Synthetic strategies, structural engineering and mechanistic insights into carbon dots for sustainable photo- and electro-catalysis

Carbon dots (CDs) have emerged as a versatile class of metal-free nanomaterials for sustainable catalytic applications owing to their low cost, tunable surface and structure functionality, excellent optoelectronic properties, and favorable biocompatibility. This review provides an overview of recent advances in CDs-based sustainable catalysis, with particular emphasis on synthetic strategies, photo- and electro-catalytic functions, and structure–activity relationships. We first summarize top-down routes, including laser ablation, arc discharge, chemical oxidation, and electrochemical oxidation, followed by bottom-up approaches, such as template method, pyrolysis, hydro/solvothermal, microwave, and discharge plasma-enabled synthesis. Next, we discuss the roles of CDs as standalone catalysts or co-catalysts in several key transformations, including photocatalytic water splitting, pollutant photodegradation, CO₂ reduction (CO₂RR), and electrocatalytic hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction reactions (ORR). Particular attention is given to charge separation governed by CD size, heteroatom doping, surface functionalization, and interfacial engineering, light harvesting, and reaction pathways. Finally, we outline the major challenges and future opportunities for rationally designing CD architectures to achieve higher activity, selectivity, and stability, underscoring their expanding potential in sustainable photo- and electro-catalysis.