Light-responsive adsorbents with tunable adsorbent–adsorbate interactions for selective CO2 capture

Abstract Amines in porous materials have been employed as active species for the selective CO2 adsorption from natural gas because of their target-specific interactions. Nevertheless, it is difficult to modulate such strong interactions to reach a high efficiency in the adsorption processes. Herein, we fabricated light-responsive adsorbents with tunable adsorbent–adsorbate interactions for CO2 capture. The adsorbents were synthesized by introducing primary and secondary amines into a mesoporous silica that had been grafted with azobenzene groups on the surfaces. The target-specific amine sites render the adsorbents significantly selective in the uptake of CO2 over CH4, and the azobenzene groups were used as light-responsive switches to influence the adsorbent–adsorbate interactions. The adsorbents can freely adsorb CO2 when the azobenzene groups are in the trans state. Ultraviolet-light irradiation makes the azobenzene groups transform to the cis configuration, which greatly hinders amines in the uptake of CO2. The caused difference of adsorption capacity can reach 34.9%. The alternative irradiation by ultraviolet- and visible-light can lead to a recyclable regulation on adsorption performance. The changes of the electrostatic potentials of amines are responsible for the light-induced regulation on adsorption.