<p>The rising contamination of aquatic environments by dyes and heavy metals poses a critical threat to ecosystems and human health, necessitating the development of effective and sustainable remediation strategies. Nano-chitosan has emerged as a frontier adsorbent due to its nanoscale surface area, abundant functional groups, biocompatibility, and environmental safety. This study provides a comprehensive systematic and bibliometric review of nano-chitosan-based adsorbents, analysing 1855 publications from 2005 to 2025 indexed in the Web of Science Core Collection. Bibliometric indicators reveal strong scientific vitality, with an annual growth rate of 21.52%, an average of 32.7 citations per article, and extensive international collaboration involving 7404 authors. Scientometric mapping identifies Asia as the leading hub, with China, India, and Iran contributing nearly 60% of global outputs. Highly cited works emphasize the development of chitosan–magnetic and oxide-based nanocomposites, which exhibit enhanced adsorption capacities exceeding 400 mg g⁻¹ for dyes and toxic metals. At the mechanistic level, the superior performance of nano-chitosan originates from its engineered nanostructure, which increases specific surface area, enhances porosity, and provides a dense array of reactive functional groups. This structural optimization facilitates electrostatic and chemical interactions while simultaneously improving mass transfer, leading to faster adsorption kinetics, higher equilibrium uptake, and robust recyclability in multifunctional wastewater treatment composites. By combining systematic insights with bibliometric evidence, this review positions nano-chitosan as a cornerstone material for next-generation water purification and outlines future research pathways for scalable, eco-friendly solutions.</p>