Traditional production methods for carbon-based nanomaterials (CNMs) rely heavily on non-renewable feedstocks and energy-intensive processes, making them unsustainable. The review provides a critical evaluation of sustainable routes for CNM production from bio-waste precursors and green carbonization methods. A crucial aspect is identifying the accessibility of inexpensive biomass sources, including agricultural waste, forestry refuse, and food waste, as carbon feedstocks for producing carbon dots, graphene-like materials, carbon nanosheets (CNs), and porous carbons. The review mainly focuses on green carbonisation methods, including hydrothermal carbonisation (HTC), microwave pyrolysis, the molten-salt technique, and solar-driven pyrolysis, which save energy and do not produce toxicants. These methods enable the customization of physicochemical features (e.g., morphology, surface functionality, porosity) in resulting CNMs, which can be used for energy storage (supercapacitors, batteries), environmental cleanup (adsorbents, sensors), and catalysis. Process limitations, such as scalability, reproducibility, and customization of nanomaterial properties from complex heterogeneous bio-waste, are thoroughly examined. The review shows that combining bio-waste precursors with green carbonization methods offers a promising circular-economy strategy, converting waste into high-value nanomaterials while reducing environmental impact. Future outlooks highlight the need for standardized life-cycle assessments and techno-economic analyses to support the industrial adoption of these sustainable synthesis methods.

Keywords: Carbon-Based Nanomaterials; Bio-Waste Valorization; Green Carbonization; Hydrothermal Carbonization; Sustainable Energy Materials;