This work focuses on adsorption kinetics and isotherm modelling in CO2-activated chitosan. Removal efficiency and adsorption capacity were measured for three anionic dyes: Brilliant Blue FCF (BBF), Congo Red (CR), Orange II (O-II) and one cationic dye: Crystal Violet (CV). While the highest removal efficiencies of BBF, O-II and CR were 97%, 91% and 48%, it was found that very low adsorption capacity occurred in the case of CV due to the repulsion between the cationic groups of CV and that of CO2-activated chitosan. In terms of adsorption kinetics, pseudo-first-order and pseudo-second-order models were applied. The adsorption in the CO2-activated system was found to follow the pseudo-first-order model. The activation of adsorption by CO2 was found to lead to a higher adsorption rate constant and a higher adsorption capacity due to the protonation of chitosan's amino groups. Interestingly, as the temperature of the CO2-activated system increased, the pseudo-first-order model predicted a decrease in adsorption rate constant, k(1). This is thought to be a result of lower CO2 dissolution into the aqueous solution, which leads to a slower protonation process of chitosan's adsorption sites. The chemical structure of the dye species affects the adsorption kinetics in the CO2-activated system. There are four charged functional groups on the CR molecule and three on the BBF molecule, which allow faster alignment onto adsorption sites compared with O-II molecules with only one charged group. In terms of adsorption isotherm, BBF adsorption was found to follow the Langmuir model in the CO2-activated system.