The
pore apertures dictate the guest accessibilities of the pores,
imparting diverse functions to porous materials. It is highly desired
to construct crystalline porous polymers with predesignable and uniform
mesopores that can allow large organic, inorganic, and biological
molecules to enter. However, due to the ease of the formation of interpenetrated
and/or fragile structures, the largest pore aperture reported in the
metal–organic frameworks is 8.5 nm, and the value for covalent
organic frameworks (COFs) is only 5.8 nm. Herein, we construct a series
of COFs with record pore aperture values from 7.7 to 10.0 nm by designing
building blocks with large conformational rigidness, planarity, and
suitable local polarity. All of the obtained COFs possess eclipsed
stacking structures, high crystallinity, permanent porosity, and high
stability. As a proof of concept, we successfully employed these COFs
to separate pepsin that is ∼7 nm in size from its crudes and
to protect tyrosinase from heat-induced deactivation.
Photocatalytic hydrogen (H2) evolution represents a promising and sustainable technology. Covalent organic frameworks (COFs)‐based photocatalysts have received growing attention. A 2D fully conjugated ethylene‐linked COF (BTT‐BPy‐COF) was fabricated with a dedicated designed active site. The introduced bipyridine sites enable a facile post‐protonation strategy to fine‐tune the actives sites, which results in a largely improved charge‐separation efficiency and increased hydrophilicity in the pore channels synergically. After modulating the degree of protonation, the optimal BTT‐BPy‐PCOF exhibits a remarkable H2 evolution rate of 15.8 mmol g−1 h−1 under visible light, which surpasses the biphenyl‐based COF 6 times. By using different types of acids, the post‐protonation is proved to be a potential universal strategy for promoting photocatalytic H2 evolution. This strategy would provide important guidance for the design of highly efficient organic semiconductor photocatalysts.
Two‐dimensional conductive metal‐organic frameworks (2D‐c‐MOFs) have attracted extensive attention owing to their unique structures and physical‐chemical properties. However, the planarly extended structure of 2D‐c‐MOFs usually limited the accessibility of the active sites. Herein, we designed a triptycene‐based 2D vertically conductive MOF (2D‐vc‐MOF) by coordinating 2,3,6,7,14,15‐hexahydroxyltriptycene (HHTC) with Cu2+. The vertically extended 2D‐vc‐MOF(Cu) possesses a weak interlayer interaction, which leads to a facile exfoliation to the nanosheet. Compared with the classical 2D‐c‐MOFs with planarly extended 2D structures, 2D‐vc‐MOF(Cu) exhibits a 100 % increased catalytic activity in terms of turnover number and a two‐fold increased selectivity. Density functional theory (DFT) calculations further revealed that higher activity originated from the lower energy barriers of the vertically extended 2D structures during the CO2 reduction reaction process.
Pore environment and aggregated structure play a vital role in determining the properties of porous materials, especially regarding the mass transfer. Reticular chemistry imparts covalent organic frameworks (COFs) with well-aligned micro/mesopores, yet constructing hierarchical architectures remains a great challenge. Herein, we reported a COF-to-COF transformation methodology to prepare microtubular COFs. In this process, the C 3 -symmetric guanidine units decomposed into C 2 -symmetric hydrazine units, leading to the crystal transformation of COFs. Moreover, the aggregated structure and conversion degree varied with the reaction time, where the hollow tubular aggregates composed of mixed COF crystals could be obtained. Such hierarchical architecture leads to enhanced mass transfer properties, as proved by the adsorption measurement and chemical catalytic reactions. This selftemplate strategy was successfully applied to another four COFs with different building units.
As an ew energy source that could replace petroleum, the global reserves of methane hydrate (combustible ice) are estimated to be approximately 20 000 trillion cubic meters. Alarge amount of methane hydrate has been found under the seabed, but the transportation and storage of methane gas far from coastlines are technically unfeasible and expensive.T he direct conversion of methane into value-added chemicals and liquid fuels is highly desirable but remains challenging.Herein, we prepare as eries of iridium complexes based on porous polycarbazoles with high specific areas and good thermochemical stabilities.T hrough structure tuning we optimized their catalytic activities for the selective monoborylation of methane.O ne of these catalysts (CAL-3-Ir) can produce methyl boronic acid pinacol ester (CH 3 Bpin) in 29 %y ield in 9hwith aturnover frequency (TOF) of approximately 14 h À1 . Because its pore sizes favor monoborylated products,i th as ah igh chemoselectivity for monoborylation (CH 3 Bpin:CH 2 -(Bpin) 2 = 16:1).
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