*3.1. X-ray Di*ff*raction (XRD) Patterns of the Nanomaterials*

The diffraction patterns of Cu2O, ZnO, Cu2O/ZnO, and N-doped Cu2O/ZnO nanoparticles are shown in Figure 1. In the XRD patterns of ZnO, Cu2O/ZnO and N-Cu2O/ZnO nanomaterials, diffraction peaks appeared at 2θ = 31.76◦, 34.40◦, 36.24◦, 47.53◦, 56.59◦, 62.85◦, 66.37◦, 67.90◦, 69.07◦ which correspond to (100), (002), (101), (102), (110), (103), (200), (112), and (201) planes of the hexagonal wurtzite structure of zinc oxide. Similar results were reported in [30]. The diffraction peaks in the XRD patterns of Cu2O, Cu2O/ZnO and N-Cu2O/ZnO at 2θ value of 29.57◦, 36.40◦, 42.32◦, 61.43◦, 73.55◦ and 77.40◦ correspond to the reflection from (110), (111), (200), (220), (311) and (222) crystal planes of the cubic structure of cuprous oxide which is in agreement with [31]. There is no other diffraction peak displayed from impurities such as CuO, Cu(OH)2 and Zn(OH)2, indicating the purity of the nanostructured materials. As shown in Figure 1d, no additional peak was displayed due to nitrogen doping which might be nitrogen introduced into the ZnO [32] and Cu2O lattices without changing their crystal structures. The insignificant shift in the diffraction peaks of N-Cu2O/ZnO nanocomposite corresponds to the possibility of substituting oxygen by nitrogen. This can be mainly attributed to the highest resemblance among nitrogen and oxygen atoms in terms of electronegativity and atomic radius.

**Figure 1.** X-ray diffractogram of (a) Cu2O, (b) ZnO, (c) Cu2O/ZnO and (d) N-doped Cu2O/ZnO nanomaterials.

The average crystallite sizes of the nanomaterials were calculated from the intensive peak using the Scherer equation:

$$\mathcal{D} = \frac{0.9\lambda}{\beta \cdot \cos\theta} \tag{2}$$

where D is the crystallite size, λ is the wavelength, θ is the Bragg angle and β is the full width at half maximum in radian. The average crystallite sizes of ZnO, Cu2O, Cu2O/ZnO and N-Cu2O/ZnO were found at 33.72 nm, 32.33 nm, 14.15 nm, and 13.57 nm, respectively. Based on these results, the size of the crystallites is decreased in N-doped Cu2O/ZnO nanocomposite compared to the Cu2O and ZnO. The effect of decreasing the crystallite size may be ascribed to the insertion of nitrogen (incorporation of dopant) in Cu2O and ZnO lattices [32,33] and this was also confirmed in the photocatalytic degradation experiment. This insertion of nitrogen into the Cu2O and ZnO lattices can disturb the growth process of the particles, which might be the reason for the reduction of crystallite size in N-Cu2O/ZnO nanocomposite compared to Cu2O and ZnO nano-level particles.

#### *3.2. Scanning Electron Microscopy (SEM) Analysis*

Surface morphology of ZnO, Cu2O, Cu2O/ZnO and N-Cu2O/ZnO nanomaterials was determined by SEM as shown in Figure 2a–d, respectively. From SEM micrographs, it was evident that the morphology of ZnO showed some agglomerated nanoparticles with irregular morphology, which is in line with [30]. However, SEM micrographs of Cu2O, Cu2O/ZnO and N-Cu2O/ZnO samples were relatively ordered and showed that the agglomerations of particles were much less (Figure 2b,d) than in ZnO NPs with the nanocrystals, which had a truncated octahedron shape; this might be due to the presence of Cu2O [34,35].

**Figure 2.** Scanning electron microscopy (SEM) morphology of (**a**) ZnO, (**b**) Cu2O, (**c**) Cu2O/ZnO and (**d**) N-doped Cu2O/ZnO nanomaterials.
