Poly(ethylene oxide) (PEO)-containing polymer membranes are attractive for CO2-related gas separations due to their high selectivity toward CO2. However, the development of PEO-rich membranes is frequently challenged by weak mechanical properties and a high crystallization tendency of PEO that hinders gas transport. Here we report a new series of highly CO2-selective, amorphous PEO-containing segmented copolymers prepared from commercial Jeffamine polyetheramines and pentiptycene-based polyimide. The copolymers are much more mechanically robust than the nonpentiptycene containing counterparts due to the molecular reinforcement mechanism of supramolecular chain threading and interlocking interactions induced by the pentiptycene structures, which also effectively suppresses PEO crystallization leading to a completely amorphous structure even at 60% PEO weight content. Membrane transport properties are sensitively affected by both PEO weight content and PEO chain length. A nonlinear correlation between CO2 permeability with PEO weight content was observed due to the competition between solubility and diffusivity contributions, whereby the copolymers change from being size-selective to solubility-selective when PEO content reaches 40%. CO2 selectivities over H2 and N2 increase monotonically with both PEO content and chain length, indicating strong CO2-philicity of the copolymers. The copolymer film with the longest PEO sequence (PEO2000) and highest PEO weight content (60%) showed a measured CO2 pure gas permeability of 39 Barrer, and ideal CO2/H2 and CO2/N2 selectivities of 4.1 and 46, respectively, at 35 °C and 3 atm, making them attractive for hydrogen purification and carbon capture.

Treatment of nontraditional source waters (e.g., produced water, municipal and industrial wastewaters, agricultural runoff) offers exciting opportunities to expand water and energy resources via water reuse and resource recovery. While conventional polymer membranes perform water/ion separations well, they do not provide solute-specific separation, a key component for these treatment opportunities. Herein, we discuss the selectivity limitations plaguing all conventional membranes, which include poor removal of small, neutral solutes and insufficient discrimination between ions of the same valence. Moreover, we present synthetic approaches for solute-tailored selectivity including the incorporation of single-digit nanopores and solute-selective ligands into membranes. Recent progress in these areas highlights the need for fundamental studies to rationally design membranes with selective moieties achieving desired separations.

2A series of polybenzimidazoles containing sulfonyl groups were synthesized in 3 Eaton's reagent for high temperature H 2 /CO 2 separation membranes. The key 4 monomer, 3,3',4,4'-tetraaminodiphenylsulfone, was prepared via a novel and 5 economical synthetic route starting from 4,4'-dichlorodiphenylsulfone. These 6 polybenzimidazoles with sulfonyl moieties had enhanced solubilities in dipolar 7 aprotic solvents relative to the commercial Celazole ® that is prepared from 8 diaminobenzidine. Thermal gravimetric analysis showed that the materials were stable 9 at elevated temperatures with 5% weight loss values of at least 485 o C in either air or 10 N 2 . Glass transition temperatures of three polybenzimidazoles in this series were 11 ascertained by dynamic mechanical analysis to be 438-480 o C. These sulfonyl-12 containing polybenzimidazoles exhibited excellent gas separation properties for 13 H 2 /CO 2 . Polymers from tetraaminodiphenylsulfone and either terephthalic or 14 isophthalic acid crossed Robeson's upper bound for H 2 /CO 2.

Properties of nanoconfined adsorbed H 2 O on mineral surfaces are distinct from those of bulk H 2 O, and this can lead to significant differences in reactivity. Here, we investigate how O-exchange between H 2 O and CO 2 depends on the thickness of H 2 O films on the mineral, forsterite (Mg 2 SiO 4 ), which at sufficient adsorbed H 2 O is highly reactive toward carbonation. Rates of O-exchange measured using Oisotopic tracers and infrared spectroscopy increase with adsorbed H 2 O concentration and are two orders of magnitude faster than those for inert substrates such as fumed silica (SiO 2 ). Quantum chemical calculations demonstrate that O-exchange can be catalyzed through interactions with active Mg 2+ sites that lower the barrier for carbonic acid formation. These active metal centers exist as Mg−bicarbonate surface complexes or dissolved Mg 2+ with predominantly bicarbonate counterions, as evidenced by infrared and nuclear magnetic resonance spectroscopies. Intermolecular proton hopping to bicarbonate can form a carbonic acid complex that readily decomposes to CO 2 and H 2 O, leading to O-isotope scrambling. Unlike fumed silica, we find no evidence that adsorbed H 2 O film structure dictates O-exchange rates. In contrast, it is mainly Mg−bicarbonate surface complexes and Mg 2+ fully dissolved within the H 2 O films that catalyze O-isotope scrambling.

Sulfur dioxide (SO 2 ) removal is a key component of many industrial processes, especially coal-fired power generation. Controlling SO 2 emissions is vital to maintaining environmental quality, as SO 2 is a contributor to acid rain, but has value as a chemical feedstock. Although a number of novel solvents/materials including ionic liquids (ILs) have recently been proposed for alternatives to limestone scrubbing for SO 2 capture/removal from point sources, the imidazole architecture presents a convenient, inexpensive and efficient class of low volatility and low viscosity solvents to accomplish this goal. On the basis of our prior work with imidazoles for CO 2 capture, we have extended our interests toward understanding the relationship between imidazole structure and SO 2 absorption. Using a series of imidazole compounds with various substituents at the 1, 2 and/or 4(5) positions of the five-membered ring, SO 2 absorption via both chemical and physical mechanisms was observed. The chemical absorption product is a relatively stable 1:1 SO 2 −imidazole complex, while physical absorption of SO 2 is dependent on pressure and temperature. Because imidazoles are relatively small molecules, they are an efficient absorption medium for SO 2 and can form adducts wherein the mass fraction of bound SO 2 is >40 wt %. The SO 2 −imidazole complexes were also observed to produce distinct color and/or phase changes that are associated with the nature of the substituents present. The chemically bound SO 2 can be released under vacuum at moderate temperature (∼100°C) and vacuum, yielding the original neat solvent, while the physically dissolved SO 2 can be readily removed at ambient temperature under vacuum. This behavior corresponds to a much smaller enthalpy of absorption for physical dissolution (−4 to −13 kJ/mol) as determined via thermodynamic relationships compared to the binding energies of chemical complexation (−35 to −42 kJ/mol) as determined via density functional theory calculations. Increasing chemical complexation energies are correlated with increased substitution on the imidazole ring. Simulations were also employed to gain insight into the structures of the SO 2 −imidazole complexes, illustrating changes in partial charge distribution before and after complexation as well as confirming a charge transfer complex is formed based on the N−S bond length.