Comparison of the sorption of anionic dyes on activated carbon and chitosan derivatives from dilute solutions

Activated carbon and chitosan were investigated for the sorption of several dyes. While the sorption on activated carbon was largely independent of the pH, the sorption of dyes on chitosan was controlled by the acidity of the solution. Anionic dye sorption onto chitosan occurred through electrostatic attraction on protonated amine groups. Sorption experiments were focused on dilute solutions and sorption capacities ranged between 200 and 2000 mumol g(-1) for chitosan and between 50 and 900 mumol g(-1) for activated carbon. Since, in most cases, equilibrium was reached within the first 12 hours of contact, sorption kinetics are relatively fast. However, both sorption capacities (sorption isotherms) and kinetics depended on the type of dyes. The attempt to correlate sorption performance to the structure of the dye failed. Sorption kinetics are strongly influenced not only by intraparticle diffusion resistance but also by the affinity of the dye for the sorbent.