Nanoengineered cellulose for sustainable selective separation of precious metals from electronic waste

Separating precious metals (PM), including gold (Au), silver (Ag), and palladium (Pd), from secondary sources, such as end-of-life products, may aid industrial sectors, spanning from electronics and automotive industry to catalysis and renewable energy, in meeting their increasing metal needs. Sustainable, eco-friendly nanotechnology may provide a viable alternative to conventional separation practices, such as solvent extraction, mitigating their environmental footprints. Here, we nanoengineer cellulose pulp to yield cationic hairy cellulose nanocrystals (CHCNC), bearing a high density of quaternary ammonium groups (∼ 2 mmol g⁻¹), to selectively remove the PM from Au-Ag-Pd ion mixtures and the complex leachates of waste printed circuit boards (WPCB). Au is recovered via the CHCNC-enabled electrostatic attraction and reduction reaction within seconds at a recovery capacity (q_e) of up to ∼ 772 mg g⁻¹. Immobilizing CHCNC on microcrystalline cellulose (MCC) via a mussel-inspired nanocellulose coating (MINC) yields mussel-inspired cationic nanocellulose-coated MCC (MINC⁺), which recovers Pd via electrostatic interactions within hours at q_e up to ∼ 559 mg g⁻¹, and Ag is stoichiometrically recovered using chloride ions. Furthermore, a multi-step batch process is developed to selectively recover Ag, Au, and Pd from the WPCB leachates. CHCNC-enabled sorbents may pave the way for developing advanced bio-based, sustainable materials for selective elemental recovery at industrial scales, promoting circular economy.