Chitosan is a natural polymer derived from chitin through the deacetylation process. It has emerged as a key ingredient in sustainable wastewater treatment, due to its biodegradability, non-toxicity, and low cost. This biopolymer possesses abundant functional groups, such as -NH₂ and -OH, that efficiently interact with pollutants. This review offers a comprehensive evaluation of pollutant separation techniques involving chitosan-based materials, including adsorption, membrane filtration, flocculation, and photocatalysis. It further examines the underlying adsorption mechanisms, emphasizing how pollutants interact with chitosan and its derivatives at the molecular level. Special focus is given to various modifications of chitosan, alongside a comparative assessment of different chitosan-based adsorbents (hydrogels, nanoparticles, nanocomposites, microspheres, nanofibers, etc.), highlighting their performance in removing heavy metals, dyes, and emerging organic pollutants. The reviewed performance of these polymeric materials from 2015–2025 not only gives an insight about the recent advancement but also points the need for the design of high-performing chitosan-based adsorbents with applications in real water matrices.

Chitosan (CS) is a biodegradable and biocompatible polysaccharide, obtained by the deacetylation of chitin. It has gained significant attention as a versatile material for biomedical applications due to its mucoadhesive properties, ease of chemical modification and intrinsic pharmacological activities. This review synthesizes two decades (2005–2025) of literature, focusing on chemical modifications of chitosan for pharmacological purposes and their therapeutic implications in non-communicable diseases (NCDs) and wound healing. Evidence highlights the roles of chitosan-based materials in anticancer, anti-inflammatory, antidiabetic, antihypertensive, and neuroprotective activities, alongside their integration in advanced wound healing strategies. Clinical trials have demonstrated the translational potential of chitosan-based materials. In general, chitosan-based materials exhibit promising dual functions as bioactive agents and drug carriers, necessitating additional investigation in clinical and regulatory frameworks to accelerate therapeutic adoption. In contrast to other studies, this study offers a mechanistic and integrative viewpoint that links chitosan’s chemical modification techniques with their pharmacological effects and clinical translation potential, providing novel perspectives on structure–activity correlations and therapeutic design.