TEMPO-oxidized cellulose hydrogel as a high-capacity and reusable heavy metal ion adsorbent

Nitroxy radical catalyzed oxidation with hypochlorite/bromide (TEMPO-mediated oxidation) was performed on a cellulose hydrogel prepared using LiOH/urea solvent. TEMPO oxidation successfully introduced carboxyl groups onto the surface of the cellulose hydrogel with retention of the gel structure and its nanoporous property. The equilibrium measurement of Cu2+ adsorption showed favorable interaction with Cu2+ and high maximum adsorption capacity. In addition, over 98% of the adsorbed Cu2+ was recovered using acid treatment, and the subsequent washing allowed the TEMPO-oxidized gels to be used repeatedly. Furthermore, the TEMPO-oxidized cellulose hydrogel showed high adsorption capacity for other toxic metal ions such as Zn2+, Fe3+, Cd2+, and Cs+.