Highly efficient and selective removal of anionic dyes from water using a cellulose nanofibril/chitosan sponge prepared by dehydrothermal treatment

To obtain cost-effective and environmentally friendly adsorbents that can selectively remove anionic dyes from wastewater, a physically cross-linked cellulose nanofibril/chitosan (CNF/CS) sponge was developed by dehydrothermal treatment (DHT). The physicochemical properties of the prepared sponge were determined by various techniques, and its adsorption performance was evaluated using reactive blue 221 (RB) as the model dye. Batch adsorption experiments reveal that the capacity of RB adsorption on the sponge increases up to 778.5 mg/g with increasing temperature. This value is greater than the maximum adsorption capacities of all other non-conventional adsorbents reported in the literature. Based on kinetic and thermodynamic assessments, the RB adsorption process is best described by pseudo-second-order kinetics and the Langmuir model, which suggests that it is actually an endothermic monolayer chemisorption process. The RB removal efficiency reaches 99.64% after five repeated continuous separations and the CNF/CS sponge can be efficiently used in five adsorption-desorption cycles. Overall, the results reported in this study indicate that the novel CNF/CS sponge developed in this study has great potential for use in applications of dye removal from wastewater. • Polysaccharide-based sponge was prepared by dehydrothermal cross-linking treatment. • The sponge showed outstanding flexibility, stability, and recyclability. • The sponge demonstrated superior selectivity towards anionic and mixed dyes.