Conductive nanocomposites were synthesized from surface modified clay and polypyrrole grafted triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS-g-PPy). The grafting of PPy was carried out on SEBS using FeCl3 as an oxidant and the formation of subsequent materials was monitored by IR, 1H NMR spectroscopy and Gel permeation chromatography (GPC). Surface treatment of the clay was carried out by ion exchange method using the cationic salt of 2,2-bis[4-(4-aminophenoxy)phenyl]propane for better adhesion with the polymer matrix. Thin composite films containing 1–8-wt.% organoclay were investigated by FTIR, XRD, TEM, tensile testing, TGA, DSC and electrical conductivity measurements. The molar mass as determined by GPC was around 37,000. XRD pattern and TEM images described good dispersion of clay platelets in the nanocomposites. Tensile testing revealed improvement in mechanical properties up to 3-wt.% of organoclay. The bulk electrical conductivity was increased up to 7-wt.% with increase in resonance of delocalized electrons of stretched PPy chains due to hydrogen bonding with organoclay in the nanocomposites. Thermal decomposition temperatures of the nanocomposites were in the range 435–448 °C. The decomposition of the nanocomposites was observed at higher temperatures relative to the pure polymer matrix with increasing clay loading. The weight retained after 900 °C was approximately equal to the amount of organoclay added in the composites. These composite materials exhibited improvement in glass transition temperature as compared to SEBS-g-PPy.
Nanoporous covalent organic polymers incorporating Troger's base functionalities for enhanced CO2 capture
J. Byun, S. H. Je, H. A. Patel, A. Coskun, C. T. Yavuz
The CO2 uptake capacity and CO2/N2 selectivity of Tröger's base-bridged nanoporous covalent organic polymers (TB-COPs) were investigated. The TB-COPs were synthesized by reacting the terminal amines of tetrahedral monomers – namely, tetraanilyladamantane and tetraanilylmethane – with dimethoxymethane in a one-pot reaction under relatively mild conditions. Interestingly, these two tetrahedral monomers formed nanoporous polymers with substantially different surface areas. While the polymer resulting from the Trögerization of the tetraanilyladamantane monomer (TB-COP-1) exhibited a high surface area of 1340 m2 g−1, that from the tetraanilylmethane monomer (TB-COP-2) was found to be only 0.094 m2 g−1. This unusual phenomenon can be explained by the proximity of the amino moieties to each other within the monomeric unit. A shorter distance between the amino groups enables intramolecular as well as intermolecular cyclization, thus resulting in a much lower porosity. TB-COP-1 exhibited significant CO2 uptake capacities of up to 5.19 and 3.16 mmol g−1 at 273 and 298 K under ambient pressure, and CO2/N2 selectivities of 79.2 and 68.9 at 273 and 298 K at 1 bar for a gas mixture of CO2[thin space (1/6-em)]:[thin space (1/6-em)]N2 at a ratio of 0.15[thin space (1/6-em)]:[thin space (1/6-em)]0.85. It is noteworthy that TB-COP-1 showed remarkable selectivity retention when increasing the temperature from 273 to 298 K.
Directing the structural features of N2-phobic nanoporous covalent organic polymers for CO2 capture and separation
H. A. Patel, S. H. Je, J. Park, Y. Jung, A. Coskun, C. T. Yavuz
A family of azo-bridged covalent organic polymers(azo-COPs) was synthesized through a catalyst-free directcoupling of aromatic nitro and amine compounds underbasic conditions. The azo-COPs formed 3D nanoporous net-works and exhibited surface areas up to 729.6 m2g1, withaCO2-uptake capacity as high as 2.55 mmolg1at 273 K and1 bar. Azo-COPs showed remarkable CO2/N2selectivities(95.6–165.2) at 298 K and 1 bar. Unlike any other porous ma-terial, CO2/N2selectivities of azo-COPs increase with risingtemperature. It was found that azo-COPs show less than ex-pected affinity towards N2gas, thus making the framework“N2-phobic”, in relative terms. Our theoretical simulations in-dicate that the origin of this unusual behavior is associatedwith the larger entropic loss of N2gas molecules upon theirinteraction with azo-groups. The effect of fused aromaticrings on the CO2/N2selectivity in azo-COPs is also demon-strated. Increasing thep-surface area resulted in an increasein the CO2-philic nature of the framework, thus allowing usto reach a CO2/N2selectivity value of 307.7 at 323 K and1 bar, which is the highest value reported to date. Hence, itis possible to combine the concepts of “CO2-philicity” and“N2-phobicity” for efficient CO2capture and separation. Iso-steric heats of CO2adsorption for azo-COPs range from24.8–32.1 kJmol1at ambient pressure. Azo-COPs are stableup to 3508C in air and boiling water for a week. A promisingcis/transisomerization of azo-COPs for switchable porosity isalso demonstrated, making way for a gated CO2uptake.
Amidoxime porous polymers for CO2 capture
S. Zulfiqar, S. Awan, F. Karadas, M. Atilhan, C. T. Yavuz, M. I. Sarwar
CO2 capture from fossil fuel based electricity generation remains costly since new power plants with monoethanol amine (MEA) as the scrubbing agent are under construction. Amidoximes are known to mimic MEA, and porous polymers with amidoximes could offer a sustainable solution to carbon capture. Here we report the first amidoxime porous polymers (APPs) where aromatic polyamides (aramids) having amidoxime pendant groups were synthesized through low temperature condensation of 4,4′-oxydianiline (ODA) and p-phenylene diamine (p-PDA) with a new type of nitrile-bearing aromatic diacid chloride. The nitrile pendant groups of the polyamides were converted to an amidoxime functionality by a rapid hydroxylamine addition (APP-1 and APP-2). The CO2 adsorption capacities of these polyamides were measured at low pressure (1 bar) and two different temperatures (273 and 298 K) and high pressure (up to 225 bar – the highest measuring pressure to date) at 318 K. The low pressure CO2 uptake of APP-1 was found to be 0.32 mmol g−1 compared with APP-2 (0.07 mmol g−1) at 273 K, whereas at high pressure they showed a substantial increase in CO2 adsorption capacity exhibiting 24.69 and 11.67 mmol g−1 for APP-1 and APP-2 respectively. Both aramids were found to be solution processable, enabling membrane applications.
Limitations and high pressure behavior of MOF-5 for CO2 capture
J. Y. Jung,‡ F. Karadas,‡ S. Zulfiqar,‡ E. Deniz, S. Aparicio, M. Atilhan, C. T. Yavuz, S. M. Han
Porous network structures (e.g. metal–organic frameworks, MOFs) show considerable potential in dethroning monoethanol amine (MEA) from being the dominant scrubber for CO2 at the fossil-fuel-burning power generators. In contrast to their promise, structural stability and high-pressure behavior of MOFs are not well documented. We herein report moisture stability, mechanical properties and high-pressure compression on a model MOF structure, MOF-5. Our results show that MOF-5 can endure all tested pressures (0–225 bar) without losing its structural integrity, however, its moist air stability points at a 3.5 hour safety window (at 21.6 °C and 49% humidity) for an efficient CO2 capture. Isosteric heats of CO2 adsorption at high pressures show moderate interaction energy between CO2 molecules and the MOF-5 sorbent, which combined with the large sorption ability of MOF-5 in the studied pressure–temperature ranges show the viability of this sorbent for CO2 capturing purposes. The combination of the physicochemical methods we used suggests a generalized analytical standard for measuring viability in CO2 capture operations.
Influence of aminosilane coupling agent on aromatic polyamide/intercalated clay nanocomposites
M. U. Alvi, S. Zulfiqar, C. T. Yavuz, H.-S. Kweon, M. I. Sarwar
Aminosilane grafted and diamine modified reactive montmorillonite was exploited to generate aromatic polyamide based nanocomposites. For better compatibility, the hydrophilic nature of montmorillonite was changed into organophilic using 1,4-phenylenediamine, and the hydroxyl groups present on the clay surface and edges were used to graft 3-aminopropyltriethoxysilane (APTS) on clay sheets. The dispersion of clay was monitored in the polyamide obtained from 1,4-phenylenediamine, 4,4′-oxydianiline, and isophthaloyl chloride. These chains were converted into carbonyl chloride ends to interact with free amine groups of grafted APTS and diamine. Thin films were probed for FTIR, XRD, SEM, TEM, tensile testing, TGA, and DSC measurements. The results described ample dispersion of clay in the nanocomposites with tensile strength increased 110% and elongation increased 172% upon the addition of 4–6 wt % clay. Thermal decomposition temperatures of the nanocomposites were in the range 425–480 °C. The glass transition temperature increased up to 142.4 °C with 6 wt % addition of organoclay.
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