Search

The design of three-dimensional covalent organic frameworks (3D COFs) using linear and trigonal linkers remains challenging due to the difficulty in achieving a specific non-planar spatial arrangement with low-connectivity building units. Here, we report the novel 3D COFs with linear and trigonal linkers, termed TMB-COFs, exhibiting srs topology. The steric hindrance provides an additional force to alter the torsion angles of peripheral triangular units, guiding the linear unit to connect with the trigonal unit into 3D srs frameworks, rather than the more commonly observed two-dimensional (2D) hcb structures. Furthermore, we comprehensively examined the hydrogen peroxide photocatalytic production capacity of the TMB-COFs in comparison with analogous 2D COFs. The experimental results and DFT calculations demonstrate a significant enhancement in photocatalytic hydrogen peroxide production efficacy through framework regulation. This work emphasizes the steric configuration using low connectivity building units, offering a fresh perspective on the design and application of 3D COFs., (© 2024 Wiley‐VCH GmbH.)

Covalent organic frameworks (COFs) are an innovative class of crystalline porous polymers composed of light elements such as C, N, O, etc., linked by covalent bonds. The distinctive properties of COFs, including designable building blocks, large specific surface area, tunable pore size, abundant active sites, and remarkable stability, have led their widespread applications in electrocatalysis. In recent years, COF-based electrocatalysts have made remarkable progress in various electrocatalytic fields, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, nitrogen reduction reaction, nitrate reduction reaction, and carbon dioxide reduction reaction. This review begins with an introduction to the design and synthesis strategies employed for COF-based electrocatalysts. These strategies include heteroatom doping, metalation of COF and building monomers, encapsulation of active sites within COF pores, and the development of COF-based derived materials. Subsequently, a systematic overview of the recent advancements in the application of COF-based catalysts in electrocatalysis is presented. Finally, the review discusses the main challenges and outlines possible avenues for the future development of COF-based electrocatalysts., (© 2024 Wiley-VCH GmbH.)

Multi-shelled hollow metal-organic frameworks (MH-MOFs) are highly promising as electrode materials due to their impressive surface area and efficient mass transfer capabilities. However, the fabrication of MH-MOFs has remained a formidable challenge. In this study, two types of double-shelled open hollow Prussian blue analogues, one with divalent iron (DHPBA-Fe(II)) and the other with trivalent iron (DHPBA-Fe(III)), through an innovative inner-outer growth strategy are successfully developed. The growth mechanism is found to involve lattice matching growth and ligand exchange processes. Subsequently, DHPBA-Fe(II) and DHPBA-Fe(III) are employed as cathodes in aqueous Zn-ion batteries. Significantly, DHPBA-Fe(II) demonstrated exceptional performance, exhibiting a capacity of 92.5 mAh g -1 at 1 A g -1 , and maintaining remarkable stability over an astounding 10 000 cycles. This research is poised to catalyze further exploration into the fabrication techniques of MH-MOFs and offer fresh insights into the intricate interplay between electronic structure and battery performance., (© 2023 Wiley‐VCH GmbH.)

Non-platinum noble metals are highly desirable for the development of highly active, stable oxygen reduction reaction (ORR) electrocatalysts for fuel cells and metal-air batteries. However, how to improve the utilization of non-platinum noble metals is an urgent issue. Herein, a highly efficient catalyst for ORR was prepared through homogeneous loading of Pd precursors by a domain-limited method in a three-dimensional covalent organic framework (COF) followed by pyrolysis. The morphology of the Pd nanoparticles (Pd NPs) was well maintained after carbonization, which was attributed to the rigid structure of the 3D COF. Thanks to the uniform distribution of Pd NPs in the carbon, the catalyst exhibited a remarkable half-wave potential of 0.906 V and a Tafel slope of 70 mV dec -1 in 0.1 M KOH, surpassing the commercial Pt/C catalyst (0.863 V and 75 mV dec -1 ). Furthermore, a maximum power density of 144.0 mW cm -2 was achieved at 252 mA cm -2 , which was significantly higher than the control battery (105.1 mW cm -2 ). This work not only provides a simple strategy for in-situ preparation of highly dispersible metal catalysts in COFs, but also offers new insights into the ORR electrocatalysis., (© 2023 Wiley-VCH GmbH.)

Humidity is one of the most important indicators affecting human health. Here, a pair of covalent organic frameworks (COFs) of positional isomers (p-COF and o-COF) for indoor humidity regulation is reported. Although p-COF and o-COF have the same sql topology and pore size, they exhibit different water adsorption behaviors due to the subtle differences in water adsorption sites. Particularly, o-COF exhibits a steep adsorption isotherm in the range of 45-65% RH with a hysteresis loop, which is perfectly suitable for indoor humidity regulation. In the laboratory experiment, when the humidity of the external environment is 20-75% RH, o-COF can control the humidity of the room in the range of 45-60% RH. o-COF has shown great potential as a dual humidification/dehumidification adsorbent for indoor humidity regulation., (© 2023 Wiley-VCH GmbH.)

Dual-atom catalysts (DAC) are deemed as promising electrocatalysts due to the abundant active sites and adjustable electronic structure, but the fabrication of well-defined DAC is still full of challenges. Herein, bonded Fe dual-atom catalysts (Fe 2 DAC) with Fe 2 N 6 C 8 O 2 configuration were developed through one-step carbonization of a preorganized covalent organic framework with bimetallic Fe chelation sites (Fe 2 COF). The transition from Fe 2 COF to Fe 2 DAC involved the dissociation of the nanoparticles and the capture of atoms by carbon defects. Benefitting from the optimized d-band center and enhanced adsorption of OOH* intermediates, Fe 2 DAC exhibited outstanding oxygen reduction activity with a half-wave potential of 0.898 V vs. RHE. This work will guide more fabrication of dual-atom and even cluster catalysts from preorganized COF in the future., (© 2023 Wiley-VCH GmbH.)

Atmospheric moisture is a sustainable clean water source that can solve the shortage of fresh water in arid areas. Herein a 2D covalent organic framework (COF-ok) was reported as a promising porous sorbent for solar-driven atmospheric water harvesting. COF-ok with ortho-ketoenamine linkage was extremely stable in harsh environment, including in boiling water, strong acids and bases. Because of the balanced hydrophilic and hydrophobic sites in channels, COF-ok showed a high water uptake of 0.33 g g -1 at a low relative humidity of 34 % featuring a characteristic S-shaped water sorption isotherm with low regeneration temperature (∼45 °C) and excellent cyclic stability. A laboratory-scale water harvesting system could collect water of 161 g kg -1 under sunlight., (© 2022 Wiley-VCH GmbH.)

Three metal covalent organic frameworks (MCOFs), namely RuCOF-ETTA, RuCOF-TPB and RuCOF-ETTBA, were synthesized by incorporating the photosensitive Ru II tris(2,2'-bipyridine) unit into the skeleton. Interestingly, each RuCOF contains three isostructural covalent organic frameworks that interlock together with the Ru II centers serving as point of registry. The covalently linked network coupling with uniformly distributed Ru II units allowed the RuCOFs to exhibit superior chemical stability, strong light-harvesting ability, and high photocatalytic activity toward hydrogen evolution (20 308 μmol g -1  h -1 ). This work illustrates the potential of developing versatile MCOFs-based photocatalysts from functionalized metal complex building unit and further enriches the MCOFs family., (© 2022 Wiley-VCH GmbH.)

Hollow structured metal-organic frameworks (MOFs) and their derivatives are desired in catalysis, energy storage, etc. However, fabrication of novel hollow MOFs and revelation of their formation mechanisms remain challenging. Herein, open hollow 2D MOFs in the form of hexagonal nut are prepared through self-template method, which can be readily scaled up at gram scale in a one-pot preparation. The evolution from the initial superstructure to the final stable MOFs is tracked by wide-angle X-ray scattering, transforming from solid hexagon to open hollow hexagon. More importantly, this protocol can be extended to synthesizing a series of open hollow structured MOFs with sizes ranging from ≈120 to ≈1200 nm. Further, open hollow structured cobalt/N-doped porous carbon composites are realized through conformal transformation of the as-prepared MOFs, which demonstrates promising applications in sustainable energy conversion technologies. This study sheds light on the kinetically controlled synthesis of novel 2D MOFs for their extended utilizations., (© 2022 Wiley-VCH GmbH.)

The construction of three-dimensional (3D) covalent organic frameworks (COFs) remains challenging due to the limited types of organic building blocks. With octahedral Ti IV complex as the building unit, this study reports on the first 3D anionic titanium-based COF (Ti-COF-1) with an edge-transitive (6, 4)-connected soc topology. Ti-COF-1 exhibits high crystallinity, superior stability, and large specific surface area (1000.4 m 2  g -1 ). Moreover, Ti-COF-1 has a broad absorption band in the UV spectrum with an optical energy gap of 1.86 eV, and exhibits high photocatalytic activity toward Meerwein addition reactions. This research demonstrates an attractive strategy for the design of 3D functional COFs., (© 2021 Wiley-VCH GmbH.)

In this work, pyrazine (A), aminopyrazine (B), quinoxaline (C), and 5,6,7,8-tetrahydroquinoxaline (D) have been screened out among a large number of pyrazine derivatives to construct Hofmann-type metal-organic frameworks (MOFs) Fe(L)[M(CN) 4 ] (M=Pt, Pd) with similar 3D pillared-layer structures. X-ray single-crystal diffraction reveals that the alternate linkage between M and Fe II ions through cyano bridges forms the 2D extended metal cyanide sheets, and ligands A-D acted as vertical columns to connect the 2D sheets to give 3D pillared-layer structures. Subsequently, a series of bivariate MOFs were constructed by pairwise combination of the four ligands A-D, which were confirmed by 1 H NMR, PXRD, FTIR, and Raman spectroscopy. The results demonstrated that ligand size and crystallization rate play a dominant role in constructing bivariate Hofmann-type MOFs. More importantly, the spin-crossover (SCO) properties of the bivariate MOFs can be finely tuned by adjusting the proportion of the two pillared ligands in the 3D Hofmann-type structures. Remarkably, the spin transition temperatures, T c ↑ and T c ↓ of Fe(A) x (B) 1-x [Pt(CN) 4 ] (x=0 to 1) can be adjusted from 239 to 254 K and from 248 to 284 K, respectively. Meanwhile, the width of the hysteresis loops can be widened from 9 to 30 K. Changing Pt to Pd, the hysteresis loops of Fe(A) x (B) 1-x [Pd(CN) 4 ] can be tuned from 9 (T c ↑=215 K, T c ↓=206 K) to 24 K (T c ↑=300 K, T c ↓=276 K). This research provides wider implications in the development of advanced bistable materials, especially in precisely regulating SCO properties., (© 2020 Wiley-VCH GmbH.)

A hexagonal porphyrin-based porous organic polymer, namely, CPF-1, was constructed by 3+2 ketoenamine condensation of the C 2 -symmetric porphyrin diamine 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin and 1,3,5-triformylphloroglucinol. This material exhibits permanent porosity and excellent thermal and chemical stability. CPF-1 can be employed as a superior supporting substrate to immobilize Au nanoparticles (NPs) as a result of the strong interactions between Au NPs and the CPF support. An Au@CPF-1 hybrid was synthesized by an interfacial solution infiltration method with NaBH 4 as reducing agent. Au NPs (5 nm) grew on CPF-1 and were distributed without aggregation. Moreover, Au@CPF-1 exhibits superior catalytic activity compared to many other reported Au-based catalysts for the reduction of 4-nitrophenol in the presence of NaBH 4 . In addition, Au@CPF-1 has excellent stability and recyclability, and it can be reused for three successive reaction cycles without loss of activity. The dense distribution of phenyl rings on the channel walls of the CPF support can reasonably be regarded as the active sites that adsorb the 4-nitrophenol molecule through hydrogen-bonding and C-H⋅⋅⋅π interactions, as was confirmed by the X-ray structure of model compound DAPP-Benz., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)