## 4 Evaluation of Exhaust Gas Degradation Effect  
### Effects of the Nano-TiO\({}_{2}\) Content on Exhaust Gas Degradation  
A total of 30 g of photocatalytic coatings with nano-TiO\({}_{2}\) content of 3%, 5%, 8%, 10%, and 15% were uniformly applied to the surface of the 300 \(\times\) 300 mm OGFC-10 slab samples to perform photocatalytic degradation of the exhaust gas test. The test specimens are shown in Figure 5. The effect of degradation of exhaust gas by photocatalytic coating with different nano-TiO\({}_{2}\) contents was studied. The test results are shown in Figures 6 and 7.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Nano-TiO\({}_{2}\) Content** & **3\%** & **5\%** & **8\%** & **10\%** & **15\%** & **Requirements [25]** & **Methods [24]** \\ \hline Color of emulsion & Brown & Brown & Brown & Brown & Brown & \(-\) & \(-\) \\ Standard viscosity C25,3 (s) & 16.56 & 16.12 & 15.98 & 15.54 & 14.65 & 12–60 & T0621 \\
5-day storage stability (\%) & 3.45 & 3.76 & 3.63 & 3.88 & 4.13 & \(<\)5 & T0655 \\ Adhesion, covering area & \textgreater{}2/3 & \textgreater{}2/3 & \textgreater{}2/3 & \textgreater{}2/3 & \textgreater{}2/3 & \textgreater{}2/3 & T0654 \\
1 h wet track abrasion loss (g/m2) & 321 & 356 & 380 & 423 & 463 & \textless{}540 & T0752 \\ \hline \hline \end{tabular}
\end{table}
Table 12: Basic properties of photocatalytic coatings with different nano-TiO\({}_{2}\) content.  
As can be seen from Figure 6, with the increase of nano-TiO\({}_{2}\) content, the performance of photocatalytic coatings for degradation of exhaust gas was better. When the content of nano-TiO\({}_{2}\) increased from 0 to 8%, the cumulative degradation rate of CO, HC, and NO increased rapidly. However, the cumulative degradation rate of the CO, HC, and NO grew slowly when the content of nano-TiO\({}_{2}\) was above 8%. Figure 7 illustrates that the nano-TiO\({}_{2}\) content had a good quadratic nonlinear  
Figure 5: Test specimens: (**a**) without photocatalytic coating, and (**b**) with sprayed photocatalytic coating.  
Figure 6: Changes of the cumulative degradation rate of the exhaust gas at different nano-TiO\({}_{2}\) contents.  
Figure 7: Changes of the degradation efficiency of the exhaust gas at different nano-TiO\({}_{2}\) contents.  
correlation with the degradation efficiency of CO, HC, and NO. With the increase of nano-TiO\({}_{2}\) content, the degradation efficiency of three kinds of exhaust gas increased gradually. However, the degradation efficiency of nano-TiO\({}_{2}\) to three kinds of exhaust gas tended to decrease when the content of nano-TiO\({}_{2}\) was above 8%.  
The exhaust gas degradation performance of the coating was related to the size of the effective contact area between the nano-TiO\({}_{2}\) and exhaust gas, and ultraviolet intensity. When the nano-TiO\({}_{2}\) content exceeded 8%, the entire surface of the slab sample was covered by a saturated nano-TiO\({}_{2}\) thin layer. Therefore, there was no substantial increase in the effective number of nano-TiO\({}_{2}\) particles touching with the exhaust gas per unit area with the continuous increase of the content of nano-TiO\({}_{2}\). The degradation performance of the photocatalytic coating was not significantly improved. Furthermore, the degradation efficiency of nano-TiO\({}_{2}\) gradually decreased.