Cheng Wang

The targeted synthesis of 3D COFs has been considered challenging, especially adopting new topologies and bearing photoelectric units. Herein, for the first time, we report the synthesis and characterization of a novel 3D pyrene-based COF (3D-Py-COF), by selectively choosing the geometry of the precursors and the connection patterns. Based on X-ray diffraction measurement and detailed simulations, 3D-Py-COF is proposed to adopt a two-fold interpenetrated pts topology, which has never been reported before. In addition, 3D-Py-COF has a narrow pore size distribution and high surface area and also features selective absorption of CO2 over N2. Interestingly, due to the existence of isolated pyrene units in the 3D framework, 3D-Py-COF is the first fluorescent 3D COF and can be used in explosive detection. Our results not only show it is possible to rationally design and synthesize 3D COFs with other topologies but also demonstrate that the incorporation of photoelectric units into 3D COFs can allow the resulting materials with interesting properties.

Abstract The construction of stable covalent organic frameworks (COFs) for various applications is highly desirable. Herein, we report the synthesis of a novel two‐dimensional (2D) porphyrin‐based sp 2 carbon‐conjugated COF (Por‐sp 2 c‐COF), which adopts an eclipsed AA stacking structure with a Brunauer—Emmett—Teller surface area of 689 m 2 g −1 . Owing to the C=C linkages, Por‐sp 2 c‐COF shows a high chemical stability under various conditions, even under harsh conditions such as 9 m HCl and 9 m NaOH solutions. Interestingly, Por‐sp 2 c‐COF can be used as a metal‐free heterogeneous photocatalyst for the visible‐light‐induced aerobic oxidation of amines to imines. More importantly, in comparison to imine‐linked Por‐COF, the inherent structure of Por‐sp 2 c‐COF equips it with several advantages as a photocatalyst, including reusability and high photocatalytic performance. This clearly demonstrates that sp 2 carbon‐linked 2D COFs can provide an interesting platform for heterogeneous photocatalysis.

UiO-66 is an archetypal metal–organic framework (MOF) with a very high surface area as well as high thermal stability. It is found that the stability can be attributed to the metal oxide node being cuboctahedral allowing for 12 extension points for 1,4-benzenedicarboxylic acid (BDC) coordination. Because of this and its exceptional tunability and functionality, which are largely due to defect control of both missing-cluster and missing-linker defects, UiO-66 has gained scientific popularity. The combination of these characteristics allows for a highly versatile material that can be adapted to many different applications. The purpose for this work is to provide a historic overview of UiO-66, outlining the major developments that changed the synthesis strategies of Zr-based MOF as well as current and future works, which include defect control, aqueous crystallization, functionality-stability trade-offs, and advanced topographies. A breakdown of the various UiO-66 structures, including isoreticular and reo-type, and different characterization techniques such as powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and nitrogen porosimetry are discussed as well.

Abstract Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H 2 , Co, Ni, Zn) and their photocatalytic activity in hydrogen generation. Our results clearly show that all four covalent organic frameworks adopt AA stacking structures, with high crystallinity and large surface area. Interestingly, the incorporation of different transition metals into the porphyrin rings can rationally tune the photocatalytic hydrogen evolution rate of corresponding covalent organic frameworks, with the order of CoPor-DETH-COF < H 2 Por-DETH-COF < NiPor-DETH-COF < ZnPor-DETH-COF. Based on the detailed experiments and calculations, this tunable performance can be mainly explained by their tailored charge-carrier dynamics via molecular engineering. This study not only represents a simple and effective way for efficient tuning of the photocatalytic hydrogen evolution activities of covalent organic frameworks at molecular level, but also provides valuable insight on the structure design of covalent organic frameworks for better photocatalysis.

The design and synthesis of three-dimensional covalent organic frameworks (3D COFs) bearing photoelectric units have been considered as a big challenge. Herein, for the first time, we reported the targeted synthesis of two 3D porphyrin-based COFs (3D-Por-COF and 3D-CuPor-COF), starting from tetrahedral (3D-Td) and square (2D-C4) building blocks connected through [4 + 4] imine condensation reactions. On the basis of structural characterizations, 3D-Por-COF and 3D-CuPor-COF are microporous materials with high surface areas, and are proposed to adopt a 2-fold interpenetrated pts topology with Pmc21 space group. Interestingly, both 3D COFs are photosensitive and can be used as heterogeneous catalyst for generating singlet oxygen under photoirradiation. However, 3D-Por-COF shows enhanced photocatalytic activity compared with 3D-CuPor-COF, indicating the properties of 3D porphyrin-based COFs can be tuned by metalation of porphyrin rings. The results reported here will greatly inspire us to design and synthesize 3D COFs bearing other metalloporphyrins for interesting applications (e.g., catalysis) in the future.