Adsorption and desorption of malachite green by using chitosan-deep eutectic solvents beads

Chitosan–deep eutectic solvent (DES) beads were prepared from chitosan and DESs. The DESs used were choline chloride–urea (DES A) and choline chloride–glycerol (DES B). Both chitosan–DES beads were used to remove malachite green (MG) dye from an aqueous solution. The optimum pH for chitosan–DES A was recorded at pH 8.0 while optimum pH for chitosan–DES B was pH 9.0. The maximum adsorption capacity obtained for chitosan–DES A and chitosan–DES B were 6.54 mg/g and 8.64 mg/g, respectively. The optimum conditions for both chitosan–DES beads to remove MG were 0.08 g of adsorbent and 20 min of agitation time. Five kinetic models were applied to analyse the data and the results showed that the pseudo-second-order and intraparticle diffusion model fitted best with R 2 > 0.999. For the adsorption capacity, results show that the Freundlich and Langmuir adsorption isotherms fitted well with chitosan–DES A and chitosan–DES B, respectively. The maximum adsorption capacities ( q max ) obtained from chitosan–DES A and chitosan–DES B were 1.43 mg/g and 17.86 mg/g, respectively. Desorption indicated good performance in practical applications. • Deep eutectic solvents (DESs) were used to prepare the chitosan beads. • Chitosan-DES beads were characterized. • Kinetic data and adsorption capacity were analysed too. • Chitosan-DES beads were successfully applied to remove malachite green.