## 3 Results and Discussion  
The crystal phases of the ZnO/ZnS and ZnO/ZnSr:GO samples were analyzed by XRD, as shown in Figure 1. The diffraction peaks observed in Figure 1a are related to the ZnO/ZnS nanocomposite, making it possible to identify the presence of characteristics peaks of ZnO and ZnS in their respective crystallization phases: hexagonal wurtzite (PDF 00-003-0888) for ZnO and cubic zinc blende (PDF 03-065-0309) for ZnS. The characteristic peaks of ZnO were absent for the ZnO/ZnSrAGO samples (Figure 1b-e). This absence could be attributed to the conversion of ZnO to ZnS, as [PERSON] and collaborators similarly discussed [7; 30]. However, in this study, the conversion factor of semiconductor materials is related to the amount of GO that was added to the samples during the synthesis. Furthermore, an increase in the peak in the range of 30\({}^{\circ}\) is observed as a function of the amount of rGO. This peak is related to the (002) plane, and its displacement is attributed to removing the oxygenated functional groups during the microwave process. Moreover, a small peak is observed at an angle of 52\({}^{\circ}\) in the ZnO/ZnS:rGO samples, indicating that the rGO does not exist perfectly as a single layer. The XRD pattern of GO can be seen in Figure S1. The GO peak observed at 9.9\({}^{\circ}\) is characteristic of the (001) plane of graphene oxide. The appearance of this peak is explained by the presence of more oxygenated functional groups due to the material's structure. Figure 2 shows the SEM-FEG images of the ZnO/ZnS sample. According to SEM-FEG for the pure ZnO/ZnS sample, it was possible to observe the growth of ZnO in the shape of hexagonal rod structures with pencil-like termination and main section diameter of the order of 500 nm emanating from a single point, forming \"flowers\" and following a pattern similar to epitaxial growth. Additionally, the ZnO rods are seen covered with ZnS nanoparticles, which, when deposited on the rods, makes it challenging to identify their facets. Furthermore, a homogeneous distribution of ZnS nanoparticles has been observed, indicating that under the tested conditions, ZnS can adhere to the surface of the hexagonal rods. This adhesion affects the structural and optical properties of the heterostructure [7; 28]. Additionally, using thioacetamide as a precursor results in higher crystallinity of the ZnS nanoparticles compared to other sulfur sources, which directly influences the degree of coating of the system [7]. Based on the images with rGO in the structure (Figure 3), there is notable coverage on the ZnO rods and the graphene sheets present in the material. Additionally, in these samples, the hexagonal facets of ZnO are not observable due to a complete covering with ZnS. This effect is reflected also by XRD, which does not indicate the presence of ZnO in the sample. A substantial reduction in the presence of ZnO rods was observed for ZnO/ZnS:2% rGO and ZnO/ZnS:4% rGO, suggesting a conversion of ZnO into ZnS. Figure 3: SEM-FEG images with magnification 20.0 K of: (**a**) ZnO/ZnS:0.5% rGO; (**b**) ZnO/ZnS:1% rGO; (**c**) ZnO/ZnS:2% rGO; and (**d**) ZnO/ZnS:4% rGO. Figure 2: SEM-FEG images with magnification 20.0 K of ZnO/ZnS. The active vibrational modes of ZnO, ZnS, and GO are identified in Figure 4 and widely discussed in the literature [34; 35; 36]. The modes at 440 cm\({}^{-1}\) and 556 cm\({}^{-1}\) belong to the ZnO compound and are related to the E\({}_{2}\)(H) and E\({}_{1}\)(L0) vibrations. The first is associated with the movement of zinc sub-networks in the wurtzite structure, while the E\({}_{1}\)(L0) peak suggests the presence of structural defects, such as oxygen vacancies. No additional characteristic peaks of ZnO were observed in the pristine ZnO/ZnS sample [34]. Therefore, the modes at 268 cm\({}^{-1}\) and 353 cm\({}^{-1}\) are characteristic of ZnS, corresponding to the first-order frequencies T\({}_{2}\)(T0) and T\({}_{2}\)(L0) for the zinc blend structure.