Removal of various pollutants from water and wastewater by modified chitosan adsorbents

Chitosan-based adsorbents have attracted increasing attention in water and wastewater treatment in recent years due to its abundance and low price, as well as rich amino and hydroxyl groups. However, there are some drawbacks hindering its practical use, such as low mechanical strength, low solubility in acidic mediums, low adsorption capacity, and lack of selectivity. Therefore, a variety of modification methods, including physical and chemical modifications, have been investigated to improve the physicochemical properties of chitosan. This review provides a summary of (a) the intrinsic nature of chitosan associated with its structure and physicochemical properties; (b) the preparation strategies for modified chitosan together with its characterization; (c) the application of chitosan-based adsorbents for the removal of both organic pollutants (e.g., dyes, PPCPs, PFOS, and humus) and inorganic pollutants (e.g., heavy metal ions, nitrate, phosphate, borate, and fluoride). Recent advances in the fabrication and application of chitosan-based adsorbents involving the intrinsic nature of pollutants are highlighted in this review, as well as the effects of process variables (e.g., pH, contact time, ionic strength, competitive ions, temperature), modeling (kinetics and isotherm), adsorption mechanisms, and regeneration.