Highly nanostructured and carboxylated wood aerogel-based adsorption membrane reconstructed by grafting of polyacrylic acid for efficient removal of heavy-metal ions

A highly nanostructured and carboxylated WA-PAA1.5 membrane was developed to remove heavy-metal ions from wastewater depended on wood nanotechnology and reconstruction of nanostructure by the grafting of polyacrylic acid (PAA). The combination of delignification and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated −oxidation treatment transformed the bulk wood into wood aerogel with a microfibril network in the cell wall, providing abundant active hydroxyl sites. As a result, the PAA polymer was efficiently grafted onto cell wall and filled in the vessel and intercellular space, which reconstructed a highly nanostructured WA-PAA1.5 membrane with rich carboxyl groups (6.5 mmol/g). Correspondingly, the WA-PAA1.5 membrane manifested a superior adsorption capacity for Cu2+, Pb2+, Cd2+, and Ni2+, which was around 248 mg/g, 268 mg/g, 255 mg/g and 276 mg/g, respectively. These values were significantly higher than most biomass-based adsorption materials due to the synergistic effect of the enhanced carboxyl groups and the reconstructed mesoporous structure. The adsorption mechanism investigation proved the chemical linkage between the carboxyl groups and Cu2+ in wastewater. Meanwhile, the WA-PAA1.5 membrane also displayed excellent recycle performance, in which the removal efficiency of Cu2+ still remained above 85 % after undergoing eight cycles. Furthermore, the multi-layer WA-PAA1.5 filtration device demonstrated exceptional removal efficiency for a variety of heavy-metal ions, indicating the availability in practical wastewater treatment. The prepared WA-PAA1.5 membrane in this study has promising potential to replace the present plastic-based materials for the removal of heavy-metal ions in wastewater because of the facile technology, high removal efficient and sustainability, as well as biodegradability.