Wood-based cellulose nanocrystals as adsorbent of cationic toxic dye, Auramine O, for water treatment

Abstract

Abstract Removal of toxic organic cationic dye, Auramine O (AO), is critical prior to its discharge to the environment. In this work, wood-based colloidal cellulose nanocrystals (CNCs) in their anionic forms (sulfated and carboxylated) were examined as nanoadsorbents for the effective removal of cationic toxic AO. Both sulfated and carboxylated CNCs were characterized by FTIR, DLS, zeta potential, AFM and XRD techniques. The impact of both surface functionalities (half-ester sulfate and carboxylate) of CNCs were studied in relation to the adsorption of AO. The batch adsorption experiments were performed at 0 and 25 °C at different contact time and the highest removal percentage (82 %) and adsorption capacity (20 mg g−1) were obtained for the sulfated CNCs for an equilibrium contact time of 30 min. The kinetic data was fitted to the pseudo-second-order adsorption model, with the highest rate constant (0.55 g mg-1. min−1) related to the sulfated CNCs for the adsorption at 0 °C. The calculated thermodynamics parameters indicated that AO adsorption on both CNC samples was a spontaneous exothermic process with a decrease in the entropy of the system for the sulfated CNCs and an increase in entropy for the carboxylated CNCs. Fitting equilibrium data to four different types of isotherms (Henry, Freundlich, Langmuir and Temkin) showed that Freundlich isotherm was the most suitable to describe the adsorption behavior of AO at either 0 or 25 °C. Overall, this study demonstrated the potential application of sustainable and biodegradable wood-based CNCs as green bioadsorbents for the adsorption of toxic cationic AO dye.