Synthesis and applications of carbon nano-onions and their composites for the remediation of organic pollutants from wastewater

Abstract

Water pollution remains a critical global concern, adversely impacting aquatic ecosystems, food security, and human health. In response, carbon nano-onions (CNOs) have emerged as promising nanomaterials for wastewater treatment due to their unique physicochemical properties, including high specific surface area, tunable surface chemistry, and multiple active sites. This review systematically explores recent advancements in the synthesis and functionalization of CNOs and their composites for the removal of organic pollutants from contaminated water. Key focus areas include adsorption capacities, photocatalytic degradation efficiencies, and reusability over multiple cycles with minimal performance loss. Mechanistic insights into pollutant–CNO interactions, including π–π stacking, electrostatic attraction, and redox reactions, are discussed in detail. Furthermore, challenges related to material regeneration, scalability, and real wastewater application are critically assessed. By consolidating current knowledge and outlining future research directions, this review aims to guide the rational design and deployment of CNO-based technologies for sustainable and high-performance water purification.