Enhanced adsorption of xylenol orange from aqueous solutions by polyethylenimine-grafted chitosan microspheres

To enhance the adsorption performance, chitosan microspheres (CS–MSs) were grafted with polyethylenimine (PEI), a cationic compound with abundant amine groups. The resulting PEI-grafted CS–MSs (PEI–CS–MSs) were used for the adsorption of xylenol orange (XO), an anionic dye. The results show that PEI–CS–MSs were in regular spherical shape without porous structure. XO molecules were adsorbed onto the amine groups of PEI–CS–MSs through electrostatic interaction. The maximum adsorption capacity of XO onto PEI–CS–MSs was 816.33 mg/g at 303 K, being much higher than that onto CS–MSs. The adsorption process could be properly described by the pseudo-second-order kinetic and Langmuir models. The adsorption of XO was a spontaneous process with exothermic nature. In addition, the adsorption capacity only decreased by 0.52 % after seven cycles of adsorption-desorption, indicating the excellent reusability of PEI–CS–MSs.