Extended MOF-74-Type Variant with an Azine Linkage: Efficient Direct Air Capture and One-Pot Synthesis.

Direct air capture (DAC) shows considerable promise for the effective removal of CO2; however, materials applicable to DAC are lacking. Among metal-organic framework (MOF) adsorbents, diamine-Mg2(dobpdc) (dobpdc4- = 4,4-dioxidobiphenyl-3,3'-dicarboxylate) effectively removes low-pressure CO2, but the synthesis of the organic ligand requires high temperature, high pressure, and a toxic solvent. Besides, it is necessary to isolate the ligand for utilization in the synthesis of the framework. In this study, we synthesized a new variant of extended MOF-74-type frameworks, M2(hob) (M = Mg2+, Co2+, Ni2+, and Zn2+; hob4- = 5,5'-(hydrazine-1,2-diylidenebis(methanylylidene))bis(2-oxidobenzoate)), constructed from an azine-bonded organic ligand obtained through a facile condensation reaction at room temperature. Functionalization of Mg2(hob) with N-methylethylenediamine, N-ethylethylenediamine, and N,N'-dimethylethylenediamine (mmen) enables strong interactions with low-pressure CO2, resulting in top-tier adsorption capacities of 2.60, 2.49, and 2.91 mmol g-1 at 400 ppm of CO2, respectively. Under humid conditions, the CO2 capacity was higher than under dry conditions due to the presence of water molecules that aid in the formation of bicarbonate species. A composite material combining mmen-Mg2(hob) and polyvinylidene fluoride, a hydrophobic polymer, retained its excellent adsorption performance even after 7 days of exposure to 40% relative humidity. In addition, the one-pot synthesis of Mg2(hob) from a mixture of the corresponding monomers is achieved without separate ligand synthesis steps; thus, this framework is suitable for facile large-scale production. This work underscores that the newly synthesized Mg2(hob) and its composites demonstrate significant potential for DAC applications.

Boc Protection for Diamine-Appended MOF Adsorbents to Enhance CO2 Recyclability under Realistic Humid Conditions.

Among the various metal-organic framework (MOF) adsorbents, diamine-functionalized Mg2(dobpdc) (dobpdc4- = 4,4-dioxidobiphenyl-3,3'-dicarboxylate) shows remarkable carbon dioxide removal performance. However, applying diamine-functionalized Mg2(dobpdc) in practical applications is premature because it shows persistent performance degradation under real flue gas conditions containing water vapor owing to diamine loss during wet cycles. To address this issue, we employed hydrophobic carbonate compounds to protect diamine groups in een-Mg2(dobpdc) (een-MOF, een = N-ethylethylenediamine). tert-Butyl dicarbonate (Boc) reacted rapidly with diamines at the pore openings of MOF particles to form dense secondary and tertiary hydrophobic amines, effectively preventing moisture ingress. The Boc-protected een-MOF-Boc1 maintained excellent CO2 adsorption even under simulated flue gas conditions containing 10% H2O. This observation indicates that Boc protection renders een groups intact during repeated wet cycles, suggesting that Boc-protected een groups are resistant to replacement by water molecules. To increase the practicability of the MOF adsorbent, we fabricated een-MOF/PAN-Boc1 composite beads by shaping MOF particles with polyacrylonitrile (PAN). Notably, the composite beads maintained their CO2 adsorption performance even after repeating the temperature swing adsorption process more than 150 times in 10% water vapor. Furthermore, breakthrough tests showed that the dynamic CO2 separation performance was retained under humid conditions. These results demonstrate that Boc protection provides an easy and effective way to develop promising adsorbents with high CO2 adsorption capacity, long-term durability, and the properties required for postcombustion applications.

Aminal-Linked Covalent Organic Frameworks with hxl-a and Quasi-hcb Topologies for Efficient C2 H6 /C2 H4 Separation.

In reticular chemistry, topology is a powerful concept for defining the structures of covalent organic frameworks (COFs). However, due to the lack of diversity in the symmetry and reaction stoichiometry of the monomers, only 5% of the two-dimensional topologies have been reported to be COFs. To overcome the limitations of COF connectivity and pursue novel topologies in COF structures, two aminal-linked COFs, KUF-2 and KUF-3, are prepared, with dumbbell-shaped secondary building units. Linear dialdehydes and piperazine are condensed at a ratio of 1:2 to construct an aminal linkage, leading to unreported hxl-a (KUF-2) and quasi-hcb (KUF-3) structures. Notably, KUF-3 displays top-tier C2 H6 /C2 H4 selectivity and C2 H6 uptake at 298 K, outperforming most porous organic materials. The intrinsic aromatic ring-rich and Lewis basic pore environments, and appropriate pore widths enable the selective adsorption of C2 H6 , as confirmed by Grand Canonical Monte Carlo simulations. Dynamic breakthrough curves revealed that C2 H6 can be selectively separated from a gas mixture of C2 H6 and C2 H4 . This study suggests that topology-based design of aminal-COFs is an effective strategy for expanding the field of reticular chemistry and provides the facile integration of strong Lewis basic sites for selective C2 H6 /C2 H4 separation.

Porous organic materials for iodine adsorption.

The nuclear industry will continue to develop rapidly and produce energy in the foreseeable future; however, it presents unique challenges regarding the disposal of released waste radionuclides because of their volatility and long half-life. The release of radioactive isotopes of iodine from uranium fission reactions is a challenge. Although various adsorbents have been explored for the uptake of iodine, there is still interest in novel adsorbents. The novel adsorbents should be synthesized using reliable and economically feasible synthetic procedures. Herein, we discussed the state-of-the-art performance of various categories of porous organic materials including covalent organic frameworks, covalent triazine frameworks, porous aromatic frameworks, porous organic cages, among other porous organic polymers for the uptake of iodine. This review discussed the synthesis of porous organic materials and their iodine adsorption capacity and reusability. Finally, the challenges and prospects for iodine capture using porous organic materials are highlighted.

Switchable Xe/Kr Selectivity in a Hofmann-Type Metal-Organic Framework via Temperature-Responsive Rotational Dynamics.

The development of adsorbents for Kr and Xe separation is essential to meet industrial demands and for energy conservation. Although a number of previous studies have focused on Xe-selective adsorbents, stimuli-responsive Xe/Kr-selective adsorbents still remain underdeveloped. Herein, a Hofmann-type framework Co(DABCO)[Ni(CN)4 ] (referred to as CoNi-DAB; DABCO = 1,4-diazabicyclo[2,2,2]octane) that provides a temperature-dependent switchable Xe/Kr separation performance is reported. CoNi-DAB showed high Kr/Xe (0.8/0.2) selectivity with significant Kr adsorption at 195 K as well as high Xe/Kr (0.2/0.8) selectivity with superior Xe adsorption at 298 K. Such adsorption features are associated with the temperature-dependent rotational configuration of the DABCO ligand, which affects the kinetic gate-opening temperature of Xe and Kr. The packing densities of Xe (2.886 g cm-3 at 298 K) and Kr (2.399 g  cm-3 at 195 K) inside the framework are remarkable and comparable with those of liquid Xe (3.057 g cm-3 ) and liquid Kr (2.413 g cm-3 ), respectively. Breakthrough experiments confirm the temperature-dependent reverse separation performance of CoNi-DAB at 298 K under dry and wet (88% relative humidity) conditions and at 195 K under dry conditions. The unique adsorption behavior is also verified through van der Waals (vdW)-corrected density functional theory (DFT) calculations and nudged elastic band (NEB) simulations.

Electronic Effect-Modulated Enhancements of Proton Conductivity in Porous Organic Polymers.

We proposed a new strategy to maximize the density of acidic groups by modulating the electronic effects of the substituents for high-performance proton conductors. The conductivity of the sulfonated 1-MeL40-S with methyl group corresponds to 2.29×10-1  S cm-1 at 80 °C and 90 % relative humidity, remarkably an 22100-fold enhancement over the nonsulfonated 1-MeL40. 1-MeL40-S maintains long-term conductivity for one month. We confirm that this synthetic method is generalized to the extended version POPs, 2-MeL40-S and 3-MeL40-S. In particular, the conductivities of the POPs compete with those of top-level porous organic conductors. Moreover, the activation energy of the POPs is lower than that of the top-performing materials. This study demonstrates that systematic alteration of the electronic effects of substituents is a useful route to improve the conductivity and long-term durability of proton-conducting materials.

Protocol for the fabrication of porous organic polymer-based composites for photocatalytic degradation of a sulfur mustard simulant.

Although porous organic polymer (POP) has been explored as a promising photosensitizer, its powdered form makes it unfavorable for practical applications. Here, we demonstrate a protocol for fabricating imidazoline-based POP composites using fabric and sponge as substrates. This fabrication is limited to POPs with aldehyde containing organic building blocks. For complete details on the use and execution of this protocol, please refer to Kim et al. (2022).

Correction: Post-synthetic modifications in porous organic polymers for biomedical and related applications.

Correction for 'Post-synthetic modifications in porous organic polymers for biomedical and related applications' by Ji Hyeon Kim et al., Chem. Soc. Rev., 2022, 51, 43-56, https://doi.org/10.1039/D1CS00804H.

Functionalization of Diamine-Appended MOF-Based Adsorbents by Ring Opening of Epoxide: Long-Term Stability and CO2 Recyclability under Humid Conditions.

Although diamine-appended metal-organic framework (MOF) adsorbents exhibit excellent CO2 adsorption performance, a continuous decrease in long-term capacity during repeated wet cycles remains a formidable challenge for practical applications. Herein, we present the fabrication of diamine-appended Mg2(dobpdc)-alumina beads (een-MOF/Al-Si-Cx; een = N-ethylethylenediamine; x = number of carbon atoms attached to epoxide) coated with hydrophobic silanes and alkyl epoxides. The reaction of epoxides with diamines in the portal of the pore afforded sufficient hydrophobicity, hindered the penetration of water vapor into the pores, and rendered the modified diamines less volatile. een-MOF/Al-Si-C17-200 (een-MOF/Al-Si-C17-y; y = 50, 100, and 200, denoting wt % of C17 with respect to the bead, respectively), with substantial hydrophobicity, showed a significant uptake of 2.82 mmol g-1 at 40 °C and 15% CO2, relevant to flue gas concentration, and a reduced water adsorption. The modified beads maintained a high CO2 capacity for over 100 temperature-swing adsorption cycles in the presence of 5% H2O and retained CO2 separation performance in breakthrough tests under humid conditions. This result demonstrates that the epoxide coating provides a facile and effective method for developing promising adsorbents with high CO2 adsorption capacity and long-term durability, which is a required property for postcombustion applications.

High Gravimetric and Volumetric Ammonia Capacities in Robust Metal-Organic Frameworks Prepared via Double Postsynthetic Modification.

Ammonia is a promising energy vector that can store the high energy density of hydrogen. For this reason, numerous adsorbents have been investigated as ammonia storage materials, but ammonia adsorbents with a high gravimetric/volumetric ammonia capacity that can be simultaneously regenerated in an energy-efficient manner remain underdeveloped, which hampers their practical implementation. Herein, we report Ni_acryl_TMA (TMA = thiomallic acid), an acidic group-functionalized metal-organic framework prepared via successive postsynthetic modifications of mesoporous Ni2Cl2BTDD (BTDD = bis(1H-1,2,3,-triazolo [4,5-b],-[4',5'-i]) dibenzo[1,4]dioxin). By virtue of the densely located acid groups, Ni_acryl_TMA exhibited a top-tier gravimetric ammonia capacity of 23.5 mmol g-1 and the highest ammonia storage of 0.39 g cm-3 at 1 bar and 298 K. The structural integrity and ammonia storage capacity of Ni_acryl_TMA were maintained after ammonia adsorption-desorption tests over five cycles. Temperature-programmed desorption analysis revealed that the moderate strength of the interaction between the functional groups and ammonia significantly reduced the desorption temperature compared to that of the pristine framework with open metal sites. The structures of the postsynthetic modified analogues were elucidated based on Pawley/Rietveld refinement of the synchrotron powder X-ray diffraction patterns and van der Waals (vdW)-corrected density functional theory (DFT) calculations. Furthermore, the ammonia adsorption mechanism was investigated via in situ infrared and vdW-corrected DFT calculations, revealing an atypical guest-induced binding mode transformation of the integrated carboxylate. Dynamic breakthrough tests showed that Ni_acryl_TMA can selectively capture traces of ammonia under both dry and wet conditions (80% relative humidity). These results demonstrate that Ni_acryl_TMA is a superior ammonia storage/capture material.

High Ammonia Uptake of a Metal-Organic Framework Adsorbent in a Wide Pressure Range.

Although numerous porous adsorbents have been investigated for NH3 capture applications, these materials often exhibit insufficient NH3 uptake, low NH3 affinity at the ppm level, and poor chemical stability against wet NH3 conditions. The NH3 capture properties of M2 (dobpdc) complexes (M=Mg2+ , Mn2+ , Co2+ , Ni2+ , and Zn2+ ; dobpdc4- =4,4-dioxidobiphenyl-3,3-dicarboxylate) that contain open metal sites is presented. The NH3 uptake of Mg2 (dobpdc) at 298 K was 23.9 mmol g-1 at 1 bar and 8.25 mmol g-1 at 570 ppm, which are record high capacities at both pressures among existing porous adsorbents. The structural stability of Mg2 (dobpdc) upon exposure to wet NH3 was superior to that of the other M2 (dobpdc) and the frameworks tested. Overall, these results demonstrate that Mg2 (dobpdc) is a recyclable compound that exhibits significant NH3 affinity and capacity, making it a promising candidate for real-world NH3 -capture applications.