Smart Materials for Dirty Waters: Reversible Aerogels Unlock Closed-Loop Heavy Metal Remediation.

Water remediation technologies urgently require materials that are sustainable, efficient, and regenerable. Here, we report a dynamic covalent aerogel derived from chitosan and formylated lignin, enabling dual functionality in heavy metal adsorption and heterogeneous catalysis. The aerogel is formed through reversible imine bonds between chitosan and aldehyde-functionalized lignin, synthesized via a mild Reimer-Tiemann reaction. The resulting monoliths exhibit high structural integrity, solvent and pH resistance (pH ≥ 7), and remarkable adsorption capacities for Cu2+, Pb2+, and Zn2+ ions (up to 32.8 mg/g for Cu2+). Density functional theory (DFT) calculations reveal tridentate coordination as the dominant binding mechanism. When loaded with Cu2+, the aerogels act as effective heterogeneous catalysts for the Chan-Lam crosscoupling reaction in ethanol. They achieve initial yields of up to 92% and retain their catalytic activity over multiple reuse cycles. Importantly, the dynamic covalent framework allows complete recovery and regeneration of all components, underscoring its potential as a circular, bio-based platform for sustainable water detoxification and green catalysis.