Design enhancement in hydroxide ion conductivity of viologen-bakelite organic frameworks for a flexible rechargeable zinc-air battery.

Quasi-solid-state rechargeable zinc-air batteries (ZABs) are suitable for the generation of portable clean energy due to their high energy and power density, safety, and cost-effectiveness. Compared to the typical alkaline aqueous electrolyte in a ZAB, polymer or gel-based electrolytes can suppress the dissolution of zinc, preventing the precipitation of undesirable irreversible zinc compounds. Their low electronic conductivity minimizes zinc dendrite formation. However, gel electrolytes suffer from capacity fade due to the loss of the volatile solvent, failing to deliver high-energy and high-power ZABs. Consequently, developing polymers with high hydroxide ion conductivity and chemical durability is paramount. We report cationic C-C bonded robust polymers with stoichiometrically controlled mobile hydroxide ions as solid-state hydroxide ion transporters. To boot, we increased the viologen-hydroxide-ion concentration through "by-design" monomers. The polymers constructed with these designer monomers exhibit a commensurate increase in their ionic conductivity. The polymer prepared with 4 OH- ion-containing monomer was superior to the one with 3 OH-. The conductivity increases from 7.30 × 10-4 S cm-1 (30 °C) to 2.96 × 10-3 S cm-1 (30 °C) at 95% RH for IISERP-POF12_OH (2_OH) and IISERP-POF13_OH (3_OH), respectively. A rechargeable ZAB (RZAB) constructed using 3_OH@PVA (polyvinyl alcohol) as the electrolyte membrane and Pt/C + RuO2 catalyst delivers a power density of 158 mW cm-2. In comparison, RZABs with a PVA interlayer provided only 72 mW cm-2. Notably, the device suffered an initial charge-discharge voltage gap of merely 0.55 V at 10 mA cm-2, which increased by only 2 mV after 50 hours of running. The battery operated at 10 mA cm-2 and worked steadily for 67 hours. We accomplished a flexible and rechargeable zinc-air battery (F-RZAB) exhibiting a maximum power density of 79 mW cm-2. This demonstration of a cationic viologen-bakelite polymer-based flexible secondary ZAB with versatile stochiometric hydroxide-ion tunability marks an important achievement in hydroxide-ion conducting solid-state electrolyte development.

Tailoring COFs: Transforming Nonconducting 2D Layered COF into a Conducting Quasi-3D Architecture via Interlayer Knitting with Polypyrrole.

Improving the electronic conductivity and the structural robustness of covalent organic frameworks (COFs) is paramount. Here, we covalently cross-link a 2D COF with polypyrrole (Ppy) chains to form a quasi-3D COF. The 3D COF shows well-defined reflections in the SAED patterns distinctly indexed to its modeled crystal structure. This knitting of 2D COF layers with conjugated polypyrrole units improves electronic conductivity from 10-9 to 10-2 S m-1. This conductivity boost is affirmed by the presence of density of states near the Fermi level in the 3D COF, and this elevates the COF's valence band maximum by 0.52 eV with respect to the parent 2D pyrrole-functionalized COF, which agrees well with the opto-electro band gaps. The extent of HOMO elevation suggests the predominant existence of a polaron state (radical cation), giving rise to a strong EPR signal, most likely sourced from the cross-linking polypyrrole chains. A supercapacitor devised with COF20-Ppy records a high areal capacitance of 377.6 mF cm-2, higher than that of the COF loaded with noncovalently linked polypyrrole chains. Thus, the polypyrrole acts as a "conjugation bridge" across the layers, lowering the band gap and providing polarons and additional conduction pathways. This marks a far-reaching approach to converting many 2D COFs into highly ordered and conducting 3D ones.

COF-supported zirconium oxyhydroxide as a versatile heterogeneous catalyst for Knoevenagel condensation and nerve agent hydrolysis.

A composite of catalytic Lewis acidic zirconium oxyhydroxides (8 wt %) and a covalent organic framework (COF) was synthesized. X-ray diffraction and infrared (IR) spectroscopy reveal that COF's structure is preserved after loading with zirconium oxyhydroxides. Electron microscopy confirms a homogeneous distribution of nano- to sub-micron-sized zirconium clusters in the COF. 3D X-ray tomography captures the micron-sized channels connecting the well-dispersed zirconium clusters on the COF. The crystalline ZrOx(OH)y@COF's nanostructure was model-optimized via simulated annealing methods. Using 0.8 mol % of the catalyst yielded a turnover number of 100-120 and a turnover frequency of 160-360 h-1 for Knoevenagel condensation in aqueous medium. Additionally, 2.2 mol % of catalyst catalyzes the hydrolysis of dimethyl nitrophenyl phosphate, a simulant of nerve agent Soman, with a conversion rate of 37% in 180 min. The hydrolytic detoxification of the live agent Soman is also achieved. Our study unveils COF-stabilized ZrOx(OH)y as a new class of zirconium-based Lewis + Bronsted-acid catalysts.

Preferential CO2 adsorption by an ultra-microporous zinc-aminotriazolato-acetate MOF.

Ultramicroporous MOFs enable tight packing of the active functional groups, directly impacting the selective guest-framework interactions. MOFs with pores simultaneously lined by methyl and amine may serve as the ultimate humid CO2 sorbent. However, structural complexity prevents taking full advantage even in a simple zinc-triazolato-acetate layered-pillared MOF.

Hydroxide ion-conducting viologen-bakelite organic frameworks for flexible solid-state zinc-air battery applications.

Adaptable polymer-based solid-state electrolytes can be a game-changer toward safe, lightweight flexible batteries. We present a robust Bakelite-type organic polymer covalently decked with viologen, triazine, and phenolic moieties. Its flexible structure with cationic viologen centers incorporates counter-balancing free hydroxide ions into the polymeric framework. By design, the aromatic groups and heteroatoms in the framework can be activated under an applied potential to prompt a push-pull drive, setting off the towing of hydroxide ions via weak electrostatic, van der Waals, and hydrogen-bond interactions. The frontier orbitals from a DFT-modeled structure certify this. The hydroxyl-polymer requires minimal KOH wetting to maintain a humid environment for Grotthuss-type transport. The hydroxide ion conductivity reaches a value of 1.4 × 10-2 S cm-1 at 80 °C and 95% RH, which is retained for over 15 h. We enhanced its practical utility by coating it as a thin solid-state separator-cum-electrolyte on readily available filter paper. The composite exhibits a conductivity of 4.5 × 10-3 S cm-1 at 80 °C and 95% RH. A zinc-air battery (ZAB) constructed using this polymer-coated paper as electrolyte yields a maximum power density of 115 mW cm-2 and high specific capacitance of 435 mA h g-1. The power density recorded for our ZAB is among the best reported for polymer electrolyte-based batteries. Subsequently, the flexible battery fabricated with IISERP-POF11_OH@FilterPaper exhibits an OCV of 1.44 V, and three batteries in series power a demo traffic signal. To underscore the efficiency of hydroxide ion transport through the complex multifunctional backbone of the polymer, we calculated the diffusion coefficient for OH- (Exp: 2.9 × 10-5 cm2 s-1; Comp. 5.2 × 10-6 cm2 s-1) using electrochemical methods and MD simulations. Climbing-edge NEB calculations reveal a large energy barrier of 2.11 eV for Zn2+ to penetrate the polymer and identify hydroxide ions within the polymer, suggesting no undesirable Zn2+ crossover. Our findings assert the readily accessible C-C-linked cationic polymer's capacity as a solid-state electrolyte for ZABs and any anion-conducting membrane.

Nanopores of a Covalent Organic Framework: A Customizable Vessel for Organocatalysis.

Covalent organic frameworks (COFs) as crystalline polymers possess ordered nanochannels. When their channels are adorned with catalytically active functional groups, their highly insoluble and fluffy powder texture makes them apt heterogeneous catalysts that can be dispersed in a range of solvents and heated to high temperatures (80-180 °C). This would mean very high catalyst density, facile active-site access, and easy separation leading to high isolated yields. Different approaches have been devised to anchor or disperse the catalytic sites into the nanospaces offered by the COF pores. Such engineered COFs have been investigated as catalysts for many organic transformation reactions. These range from Suzuki-Miyaura coupling, Heck coupling, Knoevenagel condensation, Michael addition, alkene epoxidation, CO2 utilization, and more complex biomimetic catalysis. Such catalysts employ COF as a "passive" support that merely docks catalytically active inorganic clusters, or in other cases, the COF itself participates as an "active" support by altering the electronics of the inorganic catalytic sites through the redox activity of its framework. Even more, catalytic organic pockets or metal complexes have been directly tethered to COF walls to make them behave like single-site organocatalysts. Here, we have listed most COF-based organic transformations by categorizing them as metal-free non-noble-metal@COF and noble-metal@COF. The initial part of this review highlights the advantages of COFs as a component of a heterogeneous catalyst, while the latter part discusses all of the current literature on this topic.

Coordination Flexibility Aided CO2 -specific Gating in an Iron Isonicotinate MOF.

Coordination flexibility assisted porosity has been introduced into an Iron-isonicotinate metal-organic framework (MOF), (Fe(4-PyC)2 ⋅ (OH). The framework showed CO2 -specific gate opening behavior, which gets tuned as a function of temperature and pressure. The MOF's physisorptive porosity towards CO2 , CH4 , and N2 was investigated; it adsorbed only CO2 via a gate opening phenomenon. The isonicotinate, representing a borderline soft base, is bound to the hard Fe3+ centre through monodentate carboxylate and pyridyl nitrogen. This moderately weak binding enables isonicotinate to spin like a spindle under the CO2 pressure opening the gate for a sharp increase in CO2 uptake at 333 mmHg (At 298 K, the CO2 uptake increases from 0.70 to 1.57 mmol/g). We investigated the MOF's potential for CO2 /N2 and CO2 /CH4 gas separation aided by this gating. IAST model reveals that the CO2 /N2 selectivity jumps from 325 to 3131 when the gate opens, while the CO2 /CH4 selectivity increases three times. Interestingly, this Fe-isonicotinate MOF did not follow the trend set by our earlier reported Hard-Soft Gate Control (established for isostructural M2+ -isonicotinate MOFs (M=Mg, Mn)). However, we account for this discrepancy using the different oxidation state of metals confirmed by X-ray photoelectron spectroscopy and magnetism.

A scalable metal-organic framework as a durable physisorbent for carbon dioxide capture.

Metal-organic frameworks (MOFs) as solid sorbents for carbon dioxide (CO2) capture face the challenge of merging efficient capture with economical regeneration in a durable, scalable material. Zinc-based Calgary Framework 20 (CALF-20) physisorbs CO2 with high capacity but is also selective over water. Competitive separations on structured CALF-20 show not just preferential CO2 physisorption below 40% relative humidity but also suppression of water sorption by CO2, which was corroborated by computational modeling. CALF-20 has a low enthalpic regeneration penalty and shows durability to steam (>450,000 cycles) and wet acid gases. It can be prepared in one step, formed as composite materials, and its synthesis can be scaled to multikilogram batches.

Three in One: Triple G-C-T Base-Coded Brahma Nucleobase Amino Acid: Synthesis, Peptide Formation, and Structural Features.

This note reports the synthesis and peptide formation of a novel triple G-C-T nucleobase amino acid (NBA) building block featuring three recognition faces: DDA (G mimic), DAA (C mimic), and ADA (T mimic). Readily obtainable in multigram scale in a remarkably easy one-step reaction, this unique NBA building block offers scope for wide ranging applications for nucleic acid recognition and nucleic acid peptide/protein interaction studies.

Deciphering the Weak CO2···Framework Interactions in Microporous MOFs Functionalized with Strong Adsorption Sites-A Ubiquitous Observation.

Carbon capture from industrial effluents such as flue gas or natural gas mixture (cf. landfill gas), the primary sources of CO2 emission, greatly aids in balancing the environmental carbon cycle. In this context, the most energy-efficient physisorptive CO2 separation process can benefit immensely from improved porous sorbents. Metal organic frameworks (MOFs), especially the ultramicroporous MOFs, built from readily available small and rigid ligands, are highly promising because of their high selectivity (CO2/N2) and easy scalability. Here, we report two new ultramicroporous Co-adeninato isophthalate MOFs. They concomitantly carry basic functional groups (-NH2) and Lewis acidic sites (coordinatively unsaturated Co centers). They show good CO2 capacity (3.3 mmol/g at 303 K and 1 bar) along with high CO2/N2 (∼600 at 313 K and 1 bar and ∼340 at 303 K and 1 bar) selectivity, working capacity, and smooth diffusion kinetics (Dc = 7.5 × 10-9 m2 s-1). The MOFs exhibit good CO2/N2 kinetic separation under both dry and wet conditions with a smooth breakthrough profile. Despite their well-defined CO2 adsorption sites, these MOFs exhibit only a moderately strong interaction with CO2 as evidenced from their HOA values. This counterintuitive observation is ubiquitous among many MOFs adorned with strong CO2 adsorption sites. To gain insights, we have identified the binding sites for CO2 using simulation and MD studies. The radial distribution function analysis reveals that despite the amine and bare-metal sites, the pore size and the pore structure determine the positions for the CO2 molecules. The most favorable sites become the confined spaces lined by aromatic rings. A plausible explanation for the lack of strong adsorption in these MOFs is premised from these collective studies, which could aid in the future design of superior CO2 sorbents.

Tuning the electronic energy level of covalent organic frameworks for crafting high-rate Na-ion battery anode.

Crystalline Covalent Organic Frameworks (COFs) possess ordered accessible nano-channels. When these channels are decorated with redox-active functional groups, they can serve as the anode in metal ion batteries (LIB and SIB). Though sodium's superior relative abundance makes it a better choice over lithium, the energetically unfavourable intercalation of the larger sodium ion makes it incompatible with the commercial graphite anodes used in Li-ion batteries. Also, their sluggish movement inside the electrodes restricts the fast sodiation of SIB. Creating an electronic driving force at the electrodes via chemical manipulation can be a versatile approach to overcome this issue. Herein, we present anodes for SIB drawn on three isostructural COFs with nearly the same Highest Occupied Molecular Orbitals (HOMO) levels but with varying Lowest Unoccupied Molecular Orbitals (LUMO) energy levels. This variation in the LUMO levels has been deliberately obtained by the inclusion of electron-deficient centers (phenyl vs. tetrazine vs. bispyridine-tetrazine) substituents into the modules that make up the COF. With the reduction in the cell-potential, the electrons accumulate in the anti-bonding LUMO. Now, these electron-dosed LUMO levels become efficient anodes for attracting the otherwise sluggish sodium ions from the electrolyte. Also, the intrinsic porosity of the COF favors the lodging and diffusion of the Na+ ions. Cells made with these COFs achieve a high specific capacity (energy density) and rate performance (rapid charging-discharging), something that is not as easy for Na+ compared to the much smaller sized Li+. The bispyridine-tetrazine COF with the lowest LUMO energy shows a specific capacity of 340 mA h g-1 at 1 A g-1 and 128 mA h g-1 at a high current density of 15 A g-1. Only a 24% drop appears on increasing the current density from 0.1 to 1 A g-1, which is the lowest among all the top-performing COF derived Na-ion battery anodes.

An Ultra-Microporous Metal-Organic Framework with Exceptional Xe Capacity.

Molecular confinement plays a significant effect on trapped gas and solvent molecules. A fundamental understanding of gas adsorption within the porous confinement provides information necessary to design a material with improved selectivity. In this regard, metal-organic framework (MOF) adsorbents are ideal candidate materials to study confinement effects for weakly interacting gas molecules, such as noble gases. Among the noble gases, xenon (Xe) has practical applications in the medical, automotive and aerospace industries. In this Communication, we report an ultra-microporous nickel-isonicotinate MOF with exceptional Xe uptake and selectivity compared to all benchmark MOF and porous organic cage materials. The selectivity arises because of the near perfect fit of the atomic Xe inside the porous confinement. Notably, at low partial pressure, the Ni-MOF interacts very strongly with Xe compared to the closely related Krypton gas (Kr) and more polarizable CO2 . Further 129 Xe NMR suggests a broad isotropic chemical shift due to the reduced motion as a result of confinement.

Fe3 SnC@CNF: A 3 D Antiperovskite Intermetallic Carbide System as a New Robust High-Capacity Lithium-Ion Battery Anode.

A 3 D intermetallic anti-perovskite carbide, Fe3 SnC, is reported as a Li-ion battery anode. Single-phase Fe3 SnC showed a reversible Li-ion capacity of 426 mAh g-1 that increased significantly (600 mAh g-1 ) upon its in situ synthesis by electrospinning and pyrolysis to render a conducting carbon nanofibre (CNF) based composite. Importantly, the Fe3 SnC@CNF composite showed excellent stability in up to 1000 cycles with a remarkable 96 % retention of capacity. The rate performance was equally impressive with a high capacity of 500 mAh g-1 delivered at a high current density of 2 A g-1 . An estimation of Li ion diffusion from the electrochemical impedance data showed a major enhancement of the rate by a factor of 2 in the case of Fe3 SnC@CNF compared to the single-phase Fe3 SnC sample. Post-cyclic characterisation revealed that the unit cell was retained despite a volume expansion upon the inclusion of four Li atoms per unit cell, as calculated from the capacity value. The cyclic voltammogram shows four distinctive peaks that could be identified as the sequential incorporation of up to four Li atoms. First-principles DFT calculations were performed to elucidate the favourable sites for the inclusion of 1-4 Li atoms inside the Fe3 SnC unit cell along with the associated strain.

Ag Nanoparticles Supported on a Resorcinol-Phenylenediamine-Based Covalent Organic Framework for Chemical Fixation of CO2.

Covalent organic frameworks are a new class of crystalline organic polymers possessing a high surface area and ordered pores. Judicious selection of building blocks leads to strategic heteroatom inclusion into the COF structure. Owing to their high surface area, exceptional stability and molecular tunability, COFs are adopted for various potential applications. The heteroatoms lining in the pores of COF favor synergistic host-guest interaction to enhance a targeted property. In this report, we have synthesized a resorcinol-phenylenediamine-based COF which selectively adsorbs CO2 into its micropores (12 Å). The heat of adsorption value (32 kJ mol-1 ) obtained from the virial model at zero-loading of CO2 indicates its favorable interaction with the framework. Furthermore, we have anchored small-sized Ag nanoparticles (≈4-5 nm) on the COF and used the composite for chemical fixation of CO2 to alkylidene cyclic carbonates by reacting with propargyl alcohols under ambient conditions. Ag@COF catalyzes the reaction selectively with an excellent yield of 90 %. Recyclability of the catalyst has been demonstrated up to five consecutive cycles. The post-catalysis characterizations reveal the integrity of the catalyst even after five reaction cycles. This study emphasizes the ability of COF for simultaneous adsorption and chemical fixation of CO2 into corresponding cyclic carbonates.

Water-stable Adenine-based MOFs with Polar Pores for Selective CO2 Capture.

Here, we report two novel water-stable amine-functionalized MOFs, namely IISERP-MOF26 ([NH2 (CH3 )2 ][Cu2 O(Ad)(BDC)]⋅(H2 O)2 (DMA), 1) and IISERP-MOF27 ([NH2 (CH3 )2 ]1/2 [Zn4 O(Ad)3 (BDC)2 ]⋅(H2 O)2 (DMF)1/2 , 2), which show selective CO2 capture capabilities. They are made by combining inexpensive and readily available terephthalic acid and N-rich adenine with Cu and Zn, respectively. They possess 1D channels decorated by the free amine group from the adenine and the polarizing oxygen atoms from the terephthalate units. Even more, there are dimethyl ammonium (DMA+ ) cations in the pore rendering an electrostatic environment within the channels. The activated Cu- and Zn-MOFs physisorb about 2.7 and 2.2 mmol g-1 of CO2 , respectively, with high CO2 /N2 and moderate CO2 /CH4 selectivity. The calculated heat of adsorption (HOA=21-23 kJ mol-1 ) for the CO2 in both MOFs suggest optimal physical interactions which corroborate well with their facile on-off cycling of CO2 . Notably, both MOFs retain their crystallinity and porosity even after soaking in water for 24 hours as well as upon exposure to steam over 24 hours. The exceptional thermal and chemical stability, favorable CO2 uptakes and selectivity and low HOA make these MOFs promising sorbents for selective CO2 capture applications. However, the MOF's low heat of adsorption despite having a highly CO2 -loving groups lined walls is quite intriguing.

Facile Exfoliation of Single-Crystalline Copper Alkylphosphates to Single-Layer Nanosheets and Enhanced Supercapacitance.

Manipulation of low-dimensional solids through soft chemical routes is an elegant way to realize newer materials. A new family of single-crystalline transition-metal layered organophosphates, with about 185 000 metal phosphate layers in a single crystal, can be exfoliated to a single-layer nanosheet by a facile and rapid solvent assisted method. This exfoliation aids the formation of high-surface-area pyrophosphates with enhanced supercapacitance.

Carbon Derived from Soft Pyrolysis of a Covalent Organic Framework as a Support for Small-Sized RuO2 Showing Exceptionally Low Overpotential for Oxygen Evolution Reaction.

Electrochemical water splitting is the most energy-efficient technique for producing hydrogen and oxygen, the two valuable gases. However, it is limited by the slow kinetics of the anodic oxygen evolution reaction (OER), which can be improved using catalysts. Covalent organic framework (COF)-derived porous carbon can serve as an excellent catalyst support. Here, we report high electrocatalytic activity of two composites, formed by supporting RuO2 on carbon derived from two COFs with closely related structures. These composites catalyze oxygen evolution from alkaline media with overpotentials as low as 210 and 217 mV at 10 mA/cm2, respectively. The Tafel slopes of these catalysts (65 and 67 mV/dec) indicate fast kinetics compared to commercial RuO2. The observed activity is the highest among all RuO2-based heterogeneous OER catalysts-a touted benchmark OER catalyst. The high catalytic activity arises from the extremely small-sized (∼3-4 nm) RuO2 nanoparticles homogeneously dispersed in a micro-mesoporous (BET = 517 m2/g) COF-derived carbon. The porous graphenic carbon favors mass transfer, while its N-rich framework anchors the catalytic nanoparticles, making it highly stable and recyclable. Crucially, the soft pyrolysis of the COF enables the formation of porous carbon and simultaneous growth of small RuO2 particles without aggregation.

Cu/Cu2O Nanoparticles Supported on a Phenol-Pyridyl COF as a Heterogeneous Catalyst for the Synthesis of Unsymmetrical Diynes via Glaser-Hay Coupling.

Covalent organic frameworks (COFs) are a new class of porous crystalline polymers with a modular construct that favors functionalization. COF pores can be used to grow nanoparticles (nPs) with dramatic size reduction, stabilize them as dispersions, and provide excellent nP access. Embedding substrate binding sites in COFs can generate host-guest synergy, leading to enhanced catalytic activity. In this report, Cu/Cu2O nPs (2-3 nm) are grown on a COF, which is built by linking a phenolic trialdehyde and a triamine through Schiff bonds. Their micropores restrict the nP to exceptionally small sizes (∼2-3 nm), and the pore walls decorated with strategically positioned hydrogen-bonding phenolic groups anchor the substrates via hydrogen-bonding, whereas the basic pyridyl sites serve as cationic species to stabilize the [CuclusterCl2]2- type reactive intermediates. This composite catalyst shows high activity for Glaser-Hay heterocoupling reactions, an essential 1,3-diyne yielding reaction with widespread applicability in organic synthesis and material science. Despite their broad successes in homocoupled products, preparation of unsymmetrical 1,3-diynes is challenging due to poor selectivity. Here, our COF-based Cu catalyst shows elevated selectivity toward heterocoupling product(s) (Cu nP loading 0.0992 mol %; turn over frequency: ∼45-50; turn over number: ∼175-190). The reversible redox activity at the Cu centers has been demonstrated by carrying out X-ray photoelectron spectroscopy on the frozen reactions, whereas the crucial interactions between the substrates and the binding sites in their optimized configurations have been modeled using density functional theory methods. This report emphasizes the utility of COFs in developing a heterogeneous catalyst for a truly challenging organic heterocoupling reaction.

Hyper-Cross-linked Porous Organic Frameworks with Ultramicropores for Selective Xenon Capture.

Exceptionally stable ultramicroporous C-C-bonded porous organic frameworks (IISERP-POF6, 7, 8) have been prepared using simple Friedel-Crafts reaction. These polymers exhibit permanent porosity with a Brunauer-Emmett-Teller surface area of 645-800 m2/g. Xe/Kr adsorptive separation has been carried out with these polymers, and they display selective Xe capture ( s(Xe/Kr) = 6.7, 6.3, and 6.3) at 298 K and 1 bar pressure. Interestingly, these polymers also show remarkable Xe/N2 ( s(Xe/N2) = 200, 180, and 160 at 298 K and 1 bar) and Xe/CO2 selectivity ( s(Xe/CO2) = 5.6, 7.4, and 5.6) for a 1:99 composition of Xe-N2/Xe-CO2. Selective removal of Xe at such low concentrations is extremely challenging; the observed selectivities are higher compared to those observed in porous carbons and metal-organic frameworks. Breakthrough studies were performed using the composition relevant to the nuclear off-gas mixture with the polymers, and we find that the polymers hold Xe for a longer time in the column, which illustrates the Xe/Kr separation performance under dynamic conditions.

Potential of ultramicroporous metal-organic frameworks in CO2 clean-up.

This article explains the need for energy-efficient large-scale CO2 capture and briefly mentions the requirements for optimal solid sorbents for this application. It illustrates the potential of ultra-microporous metal-organic frameworks (MOFs, pore size: <7.0 Å) for the separation of CO2 from industrially abundant greenhouse gas mixtures. Some high-performing and well-studied MOFs are discussed to communicate the present status of the field. From their structural features, some successful design principles for creating such ultra-microporous MOFs are derived. Towards the close, favorable CO2 diffusion in many of these small pore MOFs is highlighted.