Encapsulation of Cyclam Inside a Covalent Organic Framework for Efficient CO ₂ and SO ₂ Removal

Covalent organic frameworks (COFs) are promising for controlling air pollutants, yet ultramicroporous COFs have rarely been explored for efficient CO2 and SO2 removal. Herein, we report the first designed synthesis of host@COF adsorbents by encapsulating cyclam molecules into a COF to obtain Cyclam@NKCOF-10 using the wetness impregnation method. Importantly, as the flexible cyclam molecule with intrinsic secondary amines is smaller than the microporous channels of NKCOF-10, new subnanometer-scale pores and more basic adsorption sites are formed in Cyclam@NKCOF-10 materials, which enhances CO2 and SO2 uptake capacities, and CO2/N2, SO2/N2 separation performance at low pressures. NKCOF-10 and Cyclam@NKCOF-10(40) show exceptionally high SO2 uptake capacities of 10.21 and 12.42 mmol g–1, respectively, at 298 K and 1 bar, and good recycling performance. Notably, NKCOF-10 exhibits an impressive SO2/CO2 selectivity of 85 at 298 K and a retention time of 765 min g–1. Cyclam@NKCOF-10(40) exhibits a longer retention time of 853 min g–1. This work demonstrates the potential of host@COF materials with tunable pore structures for improving gas adsorption and separation.