*3.1. XRD Patterns Study*

The crystal structure of the nanomaterials was confirmed by X−ray diffraction. Figure 1 displays the XRD patterns of the ZnO and with different copper contents CuO/ZnO nanocomposites. Major peaks were observed at around 31.82◦ (100), 34.50◦ (002), and 36.32◦(101) of the undoped ZnO (JCPDS no.36–1451) [31]. CuO/ZnO nanocomposites displayed a very minor peak at 38.8◦, which was indexed to the (111) of CuO [24]. With the addition of Cu in ZnO, the diffraction intensities and angles changed remarkably. The diffraction peak of CuO (111) was found with 5 and 7 wt % of copper content. In addition, with increased amounts of copper, no other peaks or appreciable shifts were observed and no solid solution was formed in between ZnO and CuO. The Scherrer equation was used to obtain the

grain size of the ZnO and CuO/ZnO nanocomposites. The estimated grains were found as ~32.16 and ~32.13 nm for ZnO and 5 wt % CuO/ZnO, respectively.

**Figure 1.** X-ray diffraction (XRD) patterns of ZnO and CuO/ZnO.
