# Photocatalytic Activity of Monosized AuZnO Composite Nanoparticles
## 3 Results and Discussion
### Transmission Electron Microscope Morphology and Nanostructures of AuZnO Composite Nanoparticles
\[D_{hkl}=\frac{180^{\circ}\kappa\lambda}{\pi B_{1/2}\cos\theta} \tag{1}\]  
where \(\lambda\) is the X-ray wavelength (1.54 A), \(\theta\) is the Bragg diffraction angle, \(k\) = 0.89, and \(B_{1/2}\) is the full width at half maximum. The XPS analysis was carried out to investigate the chemical composition of the AuZnO nanoparticles, and the corresponding experimental results are shown in Figure 3. The binding energy in the XPS spectra was calibrated using C 1s (284.8 eV). There are no peaks for other elements, except for Zn, O, Au, and C observed from the full XPS spectra of Figure 3a. The presence of carbon comes largely from the surfactant (PEO-PPO-PEO) molecules on the surface of the resulting nanoparticles. Therefore, it is concluded that the nanoparticle is mostly composed of three elements: Zn, Au, and O. In Figure 3a, the composite nanoparticles display a doublet at about 1022 and 1045 eV, corresponding to the Zn 2p\({}_{3/2}\) and 2p\({}_{1/2}\) core levels [29]. The first peak is attributed to Zn\({}^{2+}\) ions in the oxygen-deficient ZnO matrix. Moreover, all of the Zn 2p\({}_{3/2}\) XPS peaks are sharp. Thus, it can be confirmed, that a Zn element exists mainly in the form of Zn\({}^{2+}\) on the samples' surfaces [30]. The peaks observed at 83.2 and 87.3 eV (Figure 3b) correspond to the Au 4f\({}_{5/2}\) and Au 4f\({}_{7/2}\) states of the metallic Au. The binding energy of the Au 4f states is shifted obviously to lower values, as observed for other AuZnO composites when compared to bulk Au (from 84.0 and 87.7 eV, respectively [31]). This effect is often ascribed to the fact that interaction between Au and ZnO-namely, the electron transfer-takes place between Au and ZnO at the interfaces where the Au and ZnO come into contact [31]. Thus, the analysis illustrates that the AuZnO nanoparticles are dominantly comprised of Au and ZnO, which is in agreement with the XRD and TEM results, as previously addressed. Figure 2: X-ray diffraction (XRD) patterns for the AuZnO composite nanoparticles, (**a**) S3, (**b**) S2, (**c**) S1, and (**d**) ZnO, with a bar diagram for the JCPDS of ZnO (squares) and Au (inverted triangles). The elemental content of the AuZnO composite nanoparticles was tested by ICAP analysis. The results show that Au element content is 7.0 \(\pm\) 0.3%, 13.1 \(\pm\) 1%, and 26.1 \(\pm\) 1% for S1, S2, and S3, respectively, while the Zn element content is 63.0 \(\pm\) 0.3%, 55.1 \(\pm\) 0.7%, and 45.0 \(\pm\) 1.3% for S1, S2, and S3, respectively. The spectra of the purified AuZnO composite nanoparticles and pure PEO-PPO-PEO macromolecules were analyzed by FTIR, indicating that PEO-PPO-PEO macromolecules are present on the surface of the AuZnO composite nanoparticles [32]. Figure 4 compares the FTIR spectra of purified AuZnO composite nanoparticles and pure PEO-PPO-PEO molecules. In Figure 4d, a strong characteristic peak at about 1122 cm\({}^{-1}\) for pure PEO-PPO-PEO molecules belongs to the C-O-C stretching vibration, which is usually between 1250 cm\({}^{-1}\) and 1000 cm\({}^{-1}\), with a characteristic peak at \(\sim\)1475 cm\({}^{-1}\) that is due to C-H bending vibration [32]. These characteristic vibration and bending modes are reproduced in the FTIR spectra of the AuZnO composite nanoparticles, but the C-O-C stretching vibration red shifts to the positions of \(\sim\)1116 cm\({}^{-1}\), \(\sim\)1118 cm\({}^{-1}\), and \(\sim\)1123 cm\({}^{-1}\) for S1, S2, and S3 composite nanoparticles (Figure 4a-c), and the C-H bending vibration shifts to \(\sim\)1589 cm\({}^{-1}\). In addition, the ribbon shape and location are significantly different for AuZnO composite nanoparticles than for pure PEO-PPO-PEO molecules, due to changes in the elastic constants that are the result of the great curvature and strong interaction. The blue shift and change in the band shape of the C-O-C stretching and C-H bending bands may involve the coordination of the oxygen atoms in the main chains of PEO-PPO-PEO to the metallic atoms [32; 33; 34].