Sorption of acid violet 17 and direct red 80 dyes on cotton fiber from aqueous solutions

Sorption of acid violet 17 and direct red 80 azo dyes on locally available cotton fiber from aqueous solution has been investigated as a function of shaking time, pH, dyes concentration and temperature. Maximum sorption of acid violet 17 and direct red 80 on cotton fiber was achieved within 30 and 60 min of shaking time and at pH 8 and 8.5, respectively. Sorption isotherms for acid violet 17 and direct red 80 dyes were obtained at pH 8 and 8.5, respectively, at constant temperature. These isotherms are L-3 types having small plateaus, and the upward trends in sorption capacity after the plateaus points towards the possibility of multilayer formation. The increasing temperature induces a negative effect on the sorption of acid violet 17 (exothermic) and positive effect on the sorption of directs red 80 (endothermic). Isosteric heat of adsorption (qst) have also been calculated at different surface coverage indicating that cotton fiber possessed heterogeneous surface with site of different activity. The results also indicate that initial sorption, whether chemical or physical means, occurs first on the most active sites and then on the sites of lesser activity.