In this backdrop, we investigate the size-dependent electrochemical transformation of melamine to its subsequent g-C3N4 QDs in IL at room temperature for oxygen reduction reaction by varying the potential with time. These g-C3N4 QDs exhibit size-dependent optical properties, as evidenced by the UV and PL results. To the best of our knowledge, this is the first report of size-dependent electrocatalytic properties of carbon nitride. Furthermore, the morphological structure of QDs based on their size distribution is revealed from transmission electron microscopy (TEM), supporting the band-gap engineering in these classes of materials. polyaddition and polycondensation processes, resulting in the two-dimensional graphite-like planar structure containing π-conjugated systems known as polymeric carbon nitride having an interlayer distance of 0.326 nm. The next step involves intercalating these two-dimensional materials with the ions (BMIM + and MIM . ) present in the electrolyte (SI; Figure (a) and (b)) and subsequent fragmentation of these materials at a constant potential (-1.5, -3, and -4.5 V), forming QDs (SI; Figure and.