Heavy metal ions in industrial sewage constitute a serious threat to human health. Nanocellulose-based adsorbents are emerging as an environmentally friendly material platform for heavy metal ion removal based on their unique properties, which include high specific surface area, excellent mechanical properties, and biocompatibility. In this review, we cover the most recent works on nanocellulose-based adsorbents for heavy metal ion removal and present an in-depth discussion of the modification technologies for nanocellulose in the process of assembling high-performance heavy ion adsorbents. By introducing functional groups, such as amino, carboxyl, aldehyde, and thiol, the assembled nanocellulose-based adsorbents both remove single heavy metal ions and can selectively adsorb multiple heavy ions in water. Finally, the remaining challenges of nanocellulose-based adsorbents are pointed out. We anticipate that this review will provide indispensable guidance on the application of nanocellulose-based adsorbents for the removal of heavy metal ions.

In this study, environmentally friendly TEMPO-oxidized cellulose nanofiber (TO-CNF)/ polyvinyl alcohol (PVA)/polyethyleneimine (PEI) nanoparticles were obtained by assembling PEI into TO-CNF/PVA aerogel, which was prepared by freezedrying method with the help of glutaraldehyde. FTIR results showed that PEI likely assembled into the TO-CNF/PVA aerogel due to appearances of bending vibration of the TO-CNF/PVA/PEI nanoparticles at 1615 cm -1 . BET results further demonstrated that PEI have successfully assembled into the aerogel since the specific surface area (22.93 m 2 /g) of TO-CNF/PVA / PEI nanoparticles was lower than that (56.37 m 2 /g) of TO-CNF/PVA aerogel. SEM results also showed that PEI could obviously regulate the morphology of TO-CNF/PVA aerogel. TGA indicated that TO-CNF/ PVA/PEI nanoparticles were structurally stable at 216.4 °C. The adsorption kinetics of the TO-CNF/ PVA/PEI nanoparticles for copper ion (Cu 2? ) removal presented good correlations with the Pseudo-secondorder kinetic and Langmuir model (R 2 [ 0.99). Its maximum adsorption capacity for Cu 2? according to Langmuir model was 156.8 mg/g. The adsorption equilibrium could reach in near one hour, and the adsorption efficiency could still maintain more than 80% after 3 cycles.