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In this contribution, we demonstrate the synthesis of hydrazone-linked COF-Paper composites (namely COF-Paper1 and COF-Paper2) constructed from two monomers of benzene-1,3,5-tricarbohydrazide (Bth) and dimethoxyterephthal-aldehyde (Dma) or 2,5-dihydroxyterephthalaldehyde (Dha) via in-situ growth method using filter paper as a matrix. Interestingly, 2D COFs paper composites display excellent luminescence in the solid-state, and the as-synthesized COF-Paper1 and COF-Paper2 can be used as turn-off fluorescence sensors to visually detect Fe3+ ions and UO 2 2+ ions by the naked eye, respectively. Moreover, the visible limit of detection for Fe3+ and UO 2 2+ was 5.6 ng cm−2 and 27 ng cm−2, respectively. XPS and FT-IR results reveal that resulting COF-Papers have significant coordination ability toward target metal ions. This effective coordination induces electron transfer from the electron-rich building module to the electron-deficient metal ion, resulting in the fluorescence quenching process. This work not only provides a methodology to grow and assemble 2D COFs into large size ensembles but also paves a new pathway for visual detection of target metal ions. • Two COF-Paper composites have been constructed via in situ growth method. • The resulting 2D COFs paper composites with excellent luminescence properties. • The synthesized COF-Papers can specifically interact with iron ions or uranyl ions. • The COF-Papers can be used as a sensor for visual detection of target metal ions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal polymeric composites based on pyrimidine-functionalized COFs (covalent organic frameworks) were fabricated. • Fe@COF-Pyr composite possesses good catalytic performance for oxygen evolution reaction. • Au-Pd@COF-Pyr can promote methane oxidation. Functionalized covalent organic frameworks (COFs) materials are used in various fields due to their unique properties. Herein, the reported pyrimidine-functionalized COFs sample named COF-Pyr is selected as the matrix to provide two COFs-based metal composites Fe@COF-Pyr and Au-Pd@COF-Pyr, which are respectively synthesized through metal coordination and in situ reduction reaction. On the one hand, Fe@COF-Pyr used as the electrocatalyst exhibits a good oxygen evolution reaction activity with the overpotential of only 430 mV at a current density of 10 mA cm−2 in the KOH solution (1 M) electrolyte. It is attributed to the large specific surface area (427 m2/g) and abundant catalytic sites of Fe@COF-Pyr, which help to improve the electrochemical performance. On the other hand, Au-Pd@COF-Pyr is an excellent catalyst for methane conversion that the products of the methane oxidation reaction can be obtained under mild reaction conditions. This work not only provides a newfangled notion for the design and preparation of COFs-based metal composites but also broadens the practical application of COFs materials in the domain of catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • The COF-Tr-BA was prepared for selective adsorption and Li-S battery. • COF-Tr-BA shows excellent selectivity for genistein isomer by chemical interaction. • The introduction of boric acid group helps to improve electrochemical performance. Functional triazine-based covalent organic frameworks (COFs) with boric acid units, COF-Tr-BA, are designed and synthesized via cycloaddition of imine-linked COFs, COF-Tr, with (4-ethynylphenyl) boronic acid. Owing to the chemical interaction between boric acid units and adjacent dihydroxyl groups, COF-Tr-BA is used as the adsorbent for the selective adsorption of genistein isomer 4′6,7-trihydroxyisoflavone, showing an excellent selectivity and great adsorption performance with 5.4 times adsorption capacity (67.5 mg g−1) as high as 4′5,7-trihydroxyisoflavone (12.5 mg g−1). Meanwhile, COF-Tr-BA as the sulfur host for lithium-sulfur (Li-S) battery also exhibits a better electrochemical property, giving an initial discharge capacity up to 1349 mA h g−1 and a substantial capacity of 627 mA h g−1 after 200 cycles at 0.5C. It is attributed to the sulfiphilic interaction between the introduced boric acid groups and polysulfides (PSs), as well as the lithiophilic interaction between N atoms from quinoline and triazine moieties on the backbone of COF-Tr-BA and lithium ions (Li+), thus alleviating the dissolution and reducing the shuttle effect of LiPSs. The boric acid functionalized material COF-Tr-BA with the dual-function for selective adsorption and Li-S battery proposed here lays a significant foundation for multifunctional COFs as a versatile platform in practical application. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new fluorescent covalent organic frameworks was synthesized. • N , O -bidentate ligation was be used to combine difluoroboron. • 50% B-COF exhibited red fluorescence under ultraviolet excitation. The multi-dentate chelate ligands containing N and O atoms have good chelating ability to boron trifluoride and their complexes show good fluorescence properties. In this work, a fluorescent covalent organic framework (COF) with good crystallinity and porosity, 50% B-COF, was successfully synthesized by coordination of starting COFs 50% COF-OH with boron trifluoride diethyl etherate via N, O-bidentate ligation. Imine bonds are highly polarized. The coordination of nitrogen and boron changes the electron cloud distribution of imine bonds, causing the non-fluorescent 50% COF-OH to be transformed into fluorescent 50% B-COF. 50% B-COF exhibited red fluorescence under ultraviolet excitation. This work provides a new strategy for the design of fluorescent COFs. [ABSTRACT FROM AUTHOR]