2D COFs paper composites fabricated by the in situ growth for visual detection of target metal ions

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 UO22+ ions by the naked eye, respectively. Moreover, the visible limit of detection for Fe3+ and UO22+ 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.