*3.3. Fourier Transform Infrared (FT–IR) Analysis*

The FT–IR bands of ZnO, Cu2O, Cu2O/ZnO and N-doped Cu2O/ZnO nanomaterials are given in Figure 3. The peaks appeared in the range of 490–505 cm−<sup>1</sup> in all the samples except in Cu2O and correspond to the stretching vibration of ZnO, which agreed with the findings of previous studies [36,37]. In the FT–IR spectra of Cu2O, Cu2O/ZnO and N-doped Cu2O/ZnO nanoparticles, there were peaks in the range of 610–630 cm−1, which corresponds to the stretching vibration of Cu2O; a similar result was reported by [34]. The peak that appeared at 3169 cm−<sup>1</sup> in the FT–IR spectrum of the N-doped Cu2O/ZnO nanocomposite might be due to N-H stretching vibration mode. The band located at 1441 cm−<sup>1</sup> might be due to N-H bending vibration mode [38]. Besides the above absorption bands, there was an additional peak located at 431 cm−<sup>1</sup> in the FT–IR spectrum of the N-doped Cu2O/ZnO nanocomposite, which might be attributed to the metal–nitrogen (M–N) stretching vibration similar results have been reported [32]. Therefore, the bands indicated the presence of ZnO, Cu2O and nitrogen in the N-doped Cu2O/ZnO nanocomposite.

**Figure 3.** Fourier transform infrared (FT–IR) spectrums of (a) ZnO, (b) Cu2O, (c) Cu2O/ZnO and (d) N-Cu2O/ZnO nanomaterials.
