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.
Phosphorus stimulated unidirectional growth of TiO2 nanostructures
L. White, M. Kim, J. Zhang, S. Kraemer, C. T. Yavuz, M. Moskovits, A. M. Wodtke, G. D. Stucky
Previously reported TiO2 nanowire fabrication from Ni catalysts shows a surprising amount of phosphorous (P) contamination incorporated into the seed particle. We proposed this unintentional P-doping of Ni particles aids the mechanism for nanowire growth and occurs by an alternative pathway from the Vapor–Liquid–Solid (VLS) mechanism. To confirm this new mechanism, mixed phase NiP/Ni2P (NixPy) and Ni2P nanoparticles were fabricated and the central role of phosphorous in TiO2 nanowire synthesis confirmed. This newly developed P-assisted fabrication method yielded crystalline rutile TiO2 nanowires. In this mechanism solid, quasi-spherical catalyst particles attached to the ends of nanowires and surrounded by a Ni/P liquid shell are responsible for the nanowire growth. The growing end of the nanowire appears to form a “tangent-plane” to the solid catalyst core with the liquid shell wetting and occupying the interstice between the catalyst and the nanowire. In NixPy assisted growth, nanowire diameters occurred as small as 12.3 nm, some of the thinnest yet reported TiO2 nanowires resulting from atmospheric-pressure chemical vapor deposition (APCVD) growth.
A combined computational and experimental study of high pressure and supercritical CO2 adsorption on Basolite MOFs
E. Deniz, F. Karadas, H. A. Patel, S. Aparicio, C. T. Yavuz, M. Atilhan
Metal organic frameworks (such as commercial Basolite®) display significant promise for CO2 capture and storage. Here, in order to monitor CO2 capture of Basolite®, we combined high pressure CO2 adsorption with high-pressure FTIR and Monte Carlo simulations. We found that Basolite® C300 show an unprecedented rise in capture capacity above 25 bars, as predicted by the DFT calculations. Adsorption isotherms were measured up to 200 bar using a state-of-the-art magnetic suspension balance, and in-situ FTIR studies as a function of pressure allowed characterizing the preferential adsorption sites, and their occupancy with increasing pressure. Monte Carlo molecular simulations were used to infer nanoscopic information of the adsorption mechanism, showing the sorbent–CO2 interactions from structural and energetic viewpoints.
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