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 photoresponsive 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@COFOCH3 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.