Design and application of ZnO/rGO nanocomposite opto-catalyst as 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 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 Tauc plot method. The photocatalytic performance was systematically optimized by varying key operational parameters including catalyst dose, NaBH4 concentration and sunlight irradiation time. The optimal conditions as 7 mg of ZnO/rGO, 15 µL of NaBH4 (0.01 M) and 12 min solar irradiation yielded the highest degradation efficiency of 98%. Besides, the composite posed 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 charged separation, light absorption thus the composite ZnO/rGO demonstrated proved to be an efficient, sunlight activated, and environmentally friendly photocatalyst for wastewater treatment.