Metal oxide/graphene photocatalysts have been attracting considerable attention in solving environmental pollution problems because of the limitations of the semiconductor-based photocatalysts. In this study, highly efficient and inexpensive zinc oxide (ZnO) nanoparticles with three different morphologies, such as nanospheres, nanodisks, and nanorods, anchored on reduced graphene oxide (RGO) were synthesized in solvent mixtures with different ethanol to water ratios. Among the three morphologies, the nanospherical ZnO/RGO (sZG) composite exhibited the highest methylene blue (MB) and rhodamine B removal efficiencies at 99% and 98%, respectively, after only 60 min under low-power (40 W) ultraviolet irradiation at a low catalyst loading of 0.1 gL(-1). This nanocomposite also showed excellent photocatalytic stability under UV irradiation, retaining 96% efficiency even after 15 cycles of MB degradation. Moreover, the sZG composite exhibited a high MB degradation efficiency of approximately 99% after 100 min at a low catalyst loading of 0.2 gL(-1) under solar light illumination. The excellent photocatalytic performance and high stability of this low-cost nanospherical ZnO/RGO composite exemplarily highlights the potential of sustainable next-generation photocatalysis for treating wastewater containing organic pollutants.