Design and application of a ZnO/rGO nanocomposite opto-catalyst as a wide-bandgap optical material for solar-driven dye degradation

In this study, a ZnO/rGO nanocomposite opto-catalyst was successfully designed and applied for sunlight-driven photocatalytic degradation of Rhodamine B dye. The structural, morphological, elemental, and optical properties of the nanocomposite were comprehensively characterized using Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron (XPS), and photoluminescence (PL) spectroscopy. The XRD confirmed the formation of crystalline ZnO with an average crystallite size of 47.6 nm, while the disappearance of the GO (001) peak and the emergence of the rGO (002) peak signaled the successful reduction of graphene oxide. SEM analysis revealed a well-exfoliated layered morphology, and EDX verified the expected elemental composition as (45.0% Zn, 34.7% O, and 20.3% C). The optical band gap was estimated by the Tauc plot method. The photocatalytic performance was systematically optimized by varying key operational parameters, including catalyst dose, NaBH 4 concentration, and sunlight irradiation time. The optimal conditions, as 7 mg of ZnO/rGO, 15 µL of NaBH 4 (0.01 M), and 12 min solar irradiation yielded the highest degradation efficiency of 98%. Besides, the composite showed strong reproducibility over multiple cycles, confirming the reliability of the optimized conditions. The results highlight the strong synergistic interaction between the ZnO and rGO, enhanced charge separation, and light absorption; thus, the composite ZnO/rGO demonstrated to be an efficient, sunlight-activated, and environmentally friendly photocatalyst for wastewater treatment.