# Catalytic Degradation of Anionic Organic Dye on Greenly Synthesized CuO/ZnO Nanocomposites
## 3 Results and Discussion
Figure 3 shows the SEM images of the five prepared samples at two different magnifications. Sample Z has a stacked layers structure with sharp edges. Adding CuO precursor to the synthesis mixture caused a huge change in the surface morphology, as obtained for sample 1C3Z, which had a mixture of spherical CuO particles and ZnO rods, with a more porous structure. Increasing the percentage of the CuO precursor in the synthesis mixture to 50% (1C1Z) resulted in irregular shapes for both CuO and ZnO with almost similar sizes. Further increase in the CuO precursor to 75% (3C1Z) resulted in flakes (ZnO) with spherical particles (CuO). Sample C, which is made of 100% CuO, has 1 irregularly shaped particle with sharp edges. Figure 4 shows the TEM images of the five prepared samples. The concentric rings shown in the SAED images confirm the crystalline structure for all samples. The TEM images were used with image J software to find the particle size distribution for each nanocomposite. Figure 4 shows that the nanocomposite Z has the narrowest particle size distribution, with 73% of the particles in the range of 5-10 nm. By increasing the percentage of the Cu precursor in the synthesis mixture, wider distribution and larger particle size were obtained. For 1C3Z, 1C1Z, and 3C1Z, 40%, 43%, and 40% of the particles, respectively, are in the range of 10-15 nm. For sample C, the particle size distribution is very widely distributed in the range of 0-50 nm, with most of the particles between 15-35 nm. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & & \multicolumn{4}{c}{**Crystalline Size (nm)**} & \multicolumn{4}{c}{**Mass \%**} \\ \cline{2-11}  & **Z** & **1C3Z** & **1C1Z** & **3C1Z** & **C** & **Z** & **1C3Z** & **1C1Z** & **3C1Z** & **C** \\ \hline CuO & - & 27 & 21 & 15 & 29 & 0.0 & 49.9 & 69.3 & 80.9 & 100.0 \\ \hline ZnO & 26 & 30 & 21 & 17 & - & 100.0 & 50.1 & 30.7 & 19.1 & 0.0 \\ \hline \end{tabular}
\end{table} 
Table 2: The crystalline size (nm) of CuO and ZnO was estimated by the Debye–Scherrer formula, and the composition of each nanocomposite was obtained from AAS analysis. Figure 3: _Cont._  
TGA analysis was performed for sample 1C1Z for the temperature range of 20-700 \({}^{\circ}\)C, as shown in Figure 5. The sample lost only 2.5% during the first period of treatment (20-175 \({}^{\circ}\)C), which is mainly related to the loss of some adsorbed gases (CO\({}_{2}\), N\({}_{2}\)) and water on the external surface of the sample. After that, the sample lost 7% before reaching 220 \({}^{\circ}\)C, which may be related to the strongly adsorbed water within the pores. After that sharp decrease in mass, the sample continued to lose mass in a slower and almost regular manner, until it reached a total loss of 18% at 700 \({}^{\circ}\)C. The last loss of material, almost 9%, may be related to the decomposition of some organic residual from the extract. This is supported by the EDEX analysis performed for the same sample (Figure 6), which shows the presence of some minerals (Na, K) and Cl ions. These ions are mainly from the plant extract used during the synthesis process. Figure 3: SEM images of Z, 1C3Z, 1C1Z, 3C1Z, and C greenly prepared via hydrothermal route (pH = 10, T = 250 \({}^{\circ}\)C, t = 2.5 h) and calcination for 2 h at 300 \({}^{\circ}\)C.  
Figure 4: _Cont._  
Figure 4: TEM images of \(Z\), 1C3Z, 1C1Z, 3C1Z, and C greenly prepared via hydrothermal route (pH = 10, T = 250 \({}^{\circ}\)C, t = 2.5 h) and calcination for 2 h at 300 \({}^{\circ}\)C.  
Figure 5: Thermal gravimetric analysis of 1C1Z greenly prepared via the hydrothermal route (pH = 10, T = 250 \({}^{\circ}\)C, t = 2.5 h) and calcination for 2 h at 300 \({}^{\circ}\)C.  
Figure 6: EDEX analysis of 1C1Z greenly prepared via the hydrothermal route (pH = 10, T = 250 \({}^{\circ}\)C, t = 2.5 h) and calcination for 2 h at 300 \({}^{\circ}\)C.  
Figure 7 shows the results of the equilibrium technique used to measure the pH of the zero point charge for each sample. This point represents the x-intercept of the \(\Delta\)pH versus pHi.