Incorporating a photo-responsive metal-organic cage into covalent organic framework for controllable CO₂ adsorption

Photo-responsive metal-organic cages (PMOCs) are intriguing supramolecular materials in gas adsorption due to their adjustable properties. However, the aggregation of bulk PMOCs hinders the free variation of photo-responsive groups in spatial dimensions, resulting in low efficiency of light regulation. Herein, a new PMOC (NUT-105) with pendant azobenzene motifs was synthesized and impregnated into the covalent organic framework (COF, COF-OCH₃). The reversible isomerization of azobenzene moieties in response to ultraviolet (UV-) and visible (Vis-) light can be improved in NUT-105@COF-OCH₃. The obtained composite materials exhibit excellent light-regulated properties of CO₂ adsorption and the CO₂ adsorption change of NUT-105@COF-OCH₃ under UV- and Vis-light is 29.2 %, significantly higher than that of bulk NUT-105 (1.5 %). Furthermore, Grand Canonical Monte Carlo (GCMC) simulations suggest that reversible isomerization of the azobenzene moieties of the NUT-105 in composite materials upon irradiation with Vis- and UV-light can lead to alterations of pore structures and the shielding or exposure of CO₂ adsorption sites, resulting in the controllable CO₂ adsorption properties. The present work provides a facile way to construct photo-responsive composite materials with PMOCs for controllable CO₂ adsorption.