Uranium is a key element in the nuclear industry, but its unintended leakage has caused health and environmental concerns. Here we report a sp 2 carbon-conjugated fluorescent covalent organic framework (COF) named TFPT-BTAN-AO with excellent chemical, thermal and radiation stability is synthesized by integrating triazine-based building blocks with amidoxime-substituted linkers. TFPT-BTAN-AO shows an exceptional UO 2 2+ adsorption capacity of 427 mg g −1 attributable to the abundant selective uranium-binding groups on the highly accessible pore walls of open 1D channels. In addition, it has an ultra-fast response time (2 s) and an ultra-low detection limit of 6.7 nM UO 2 2+ suitable for on-site and real-time monitoring of UO 2 2+ , allowing not only extraction but also monitoring the quality of the extracted water. This study demonstrates great potential of fluorescent COFs for radionuclide detection and extraction. By rational designing target ligands, this strategy can be extended to the detection and extraction of other contaminants.

Uranium is a key resource for the development of the nuclear industry, and extracting uranium from the natural seawater is one of the most promising ways to address the shortage of uranium resources. Herein, a semiconducting covalent organic framework (named NDA‐TN‐AO) with excellent photocatalytic and photoelectric activities was synthesized. The excellent photocatalytic effect endowed NDA‐TN‐AO with a high anti‐biofouling activity by generating biotoxic reactive oxygen species and promoting photoelectrons to reduce the adsorbed UVI to insoluble UIV, thereby increasing the uranium extraction capacity. Owing to the photoinduced effect, the adsorption capacity of NDA‐TN‐AO to uranium in seawater reaches 6.07 mg g−1, which is 1.33 times of that in dark. The NDA‐TN‐AO with enhanced adsorption capacity is a promising material for extracting uranium from the natural seawater.

Covalent organic framework nanosheets (COF NSs) provide well-ordered π–π structures that can be used to develop luminescent materials. However, most COF NSs have problems of weak luminescence and low fluorescence quantum yield. In this work, we prepared covalent organic framework nanosheets (Bpy-NSs) with good water dispersibility, nitrogen-rich functional groups, and regular pore structure. We explored the coordination of Bpy-NSs with Al3+ to eliminate the fluorescence quenching process caused by photoinduced electron transfer (PET). Thus, the fluorescence “turn-on” signal linearly increases with Al3+ concentration, achieving a 15.7-fold improved in fluorescence, and the absolute fluorescence quantum yield increased from 0.15 to 1.74%. Furthermore, this is the first COF fluorescence sensor that can be used for high sensitivity and selectivity detection of Al3+ in the aqueous phase. We anticipate that the expansion of metal ions coordination strategy in the aqueous phase will not only significantly enhance the fluorescence of COF NSs but also extend the functional range of COF NSs.

Covalent organic frameworks (COFs) have shown extensive applications in energy storage, catalysis, and gas adsorption because of their regular pore structure, flexible topological connectivity, and excellent adjustable functionality. However, their potential applications in colorimetric sensing have not yet been explored. In this study, we synthesized bipyridine-containing covalent organic framework nanosheets (Tp-Bpy NSs) with a regular pore structure and abundant nitrogen-containing functional groups that function as active sites for the in situ generation of AuNPs to form AuNPs@Tp-Bpy. The anchoring of AuNPs onto Tp-Bpy NSs through coordination bonds can significantly enhance the dispersibility, stability, and catalytic activity of the AuNPs. We find that the synergistic effect of increased mimetic activity of gold amalgam and the higher access probability of Hg 2+ provided by Tp-Bpy nanosheets makes the AuNPs@Tp-Bpy nanocomposite exhibit a high performance for the detection of Hg 2+ with an ultralow detection limit of 0.33 nM. This sensing platform has been successfully used for the sensitive and stable detection of Hg 2+ in various environmental samples. The present study extends the application of COFs and opens a new frontier for the design of novel nanocomposites for a variety of potential applications.

Mercury is one of the most toxic elements in the environment. Recently, a number of covalent organic frameworks (COFs) were developed for simultaneous detection and removal of mercury. They rely on post-synthetically modified sulfur-based ligands for irreversible mercury binding. In addition, their rigid structures resulted in low fluorescence yields. Herein, a novel highly luminescent COF named TFPPy-CHYD with a quantum yield of 13.6% was designed by integrating a pyrene-based building block with a flexible carbohydrazide linker. The nitrogen-based ligand allows reversible and highly selective binding of Hg2+. As a sensing platform, it has an ultralow detection limit of 17 nM mercury. More importantly, TFPPy-CHYD exhibits excellent performance in removing mercury from both air and water, providing very high Hg0 and Hg2+ adsorption capacities of 232 and 758 mg g–1, respectively. This work demonstrates enormous potential of luminescent COF for metal detection and remediation. By rational introducing metal ligands, a suite of new COF materials might be synthesized for the detection and removal of other metal ions.