Chitin‐Chitosan Cryogels for the Reversible Sequestration and Recovery of Heavy Metals From Wastewater

ABSTRACT Naturally occurring polymers comprise a range of characteristics that make them especially suitable for sustainable water treatment purposes. Particularly, chitin, and its derivative chitosan emerge as strong contenders due to their widespread availability from various biomass sources, ease of processing into tailored geometries, and multiple hydroxyl and amine/acetamide groups that enable hydrogen bonding and electrostatic interactions with water contaminants. Thus, here we develop 3.5 wt.% chitin and chitosan cryogel adsorbents with degrees of N ‐acetylation from 12.2 to 71.4%. The materials are tested for As 5 + , Co 2 + and Cu 2 + removal by colorimetry and advanced differential pulse voltammetry, with adsorption capacities of 9.5–12.0 mg·g −1 achieved depending on the metal and chitin:chitosan ratio. Higher concentrations of chitosan result particularly effective in sequestering As 5 + . Contrarily, for cationic Co 2 + and Cu 2 + , chitin is desired. Kinetic modelling showed adsorption equilibrium within 2–4 h. Recovery studies indicated superior pollutant recovery for pure chitosan cryogels through competitive ion exchange with Ca 2 + , with >50% of the adsorbed Co 2+ being selectively released using an acid‐desorption strategy. The removal efficiencies obtained for As 5 + , Co 2 + and Cu 2 + , combined with the gel recovery ability, demonstrate the potential of chitosan and chitin as competitive alternatives to conventional water purification sorbents derived from fossil carbon sources.