Highly selective removal of triarylmethane dyes by molecular switched adsorbents via charge-assisted hydrogen bond

Exploring novel adsorbents for efficient water treatment is an essential and urgent task. Herein, we developed a cage-based molecular switched adsorbent for the selective removal of triphenylmethane dyes from water. The adsorbent's negatively charged ring-opening tautomer could remove >95 % of triphenylmethane dyes within 60 min, with the removal of other dyes being <50 %. The maximum adsorption capacities for malachite green, crystal violet, and methyl blue were 340, 370, and 729 mg/g, respectively, corresponding to forming a 1:1 host–guest complex with the cage-based adsorbent molecules. The adsorbent can be easily regenerated through simple elution in a dilute alkaline solution and exhibited excellent reusability. The mechanistic analysis highlights the paramount influence of charge-assisted hydrogen bonding between the adsorbent and the dye in governing the adsorption process. Its strength can be predicted using the pKa slide rule theory and consistently aligned with the experimental observations. Our research offers valuable insights into the rational design of adsorbent structures.