## 4 Evaluation of Exhaust Gas Degradation Effect
### Effects of the Spraying Amount on Exhaust Gas Degradation  
Separately, 10 g, 20 g, 30 g, 40 g, and 55 g of photocatalytic coatings with 8% nano-TiO\({}_{2}\) were uniformly sprayed on the slab samples of OGFC-10 to perform the photocatalytic degradation of exhaust gas test. The performances of nano-TiO\({}_{2}\) photocatalytic coatings with different spraying amounts on the degradation of exhaust gas were studied. The test results are shown at Figures 8 and 9.  
Figure 8: Changes of the cumulative degradation rate of the exhaust gas at different nano-TiO\({}_{2}\) spraying amounts.  
Figure 9: Changes of the degradation efficiency of the exhaust gas at different nano-TiO\({}_{2}\) spraying amounts.  
As can be seen from Figure 8. The cumulative degradation rate of CO, HC, and NO increased gradually with the increase of the amount of photocatalytic coating. However, when the spraying amount was over 333.3 g/m\({}^{2}\), the cumulative degradation rate of CO, HC, and NO gas remained unchanged with the continuous increasing of spraying amount. When the spraying amount of nano-TiO\({}_{2}\) photocatalytic coating was less than 333.3 g/m\({}^{2}\), with the increase of spraying amount, the number of nano-TiO\({}_{2}\) particles on the surface of the slab sample and the effective contact area with the exhaust gas and the ultraviolet light gradually increased and the effect of degradation improved. When the nano-TiO\({}_{2}\) photocatalytic coating spraying amount reached 333.3 g/m\({}^{2}\), the effective contact area and quantities of nano-TiO\({}_{2}\) with the car exhaust and ultraviolet also achieved a peak value. After that, the increase of the spray volume only resulted in an even thicker coating that had little effect on improving the effect of degradation on vehicle exhaust gas.  
As can be seen from Figure 9, with the continuous increase in the spraying amount of photocatalytic nano-TiO\({}_{2}\), the degradation efficiency of CO, HC, and NO decreased gradually. This was mainly because a small amount of coating being sprayed on the surface of the slab samples can form a very thin film layer. At this time, most of the nano-TiO\({}_{2}\) could act in its photocatalytic role. However, with the increase of the spraying amount, the thickness of the coating film also increased. Those nano-TiO\({}_{2}\) particles at the bottom of film could not effectively contribute to photocatalytic reactions, resulting in the decrease of degradation efficiency.  
After comprehensive consideration, when the added content of nano-TiO\({}_{2}\) in the coating reached 8%, the photocatalytic coating had the best performance of degradation of the automobile exhaust gas. When the dosage of nano-TiO\({}_{2}\) increased to more than 8%, the ability of photocatalytic degradation exhaust was no longer a definite improvement with the increase of nano-TiO\({}_{2}\). In addition, the photocatalytic coating containing 8% of nano-TiO\({}_{2}\) was evenly sprayed on the slabs for the photocatalytic degradation of the exhaust gas test. It indicated that with the continuous increase of the spraying amount of coating, the photocatalytic degradation property of exhaust gas was gradually improved. However, the performance of the photocatalytic degradation property of exhaust gas basically kept at the same level after the spraying amount was over 333.3 g/m\({}^{2}\).