Ferric Cl-doped CQDs were reported as a photocatalyst which synthesized via a feasible hydrothermal method and characterized using various techniques such as HRTEM imaging, EDS, EDS mapping, XRD, XPS, PL, FTIR, and UV–Vis spectroscopies. The photocatalytic activity of monometallic Fe@ClCQDs was scrutinized toward the photoconversion of RhB dye from water. The photoconversion of RhB dye in the presence of 6 mg of photocatalyst and 25 µL H₂O₂ was impressive (89%) in 90 s. The effect of catalyst dosage, light intensity, pH, H₂O₂ concentration, and temperature on dye conversion was studied. The results of using different scavengers indicated that ^˚OH has an important role in photocatalytic conversion. More importantly, the photoactivity of monometallic Fe@ClCQDs remains > 89% after eleven times, which shows their good stability and utility. Hence, the monometallic Fe@ClCQDs are promising photocatalysts for extraordinarily efficient dye conversion in an extremely short time.