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

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.