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.

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In the present study, carboxymethyl cellulose nanofibrils (CMCNFs) with different carboxyl content (0.99–2.01 mmol/g) were prepared via controlling the ratio of monochloroacetic acid (MCA) and sodium hydroxide to Eucalyptus bleached pulp (EBP). CMCFs-PEI aerogels were obtained using the crosslinking reaction of polyethyleneimine (PEI) and CMCNFs with the aid of glutaraldehyde (GA). The effects of pH, contact time, temperature, and initial Cu2+ concentration on the Cu2+ removal performance of CMCNFs-PEI aerogels was highlighted. Experimental data showed that the maximum adsorption capacity of CMCNF30-PEI for Cu2+ was 380.03 ± 23 mg/g, and the adsorption results were consistent with Langmuir isotherm (R2 > 0.99). The theoretical maximum adsorption capacity was 616.48 mg/g. After being treated with 0.05 M EDTA solution, the aerogel retained an 85% removal performance after three adsorption–desorption cycles. X-ray photoelectron spectroscopy (XPS) results demonstrated that complexation was the main Cu2+ adsorption mechanism. The excellent Cu2+ adsorption capacity of CMCNFs-PEI aerogels provided another avenue for the utilization of cellulose nanofibrils in the wastewater treatment field.

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Heavy metal ion pollutions are of serious threat for our human health, and advanced technologies on removal of heavy metal ions in water or soil are in the focus of intensive research worldwide. Nanocellulose based adsorbents are emerging as an environmentally friendly appealing materials platform for heavy metal ions removal as nanocellulose has higher specific surface area, excellent mechanical properties and good biocompatibility. In this review, we briefly compare the differences of three kinds of nanocellulose and their preparation method. Then we cover the most recent work on nanocellulose based adsorbents for heavy metal ions removal, and present an in-depth discussion of the modification technologies for nanocellulose in assembling high performance heavy ions adsorbent process. By introducing functional groups, such as amino, carboxyl, phenolic hydroxyl, and thiol, the nanocellulose based adsorbents not only remove single heavy metal ions through ion exchange, chelation/complexation/coordination, electrostatic attraction, hydrophobic actions, binding affinity and redox reactions, but also can selectively adsorb multiple heavy ions in water. Finally, some challenges of nanocellulose based adsorbents for heavy metal ions are also prospected. We anticipate that the review supplies some guides for nanocellulose based adsorbents applied in heavy metal ions removal field.