Encapsulation of Cyclam Inside a Covalent Organic Framework for Efficient CO₂ and SO₂ 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.