The optoelectronic properties of the quantum dots (QDs) have a significant effect on the photocatalytic efficiency. Presently, I−III−VI group QDs is becoming the conformist light harvesting resources in photocatalytic reactions. Herein, we have designed Cu-In-S (CIS) ternary QDs, ZnCuInS (ZCIS) quaternary, and quinary Zn-Cu-In-S-Se (ZCISSe) alloyed QDs by a cation-anion co-alloying approach. The optoelectronic properties of the prepared QDs, which includes bandgap energy, band-edge potentials, and charge carrier separation abilities can be handily tailored. Experimental outcomes revealed that, cation/anion co-doped quinary ZCISSe alloyed QDs can conquer a superlative equilibrium among light absorption ability, exciton separation-migration efficiencies in photocatalytic reactions in comparison to single cation doped ZCIS QDs. Thus, ZCISSe quinary QDs exhibits enhanced photocatalytic H2O2 production (2565.5 μmol. h−1. g−1) which is about 2 times higher than ZCIS and 8 times greater than CIS QDs with SCC of 0.36%. As well as the quinary QD shows a GMF degradation rate of 98.8% (k1–258×10−4 min−1) in 2 h of visible light illumination. Besides, this work is conferring a depth study by varying pH, scavengers, proton donors, and different environments of micropollutant degradation and O2 reduction, which promotes further expansion of effective multinary alloyed QDs, based photocatalytic materials.