Review: nanocellulose-based hydrogels for heavy metal removal from water

Abstract

Heavy metal contamination in aquatic environments has emerged as a critical global environmental concern due to its high toxicity, non-biodegradability, and bioaccumulation risks. Conventional adsorbents generally suffer from limited adsorption capacity, poor recyclability, and non-sustainable feedstock sources, which restrict their large-scale application. This review systematically summarizes recent advances in nanocellulose-based hydrogels for heavy metal removal from water. The preparation and modification strategies of nanocellulose, construction approaches of cellulose nanocrystal (CNC)– and cellulose nanofibril (CNF)– based hydrogels, adsorption performance, stimuli-responsive functional design, and low-cost production routes using agricultural waste feedstocks are comprehensively discussed. Distinct adsorption mechanisms underpinning the two hydrogel systems are elucidated: CNC-based hydrogels achieve synergistic adsorption via crystal surface functional groups and composite networks, enabling complexation and ion exchange, whereas CNF-based hydrogels exhibit synergistic effects through continuous fiber networks, mass transfer, and surface binding, mainly driven by electrostatic attraction and pore entrapment. Furthermore, the current status and remaining gaps for practical wastewater treatment are critically assessed. Finally, existing challenges including scalable low-cost preparation and antifouling performance in complex water matrices are outlined, and future development directions are proposed to facilitate the engineering translation of this green adsorbent technology.

Graphical abstract