A review of sustainable approaches for the synthesis of carbon quantum dots-polymer nanocomposites

Carbon quantum dots (CQDs) are emerging innovative materials with distinctive optical and electronic properties, making them highly promising for diverse applications, including optoelectronic devices like photovoltaic cells and LEDs, as well as advanced biomedical sensors that can revolutionize healthcare diagnostics and monitoring. The growing emphasis on sustainable development implies the adoption of environmentally responsible approaches to minimize ecological footprints of any innovative technology. This review critically examines the synthesis of CQDs via both conventional and emerging methodologies, with particular emphasis on quantum yield, surface passivation, and functional group tunability. Among the most sustainable approaches is the valorisation of waste-derived precursors—including agricultural residues, food waste, and industrial by-products—which mitigates environmental pollution and enables cost-effective and scalable CQD production. The production of CQD-polymer nanocomposites is highlighted as a major development as their mechanical robustness, thermal stability, and multifunctionality, are significantly improved thereby expanding their potential across various technological domains. Recent advancements in green synthesis techniques for these nanocomposites relate to the use of renewable, bio-based polymers, benign solvents, and low-energy fabrication processes. These strategies are aligned with circular economy principles and contribute to the development of safer, more sustainable nanomaterials. In the area of wastewater treatment, CQD-based nanocomposites have demonstrated remarkable efficacy in pollutant sensing, adsorption, and photocatalytic degradation under visible light irradiation. Their tunable surface chemistry, high surface area, and strong photoluminescence enable efficient removal of a wide range of contaminants, including heavy metals, synthetic dyes, and pharmaceutical residues. The review concludes by outlining future perspectives, emphasising the need for standardised synthesis protocols, comprehensive life cycle assessments, and the development of multifunctional CQD systems. Advancing these areas will be critical for the large-scale deployment of CQD-based technologies in environmental remediation and beyond.