Synthesis of Diaminopyridine-Incorpated Hydrogel Enables Colorimetric Sensoring, Responsive Swelling and Highly Adsorption Capacity of Copper(II)

Hydrogel is a promising tool used in the removal and detection of heavy metal ions in aqueous systems.However, the metal ion usually serves as an additional crosslinking point in conventional ion adsorbent hydrogels, which usually suffer from unexpected shrinkage and thus have limited adsorption capacities.In this work, a diaminopyridine (DAPy)-based monomer, N-(6acetamidopyridin-2-yl)acrylamide (NAcAPAAm), was synthesized and then copolymerized with polyethylene glycol diacrylate (PEGDA) to afford the chemically-crosslinked hydrogel, poly(N-(6acetamidopyridin-2-yl)acrylamide-co-glycol) hydrogel (G2).The DAPy moiety in the hydrogel matrix can form a 1:1 type complex with Cu 2+ and give rise to the pronounced color change from colorless to green.The formation of the 1:1 complex results in the adsorption of Cu 2+ and the improvement of the swelling degree of the hydrogel with high specificity, rather than crosslinking-induced shrinkage.Its maximum adsorption capacity for Cu 2+ could reach 241.8 mg/g.Furthermore, it was found that the adsorption behaviors of Cu 2+ on G2 conformed to the pseudo-second-order kinetic model, with excellent mechanical stability, high tolerance to extreme pH, and desirable reusability.This work provides a promising candidate for simultaneously detecting and adsorbing Cu 2+ in aqueous systems.