Self-Standing Covalent Organic Framework Membranes for H2/CO2 Separation

International audienceCovalent organic frameworks (COFs) are proposed as promising candidates for engineering advanced molecular sieving membranes due to their precise pore sizes, modifiable pore environment, and superior stability. However, COFs are insoluble in common solvents and do not melt at high temperatures, which presents a great challenge for the fabrication of COF-based membranes (COFMs). Herein, for the first time, a new synthetic strategy is reported to prepare continuous and intact self-standing COFMs, including 2D N-COF membrane and 3D COF-300 membrane. Both COFMs show excellent selectivity of H2/CO2 mixed gas (13.8 for N-COF membrane and 11 for COF-300 membrane), and especially ultrahigh H2 permeance (4319 GPU for N-COF membrane and 5160 GPU for COF-300 membrane), which is superior to those of COFMs reported so far. It should be noted that the overall separation performance of self-standing COFMs exceeds the Robeson upper bound. Furthermore, a theoretical study based on Grand Canonical Monte Carlo (GCMC) simulation is performed to explain the excellent separation of H2/CO2 through COFMs. Thus, this facile preparation method will provide a broad prospect for the development of self-standing COFMs with highly efficient H2 purification

Self-Standing Covalent Organic Framework Membranes for H2/CO2 Separation

Covalent organic frameworks (COFs) have been proposed as promising candidates for engineering advanced molecular sieving membranes due to their precise pore sizes, modifiable pore environment, and superior stability. However, COFs are insoluble in common solvents and do not melt at high temperatures, which presents a great challenge for the fabrication of COF-based membranes (COFMs). Herein, for the first time, we report a new synthetic strategy to prepare continuous and intact self-standing COFMs, including 2D N-COF membrane and 3D COF-300 membrane. Both COFMs show excellent selectivity of H2/CO2 mixed gas (26 for N-COF membrane and 18.4 for COF-300 membrane), and especially ultrahigh H2 permeance (13165 GPU for N-COF membrane and 12475 GPU for COF-300 membrane), which is superior to those of COFMs reported so far. It should be noted that the overall separation performance of self-standing COFMs exceeds the Robeson upper bound. Furthermore, a theoretical study based on Grand Canonical Monte Carlo simulation is performed to explain the excellent separation of H2/CO2 through COFMs. Thus, this facile preparation method will provide a broad prospect for the development of self-standing COFMs with highly efficient H2 purification

Three‐Dimensional Triptycene‐Functionalized Covalent Organic Frameworks with hea Net for Hydrogen Adsorption

International audienceOwing to the confined building blocks and difficulty in structural identification, it remains a tremendous chal-lenge to directionally design and synthesize three-dimensional covalent organic frameworks (3D COFs) with predetermined topologies. Herein, we report the first two cases of 3D COFs with the hea topology, termed JUC-596 and JUC-597, by using the combination of tetrahedral and triangular prism building units. Due to the presence of triptycene functional group, JUC-596 exhibits an excep-tional performance in the H2 adsorption up to 356 cm3/g (or 3.18 wt%) at 77 K and 1 bar, which is higher than previ-ous benchmarks from porous materials reported so far, including porous carbon, metal-organic frameworks, amorphous porous polymers, and other COFs. Further-more, the strong interaction between H2 and COF materi-als is validated through the DFT theoretical calculation. This work represents a triumphant example of rational design of functional COFs based on a reticular chemistry guide and demonstrates its promising application in clean energy storage

Metal-Free Covalent Organic Frameworks Containing Precise Heteroatoms for Efficient Oxygen Reduction Reaction

Heteroatom-doped carbon-based nanomaterials are one of the most promising metal-free electrocatalysts due to their high activity, low cost, long lifetime, and environmental friendliness. However, the precise atomic position is hard to tune; moreover, the specific role of those heteroatom species is still unclear. Herein, we report a series of metal-free benzotrithiophene-based covalent organic frameworks containing various heteroatoms (Se, S or O), BTT-COFs (named JUC-616, JUC-617, and JUC-618, respectively), and explore their oxygen reduction reaction (ORR) catalytic activity. Remarkably, JUC-616 involving precise Se atoms exhibits an onset potential of 1.02 V and half-wave potential of 0.78 V, which is the best among metal- and pyrolysis-free COF-based electrocatalysts reported so far. Furthermore, we demonstrate that the high ORR catalytic performance of JUC-616 can be attributed to the small free energy and overpotential by DFT calculations. This work thus promotes the promising potential of functionalized COFs with precise heteroatoms for electrocatalysts

Three-Dimensional Covalent Organic Frameworks with nia Nets for Efficient Separation of Benzene/Cyclohexane Mixtures

The synthesis of three-dimensional (3D) covalent organic frameworks (COFs) with highly connected building blocks presents a significant challenge. In this study, we report two novel 3D COFs with the nia topology, named JUC-641 and JUC-642, by introducing planar hexagonal and triangular prism nodes for the first time. The resulting materials display high crystallinity, excellent thermal/chemical stability, a through-hole structure, and a large specific surface area. Notably, our adsorption studies and breakthrough experiments reveal that both COFs exhibit exceptional separation capabilities, surpassing previously reported 3D COFs and most porous organic polymers, with a separation factor of up to 2.02 for benzene and cyclohexane. Additionally, dispersion-corrected density functional theory analysis suggests that the outstanding performance of these 3D COFs can be attributed to the incorporation of highly aromatic building blocks and the presence of extensive pore structures. Consequently, this research not only expands the diversity of COFs but also highlights the potential of functional COF materials as promising candidates for environmentally-friendly separation applications

Metal-free covalent organic frameworks containing precise heteroatoms for electrocatalytic oxygen reduction reaction

Covalent organic frameworks (COFs) have been used for electrocatalytic oxygen reduction reaction (ORR) due to their structural tunability, well-defined electroactive sites, and easy introduction of heteroatoms. Researchers have incorporated heteroatoms into COF architectures to enhance their performance by tuning the electronic environment of oxygen intermediates. However, only a few heteroatoms (O, S, N, P) have been introduced into the backbone of COFs, and the effects of different types of heteroatoms on the electronic structure of COFs have not been specifically investigated. Furthermore, the development of COF electrocatalysts with highly active ORR is still at an early stage. Herein, we report a series of metal-free benzotrithiophene-based COFs containing various heteroatoms (Se, S or O), BTT-COFs (named JUC-616, JUC-617, and JUC-618, respectively), and explore their ORR catalytic activity. Remarkably, JUC-616 involving precise Se atoms exhibits a half-wave potential of 0.78 V and a high turnover frequency (TOF) of 0.0062 s−1 at 0.75 V vs. the reversible hydrogen electrode (RHE), which is the best among the metal- and pyrolysis-free COF-based electrocatalysts reported so far. Thus, this work shows the promising potential of functionalized COFs with precise heteroatoms for electrocatalysis

Gating Effects for Ion Transport in Three-Dimensional Functionalized Covalent Organic Frameworks

International audienceThe development of bioinspired nano/subnano-sized (<2 nm) ion channels is still considered a great challenge due to the difficulty in precisely controlling pore's internal structure and chemistry. Herein, for the first time, we report that three-dimensional functionalized covalent organic frameworks (COFs) can act as an effective nanofluidic platform for intelligent modulation of the ion transport. By strategic attachment of 12-crown-4 groups to the monomers as ion-driver door locks, we demonstrate that gating effects of functionalized COFs can be activated by lithium ions. The obtained materials exhibit an outstanding selective ion transmission performance with a high gating ratio (up to 23.6 for JUC-590), which is among the highest values in metal ion-activated solid-state nanochannels reported so far. Furthermore, JUC-590 offers high tunability, selectivity, and recyclability of ion transport proved by the experimental and simulated studies

Design and Synthesis of a Zeolitic Organic Framework

The development of three-dimensional (3D) architectures in COFs has been considered important owing to their prospective ad-vantages in high surface areas and plentiful active sites. Herein, we report the first example of a 3D COF with zeolitic network, namely the zeolitic organic framework (ZOF). By combining two kinds of tetrahedral building blocks with fixed or relatively free bond angles, ZOF-1 with the zeolitic crb net has been successfully synthesized. Its structure was determined by the single-crystal 3D electron dif-fraction technique. Remarkably, ZOF-1 shows high chemical stabil-ity, large pore size (up to 16 Å), and excellent specific surface area (~ 2785 m2/g), which is superior to its analogues with the same network, including traditional aluminosilicate zeolites and zeolitic imidazole frameworks. This study thus opens a new avenue to construct 3D COFs with zeolitic topologies and promotes the struc-tural diversity and practical applications of COF materials

Three-Dimensional Covalent Organic Frameworks Constructed from Irregular Polyhedral Building Blocks

Developing three-dimensional (3D) covalent organic frameworks (COFs) has paramount significance across numerous applications. However, the conventional design approach that relies on regular building blocks significantly restricts the structural diversity of COFs. In this study, we successfully designed and synthesized two 3D COFs, named JUC-643 and JUC-644, employing a novel strategy based on irregular 8-connected (8-c) building blocks. By using a continuous rotation electron diffraction technique combined with powder X-ray diffraction patterns, their structures were solved and revealed a unique linkage with double helical structure, a phenomenon previously unreported in COFs. In order to precisely describe the topology, these structures should be deconstructed into the unprecedented [4+3(+2)]-c nets instead of the traditional [8(+2)]-c or [6(+2)]-c net. Furthermore, one of the materials (JUC-644) has demonstrated exceptional adsorption capability towards C3H8 and n-C4H10 (11.28 and 10.45 mmol g-1 at 298 K and 1 bar respectively), surpassing the adsorption performance of all known porous materials, and breakthrough experiments have also highlighted the remarkable C3H8/C2H6 and n-C4H10/C2H6 selectivity. This pioneering concept of incorporating irregular building blocks in 3D COFs introduces a promising avenue for designing intricate architectures while enhancing their potential application in the recovery of C2H6 from natural gas liquids

Three-dimensional covalent organic frameworks with nia nets for efficient separation of benzene/cyclohexane mixtures

Abstract The synthesis of three-dimensional covalent organic frameworks with highly connected building blocks presents a significant challenge. In this study, we report two 3D COFs with the nia topology, named JUC-641 and JUC-642, by introducing planar hexagonal and triangular prism nodes. Notably, our adsorption studies and breakthrough experiments reveal that both COFs exhibit exceptional separation capabilities, surpassing previously reported 3D COFs and most porous organic polymers, with a separation factor of up to 2.02 for benzene and cyclohexane. Additionally, dispersion-corrected density functional theory analysis suggests that the good performance of these 3D COFs can be attributed to the incorporation of highly aromatic building blocks and the presence of extensive pore structures. Consequently, this research not only expands the diversity of COFs but also highlights the potential of functional COF materials as promising candidates for environmentally-friendly separation applications