Isolated cellulose nanofibers for Cu (II) and Zn (II) removal: performance and mechanisms

TEMPO-oxidized cellulose nanofibers (TOCNFs) were prepared and investigated as low-cost adsorbents for the removal of Cu (II) and Zn (II) from synthetic and natural waters. The adsorption equilibrium was reached within 2 min and adsorption capacity was as high as 102.9 mg g(-1) for Cu (II) and 73.9 mg g(-1) for Zn (II). Ionic strength showed adverse effect on adsorption capacity, however, TOCNEs with higher carboxymethyl content were less influenced due to their resistance to aggregation. Copper adsorption exhibited strong selectivity over the tested common cations. The adsorptions of Cu (II) and Zn (II) onto TOCNF were endothermic but spontaneous processes, and the binding was driven by entropy increase. A combined interaction mechanism, including ion exchange, coordination and accumulation, was proposed based on the study. All the findings confirmed the great potential of TOCNF application in water purification and reclamation approaches.