SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A further improvement has been made in the synthesis of an N-type porous polymer for the separation of permanent gases. Changing the ratios of reactants and diluting the Hi-DVB with styrene led to a porous polymer gas chromatographic packing which is superior to commercial products and to the author's own previously reported custom-made polymer.
Stable porphyrin based porous polymer networks, PPN-23 and PPN-24, have been synthesized through a facile one-pot approach by the aromatic substitution reactions of pyrrole and aldehydes. We report PPN-24(Fe) shows high catalytic efficiency as a biomimetic catalyst in the oxidation reaction of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) in the presence of H 2 O 2 .
Porous polymer networks (PPNs) are attractive materials for capacitive energy storage because they offer high surface areas for increased double-layer capacitance, open structures for rapid ion transport, and redox-active moieties that enable faradaic (pseudocapacitive) energy storage. Here we demonstrate a new attractive feature of PPNs—the ability of their reduced forms (radical anions and dianions) to interact with small radii cations through synergistic interactions arising from densely packed redox-active groups, only when prepared as thin films. When naphthalene diimides (NDIs) are incorporated into PPN films, the carbonyl groups of adjacent, electrochemically generated, NDI radical anions and dianions bind strongly to K+, Li+, and Mg2+, shifting the formal potentials of NDI’s second reduction by 120 and 460 mV for K+ and Li+-based electrolytes, respectively. In the case of Mg2+, NDI’s two redox waves coalesce into a single two-electron process with shifts of 240 and 710 mV, for the first and second reductions, respectively, increasing the energy density by over 20 % without changing the polymer backbone. In contrast, the formal reduction potentials of NDI derivatives in solution are identical for each electrolyte, and this effect has not been reported for NDI previously. This study illustrates the profound influence of the solid-state structure of a polymer on its electrochemical response, which does not simply reflect the solution-phase redox behavior of its monomers.
Aromatic porous polymer networks (PPNs) are promising candidate materials for organic solvent nanofiltration (OSN) membranes, in which molecular-sieving selectivity, high permeability, and chemical/structural stability can be integrated. In this work, aromatic PPN membranes p-PPN, m-PPN and tri-PPN are fabricated by in situ aldol triple condensation cross-linking. These membranes demonstrate high stability, permeability and sharp selectivity in OSN, thanks to the aromatic nature of the backbone, high surface area (up to 1235 m 2 g -1 ), and narrowly distributed pore sizes. They possess a high organic solvent permeability so that a good permeance is achieved despite a thickness of over 100 μm. The molecular weight cut-off and molecular weight retention onset of these membranes are ~600 g mol -1 and 350 g mol -1 , respectively, making it possible to efficiently separate molecules from a complex mixture composed of compounds with only marginally different molecular weights. As a result of the highly stable nature of the aromatic backbones, these PPN membranes show retained structural integrity and OSN performance in the presence of either a strong acid or strong base for over 50 h. The extraordinary stability integrated with excellent permeability and selectivity renders these PPN membranes promising candidates for challenging OSN applications under extreme conditions.
Porous polymeric networks and composite materials comprising metal nanoparticles distributed in the polymeric networks are provided. Also provided are methods for using the polymeric networks and the composite materials in liquid- and vapor-phase waste remediation applications. The porous polymeric networks, are highly porous, three-dimensional structures characterized by high surface areas. The polymeric networks comprise polymers polymerized from aldehydes and phenolic molecules.
Porous polymeric networks and composite materials comprising metal nanoparticles distributed in the polymeric networks are provided. Also provided are methods for using the polymeric networks and the composite materials in liquid- and vapor-phase waste remediation applications. The porous polymeric networks, are highly porous, three-dimensional structures characterized by high surface areas. The polymeric networks comprise polymers polymerized from aldehydes and phenolic molecules.
The Zhou group has long been interested in the development of CO2 capture sorbents, having investigated both metal-organic frameworks (MOFs) and porous polymer networks (PPNs). In this work, we have begun an investigation of a new generation of PPN based sorbents. These PPN sorbents are low cost alternatives to expensive MOF sorbents, while achieving the low heats of adsorption necessary for economic CO2 capture.
Ether-thioether functionalized porous aromatic framework (PAF) polymers provide high selectivity for iron(II) and iron(III) adsorption in aqueous samples.
Heparins are widely used anticoagulants for surgical procedures and extracorporeal therapies. However, all of them have bleeding risks. Protamine sulfate, the only clinically approved antidote for unfractionated heparin (UFH), has adverse effects. Moreover, protamine can only partially neutralize low-molecular-weight heparins (LMWHs) and is not effective for fondaparinux. In this report an inclusion–sequestration strategy for efficient neutralization of heparin anticoagulants by cationic porous supramolecular organic frameworks (SOFs) and porous organic polymers (POPs) is reported. Isothermal titration calorimetric and fluorescence experiments show strong binding affinities of these porous polymers toward heparins, whereas dynamic light scattering and zeta potential analysis confirm that the heparin sequences are adsorbed into the interior of the porous hosts. Activated partial thromboplastin time, anti-FXa, and thromboelastography assays indicate that their neutralization efficacies are higher than or as high as that of protamine for UFH and generally superior to protamine for LMWHs and fondaparinux, which is further confirmed by tail-transection model in mice and ex vivo aPTT or anti-FXa analysis in rats. Acute toxicity evaluations reveal that one of the SOFs displays outstanding biocompatibility. This work suggests that porous polymers can supply safe and rapid reversal of clinically used heparins, as protamine surrogates, providing an improved approach for their neutralization.
We designed and synthesized the cyclodextrin (CD)-based hyper-crosslinked porous polymers (HCPPs) for selective CO 2 adsorption and storage. We also explored the effect of monomer size on micropore formation, and determined a feasible way to tailor the porosity of the materials during the hyper-crosslinking process.
A hyper-crosslinked β-cyclodextrin porous polymer (BnCD-HCPP) was designed and synthesized facilely by β-cyclodextrin benzylation and subsequent crosslinking via a Friedel–Crafts alkylation route. The BnCD-HCPP shows an extremely high BET surface area, large pore volume, and high thermal stability, making it a highly efficient adsorbent for removal of aromatic pollutants from water. The adsorption efficiency in terms of distribution coefficient, defined as the ratio of adsorption capacity to equilibrium adsorbate concentration, ranged from 10 3 to 10 6 mL g -1 within a concentration of 0–100 ppm, one order of magnitude higher than that of other β-cyclodextrin-based adsorbents reported previously. The molar percentage of adsorbate to β-cyclodextrin exceeded 300%, suggesting that the adsorption occurred not only in the cyclodextrin cavities via a 1 : 1 complexation, but also in the nanopores of the BnCD-HCPP created during the hyper-crosslinking. The BnCD-HCPP can be further functionalized by incorporation of gold nanoparticles for catalytic transformation of adsorbed phenolic compounds such as 4-nitrophenol to 4-aminophenol.
The industrial scale capture of CO 2 from flue gas streams is becoming an increasingly important environmental issue. However, many of the existing CO 2 capture systems either have regenerative energy demands that are too high or are cost prohibitive. A promising solution is the utilization of functionalized solid sorbents, such as porous polymer networks (PPNs). PPNs are attractive due to their inherent structural stability, flexibility, high surface areas, and ability to incorporate various functional groups within the chemical scaffold. Herein, a low cost, scalable alternative to common carbon capture systems using a series of robust mesoporous melamine-formaldehyde resins (mPMFs) loaded with active alkylamine sorbents is presented, which is dubbed as the PPN-150 family. The variants within this material class are differentiated based on the incorporation of functionalized dopants; small molecules added at low molar percent concentrations to impart additional functionality into the PPN in order to achieve low cost noncovalent tethering of alkylamines. The cyanuric acid doped PPN-151-DETA (DETA = diethylenetriamine) demonstrate unique features such as improved cycling capacity and heat of adsorption. To show its scalability, PPN-151-DETA is successfully synthesized at the 250 g scale without loss of the sorbent properties.
Functional organic–inorganic hybrid materials with tunable properties are useful across many application areas, ranging from gas storage to electronics, flame retardants, separations, and catalysis. Combining polymers, with a suite of functional groups and conformational flexibility, and inorganic nanoparticles, with tunable surface chemistry and composition, yields hybrids with novel functional properties. Specifically, in catalysis, control of the electronic environment at a metal interface is paramount in determining the catalytic properties. In this contribution, we describe a modular process to prepare porous polymer–nanocrystal (NC) composites in a hierarchical, multilayered synthesis, in which multiple parameters can be accurately tuned: polymer functional groups and the corresponding pore structure, the polymer layer thickness, and the NC size, shape, and composition. This process provides for a variety of controlled materials with high surface area, tunable chemistry, and thermal and chemical stabilities. Furthermore, we demonstrate their utility for shape- and size-selective catalytic conversions both in oxidation and hydrogenation reactions, where they show increased selectivity by orders of magnitude compared to conventional polymer-supported metal catalysts. In light of the high degree of control in the composite structure, this method allows for the design and realization of catalysts for several reactions and reaction environments and for nanomaterials with other applications.
Toxic per- and polyfluoroalkyl substances (PFAS) are now found in nearly every water source on the planet. Exposure to these molecules can have negative health consequences, but the low concentration of PFAS relative to other solutes in water makes their removal challenging. Adsorbents offer a promising treatment route, but often exhibit low selectivities and removal capacities, as well as slow kinetics. The performance in these metrics can be improved by chemically optimizing PFAS binding sites and maximizing PFAS-adsorbent interactions. To explore how to achieve this, a porous polymer network solid (PPN-6, also known as PAF-1) was postsynthetically modified with various chemical moieties capable of leveraging unique combinations of electrostatic, hydrogen-bonding, hydrophobic, and fluorophilic interactions with PFAS molecules. Batch adsorption experiments and computational studies revealed that electrostatic and hydrogen-bonding interactions drive short-chain PFAS adsorption, while hydrophobic and fluorophilic interactions improve long-chain PFAS adsorption. In complex water matrices, a combination of electrostatic and fluorophilic interactions led to the greatest total PFAS removal. The best-performing material, functionalized with a fluorinated alkylammonium (PPN-6-FNDMB), selectively adsorbs PFAS with high capacity (up to 4.0 mmol/g) and rapid kinetics (equilibrium reached in <30 s). Furthermore, PPN-6-FNDMB outperforms several commercial adsorbents, achieving near-complete removal of 21 different PFAS from a groundwater sample collected at a US Air Force base. The PFAS could subsequently be desorbed from PPN-6-FNDMB, concentrating them by a factor of over 50 times. The recycled PPN-6-FNDMB could then be reused with minimal losses in long-chain PFAS adsorption capacity over four cycles.
Future advances and usage of all-organic polymeric materials with permanent void spaces and high surface areas, in applications such as separations or as supports, depends heavily on the development of processing techniques to produce complex geometry objects. Here, the high free volume glassy microporous polymer PIM-1 was fabricated, as a major component in a polymer blend, into complex and customizable 3D objects by fused filament fabrication (FFF). PIM-1 was found to be compatible with polycaprolactone (PCL) and polylactic acid (PLA) and thus could be processed by extrusion into filaments with high loadings of PIM-1 (50% by mass). Ternary PCL/PLA/PIM-1 composite filaments provided an optimal balance of durability and melt flow characteristics for consistent FFF 3D printing of intricate structures. As printed, the micropores of PIM-1 were blocked and inaccessible to N2 during sorption experiments; however, the ternary composite structures displayed significant meso- and macroporosity and nanostructured phase separation. Postprinting immersion in 3-chloro-1-propanol was identified to selectively remove PCL within the composites, re-expose the characteristic micropores of PIM-1, and retain the macrostructure of the printed object. After postprinting treatments, specific surface areas by the Brunauer–Emmett–Teller method (as high as 460 m2 g–1) were found to directly correlate with the PCL content originally present. In conclusion, the extrusion-based processing methodology provides a new approach for production of intrinsically porous polymer objects in custom and complex shapes by reinforcement with thermoplastics (PCL and PLA).
The synthesis of highly porous benzoxazole- and benzothiazole-linked organic polymers by condensation routes is reported; the new polymers exhibit high selectivity towards CO 2 capture from gas mixtures.
The Zhou group has developed a novel PPN based CO2 capture sorbent based on a melamine-formaldehyde resin. By incorporating an alkylamine within the basic framework we can achieve uptakes in excess of 10%wt. We have developed an alternative method of improving the cycling capacity of these PPN systems through the incorporation of dopant molecules. The dopant molecule, cyanuric acid, results in a material that only loses 4% of its uptake capacity over 30 cycles as opposed to a 20% loss without the dopant.
Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young’s Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with -60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica’s impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures.