Sorption studies of a model anionic dye on crosslinked chitosan

The sorption of Methyl Orange by chitosan crosslinked particles was approached using equilibrium and kinetic analyses at different pH’s. Besides the standard pseudo-order analysis normally effectuated (i.e. pseudo-first order and pseudo-second order), a novel approach involving a pseudo-nth-order kinetics was used, n being determined via non-linear regression, using the Levenberg–Marquardt method. Zeta potential measurements indicated that electrostatic interactions were important for the sorption process. Regarding equilibrium experiments, data were well fitted to a hybrid Langmuir–Freundlich isotherm. Considering the kinetics of sorption, although a pseudo-nth-order description yielded good fits, a kinetic equation involving diffusion–adsorption phenomena was found to be more consistent, in terms of a physicochemical description of the sorption process.