Mechanisms and valorization of selective adsorption of Sb(III) by amino-functionalized lignin-based porous biochar

Antimony contamination in aquatic environment raises tremendous concerns for human health and ecosystem safety, while there is a lack of methods for efficient and selective adsorption of antimony. In this study, an adsorbent for trivalent antimony (Sb(III)) removal is obtained by cross-linking polyethyleneimine (PEI) onto phosphoric acid-modified lignin-based porous biochar (PPLB). PPLB exhibits efficient adsorption of Sb(III) with a maximum value of 371.7 mg/g, which is also highly selective as the Sb(III) removal capability by PPLB remains unaffected under the common co-existing anions (Cl ^-, NO ₃ ^–, PO ₄ ^3-, and CO ₃ ^2–) and less affected with the co-existing cations (Cd ²⁺, Zn ²⁺, Cu ²⁺, and Pb ²⁺). Such a performance is validated in three simulated Sb(III)-contaminated water bodies (Zijiang River water, industrial wastewater, and mining area water). Understanding of the adsorption mechanisms is further established via density functional theory calculations, revealing the dominant adsorption site of Sb(III) on PPLB is –NH- groups. It's finally concluded that the removal of Sb(III) by PPLB is governed by complexation, with also the contribution from ligand exchange and hydrogen bonding. As a proof of concept, the spent PPLB adsorbed with Sb(III) is valorized into an active material of sodium ion battery, demonstrating a specific capacity of 192.4 mA h/g for 1000 cycles with a good long-term stability.