Engineering linkage as functional moiety into irreversible thiourea-linked covalent organic framework for ultrafast adsorption of Hg(II)

Development of novel functionalized covalent organic frameworks (COFs) as adsorbent for removal of mercury from environment is of great significance, but the conventional strategies for functionalizing COFs always sacrifice porous properties and suppress the exposure of functional sites, which goes against the rapid adsorption of Hg(II). Here, we show the rational design and preparation of the first thiourea-linked COFs via engineering the COFs linkage as functional moiety for ultrafast and selective adsorption of Hg(II). Two thiourea-linked COFs JNU-3 and JNU-4 were prepared via tautomerism reaction of 1,3,5-triformylphloroglucinol with 1,4-phenylenebis(thiourea) and 1,4-biphenylenebis(thiourea), respectively. The thiourea serves as not only linkage to connect the building block into irreversible crystalline structure, but also functional moiety to give no occupation of the COF pore and full exposure to Hg(II) with strong affinity, offering the JNU-3 and JNU-4 large adsorption capacity (960 and 561 mg g-1, respectively) and ultrafast kinetics (equilibrium time of 10 s) for Hg(II). The proposed strategy for the design of functional COFs with inherent linkage as functional moiety largely promotes the performance of COFs for diverse applications.