Carbon Quantum Dots: Sustainable synthesis, enhanced properties, and cross-disciplinary applications

Abstract This review delves into carbon quantum dots (CQDs), highlighting their synthesis, unique properties, and broad applications across environmental, biomedical, and industrial fields. CQDs, with their tunable fluorescence, high biocompatibility, and sustainable production methods, are increasingly valuable for pollutant sensing, bioimaging, drug delivery, and photocatalysis. Structurally, CQDs feature a graphitic core and surface functional groups that govern their optical and chemical characteristics, while functionalization and doping can enhance their stability and fluorescence. However, obstacles such as low quantum yields, synthesis reproducibility, and toxicity concerns still limit their potential in broader applications. In environmental uses, CQDs are effective as photocatalysts and adsorbents, aiding in pollutant removal and water purification. In biomedicine, their low toxicity and targeted fluorescence make CQDs suitable for drug delivery and antimicrobial and anticancer therapies. The review also explores the use of green, waste-based materials for CQD production, supporting sustainable and scalable manufacturing. Looking forward, research aims to develop multifunctional CQD hybrids for use in nanoelectronics and photovoltaics, and to optimize CQD properties for greater reliability in real-world applications. By addressing these challenges and prioritizing scalable, eco-friendly production, CQDs have the potential to be transformative materials, enabling sustainable advances across various scientific and industrial domains.