Cross-Linked Chitosan-Based Hydrogels for Dye Removal

Synthetic dyes are a major class of recalcitrant organic compounds, often occurring in the environment as a result of their wide industrial use. More than 100,000 dyes are commercially available. Synthetic dyes are common contaminants, many of them being toxic or carcinogenic. Colored effluents from industrial plant are also perceived by the public as an indication of the presence of a dangerous pollution. Even at very low concentrations, dyes are both highly visible, inducing an esthetic pollution, and impacting the aquatic life and food chain, as a chemical pollution. Dye contamination of water is a major problem worldwide and the treatment of wastewaters before their discharge into the environment is a priority. Dyes are difficult to treat due to their complex aromatic structure and synthetic origin. In general, a combination of different physical, chemical and biological processes is often used to obtain the desired water quality. However, there is a need to develop new removal strategies and decolorization methods that are more effective, acceptable in industrial use, and ecofriendly. Currently, there is an increasing interest for biological materials as effective adsorbents for dye removal. In particular, crosslinked chitosan-based hydrogels are popular biosorbents. Between 2013 and 2017, 18,430 chitosan-related publications have been published. In this chapter, we describe technologies for color removal, chitosan-based hydrogels and biosorption basics. Then we highlight cases studies published over the last 5 years. We found that chitosan-based hydrogels display outstanding removal capabilities for some dyes.