Fabrication of a CO2-responsive chitosan aerogel as an effective adsorbent for the adsorption and desorption of heavy metal ions

In the traditional desorption method, strong acid is commonly used as an eluent for the regeneration of adsorbents. It is of critical economic and environmental significance to develop a chemical-free desorption method. In this study, a new CO2-responsive chitosan aerogel adsorbent was synthesized from CO2-responsive poly(acrylic acid-2-(dimethylamino)ethyl methacrylate) and chitosan by physicochemical double crosslinking for the adsorption of Cu2+. Compared with the chitosan aerogel, the adsorption capacity of Cu2+ and mechanical properties of CO2-responsive chitosan aerogel increased by 162% and 660%, respectively. Most importantly, after the adsorption of Cu2+ by CO2-responsive chitosan aerogel, the Cu2+ could be desorbed by CO2 bubbling, and the desorption rate of metal ions was more than 80%. The adsorption of Cu2+ by aerogel was attributed to chelation and complexation. The desorption of porous chitosan/P(AA-co-DMAEMA) aerogels (CPA) by CO2 mainly occurred through charge repulsion of protonated ‒NH2 and ‒N‒ groups. After 6 cycles, the adsorption capacity of CPA for metal ions still reached 70% of the initial adsorption capacity, and the desorption rate reached 75%. This novel CO2-responsive chitosan aerogel is a highly efficient and environmentally friendly adsorbent for the adsorption and recovery of metal ions.