Molecularly engineering cellulose to functional cellulose-based aerogel adsorbent for precious metals recovery from e-waste

The demand for the recovery of precious metals has become increasingly prominent due to their scarcity and wide application, while the facile preparation of sustainable absorption and separation materials via molecular engineering still face great challenge by using renewable polymer resources. Herein, a water-soluble cellulose levulinate ester (CLE) with ketocarbonyl groups was utilized as 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 allowed 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 for Au(III) at 298 K which was superior than that of Pt(IV) (1420.5 mg/g) and Pd(II) (495.1 mg/g). The adsorption process followed pseudo-second-order kinetic model and Langmuir isotherm behavior, respectively. Additionally, the positively charged CLE@50PEI exhibited excellent selectivity for precious metals in multi-metal mixtures. The outstanding adsorption performance of the CLE@50PEI may be due to the new “adsorption-in situ reduction” mechanism, in which the process primarily involved the ion exchange coupled with electrostatic interaction and complexation, and the in situ reduction of absorbed Au(III) to single crystalline flakes. Moreover, quantitative desorption of the CLE@50PEI-loaded metals was achieved in acidic thiourea solution.