Investigation of adsorption of basic dyestuffs from aqueous solution by modified chitosan

In this study chitosan was firstly modified with some cyclic anhydrides (phthalic anhydride, maleic anhydride, and trimellitic anhydride). Chitosan, chitosan modified with phthalic anhydride (FAC), chitosan modified with maleic anhydride (MAC) and chitosan modified with trimellitic anhydride (TAC) were compared with respect to their capacity to adsorp brilliant green and methylene blue from aqueous solution. It was seen that TAC adsorbed these dyestuffs more than other adsorbents.Then, adsorption of brilliant green and methylene blue from aqueous solution by TAC was investigated depending on temperature and pH. The kinetic data obtained for each dyestuff at different temperatures were applied to Lagergren, Ho-McKay and Weber Morris equations, and pseudo second-order rate constants (k2) and pore diffusion rate constants (kp) were determined. As for pseudo first-order rate constants (k1) could not determined due to Lagergren plots related to both dyestuffs were not linear. Pseudo second order rate constants were applied to Arrhenius equation because of kinetic data related to the adsorption of brilliant green and methylene blue from aqueous solution by TAC fitted Ho-McKay equation, and activation energies (Ea) related to the adsorption of these dyestuffs on TAC were determined.In addition, adsorption isotherms at different temperatures related to brilliant green and methylene blue from aqueous solution by TAC were determined. Since adsorption isotherm at 298 K of brilliant green from aqueous solution by TAC fitted Langmuir adsorption isotherm, isotherm data at this temperature were applied to linear form of Langmuir adsorption isotherm, and Langmuir constants (qm and b) were calculated. Since adsorption isotherm of methylene blue from aqueous solution by TAC fitted Freundlich adsorption isotherm, isotherm data were applied to linear form of Freundlich adsorption isotherm, and Freundlich constants (k and n) were calculated.