Sustainable synthesis of carbon nanomaterials: Green methods from biomass waste for theranostic and bioremediation applications

Carbon nanomaterials (CNMs) have attracted considerable interest in theranostics due to their unique properties, such as low cytotoxicity, high water solubility, tunable fluorescence, large surface area, and ease of modification. Green synthesis of CNMs is an emerging field that aligns with green chemistry, sustainability, and circular economy. This review focuses specifically on green synthesis methods that utilize biomass waste as a precursor and use only water as solvent, in contrast to approaches often labeled as "green" but still relying on non-renewable carbon sources or organic solvents. Biomass waste provides an environmentally friendly, cost-effective, and sustainable alternative to conventional carbon precursors such as graphite or carbon black. This review discusses the synthesis of carbon and graphene quantum dots (C/GQDs), graphene oxide (GO), and reduced graphene oxide (rGO), with a focus on their optical properties, particularly photoluminescence, which is essential for bioimaging and theranostic applications. Additionally, the potential of CNMs in bioremediation is considered, specifically their ability to remove environmental pollutants. The review evaluates the benefits and limitations of major green synthesis techniques and underscores the importance of utilizing biomass waste to ensure sustainable CNMs’ production.