Design and Synthesis of Polyimides Based on Carbocyclic Pseudo-Tröger’s Base-Derived Dianhydrides for Membrane Gas Separation Applications

Two novel carbocyclic pseudo-Tröger’s base-derived dianhydrides, 5,6,11,12-tetrahydro-5,11-methanodibenzo­[<i>a,e</i>]­[8]­annulene-2,3,8,9-tetracarboxylic anhydride (CTB1) and its dione-substituted analogue 6,12-dioxo-5,6,11,12-tetrahydro-5,11-methano­dibenzo­[<i>a,e</i>]­[8]­annulene-2,3,8,9-tetra­carboxylic dianhydride (CTB2), were made and used for the synthesis of soluble polyimides of intrinsic microporosity with 3,3′-dimethyl­naphthidine (DMN). The polyimides CTB1-DMN and CTB2-DMN exhibited excellent thermal stability of ∼500 °C and high BET surface areas of 580 and 469 m² g^–1, respectively. A freshly made dione-substituted CTB2-DMN membrane demonstrated promising gas separation performance with O₂ permeability of 206 barrer and O₂/N₂ selectivity of 5.2. A higher O₂ permeability of 320 barrer and lower O₂/N₂ selectivity of 4.2 were observed for a fresh CTB1-DMN film due to its higher surface area and less tightly packed structure as indicated by weaker charge-transfer complex interactions. Physical aging over 60 days resulted in reduction in gas permeability and moderately enhanced selectivity. CTB2-DMN exhibited notable performance with gas permeation data located between the 2008 and 2015 permeability/selectivity upper bounds for O₂/N₂ and H₂/CH₄

Facile Synthesis of a Hydroxyl-Functionalized Tröger’s Base Diamine: A New Building Block for High-Performance Polyimide Gas Separation Membranes

Two intrinsically microporous polyimides (PIM-PIs) were synthesized by the polycondensation reaction of 4,4′-(hexafluoro­isopropylidene)­diphthalic anhydride (6FDA) and 3,3,3′,3′-tetramethyl­spirobisindane-6,7,6′,7′-tetracarboxylic dianhydride (SBI) with a newly designed <i>o</i>-hydroxyl-functionalized Tröger’s base diamine, 1,7-diamino-6<i>H</i>,12<i>H</i>-5,11-methanodibenzo­[1,5]­diazocine-2,8-diol (HTB). Both amorphous PIM-PIs were soluble in aprotic solvents and showed excellent thermal stability with onset decomposition temperature of ∼380 °C. SBI-HTB displayed a higher CO₂ permeability (466 vs 67 barrer) than 6FDA-HTB but a significantly lower selectivity for CO₂/CH₄ (29 vs 73), H₂/CH₄ (29 vs 181), O₂/N₂ (4.6 vs 6.0), and N₂/CH₄ (1 vs 2.5). 6FDA-HTB displayed the highest gas-pair permselectivity values of all reported OH-functionalized PIM-PIs to date. The high permselectivity of 6FDA-HTB resulted primarily from exceptional diffusion selectivity due to strong size-sieving properties caused by hydrogen bonding between the proton of the hydroxyl group and the nitrogen atoms in the tertiary amine of the Tröger’s base (O–H···N)

Novel Spirobifluorene- and Dibromospirobifluorene-Based Polyimides of Intrinsic Microporosity for Gas Separation Applications

Two series of novel intrinsically microporous polyimides were synthesized from 9,9′-spirobifluorene-2,2′-diamine (SBF) and its bromine-substituted analogue 3,3′-dibromo-9,9′-spirobifluorene-2,2′-diamine (BSBF) with three different dianhydrides (6FDA, PMDA, and SPDA). All polymers exhibited high molecular weight, good solubility in common organic solvents, and high thermal stability. Bromine-substituted polyimides showed significantly increased gas permeabilities but slightly lower selectivities than the SBF-based polyimides. The CO₂ permeability of PMDA–BSBF (693 Barrer) was 3.5 times as high as that of PMDA–SBF (197 Barrer), while its CO₂/CH₄ selectivity was similar (19 vs 22). Molecular simulations of PMDA–SBF and PMDA–BSBF repeat units indicate that the twist angle between the PMDA and fluorene plane changes from 0° in PMDA–SBF to 77.8° in PMDA–BSBF, which decreases the ability of the polymer to pack efficiently due to severe steric hindrance induced by the bromine side groups

Unusual 3,4-Oxidative Coupling Polymerization on 1,2,5-Trisubstituted Pyrroles for Novel Porous Organic Polymers

Porous organic polymers (POPs) have demonstrated promising task-specific applications due to their structure designability and thus functionality. Herein, an unusual 3,4-polymerization on 1,2,5-trisubstituted pyrroles has been developed to give linear polypyrrole-3,4 in high efficiency, with Mn of 20000 and PDI of 1.7. This novel polymerization technique was applied to prepare a series of polypyrrole-based POPs (PY-POP-1–4), which exhibited high BET surface areas (up to 762 m2 g–1) with a meso–micro–supermicro hierarchically porous structure. Furthermore, PY-POPs were doped in the mixed matrix membranes based on the polysulfone matrix to enhance the gas permeability and gas pair selectivity, with H2/N2 selectivity up to 84.6 and CO2/CH4 and CO2/N2 selectivity up to 46.8 and 39.6

Direct Conversion of Cellulose to Glycolic Acid with a Phosphomolybdic Acid Catalyst in a Water Medium

Direct conversion of cellulose to fine chemicals has rarely been achieved. We describe here an eco-benign route for directly converting various cellulose-based biomasses to glycolic acid in a water medium and oxygen atmosphere in which heteromolybdic acids act as multifunctional catalysts to catalyze the hydrolysis of cellulose, the fragmentation of monosaccharides, and the selective oxidation of fragmentation products. With commercial α-cellulose powder as the substrate, the yield of glycolic acid reaches 49.3%. This catalytic system is also effective with raw cellulosic biomass, such as bagasse or hay, as the starting materials, giving rise to remarkable glycolic acid yields of ∼30%. Our heteropoly acid-based catalyst can be recovered in solid form after reaction by distilling out the products and solvent for reuse, and it exhibits consistently high performance in multiple reaction runs

Synthesis and Effect of Physical Aging on Gas Transport Properties of a Microporous Polyimide Derived from a Novel Spirobifluorene-Based Dianhydride

A novel generic method is reported for the synthesis of a spirobifluorene-based dianhydride (SBFDA). An intrinsically microporous polyimide was obtained by polycondensation reaction with 3,3′-dimethylnaphthidine (DMN). The corresponding polymer (SBFDA-DMN) exhibited good solubility, excellent thermal stability, as well as significant microporosity with high BET surface area of 686 m²/g. The O₂ permeability of a methanol-treated and air-dried membrane was 1193 Barrer with a moderate O₂/N₂ selectivity of 3.2. The post-treatment history and aging conditions had great effects on the membrane performance. A significant drop in permeability coupled with an increase in selectivity was observed after long-term aging. After storage of 200 days, the gas separation properties of SBFDA-DMN were located slightly above the latest Robeson upper bounds for several gas pairs such as O₂/N₂ and H₂/N₂

Theoretical Modeling, Facile Fabrication, and Experimental Study of Optimally Bound Bilirubin Oxidase on Palladium Nanoparticles for Enhanced Oxygen Reduction Reaction

This paper presents an optimally bound bilirubin oxidase (BOD) (Myrothecium verrucaria) on palladium nanoparticles (Pd NPs) for enhanced oxygen reduction reaction (ORR). Theoretical modeling of BOD on Pd demonstrated that Pd has strong preferential binding to BOD via T1 copper (Cu) site because of its high adsorption energy. This preferential binding was accompanied by a reduction in distance between the Cu active sites and Pd which would result in an increase in electron transfer rate (<i>k</i>_cat) and an enhancement in catalytic activity of BOD. Inspired by the computational results, a biocathode comprising carbon nanotube (CNT), Pd NPs, and BOD (CNT-Pd-BOD) was facilely fabricated using an electroless deposition method. The CNT-Pd-BOD biocathode exhibited higher catalytic activity (1.52 times) and <i>k</i>_cat (1.71 times) when compared with CNT-BOD only biocathode. These results demonstrate Pd NPs as a suitable substrate for preferential binding with BOD to increase catalytic activity

Mixed-Penetrant Sorption in Ultrathin Films of Polymer of Intrinsic Microporosity PIM‑1

Mixed-penetrant sorption into ultrathin films of a superglassy polymer of intrinsic microporosity (PIM-1) was studied for the first time by using interference-enhanced in situ spectroscopic ellipsometry. PIM-1 swelling and the concurrent changes in its refractive index were determined in ultrathin (12–14 nm) films exposed to pure and mixed penetrants. The penetrants included water, <i>n</i>-hexane, and ethanol and were chosen on the basis of their significantly different penetrant–penetrant and penetrant–polymer affinities. This allowed studying microporous polymer responses at diverse ternary compositions and revealed effects such as competition for the sorption sites (for water/<i>n</i>-hexane or ethanol/<i>n</i>-hexane) or enhancement in sorption of typically weakly sorbing water in the presence of more highly sorbing ethanol. The results reveal details of the mutual sorption effects which often complicate comprehension of glassy polymers’ behavior in applications such as high-performance membranes, adsorbents, or catalysts. Mixed-penetrant effects are typically very challenging to study directly, and their understanding is necessary owing to a broadly recognized inadequacy of simple extrapolations from measurements in a pure component environment

Highly Compatible Hydroxyl-Functionalized Microporous Polyimide-ZIF‑8 Mixed Matrix Membranes for Energy Efficient Propylene/Propane Separation

Mixed-matrix membranes composed of mechanically strong, solution-processable polymers and highly selective ultramicroporous fillers (pore size < 7 Å) are superior candidate membrane materials for various energy-intensive gas separation applications because of their structural tunability to achieve enhanced gas permeability and gas–pair selectivity. However, their industrial implementation has been severely hindered because inefficient compatibility of the polymer matrices and crystalline fillers results in poorly performing membranes with low filler capacity and interfacial defects. Herein, we report for the first time a unique strategy to fabricate highly propylene/propane selective mixed-matrix membranes (MMMs) composed of a hydroxyl-functionalized microporous polyimide (PIM-6FDA-OH) and an ultramicroporous, strongly size-sieving zeolitic imidazolate framework (ZIF-8). Excellent compatibility between PIM-6FDA-OH and ZIF-8 with selective filler loading up to 65 wt % resulted from N···O–H induced hydrogen bonding as evidenced by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The newly developed MMMs demonstrated <i>unprecedented mixed-gas performance</i> for C₃H₆/C₃H₈ separation and outstanding plasticization resistance of up to at least 7 bar feed pressure. The reported fabrication concept is expected to be applicable to a wide variety of OH-functionalized polymers and alternative tailor-made imidazolate framework materials designed for MMMs to achieve optimal gas separation performance

How Do Organic Vapors Swell Ultrathin Films of Polymer of Intrinsic Microporosity PIM-1?

Dynamic sorption of ethanol and toluene vapor into ultrathin supported films of polymer of intrinsic microporosity PIM-1 down to a thickness of 6 nm are studied with a combination of in situ spectroscopic ellipsometry and in situ X-ray reflectivity. Both ethanol and toluene significantly swell the PIM-1 matrix and, at the same time, induce persistent structural relaxations of the frozen-in glassy PIM-1 morphology. For ethanol below 20 nm, three effects were identified. First, the swelling magnitude at high vapor pressures is reduced by about 30% as compared to that of thicker films. Second, at low penetrant activities (below 0.3<i>p</i>/<i>p</i>₀), films below 20 nm are able to absorb slightly more penetrant as compared with thicker films despite a similar swelling magnitude. Third, for the ultrathin films, the onset of the dynamic penetrant-induced glass transition <i>P</i>_g has been found to shift to higher values, indicating higher resistance to plasticization. All of these effects are consistent with a view where immobilization of the superglassy PIM-1 at the substrate surface leads to an arrested, even more rigid, and plasticization-resistant, yet still very open, microporous structure. PIM-1 in contact with the larger and more condensable toluene shows very complex, heterogeneous swelling dynamics, and two distinct penetrant-induced relaxation phenomena, probably associated with the film outer surface and the bulk, are detected. Following the direction of the penetrant’s diffusion, the surface seems to plasticize earlier than the bulk, and the two relaxations remain well separated down to 6 nm film thickness, where they remarkably merge to form just a single relaxation