Sustainable Conversion of Chitosan Waste into Nitrogen-Doped Graphene Quantum Dots: Green Synthesis Pathways and Biomedical Potential

Abstract

The sustainable conversion of bio-waste into functional nanomaterials represents a critical step toward achieving circular material cycles and environmentally responsible innovation. Chitosan, a nitrogen-rich polysaccharide derived from seafood shell waste, has gained significant attention as a renewable and biodegradable precursor for greenly synthesising nitrogen-doped graphene quantum dots (N-GQDs). This review comprehensively examines the progress made over the past decade in developing eco-friendly synthesis routes, including hydrothermal, microwave-assisted, and plasma-based methods that utilise chitosan as a carbon and an intrinsic nitrogen source. Emphasis is placed on the physicochemical characterisation of chitosan-derived N-GQDs, including their size, morphology, structural defects, nitrogen doping profiles, surface functionalities, and photoluminescent behaviour. Comparative analysis with alternative nitrogen dopants underscores the advantages of chitosan in terms of sustainability, doping efficiency, and biocompatibility. Furthermore, the biomedical potential of these quantum dots is critically reviewed, highlighting applications in bioimaging, drug delivery, tissue engineering, and biosensing. Chitosan-based N-GQDs demonstrate exceptional promise as non-toxic, traceable, and multifunctional nanoplatforms for next-generation healthcare technologies. This review bridges green chemistry, waste valorisation, and nanomedicine, offering a roadmap for future research into sustainable carbon nanomaterials derived from bio-origin resources.