Enhanced Gas Separation Properties of Tröger’s Base Polymer Membranes Derived from Pure Triptycene Diamine Regioisomers

Most high-performance Tröger’s base (TB) polymers for gas separation membranes are from mixed diamine isomers, and the configuration differences in the polymer chain packing that arise from these isomers are still unknown. Herein three triptycene-containing Tröger’s-base-based polymers, CTTB (from pure Trip-2,6-diamine), MTTB (from pure Trip-2,7-diamine), and ITTB (from 50/50 Trip-2,6-diamine/Trip-2,7-diamine mixed regioisomers), were successfully synthesized and fully characterized. All polymers exhibited high thermal stability and rigidity, a large Brunauer–Emmett–Teller surface area, and distinct microporosity (pores > MTTB (6.15 Å) > CTTB (5.68 Å)) and pore-size distributions (ITTB (6.14–8.0 Å) > CTTB (5.48–7.0 Å) > MTTB (6.09–6.90 Å)). MTTB and CTTB showed outstanding H2/CH4, H2/N2, and O2/N2 separation performance that successfully surpassed the 2015 trade-off curves, better than those of the most recently reported state-of-the-art gas separation membranes and ITTB, due to their more uniform polymer main chain arrangement. This result shed light on the future high-performance gas separation polymer designs

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

Plasticization-Resistant Carboxyl-Functionalized 6FDA-Polyimide of Intrinsic Microporosity (PIM–PI) for Membrane-Based Gas Separation

A novel trimethyl-substituted carboxyl-containing polyimide was synthesized via a one-pot high-temperature polycondensation reaction of 4,4′-(hexafluoroisopropylidene)­diphthalic anhydride (6FDA) and 3,5-diamino-2,4,6-trimethylbenzoic acid (TrMCA). The polyimide (6FDA-TrMCA) displayed a Brunauer–Emmett–Teller surface area of 260 m2 g–1, demonstrating intrinsic microporosity, in contrast to the related low-free volume COOH-functionalized polyimide 6FDA-DABA. Compared to the nonfunctionalized 6FDA polyimide analogue made from 2,4,6-trimethyl-m-phenylenediamine (TrMPD)also known as 6FDA-DAMcarboxyl functionalization in 6FDA-TrMCA resulted in reduced surface area, lower fractional free volume, and tighter average chain spacing. Gas permeabilities of 6FDA-TrMCA were typical of functionalized polyimides of intrinsic microporosity (PIM–PIs). For example, at 2 atm and 35 °C, 6FDA-TrMCA showed pure-gas H2 and CO2 permeability of 193 and 144 barrer, coupled with H2/CH4 and CO2/CH4 selectivity of 61 and 45, respectively. Notably, in mixed-gas permeation tests with an equimolar CO2–CH4 mixture at a CO2 partial pressure of 12 atm, 6FDA-TrMCA demonstrated performance located on the 2018 mixed-gas upper bound with a CO2 permeability of ∼98 barrer and CO2/CH4 permselectivity of 38. As the first reported COOH-functionalized PIM–PI homopolymer, 6FDA-TrMCA revealed excellent resistance against CO2-induced plasticization at least up to a CO2 partial pressure of 15 atm, covering the range of typical wellhead CO2 partial pressures (5–10 atm)

High-Pressure CO₂ Sorption in Polymers of Intrinsic Microporosity under Ultrathin Film Confinement

Ultrathin microporous polymer films are pertinent to the development and further spread of nanotechnology with very promising potential applications in molecular separations, sensors, catalysis, or batteries. Here, we report high-pressure CO2 sorption in ultrathin films of several chemically different polymers of intrinsic microporosity (PIMs), including the prototypical PIM-1. Films with thicknesses down to 7 nm were studied using interference-enhanced in situ spectroscopic ellipsometry. It was found that all PIMs swell much more than non-microporous polystyrene and other high-performance glassy polymers reported previously. Furthermore, chemical modifications of the parent PIM-1 strongly affected the swelling magnitude. By investigating the behavior of relative refractive index, nrel, it was possible to study the interplay between micropores filling and matrix expansion. Remarkably, all studied PIMs showed a maximum in nrel at swelling of 2–2.5% indicating a threshold point above which the dissolution in the dense matrix started to dominate over sorption in the micropores. At pressures above 25 bar, all PIMs significantly plasticized in compressed CO2 and for the ones with the highest affinity to the penetrant, a liquidlike mixing typical for rubbery polymers was observed. Reduction of film thickness below 100 nm revealed pronounced nanoconfinement effects and resulted in a large swelling enhancement and a quick loss of the ultrarigid character. On the basis of the partial molar volumes of the dissolved CO2, the effective reduction of the Tg was estimated to be ∼200 °C going from 128 to 7 nm films

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

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

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

Pristine and Carboxyl-Functionalized Tetraphenylethylene-Based Ladder Networks for Gas Separation and Volatile Organic Vapor Adsorption

A novel tetraphenylethylene-based ladder network (MP1) made by polycondensation reaction from 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)­tetrakis­(benzene-1,2-diol) and 2,3,5,6-tetrafluoroterephthalonitrile and its COOH-functionalized analogue (MP2) were synthesized for the first time. Their structures were confirmed by solid-state nuclear magnetic resonance (13C cross-polarization magic angle spinning), Fourier transform infrared spectroscopy, and elementary analysis. MP1 exhibited a high Brunauer–Emmett–Teller surface area (1020 m2 g–1), whereas the COOH-functionalized MP2 showed a much smaller surface area (150 m2 g–1) but displayed a more uniform pore size distribution. Because of the high density of nitrile groups in the network polymers of intrinsic microporosity (PIMs) and strong interaction with quadrupole CO2 molecules, MP1 exhibited a high CO2 adsorption capacity of 4.2 mmol g–1 at 273 K, combined with an isosteric heat of adsorption (Qst) of 29.6 kJ mol–1. The COOH-functionalized MP2 showed higher Qst of 34.2 kJ mol–1 coupled with a modest CO2 adsorption capacity of 2.2 mmol g–1. Both network PIMs displayed high theoretical ideal adsorbed solution theory CO2/N2 selectivities (51 and 94 at 273 K vs 34 and 84 at 298 K for MP1 and MP2, respectively). The high selectivities of MP1 and MP2 were confirmed by experimental column breakthrough experiments with CO2/N2 selectivity values of 23 and 45, respectively. Besides the promising CO2 capture and CO2/N2 selectivity properties, MP1 also demonstrated high sorption capacity for toxic volatile organic vapors. At 298 K and a relative pressure of 0.95, benzene and toluene sorption uptakes reached 765 and 1041 mg g–1, respectively. Moreover, MP1 also demonstrated some potential for adsorptive separation of xylene isomers with adsorptive selectivity of 1.75 for m-xylene/o-xylene

Large-Scale Production of Electrothermal Films with GNSs/CNTs/CB Three-Dimensional Structure Ink by Screen Printing

With the development of flexible electronic technology, there is a growing demand for electrothermal materials that are environmentally friendly, safe, low-cost, and large-scale producible for efficiently solving thermal management issues. In this study, low-cost water-based carbon series electrothermal ink is prepared by a dispersion and grinding method, and the electrothermal films with various areas can be prepared on a large scale by screen printing. Simultaneously, the three-dimensional (3D) conductive network structure of graphene nanosheets (GNSs)/multiwalled carbon nanotubes (MWCNTs)/carbon black (CB) is built by the ball milling dispersion process. Due to the low percolation threshold network formed by GNSs/CNTs/CB, the prepared ink has excellent conductivity, and the square resistance (Rsq) reaches 4.3 Ω sq–1 with a thickness of 25 μm. Moreover, the saturation temperature (Ts) of the screen-printed electrothermal film (4 cm × 4 cm) can reach 165 °C with an input voltage of 10 V, and it has extremely low power consumption (444.75 cm2 W–1). The electrothermal film also maintains relatively stable electrical properties in a bending test of 115 000 cycles. When the heating device (9 cm × 31 cm) is applied to the expanded polypropylene (EPP) box, the food temperature can be kept around 60 °C and the flavor can be well preserved

Ti₃C₂T_<i>x</i> MXene Nanoflakes Embedded with Copper Indium Selenide Nanoparticles for Desalination and Water Purification through High-Efficiency Solar-Driven Membrane Evaporation

Solar-driven interface evaporation recently emerges as one of the most promising methods for seawater desalination and wastewater purification, mainly due to its low energy consumption. However, there still exist special issues in the present material system based on conventional noble metals or two-dimensional (2D) nanomaterials etc., such as high costs, low light-to-heat conversion efficiencies, and unideal channels for water transport. Herein, a composite photothermal membrane based on Ti3C2Tx MXene nanoflakes/copper indium selenide (CIS) nanoparticles is reported for highly efficient solar-driven interface evaporation toward water treatment applications. Results indicate that the introduction of CIS improves the spatial accessibility of the membrane by increasing the interlayer spacings and wettability of MXene nanoflakes and enhances light absorption capability as well as reduces reflection for the photothermal membrane. Simultaneously, utilization of the MXene/CIS composite membrane improves the efficiency of light-to-heat conversion probably due to formation of a Schottky junction between MXene and CIS. The highest water evaporation rate of 1.434 kgm–2 h–1 and a maximum water evaporation efficiency of 90.04% as well as a considerable cost-effectiveness of 62.35 g h–1/$ are achieved by using the MXene/CIS composite membrane for solar interface evaporation, which also exhibits excellent durability and light intensity adaptability. In addition, the composite photothermal membrane shows excellent impurity removal ability, e.g., >98% for salt ions, >99.8% for heavy metal ions, and ∼100% for dyes molecules. This work paves a promising avenue for the practical application of MXene in the field of water treatment