Synthesis and Modification Strategies of Chitosan and Its Interaction with Metal Ions

Chitosan is one of the most important and widely available biomaterials produced by nature for remediation of its resources. It is obtained by deacetylation of chitin extracted from marine waste materials and highly useful to adsorb the toxic ions existing in the water body as it has a large number of active functionalities of hydroxyl and amine groups. The chitosan has several advantages including low cost, bio-degradable, and bio-compatibility over other chemically synthesized materials in the laboratory. Different chitosan-based materials have been identified and tested in the removal of toxic anions, especially, metals, metalloids, dyes, hydrocarbons, organic pesticides, etc. In this review, we focused on the functionalized forms of chitosan with metal ions and their adsorption on toxic ions, such as fluoride, phosphate, nitrate, and arsenic from waters using batch experiments. Also, it intensively focused on the synthetic methods, feasibility, and the regeneration/reusability of the materials. The results of this review indicated that the metal-loaded chitosan-based composite materials have shown much higher efficiency than the raw forms of chitosan and metal/metal oxides or hydroxides due to the synergistic interaction and the affinity of the materials. In particular, the mechanism of interactions of toxic ions and the metal ions present in the composites was thoroughly reviewed using analytical and the experimental data that existed in the literature. The reported adsorption densities, collected by recently reported materials, and the selectivity test results were much higher than those of other bio-based materials and inorganic nanocomposites. This review critically discussed the real-water analysis, cost-effectiveness of the reported materials. Importantly, the clean-up and the disposal methods for the pollutant sorbed materials and other areas requiring further research were addressed.