## 3 Testing and Analysis  
### XRD Analysis of Zinc Oxide  
Diffraction of X-rays (XRD) use monochromatic X-rays as the diffraction source and it generally penetrates the solid to verify its internal structure. As a result, XRD (Siemen X-ray Diffractometer D 5000, Berlin, Germany) provides information about the material's bulk structure. XRD is mostly based on qualitative phase analysis, but the quantitative analysis is also possible [34]. By comparing the X-ray diffraction spectrum of the sample to be tested with the X-ray diffraction spectrum of the reference material, the phase composition of the sample can be qualitatively analysed. Quantitative analysis of the phase composition of the sample can be completed by assessing, as well as calculating, the diffraction intensity data of the sample. The material composition of zinc oxide can be determined in this experiment by examining the spectral data. According to the XRD spectrum information, it can be determined whether the sample is amorphous or crystalline: the amorphous sample has a large peak, and with no fine peak structure, the crystal has rich spectral characteristics. The sample to be tested in this experiment is a crystal. The principle is that if the crystalline elements or groups are different or their structures are different, their diffraction patterns will show differences in the number of diffraction peaks, angular position, relative intensity, and diffraction peak shape (based on the Bragg equation: 2 dsin \(\theta\) = n \(\lambda\) (n = 1, 2... ) where theta is the angle between the incoming ray (or reflected line) and the crystal plane, also known as the grazing angle or the reflection angle. The diffraction angle refers to the angle at which the light path changes when the light is diffracted. In the X-ray diffractometer, 20 is the diffraction angle, because 20 is the angle that changes the direction after X-ray diffraction; d is the interplanar spacing, \(\lambda\) is the wavelength of the X-ray, and n is the number of reflections. The data was shown in Table 1.  
The XRD scanning speed is 4\({}^{\circ}\) /min, and the interval angle is 0.02\({}^{\circ}\). The peak of pH 8.5 and pH 9.0 samples is 20 = 34.46\({}^{\circ}\) and 61.70\({}^{\circ}\), and the diffraction line of pH 9.5 and pH 10.0 samples is 20 = 34.42\({}^{\circ}\) and 81.78\({}^{\circ}\). Cu K\(\alpha\) radiation (\(\lambda\) = 1.5406 A\({}^{\circ}\)) was used to obtain the X-ray diffraction data. According to the Bragg equation: 2 dsin \(\theta\) = n \(\lambda\). It is in the air, so n = 1.0. d = n \(\lambda\)/2 sin \(\theta\). Then, we could calculate d\({}_{1}\) = 2.60, d\({}_{2}\) = 1.47, d\({}_{3}\) = 2.47, d\({}_{4}\) = 1.91, d\({}_{5}\) = 1.62, and d\({}_{6}\) = 1.18. The interplanar spacing and h, k, and l would be presented in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline
**d (Å)** & **h** & **k** & **1** \\ \hline
1.18 & 1 & 0 & 4 \\
1.47 & 1 & 0 & 3 \\
2.6 & 0 & 0 & 2 \\
1.91 & 1 & 0 & 2 \\
1.62 & 1 & 1 & 0 \\
2.47 & 1 & 0 & 1 \\ \hline
**pH** & & **20 (\({}^{\circ}\))** & \\ \hline
8.5 & & 34.50 & \\
9.0 & & 61.70 & \\
9.5 & & 34.40 & \\
10.0 & & 81.80 & \\ \hline \end{tabular}
\end{table} 
Table 1: Table list of some (h, k, and l) and 20 for ZnO samples. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**pH** & **FWHM** & **2-Theta (\({}^{\circ}\))** & **D (nm)** & **pH** & **FWHM** & **2-Theta (\({}^{\circ}\))** & **D (nm)** \\ \hline pH 8.5 & 1.176 & 15.061 & 6.82 & pH 9.5 & 0.201 & 34.414 & 41.409 \\  & 0.226 & 34.4 & 36.827 & & 0.235 & 36.144 & 35.588 \\  & 0.217 & 37.402 & 38.681 & & 0.173 & 37.383 & 48.517 \\  & 0.89 & 47.741 & 9.769 & & 0.257 Figure 1 shows that when the pH rises, more ZnO peaks appear. However, for 4 h of HCD ZnO oxide, it will be the clearest one. Compared with the references of the XRD samples, it could show seven kinds of peaks in the figures: one for Si, six for ZnO. The Si peak is about 69\({}^{\circ}\) and the intensity of those peaks are around 25,000-30,000. When the pH for HCD changes, the crystal type changes as well.