Fabrication of cationic cellulose nanofibrils/sodium alginate beads for Congo red removal

Congo red is hard to remove from dye wastewater due to its structure stability and high chemical oxygen demand. In this study, cationic cellulose nanofibrils (CCNF) prepared from herb residues was physically crosslinked with sodium alginate (SA) in the presence of calcium ions, and the obtained CCNF/SA beads were used to adsorb Congo red. Results showed that CCNF/SA beads with porous internal structure were beneficial to adsorption. The maximum adsorption capacity of Congo red could reach to 518.4 mg/g, which was superior to most cellulose-based adsorption materials. Furthermore, the equilibrium adsorption isotherms and XPS analysis indicated the adsorption for Congo red was a physical process, and hydrogen bond and electrostatic adsorption were proposed as dominant adsorption mechanism. In addition, the Congo red removal efficiency of the beads was still higher than 70% after three cycles. Therefore, this high efficiency and green beads have great potential as adsorbents for anionic dyes removal.