Carbon dots for sustainable energy and advanced materials: synthesis, mechanisms, and application-driven design

Carbon dots (CDs) have emerged as versatile zero-dimensional carbon nanomaterials with tunable physicochemical properties and wide-ranging applications in energy, environmental, and advanced material systems. This review critically summarizes recent advances in CD synthesis, structure–property relationships, photoluminescence mechanisms, and application-driven performance. Both top-down and bottom-up synthesis routes are comparatively evaluated, with particular emphasis on sustainable biomass-derived and green synthesis strategies for scalable and environmentally benign production. The review highlights the influence of carbon core structure, surface functionalization, defect states, and heteroatom doping on the optical, electronic, and electrochemical behavior of CDs. Recent studies reporting quantum yields approaching ∼80% and tunable visible-light emission (400–700 nm) are critically analyzed to establish generalized design principles governing luminescence and charge-transfer mechanisms. The integration of CDs into supercapacitors, batteries, photocatalytic systems, and multifunctional composites is also discussed, where they contribute to enhanced catalytic activity, electrochemical stability, mechanical strength, and thermal conductivity. Despite substantial progress, challenges related to reproducible synthesis, structural heterogeneity, and large-scale manufacturing remain unresolved. This review identifies these limitations and outlines future directions focused on standardized synthesis protocols, mechanistic understanding, and scalable sustainable production. By bridging fundamental insights with application-oriented design, this work positions CDs as promising materials for next-generation sustainable energy and advanced material technologies.