mixing between the polymer and the additive to eliminate nonselective transport, improve selectivity, and resist physical aging. Polymers of intrinsic microporosity (PIMs) have inherently promising gas transport properties. Here, we show that porous additives can improve transport and resist aging in PIM-1. We develop a simple, low-cost, and scalable hyper-cross-linked polymer (poly-dichloroxylene, pDCX), which was hydroxylated to form an intimate mixture with the polar PIM-1. Solvent variation allowed control of physical aging rates and improved selectivity for smaller gases. This detailed study has allowed many interactions within mixed matrix membranes to be directly elucidated and presents a practical means to stabilize porous polymers for separation applications.

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Conspectus Since the discovery of polymers of intrinsic microporosity (PIMs) in 2004, the fast size-selective interconnected pore cavities of the polymers have caused the upper bound of membrane performance to be revised, twice. Simultaneously, porous materials have meant that mixed matrix membranes (MMMs) are now a relatively simple method of enhancing transport properties. While there are now reliable routes with mixed matrices to improve the fundamental transport properties of membrane materials, many of the other properties crucial for separation applications remain largely unaddressed. Physical aging severely affects membrane performance over time, especially for those prepared from high fractional free volume polymers. Gradual densification of the glassy polymer chains causes the connected pore channels present in these materials to constrict. Studies now suggest that aging of superglassy polymer materials is a two-step process; a rapid densification occurs within the first few days, followed by a gradual rearrangement of packed chains over longer time frames toward a theoretical equilibrium state. Although advantageous in terms of size selectivity, the considerable drop in permeation over the days and weeks after manufacture greatly impacts material applicability. While often still permeating faster than traditional membrane materials, the continuous gradual collapse of cavities in these polymers are a significant challenge in the application of high free volume polymer membranes. In 2014, we discovered that the porous aromatic framework PAF-1 not only greatly improved the membrane’s void space and speed of gas transport but also seemingly froze several glassy polymers in a low-density state, holding the polymer’s pore channels open, a process termed as Porosity Induced Side chain Adsorption (PISA). This discovery of PISA fundamentally challenged the conventional wisdom at the time that the aging rate could only be addressed by densification of the polymer. Unlike other high-performance glassy polymers, membranes containing PAF-1 can retain their high permeability for more than a year. Several other examples of antiaging behavior have been subsequently reported by the team, where control of aging rate as a function of gas penetrant, selectivity increases, and stability at higher pressures was reported. These works also demonstrate that these mixed matrix systems had applicability for several other separations, including pervaporation, solvent nanofiltration, and as separators for energy applications. In our subsequent studies, the antiaging mechanism has been elucidated as an effect of the interaction between the polymer’s accessible pendant methyl group and the aromatic pore surface of PAF-1 or other antiaging additives. In otherwise identical MMMs, where this hypothesized methyl−π interaction is either absent or interrupted, we find that the antiaging behavior expected by the fixation of the polymer chains to the pore surface and PAF-1 does not occur. As a design approach for mixed matrix membranes, targ...

A ZnxCd1−xS solid solution in uniform nanoparticles prepared using a supercritical solvothermal route achieved high photocatalytic activity and durability.

No abstract

Ag/BiOBr film coated on the glass substrate was synthesized by a solvothermal method and a subsequent photoreduction process. Such a Ag/BiOBr film was then adhered to a hollow rotating disk filled with long-afterglow phosphor inside the chamber. The Ag/BiOBr film exhibited high photocatalytic activity for organic pollutant degradation owing to the improved visible-light harvesting and the separation of photoinduced charges. The long-afterglow phosphor could absorb the excessive daylight and emit light around 488 nm, activating the Ag/BiOBr film to realize round-the-clock photocatalysis. Because the Ag nanoparticles could extend the light absorbance of the Ag/BiOBr film to wavelengths of around 500 nm via a surface plasma resonance effect, they played a key role in realizing photocatalysis induced by long-afterglow phosphor.

As the potential for a Hydrogen economy re-emerges globally, its distribution is a key enabling capability to master. One option is to utilise the existing reticulated natural gas infrastructure, mixing...