Adsorption of textile dyes present in aqueous solution and wastewater using polyelectrolytes derived from chitosan

BACKGROUND Adsorption is one of the most commonly used methods for the removal of textile dyes because of its low cost and ease of operation. Nowadays, unconventional materials capable of specific interactions such as polyelectrolytes are being proposed to be used as adsorbents. This work presents the results of the application of chemically modified polyelectrolytes derived from chitosan containing amino and sulfonate groups in the adsorption of four textile dyes, as well as the treatment of wastewater from the textile industry. RESULTS By optimizing the conditions of static adsorption, approximately 90% of the cationic dyes present in an aqueous solution with an initial concentration of 300 mg dm−3 and a basic pH of around 11.5 were removed. Anionic dyes almost reach 100% adsorption on the polyampholytes. The point of zero charge (pHpzc) was determined, and it was found that both polyampholytes exhibited a basic character on their surface (pHpzc > 8.7). The adsorption isotherms for the cationic and anionic dyes fit Langmuir's model, and the values for RL indicated that the process of adsorption for cationic and anionic dyes is energetically favorable on both polyampholytes. CONCLUSIONS The chemical modification introducing sulfonate groups on chitosan does not affect its natural ability to adsorb anionic dyes, but it also allows it to adsorb high concentrations of cationic dyes. This way, semisynthetic polyelectrolytes were capable of improving the quality of wastewaters treated by adsorption by reducing their pH, making it less alkaline, and decreasing the color, contents of suspended solids, and COD. © 2017 Society of Chemical Industry