# Enhancing Methyl Orange Degradation with Laser-Generated ZnO and Ce-Doped ZnO Nanoparticles
## 3 Results and Discussion
### Photocatalytic Degradation of MO Dye
Additionally, the presence of numerous free surface sites available for adsorption in the absence of light further facilitates this reaction [32]. Consequently, these electrons initiate a series of reactions, forming hydroxyl radicals. These species emerge as the primary oxidative species responsible for the degradation of MO, both in both dark and illuminated conditions, as indicated by our findings [35]. Figure 6: The absorption curves of the MO solution in the presence of 1% Ce/ZnO NPs: (**a**) before and (**c**) after annealing under UV light, as well as (**b**) before and (**d**) after annealing under sunlight. Additionally, the absorption curves of ZnO NPs are shown: (**e**) before and (**g**) after annealing under UV light, and (**f**) before and (**h**) after annealing under sunlight. Figure 8a,b presents the photodegradation of MO dye using ZnO NPs and 1% Ce/ZnO NP photocatalysts before and after annealing under UV and sunlight irradiation. The results show a consistent trend, where the absorption of MO dye (lower MO concentration) decreases with increasing irradiation time for all types of radiation and photocatalysts within the first 90 min. The remarkable performance of 1% Ce/ZnO NPs, which exhibit nearly complete photodegradation of MO dye after 90 min, is shown. This photocatalyst demonstrates a regular and gradual degradation behavior compared to ZnO NPs. The variability noted in the degradation curves of ZnO NPs may be linked to the instability in the adsorption/desorption equilibrium. Numerous research papers have provided comprehensive analyses and discussions on the topic of dye degradation [36; 37; 38; 39; 40]. However, the excellent performance can be attributed to the high surface area offered by the nanoparticles, making it a favorable choice for solar photocatalysis. The abundance of surface-active sites enhances interfacial charge carrier transfer during photocatalysis, leading to efficient adsorption of pollutants and achieving a higher degradation rate. In Figure 8c,d, the -ln (\(C_{\text{f}}/C_{\text{o}}\)) plots exhibit a linear correlation with the irradiation time, indicating that the MO photodegradation follows a pseudo-first-order kinetic reaction. The figure also shows the linear relationship fit for 1% Ce-doped ZnO NPs, both before and after annealing, when exposed to UV and sunlight, respectively. ZnO NPs, when subjected to UV and sunlight, also demonstrate acceptable linear fits, as summarized in Table 3. The rate constants (\(k\)) for the degradation of MO dye, calculated using Equation (4) [41], demonstrate an approximately 1-fold increase in the reaction rate for non-annealed and annealed ZnO NPs under UV and sunlight. In contrast, for 1% Ce-doped ZnO NPs, \(k\) increases by approximately 2-fold under UV and 3-fold under sunlight for both non-annealed and annealed samples. This substantial enhancement in photocatalytic activity can be \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Sample**} & \multicolumn{6}{c}{**UV Radiation**} & \multicolumn{6}{c}{**Sunlight**} \\ \cline{2-13}  & \multicolumn{3}{c}{**E\%–before**} & \multicolumn{3}{c}{**E\%–after**} & \multicolumn{3}{c}{**E\%–before**} & \multicolumn{3}{c}{**E\%–after**} \\ \cline{2-13}  & \({}^{*}\)**0-30** & **30-40** & **40-120** & \({}^{*}\)**0-30** & **30-40** & **40-120** & \({}^{*}\)**0-30** & **30-40** & **40-120** & \({}^{*}\)**0-30** & **30-40** & **40-120** \\  & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** & **(min)** \\ \hline ZnO NPs & 61 & 28 & 82 & 62 & 71 & 85 & 63 & 49 & 83 & 64 & 66 & 89 \\ \hline
1\% Ce-doped ZnO NPs & 67 & 68 & 87 & 78 & 77 & 92 & 70 & 72 & 91 & 78 & 80 & 95 \\ \hline \hline \end{tabular}  
* \({}^{*}\)0–30 min in dark and 30–120 min in light.  
\end{table} 
Table 2: Variation of percentage efficiencies in detail under UV light and sunlight for undoped ZnO NPs and 1% Ce/ZnO NPs before and after annealing.