Instantaneous adsorption and synergic effect in simultaneous removal of complex dyes through nanocellulose/graphene oxide nanocomposites: Batch, fixed-bed experiments and mechanism

This study aimed at an instantaneous adsorption of a mixture of complex dyes by nanocomposites of non-toxic cellulose nanocrystals (CNC) and graphene oxide (GO). Despite advances in adsorption, the removal of complex dye with four or more aromatic rings is the least reported in the literature. Herein, we prepared and characterized three novel CNC:GO composites and applied them for removing complex dyes basic blue 7 (BB7), reactive orange 122 (RO) and rhodamine B (RhB) in a binary systems with the non-complex dyes methyl orange (MO) and basic brown 4 (BB4). The adsorption capacity of nanocomposite increased with the amount of aromatic ring in dyes’ structure. The CNC:GO 70:30 composite was the most efficient for removing BB7, showing incredible instantaneous adsorption capacity of 1943 mg g −1 (0.1 g.L -1 CNC:GO and 100 mg.L -1 BB7). Under real conditions, the BB7 removal rate from river water sample was 77%. Also, a complex dye (RO) and MO were not adsorbed in single systems, however in the presence of BB7 the q max was 681 and 516 mg g −1 (0.1 g.L -1 CNC:GO and 100 mg.L -1 of dye), respectively, indicating a synergic effect. In the presence of a complex (RhB) and BB4 cationic dyes, BB7 was preferentially adsorbed. BB7 adsorption was also studied in a dynamic fixed-bed process, whose 80% breakthrough time occurred after 13.5 h (q max of 213 mg g −1 ). XPS and FTIR analyses confirmed that electrostatic and ion exchange are the main adsorption mechanism. CNC:GO composite has potential for removing mixtures of complex and ordinary dyes.