A catalytic role of surface silanol groups in CO2 capture on the amine-anchored silica support

M. Cho, J. Park, C. T. Yavuz, Y. Jung*
Phys. Chem. Chem. Phys., 20, 12149-12156 (2018).
DOI: 10.1039/C7CP07973G

A new mechanism of CO2 capture on the amine-functionalized silica support is demonstrated using density functional theory calculations, in which the silica surface not only acts as a support to anchor amines, but also can actively participate in the CO2 capture process through a facile proton transfer reaction with the amine groups. The surface-mediated proton transfer mechanism in forming a carbamate–ammonium product has lower kinetic barrier (8.1 kcal mol−1) than the generally accepted intermolecular mechanism (12.7 kcal mol−1) under dry conditions, and comparable to that of the water-assisted intermolecular mechanism (6.0 kcal mol−1) under humid conditions. These findings suggest that the CO2 adsorption on the amine-anchored silica surface would mostly occur via the rate-determining proton transfer step that is catalyzed by the surface silanol groups.

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EEWS 2016: Progress and Perspectives of Energy Science and Technology

J. Oh, J. W. Choi, C. T. Yavuz, S. Y. Chung, J. Y. Park, Y. Jung*
ACS Energy Lett., 2, 592–594, (2017).
DOI: 10.1021/acsenergylett.6b00640

Established in 2009, the Graduate School of EEWS (Energy, Environment, Water, and Sustainability) at the Korea Advanced Institute of Science and Technology (KAIST) is the first of its kind, an interdisciplinary department at KAIST collectively addressing with interdisciplinary approaches for the emerging and urgent issues in energy, environment, water, and natural resources of the twenty-first century for sustainable society through science, technology, and education (http://eewseng.kaist.ac.kr). Currently housing 12 research groups with diverse backgrounds in chemistry; physics; chemical, electrical, mechanical, and environmental engineering; and materials science, the EEWS is the culmination of unprecedented collaboration under the same roof with close interaction of students and faculty from unlikely backgrounds (Figure). The output in a relatively short period of time is remarkable; the collaborative research combining basic and applied disciplines of seemingly different subjects have produced many novel concepts and approaches in various energy science and technology fields that are otherwise difficult to conceive in a traditional way. In an effort to critically assess the current status of the energy research, identify major challenges, and further stimulate active interactions among the disciplines to solve the challenges, we held the first EEWS forum, “EEWS 2016: Progress and Perspectives of Energy Science and Technology”, in the KI Fusion Hall of KAIST on October 20, 2016. The meeting featured eight internationally recognized energy experts from around the world introducing their cutting-edge research covering a wide range of topics in energy materials, advanced characterization tools, and catalysis, from both experimental and theoretical viewpoints.

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Observation of wrapping mechanism in amine carbon dioxide molecular interactions on heterogeneous sorbents

D. Thirion, V. Rozyyev, J. Park, Y. Jung, M. Atilhan, C. T. Yavuz*
Phys. Chem. Chem. Phys., 18, 14177-14181, (2016). DOI: 10.1039/C6CP01382A

Liquid, solvated amine based carbon capture is the core of all commercial or planned CO2 capture operations. Despite the intense research, few have looked systematically into the nature of amine molecules and their CO2 interaction. Here, we report a systematic introduction of linear ethylene amines on the walls of highly porous Davankov type network structures through simple bromination intermediates. Surprisingly, isosteric heats of CO2 adsorption show a clear linear trend with the increase in the length of the tethered amine pendant groups, leading to a concerted cooperative binding with additional H-bonding contributions from the unassociated secondary amines. CO2 uptake capacities multiply with the nitrogen content, up to an unprecedented four to eight times of the starting porous network under flue gas conditions. The reported procedure can be generalized to all porous media with the robust hydrocarbon framework in order to convert them into effective CO2 capture adsorbents.

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Systematic Investigation of the Effect of Polymerization Routes on the Gas Sorption Properties of Nanoporous Azobenzene Polymers

O. Buyukcakir, S. H. Je, J. Park, H. A. Patel, Y. Jung, C. T. Yavuz*, A. Coskun*
Chem. Eur. J., 21 (43), 15320–15327, (2015). DOI: 10.1002/chem.201501233.

Functional-group-oriented polymerization strategies have contributed significantly to the initial development of porous polymers and have led to the utilization of several well-known organic transformations in the synthesis of these polymers. Because there are multiple polymerization routes that can be used to introduce the same chemical functionality, it is very important to demonstrate the effect of different polymerization routes on the gas-sorption properties of these chemically similar polymers. Herein, we have studied the rich chemistry of azobenzenes and synthesized four chemically similar nanoporous azobenzene polymers (NABs) with surface areas of up to 1021 m2 g−1. The polymerization routes have a significant impact on the pore-size distributions of the NABs, which directly affects the temperature dependence of the CO₂/N₂ selectivity. A pore-width maximum of 6–8 Å, narrow pore-size distribution, and small particle size (20–30 nm) were very critical for high CO₂/N₂ selectivity and N₂ phobicity, which is associated with azo linkages and realized at warm temperatures. Our findings collectively suggest that an investigation of different polymerization routes for the same chemical functionalization is critical to understand fully the combined effect of textural properties, local environment, and chemical functionalization on the gas-sorption properties of nanoporous polymers.

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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*
Chem. Eur. J., 20, 772-780, (2014). [DOI] [pdf] [WOS]

A family of azo-bridged covalent organic polymers (azo-COPs) was synthesized through a catalyst-free direct coupling of aromatic nitro and amine compounds under basic conditions. The azo-COPs formed 3D nanoporous networks and exhibited surface areas up to 729.6 m² g⁻¹, with a CO₂-uptake capacity as high as 2.55 mmol g⁻¹ at 273 K and 1 bar. Azo-COPs showed remarkable CO₂/N₂ selectivities (95.6–165.2) at 298 K and 1 bar. Unlike any other porous material, CO₂/N₂ selectivities of azo-COPs increase with rising temperature. It was found that azo-COPs show less than expected affinity towards N₂ gas, thus making the framework “N₂-phobic”, in relative terms. Our theoretical simulations indicate that the origin of this unusual behavior is associated with the larger entropic loss of N₂ gas molecules upon their interaction with azo-groups. The effect of fused aromatic rings on the CO₂/N₂ selectivity in azo-COPs is also demonstrated. Increasing the π-surface area resulted in an increase in the CO₂-philic nature of the framework, thus allowing us to reach a CO₂/N₂ selectivity value of 307.7 at 323 K and 1 bar, which is the highest value reported to date. Hence, it is possible to combine the concepts of “CO₂-philicity” and “N₂-phobicity” for efficient CO₂ capture and separation. Isosteric heats of CO₂ adsorption for azo-COPs range from 24.8–32.1 kJ mol⁻¹ at ambient pressure. Azo-COPs are stable up to 350 °C in air and boiling water for a week. A promising cis/trans isomerization of azo-COPs for switchable porosity is also demonstrated, making way for a gated CO₂ uptake.

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Unprecedented high-temperature CO2 selectivity in N2-phobic nanoporous covalent organic polymers

H. A. Patel, S. H. Je, J. Park, D. P. Chen, Y. Jung, C. T. Yavuz*, A. Coskun*
Nature Commun., 4, 1357, (2013). [DOI] [pdf] [WOS]

With CO₂/N₂ selectivity of 288, Azo-COP-2 (COP-69) holds the current world record
Highlighted in Chemical & Engineering News, Chemistry World, Yeni Asir (Turkish)(another link), Aktif Haber (Turkish), Zaman (Turkish), Bugun (Turkish), Enerji Enstitusu (Turkish), Daejeon Ilbo (Korean), MK News (Korean), Yonhap News (Korean) 

Post-combustion CO₂ capture and air separation are integral parts of the energy industry, although the available technologies remain inefficient, resulting in costly energy penalties. Here we report azo-bridged, nitrogen-rich, aromatic, water stable, nanoporous covalent organic polymers, which can be synthesized by catalyst-free direct coupling of aromatic nitro and amine moieties under basic conditions. Unlike other porous materials, azo-covalent organic polymers exhibit an unprecedented increase in CO₂/N₂ selectivity with increasing temperature, reaching the highest value (288 at 323 K) reported to date. Here we observe that azo groups reject N₂, thus making the framework N₂-phobic. Monte Carlo simulations suggest that the origin of the N₂ phobicity of the azo-group is the entropic loss of N₂ gas molecules upon binding, although the adsorption is enthalpically favourable. Any gas separations that require the efficient exclusion of N₂ gas would do well to employ azo units in the sorbent chemistry.

Live on S Haber

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Highly Stable Nanoporous Sulfur bridged Covalent Organic Polymers for Carbon Dioxide Removal

H. A. Patel, F. Karadas, J. Byun, J. Park, E. Deniz, A. Canlier, Y. Jung,* M. Atilhan*, C. T. Yavuz*
Adv. Funct. Mater., 23, 2270–2276 (2013). [DOI] [pdf]

Carbon dioxide capture and separation requires robust solids that can stand harsh environments where a hot mixture of gases is often found. Herein, the first and comprehensive syntheses of porous sulfur-bridged covalent organic polymers (COPs) and their application for carbon dioxide capture in warm conditions and a wide range of pressures (0–200 bar) are reported. These COPs can store up to 3294 mg g−1 of carbon dioxide at 318 K and 200 bar while being highly stable against heating up to 400 °C. The carbon dioxide capacity of the COPs is also not hindered upon boiling in water for at least one week. Physisorptive binding is prevalent with isosteric heat of adsorptions around 24 kJ mol−1. M06–2X and RIMP2 calculations yield the same relative trend of binding energies, where, interestingly, the dimer of triazine and benzene play a cooperative role for a stronger binding of CO₂ (19.2 kJ mol−1) as compared to a separate binding with triazine (13.3 kJ mol−1) or benzene (11.8 kJ mol−1).

Click here for the supporting information

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High capacity carbon dioxide adsorption by inexpensive covalent organic polymers

H. A. Patel, F. Karadas, A. Canlier, J. Park, E. Deniz, Y. Jung, M. Atilhan*, C. T. Yavuz*
J. Mater. Chem., 22, 8431-8437, (2012). [DOI] [pdf]

With 5616 mg/g, COP-1 sets the new world record for the highest CO₂ capture capacity

At infinite selectivity, COP-2 holds the world record in CO₂/H₂ separation

Efficient CO₂ scrubbing without a significant energy penalty remains an outstanding challenge for fossil fuel-burning industry where aqueous amine solutions are still widely used. Porous materials have long been evaluated for next generation CO₂ adsorbents. Porous polymers, robust and inexpensive, show promise as feasible materials for the capture of CO₂ from warm exhaust fumes. We report the syntheses of porous covalent organic polymers (COPs) with CO₂ adsorption capacities of up to 5616 mg/g (measured at high pressures, i.e.200 bar) and industrially relevant temperatures (as warm as 65 ^oC). COPs are stable in boiling water for at least one week and near infinite CO₂/H₂ selectivity is observed.

Top five in CO₂ capture capacity*:
1. COP-1: 5616 mg/g
2. MOF-210: 2870 mg/g
3. NU-100: 2315 mg/g
4. PPN-4: 2121 mg/g
5. COP-2: 2086 mg/g

*These capacities reflect the highest recorded values, regardless of the conditions. In addition, according to our recent high pressure data on common solids, we believe the rankings won't change much even if the pressures are raised. 

+ This paper was published as is in 16 days after initial receipt

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Amidoximes: Promising Candidates for CO2 Capture

S. Zulfiqar, F. Karadas, J. Park, E. Deniz, G. D. Stucky, Y. Jung*, M. Atilhan*, C. T. Yavuz*
Energy Environ. Sci., 4, 4528-4531, (2011). [DOI] [pdf]

Monoethanolamine (MEA) dominates power plant carbon dioxide (CO2) scrubbing processes, though with major disadvantages such as a 8–35% energy penalty. Here we report that structurally comparable amidoximes are promising CO2 capture agents based on RIMP2 electronic structure calculations. This was experimentally verified by the synthesis and testing of representative amidoximes for capture efficiencies at pressures as high as 180 bar. Acetamidoxime, which has the highest percent amidoxime functionality showed the highest CO2 capacity (2.71 mmol/g) when compared to terephthalamidoxime (two amidoximes per molecule) and tetraquinoamidoxime (four amidoximes per molecule). Polyamidoxime surpassed activated charcoal Norit RB3 for CO2 capture per unit surface area. Adsorption isotherms exhibit Type IV behavior and acetamidoxime found to increase CO2 capture with temperature, a less observed anomaly. Porous amidoximes are proposed as valuable alternatives to MEA.

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