## 2 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**XRD**} & \multicolumn{2}{c}{**FE-SEM**} & \multicolumn{2}{c}{**UV-Visible**} \\ \cline{2-7}  & \multicolumn{2}{c}{**Wurtzite Hexagonal**} & \multicolumn{2}{c}{**Cubic-Structured CeO\({}_{2}\)**} & \multicolumn{2}{c}{**Average Particle Size (nm)**} & \multicolumn{2}{c}{**E\({}_{g}\) (eV),**} \\ \cline{2-7}  & **a (Å)** & **c (Å)** & **Crystal Size (nm)** & **a (Å)** & & \\ \hline ZnO & 3.253 & 5.211 & 92.6 & - & 432 & 3.06, 0.970 \\
3\% Ce/ZnO & 3.252 & 5.211 & 93.3 & 5.400 & 674 & 2.93, 0.991 \\
5\% Ce/ZnO & 3.252 & 5.208 & 85.3 & 5.405 & 695 & 2.48, 0.990 \\
3\% Ce/ZnO & 3.251 & 5.207 & 86.0 & 5.405 & 691 & 2.22, 0.994 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Lattice parameters, crystalline sizes, average particle sizes, and optical energy band gaps. Figure 1: X-ray diffraction patterns of pristine ZnO, CeO\({}_{2}\)[37], and as-synthesized Ce/ZnO samples. and elemental composition. HR-TEM images and SAED patterns of pristine ZnO and 7% Ce/ZnO are demonstrated in Figure 3. Based on the HR-TEM of pristine ZnO in Figure 3a, the interplanar spacing was measured to be 0.24 nm, corresponding to the (101) reflection plane of a wurtzite hexagonal ZnO structure. Additionally, the SAED pattern further confirmed the structure of pristine ZnO, as shown in Figure 3b. HR-TEM images and SAED patterns of ZnO with 7% Ce doping samples (Figure 3c,d) revealed the presence of ZnO and CeO\({}_{2}\) in Ce/ZnO samples. Energy dispersive spectroscopy (EDS) mapping was also provided, as shown in Figure 3e. This strongly indicates the successful doping of Ce into the ZnO matrix. The surface compositions and chemical states of pristine ZnO and 7% Ce/ZnO samples were clarified using X-ray photoelectron spectroscopy (XPS) as presented in Figure 4. The XPS survey (Figure 4a) reveals the respective elements with the corresponding characteristic peaks and compositions (Zn, Ce, O, and C). The summary of the XPS peak positions and the % area of ZnO and 7% Ce/ZnO samples are supplied in Table S2. The deconvoluted Zn 2p peak of pristine ZnO and Ce/ZnO was fitted with two Gaussian peaks corresponding to Zn 2p\({}_{1/2}\) (1022.30 eV) and Zn 2p\({}_{3/2}\) (1045.69 eV), as shown in Figure 4b. The deconvoluted O 1s peaks (Figure 4c) show two types of surface oxygen on pristine ZnO at 533.33 and 536.44 eV, which are associated with Zn\({}^{2+}\) and chemisorbed oxygens (surface hydroxyl groups) [43]. The 7% Ce/ZnO sample shows two peaks, i.e., the same as the pristine ZnO with an additional peak at 529.32 nm, which contributed to Ce\({}^{3+}\)/Ce\({}^{4+}\) ion bonding with oxygen due to the introduction of Ce into the ZnO lattice [44]. Figure 4d shows the deconvoluted Ce 3d peaks, which consist of binding energies, representing the integrated peaks of Ce\({}^{4+}\) (884.09, 889.53, 898.21, 900.62, 908.37, and 917.26 eV). No peaks related to Ce\({}^{3+}\) were noted, indicating the existence of Ce\({}^{4+}\) in the ZnO matrix [45]. Along with the XRD results, after Ce doping, the peak intensity of the ZnO crystal decreased and became broadened. It could be pointed out that the introduction of Ce into the ZnO matrix can cause impurity/defect formation. Figure 2: Field-emission scanning electron microscopy (FE-SEM) images of (**a**) pristine ZnO, (**b**) 3% Ce/ZnO, (**c**) 5% Ce/ZnO, and (**d**) 7% Ce/ZnO samples. Figure 3: HR-TEM images and SAED patterns of (**a**,**b**) pristine ZnO and (**c**,**d**) 7% Ce/ZnO nanocomposites; (**e**) energy dispersive spectroscopy (EDS) mapping of 7% Ce/ZnO samples. The optical properties of the pristine ZnO and Ce/ZnO samples were investigated by UV-visible spectroscopy. Figure 5a exhibits the absorption spectra of as-prepared Ce/ZnO with different % Ce doping. As shown in Figure 5, the absorption wavelength of pristine ZnO was observed at 365 nm. The absorption wavelength of Ce/ZnO shifted to lower wavelengths with an increase in Ce ion doping.