We developed a novel metal adsorbent composed of bio-based materials, cellulose and a protein. The approach involved the immobilization of a hexa-histidine tag (His6), which shows an affinity for an intermediate acid (metal ion) in Hard and Soft Acids and Bases (HSAB) theory, on cellulose by fusing with a carbohydrate-binding module (CBM). The results show that CBM-His6-bound cellulose has adsorption selectivity reflecting the original properties of His6. Additionally, we prepared three configurations of CBM-His6 proteins, which were subsequently immobilized on filter paper for Ni2+ ion adsorption. Of these configurations, we found that the protein containing two His6 tags at each terminus (N- and C-) of CBM exhibited the highest metal adsorption ability. Furthermore, XPS analysis confirmed the binding of Ni2+ ions on the cellulose.
Keywords: Carbohydrate-binding module; immobilization; metal affinity tag; transition metals.