Comparison of chitosan with different physical forms to remove Reactive Black 5 from aqueous solutions

• Chitosans in powder (CP) and in films (CF) were compared as adsorbents for RB5.
• Over 99% of Reactive Black 5 in aqueous solution was removed, at pH 4.0, for both adsorbents.
• The maximum adsorption capacities were 654.3 and 589.5 mg g−1, respectively, for CP and CF.
• The adsorption processes were spontaneous, favorable and exothermic.
• CF were reused three times, while CP cannot be reused.

Studies have demonstrated that the chitosan powder (CP) and chitosan films (CF) are attractive alternatives to remove dyes from aqueous solutions, but powder and films were evaluated separately. In this work, CP and CF are compared as adsorbents to remove Reactive Black 5 (RB5), which is a hazardous dye of textile effluents. Chitosan samples were produced with different deacetylation degrees (from 65% to 95%). Adsorption isotherms and kinetics were studied at various values of pH, temperature, stirring rate and deacetylation degree. Adsorption–desorption cycles were performed. CP and CF with deacetylation degree of 95% were the best adsorbents, removing more than 99% of RB5, in pH 4.0 at 298 K. The Langmuir model was the more suitable to fit of the equilibrium data for both adsorbents (R2 ≥ 0.9852 and ARE ≤ 1.93), and CP showed an adsorption capacity slightly higher. The adsorption kinetics of RB5 onto both adsorbents was better represented by the Elovich model (R2 ≥ 0.9990 and ARE ≤ 5.21). The interactions analyses indicated that electrostatic interactions occurred between the adsorbents and RB5. CF were easily separated from the liquid phase during the adsorption–desorption cycles and were reused three times, while CP cannot be reused.

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