A combined experimental and theoretical study on gas adsorption performance of amine and amide porous polymers

R. Ullah, H. A. Patel, S. Aparicio, C. T. Yavuz*, M. Atilhan*
Micropor. Mesopor. Mater., 279, 61-72 (2019).
DOI: 10.1016/j.micromeso.2018.12.011

In this manuscript, we report synthesis, characterization and application of amine and amide type covalent organic frameworks as CO2 adsorbent materials at various isotherms and wide pressure conditions. Furthermore, we also report a detailed density functional theory investigation of the studied adsorbents in order to explain their adsorption behaviors and provide comparisons with experimental results. The objective of this work was to investigate custom design porous polymers by building amine and amide functionalities in the final structures, whether they have efficient CO2 capturing performances at wide process conditions that covers both low and high pressure end applications to cover either pre- or post-combustion processes. On the other hand, energy storage performances of these materials were tested by performing H2 sorption experiments as well. Two porous polymers, namely COP-9 and COP-10, were characterized with BET, TGA and FTIR to evaluate the physical properties of studied porous polymers and then were tested for CO2, N2 and H2 adsorption both at low and high pressures. Studied materials were found to have compelling adsorption capacity mostly at high pressures and have very good selectivity for CO2/N2 and CO2/H2 respectively.

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Sustainable nanoporous benzoxazole networks as metal-free catalysts for one-pot oxidative self-coupling of amines by air oxygen

S. Subramanian, H. A. Patel, Y. Song, C. T. Yavuz*
Adv. Sustain. Syst., 1, 1700089, (2017).
DOI: 10.1002/adsu.201700089

The development of sustainable organocatalysts with porosity, high stability, and excellent catalytic activity offers a clean and green alternative to precious metal catalysts. Here, an efficient, nanoporous, heterogeneous benzoxazole catalyst is reported for aerobic oxidative coupling of amines. A molecular design strategy is presented to functionalize primary amines to produce valuable products under one-pot, open-air reaction conditions. Unprecedented and previously unknown, the stable imine intermediate catalyzes its own formation, also known as autocatalysis, enabling a direct and favorable access to amino acids, even if the catalysts are absent. The biomimetic benzoxazole catalysts developed here provide quantitative catalytic activity over 50 cycles with favorable kinetics with no degradation. This work also marks the first use of benzoxazoles for oxidative catalytic reactions.

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Reversible water capture by a charged metal-free porous polymer

J. Byun, H. A. Patel, D. Thirion, C. T. Yavuz*
Polymer, 126, 308-313, (2017).
Invited paper for the special issue on Porous Polymers
DOI: 10.1016/j.polymer.2017.05.071

Climate change and industrial pollution threatens the availability of clean water. Although established protocols of water treatment exist, water capture by porous materials has emerged as a viable alternative to energy intensive processes. Here we introduce a new charged porous polymer that is capable of capturing and releasing water by simple humidity or temperature swings. The quaternary amines on the framework structure attract water molecules and further solvate by coordination. The porosity of the network structure also provides enough void where water can diffuse throughout the solid. Water uptake capacity of the porous polymer surpasses common desiccants like silica gel and molecular sieves, and has the potential to act as an organic desiccant in applications like electronics or food packaging.

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Selective removal of heavy metal ions by disulfide linked polymer networks

D. Ko, J. S. Lee, H. A. Patel, M. H. Jakobsen, Y. Hwang, C. T. Yavuz, H. C. B. Hansen, H. R. Andersen*
J. Hazard. Mater., 332, 140–148, (2017).
DOI: 10.1016/j.jhazmat.2017.03.007.

Heavy metal contaminated surface water is one of the oldest pollution problems, which is critical to ecosystems and human health. We devised disulfide linked polymer networks and employed as a sorbent for removing heavy metal ions from contaminated water. Although the polymer network material has a moderate surface area, it demonstrated cadmium removal efficiency equivalent to highly porous activated carbon while it showed 16 times faster sorption kinetics compared to activated carbon, owing to the high affinity of cadmium towards disulfide and thiol functionality in the polymer network. The metal sorption mechanism on polymer network was studied by sorption kinetics, effect of pH, and metal complexation. We observed that the metal ions–copper, cadmium, and zinc showed high binding affinity in polymer network, even in the presence of competing cations like calcium in water.

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Carbon Dioxide Capture Adsorbents: Chemistry and Methods, A Tutorial Review

H. A. Patel, J. Byun, C. T. Yavuz*
ChemSusChem, 10, 7, 1303-1317, (2017). DOI: 10.1002/cssc.201601545.
View PDF here

Graphical Art by Ella Marushchenko.

Excess carbon dioxide (CO₂) emissions and the inevitable consequences continuing to stimulate hard debate and awareness in both academic and public spaces, despite the clutter on understanding what really is needed to capture and store the unwanted CO₂. Capture is the most costly, nearly 70 % of the price tag on the entire carbon capture and storage (CCS) operation. In this tutorial review, we describe and evaluate CO₂ capture science and technology based on adsorbents in the context of chemistry and methods, after briefly introducing current status of CO₂ emissions. An effective sorbent design is suggested, where six checkpoints are expected to be met: cost, capacity, selectivity, stability, recyclability and fast kinetics.

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Charge-specific size-dependent separation of water-soluble organic molecules by fluorinated nanoporous networks

J. Byun, H. A. Patel, D. Thirion, C. T. Yavuz*
Nature Commun., 7, 13377, (2016). OpenAccess
DOI: 10.1038/ncomms13377. ReadCube: rdcu.be/mw1d.
Highlighted in Chemical & Engineering News by Stephen K. Ritter

Molecular architecture in nanoscale spaces can lead to selective chemical interactions and separation of species with similar sizes and functionality. Substrate specific sorbent chemistry is well known through highly crystalline ordered structures such as zeolites, metal organic frameworks and widely available nanoporous carbons. Size and charge-dependent separation of aqueous molecular contaminants, on the contrary, have not been adequately developed. Here we report a charge-specific size-dependent separation of water-soluble molecules through an ultra-microporous polymeric network that features fluorines as the predominant surface functional groups. Treatment of similarly sized organic molecules with and without charges shows that fluorine interacts with charges favourably. Control experiments using similarly constructed frameworks with or without fluorines verify the fluorine-cation interactions. Lack of a σ-hole for fluorine atoms is suggested to be responsible for this distinct property, and future applications of this discovery, such as desalination and mixed matrix membranes, may be expected to follow.

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Investigation of Ester- and Amide-Linker-Based Porous Organic Polymers for Carbon Dioxide Capture and Separation at Wide Temperatures and Pressures

R. Ullah§, M. Atilhan*, B. Anaya, S. Al-Muhtaseb, S. Aparicio, H. A. Patel§, D. Thirion, C. T. Yavuz*
ACS Appl. Mater. Interfaces , 8 (32), 20772–20785, (2016). §: Equal contribution. DOI: 10.1021/acsami.6b05927.

Organic compounds, such as covalent organic framework, metal–organic frameworks, and covalent organic polymers have been under investigation to replace the well-known amine-based solvent sorption technology of CO2 and introduce the most efficient and economical material for CO2 capture and storage. Various organic polymers having different function groups have been under investigation both for low and high pressure CO2 capture. However, search for a promising material to overcome the issues of lower selectivity, less capturing capacity, lower mass transfer coefficient and instability in materials performance at high pressure and various temperatures is still ongoing process. Herein, we report synthesis of six covalent organic polymers (COPs) and their CO2, N2, and CH4 adsorption performances at low and high pressures up to 200 bar. All the presented COPs materials were characterized by using elemental analysis method, Fourier transform infrared spectroscopy (FTIR) and solid state nuclear magnetic resonance (NMR) spectroscopy techniques. Physical properties of the materials such as surface areas, pore volume and pore size were determined through BET analysis at 77 K. All the materials were tested for CO2, CH4, and N2 adsorption using state of the art equipment, magnetic suspension balance (MSB). Results indicated that, amide based material i.e. COP-33 has the largest pore volume of 0.2 cm2/g which can capture up to the maximum of 1.44 mmol/g CO2 at room temperature and at pressure of 10 bar. However, at higher pressure of 200 bar and 308 K ester-based compound, that is, COP-35 adsorb as large as 144 mmol/g, which is the largest gas capturing capacity of any COPs material obtained so far. Importantly, single gas measurement based selectivity of COP-33 was comparatively better than all other COPs materials at all condition. Nevertheless, overall performance of COP-35 rate of adsorption and heat of adsorption has indicated that this material can be considered for further exploration as efficient and cheaply available solid sorbent material for CO2 capture and separation.

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Rapid extraction of Uranium ions from seawater using novel porous polymeric adsorbents

Y. Sihn,§ J. Byun,§ H. A. Patel, W. Lee*, C. T. Yavuz*
RSC Adv., 6, 45968-45976, (2016). §: Equal contribution. DOI: 10.1039/C6RA06807C

Seawater contains uranium in surprisingly high quantities that can supply vast energy, if recovered economically. Attempts to design effective sorbents led to the identification of organic functional groups such as amidoximes. Here we report a porous polymer, a polymer of intrinsic microporosity (PIM) with permanent pores that feature amidoxime pendant groups, which is capable of removing more than 90% uranyl [U(VI)] from seawater collected from the Ulleung basin of the East Sea of the Republic of Korea. From this uptake, over 75% was collected in less than six hours, leading to highly feasible field applications. When the seawater was acidified by bubbling CO2 (pH = 5.4), the uptake increased dramatically. Regeneration studies showed full recovery of sorbents and no loss in capture capacity. Our results indicate that successful uranium recovery can be realized by scalable applications of porous polymeric networks and when low cost CO2 is co-administered, uptake can be significantly enhanced.

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Nanoporous networks as effective stabilisation matrixes for nanoscale zero valent iron and groundwater pollutant removal

P. D. Mines, J. Byun, Y. Hwang, H. A. Patel, H. R. Andersen, C. T. Yavuz*
J. Mater. Chem. A, 4, 632-639 (2016). DOI: 10.1039/C5TA05025A.

Nanoscale zero-valent iron (nZVI), with its reductive potentials and wide availability, offers degradative remediation of environmental contaminants. Rapid aggregation and deactivation hinder its application in real-life conditions. Here, we show that by caging nZVI into the micropores of porous networks, in particular Covalent Organic Polymers (COPs), we dramatically improved its stability and adsorption capacity, while still maintaining its reactivity. We probed the nZVI activity by monitoring azo bond reduction and Fenton type degradation of the naphthol blue black azo dye. We found that depending on the wettability of the host COP, the adsorption kinetics and dye degradation capacities changed. The hierarchical porous network of the COP structures enhanced the transport by temporarily holding azo dyes giving enough time and contact for the nZVI to act to break them. nZVI was also found to be more protected from the oxidative conditions since access is gated by the pore openings of COPs.

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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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Highly Optimized CO2 Capture by Inexpensive Nanoporous Covalent Organic Polymers and Their Amine Composites

H. A. Patel, C. T. Yavuz*
Faraday Discuss., 183, 401-412, (2015). DOI: 10.1039/C5FD00099H.

Carbon dioxide (CO₂) storage and utilization requires effective capture strategies that limit energy penalties. Polyethylenimine (PEI)-impregnated covalent organic polymers (COPs) with a high CO₂ adsorption capacity are successfully prepared in this study. A low cost COP with a high specific surface area is suitable for PEI loading to achieve high CO₂ adsorption, and the optimal PEI loading is 36 wt%. Though the adsorbed amount of CO₂ on amine impregnated COPs slightly decreased with increasing adsorption temperature, CO₂/N₂ selectivity is significantly improved at higher temperatures. The adsorption of CO₂ on the sorbent is very fast, and a sorption equilibrium (10% wt) was achieved within 5 min at 313 K under the flow of simulated flue gas streams. The CO₂ capture efficiency of this sorbent is not affected under repetitive adsorption–desorption cycles. The highest CO₂ capture capacity of 75 mg g−1 at 0.15 bar is achieved under dry CO₂ capture however it is enhanced to 100 mg g−1 in the mixed gas flow containing humid 15% CO₂. Sorbents were found to be thermally stable up to at least 200 °C. TGA and FTIR studies confirmed the loading of PEIs on COPs. This sorbent with high and fast CO₂ sorption exhibits a very promising application in direct CO₂ capture from flue gas.

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Nanoporous Networks as Caging Supports for Uniform, Surfactant-free Co3O4 Nanocrystals and Their Applications in Energy Storage and Conversion

J. Byun, H. A. Patel, D. J. Kim, C. H. Jung, J. Y. Park*, J. W. Choi*, C. T. Yavuz* 
J. Mater. Chem. A, 3, 15489 - 15497, (2015). DOI: 10.1039/C5TA02825F.
Selected among "Hot Papers of 2015"

We report a new, surfactant-free method to produce Co₃O₄ nanocrystals with controlled sizes and high dispersity by caging templation of nanoporous networks. The morphologies of Co₃O₄ nanoparticles differ from wires to particulates by simply varying solvents. The composites of nanoparticles within network polymers are highly porous and are promising for many applications where accessible surface and aggregation prevention are important. The electrochemical performance of the composites demonstrates superior capacity and cyclic stability at a high current density (∼980 mA h g−1 at the 60th cycle at a current density of 1000 mA g−1). In a catalytic oxidation reaction of carbon monoxide, the composites exhibit a remarkable stability (in excess of 35 hours) and catalytic performance (T100 = 100 °C).

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Synthesis of a nanoporous 1,2,4-oxadiazole network with high CO2 capture capacity

D. Ko, H. A. Patel, C. T. Yavuz*
Chem. Commun., 51, 2915-2917 (2015). [DOI]

Developing an adsorbent to mitigate carbon dioxide without large energy penalty is highly desired. Here, we present a silylation synthetic route to form a processable and otherwise impossible porous 1,2,4-oxadiazole network, which achieves 2 mmol/g of CO2 capacity owing to nitrogen-rich structure. This network shows high CO2/N2-selectivity, thermal stability up to 450 oC, and low-heat of adsorption (26.4 kJ/mol), facilitating easy regeneration.

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Magnetic BaFe12O19 nanofiber filter for effective separation of Fe3O4 nanoparticles and removal of arsenic

J. Byun, H. A. Patel, C. T. Yavuz*
J. Nanopart. Res., 16:2787 (2014). [DOI]

Magnetic nanoparticles are promising in applications where magnetic separation is intended, although material losses via leaching mechanisms are often inevitable. Magnetic separations with widely available permanent magnets can effectively trap particles, leading to a complete removal of used or waste particles. In this report, we first demonstrate the synthesis of the thinnest (112.7 ± 16.4 nm) and most magnetic (71.96 emu g−1) barium hexaferrite (BaFe₁₂O₁₉, BHF—fridge magnet) via an organic solvent-free electrospinning procedure. When the fibers are then packed into a column, they clearly remove 12 nm magnetite (Fe₃O₄) nanoparticles quantitatively. The same BHF cartridge also removes more than 99.9 % As-treated magnetite nanoparticles at capacities up to 70 times of its weight. As a result, one liter of 150 μg L−1 As-contaminated water can be purified rapidly at a material cost of less than 2 US cents.

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Nanoporous Benzoxazole Networks by Silylated Monomers, Their Exceptional Thermal Stability, and Carbon Dioxide Capture Capacity

H. A. Patel, D. Ko, C. T. Yavuz*
Chem. Mater., 26 (23), 6729–6733 (2014). [DOI]

The pursuit of synthetic routes for design and preparation of nanoporous polymeric networks with inherent permanent microporosity and functionality through bottom-up methodologies remains a driving force in developing CO₂-philic materials. We report nanoporous, processable, benzoxazole-linked covalent organic polymers (Box-COPs) that show exceptional thermal stability up to 576 °C. Box-COPs can be formed into films thanks to the silylation that is used to guide polymeric network formation. Surface areas of up to 606 m2 g–1 and narrow pore sizes of 4.36 Å were observed with a CO₂ uptake capacity of 139.6 mg g–1 at 273 K and 1 bar. Box-COPs were stable in boiling water for a week without deteriorating CO₂ capture capacity.

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Exceptional organic solvent uptake by disulfide-linked polymeric networks

H. A. Patel, M. S. Yavuz, C. T. Yavuz*
RSC Adv., 4 (46), 24320 - 24323, (2014). [DOI] [pdf] [WOS]

Disulfide-linked covalent organic polymers (COPs) were prepared through catalyst-free oxidative coupling polymerization. Owing to the excellent swelling behavior, low cost, and efficient synthesis, these materials can be promising materials for removal of organics in concentrated streams. COPs show 1,4-dioxane uptake up to 1.8 g g⁻¹.

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Nanoporous covalent organic polymers incorporating Tröger’s base functionalities for enhanced CO2 capture

J. Byun, S. H. Je, H. A. Patel, A. Coskun,* C. T. Yavuz*
J. Mater. Chem. A, 2, 12507-12512, 2014. [DOI] [pdf] [WoS]

The CO₂ uptake capacity and CO₂/N₂ selectivity of Tröger’s base–bridged nanoporous covalent organic polymers (TB-COPs) were investigated. TB-COPs were synthesized by reacting amine terminals 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 trögerization of tetraanilyladamantane monomer (TB-COP-1) exhibit high surface area of 1340 m2 g-1, that of tetraanilylmethane monomer (TB-COP-2) is found to be only 0.094 m2 g-1. This unusual phenomenon can be explained by the proximity of amino moieties to each other within the monomeric unit. Shorter distance between the amino groups enables intramolecular cyclization along with the intermolecular one, thus resulting in much lower porosity. TB-COP-1 exhibits significant CO2 uptakes up to 5.19 and 3.16 mmol g-1 at 273 and 298K under ambient pressure, and CO₂/N₂ selectivities of 79.2 and 68.9 at 273 and 298K at 1 bar for the gas mixture of CO₂:N₂ in the ratio of 0.15:0.85. It is noteworthy that TB-COP-1 showed remarkable selectivity retention with rising temperature from 273 to 298 K.

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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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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*
Micropor. Mesopor. Mat., 175, 34-42 (2013). [DOI] [pdf] [WOS]

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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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.

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