Bifunctional thiophene-based covalent organic frameworks for Hg2+ removal and I2 vapor adsorption

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Novel bifunctional thiophene-based COFs were constructed according to Schiff base reaction between tetrakis(4-aminophenyl)-ethane and 2,5-thiophenedicarboxaldehyde/ thieno[3;2-b]thiophene-2,5-dicarboxaldehyde. The loading of N/S heteroatoms in the skeleton not only take the COFs abundant functional groups, but also elevate the stability of the functional groups, and avoid the blocking of the pores from the post-functionlization of functional groups. The thiophene-based COFs all showed good crystalline structure, high Brunauer–Emmett–Teller (BET) surface area (SBET), pore volume (Vtotal), and N/S content, indicative of the COFs good performance in Hg2+ adsorption and I2 vapor capture. Especially, the COF-S1, which showed high SBET of 2133 m2/g and Vtotal of 1.672 cm3/g, exhibited a relative high I2 vapor capacity of 7.74 g/g. Although COF-S2 showed lower SBET (1430 m2/g) and Vtotal (1.186 cm3/g), the higher N/S content make COF-S2 higher Hg2+ adsorption capacity of 834 mg/g. The COFs also showed outstanding adsorption selectivity and good recyclability. This work provides guidance for the design and preparation of multi-functional adsorbents.