Molecularly engineering cellulose into a functional cellulose-based aerogel adsorbent for the recovery of precious metals from e-waste

Abstract

The demand for the recovery of precious metals has become increasingly prominent owing to their scarcity and wide application, while the facile preparation of sustainable absorption and separation materials via molecular engineering still face great challenges owing to the use of renewable polymer resources. Herein, a water-soluble cellulose levulinate ester (CLE) with ketocarbonyl groups was utilized as a 3D network scaffold to fabricate a cellulose-based aerogel adsorbent (CLE@PEI) by introducing polyethyleneimine (PEI) with multiple amine groups. The abundant functional groups and porous architecture enabled CLE@PEI to efficiently capture Au(III), Pt(IV) and Pd(II). The maximum adsorption capacity of CLE@50PEI reached a staggering 1752.0 mg g⁻¹ for Au(III) at 298 K, which was superior to those of Pt(IV) (1420.5 mg g⁻¹) and Pd(II) (495.1 mg g⁻¹). The adsorption process followed the pseudo-second-order kinetic model and Langmuir isotherm behavior. Additionally, the positively charged CLE@50PEI exhibited excellent selectivity for precious metals in multi-metal mixtures. The outstanding adsorption performance of CLE@50PEI may be attributed to the new “adsorption-in situ reduction” mechanism, in which the process primarily involved ion exchange coupled with electrostatic interaction and complexation as well as the in situ reduction of absorbed Au(III) to single crystalline flakes. Moreover, quantitative desorption of the CLE@50PEI-loaded metals was achieved in an acidic thiourea solution.