Chitosan-based materials for heavy metal adsorption: Recent advancements, challenges and limitations

The advancement of industrialization has put the environment at risk of getting saturated with different contaminants. Heavy metals (HMs) emerging from industries, reaching the water bodies expose marine biota to these stressors, leading to negative effects on growth and development. Thus, it is imperative to detoxify the environment from these HM contaminants through degradation, and adsorption. Several mechanical and chemical methods have been developed and implied for the purpose of minimizing HM contamination, but they often give rise to certain by-products that are toxic in nature. Over the years, chitosan has emerged as a potent adsorption material for reducing HM contamination. Chitosan is obtained from multiple natural sources, and owing to its versatile nature, it shows significant capacity for adsorbing different HMs and HM ions. Chitosan is used in synergy with some of the agents to increase its adsorption efficiency. The preparation of graft, beads, functionalized chitosan, crosslinkers, nanoparticles, and nanotubes are some of the potential methods that have been used in modifying chitosan. This paper gives an overview of the ecotoxicological effects of HMs, besides mentioning the fundamental sources of chitosan. The individual role of chitosan and its synergistic role have been discussed in greater detail. Moreover, the limitations associated with chitosan as an HM adsorbent have been delineated.