## 3 Results and Discussion
### Photocatalytic Performance
Figure 8: Photocatalytic activity of PCS to benzene; **(a)** 1 PCS-n-UA (PCS with ultrasonic activation, n = 0.1–0.6, 0.6–1.25, 1.25–2.35 mm), 1 PCS-1.25–2.35-AC (PCS alkali activated), surface coating (the mortars with TiO\({}_{2}\) on the surface), surface coating-1 month (the mortars with TiO\({}_{2}\) on the surface after 1 month of atmospheric environment exposure), Incorporation (the mortars with TiO\({}_{2}\) incorporated) and TiO\({}_{2}\) (P25); **(b)** different TiO\({}_{2}\) coating concentrations. Figure 7: Preparation and catalytic mechanism of PCS. Figure 9 revealed that 4 PCS-1.25-2.35 still presented excellent photocatalytic effect after being loaded on the surface of cement materials. As we can see, the adsorption of benzene on surface of mortars without photocatalysts hardly had influence on experiment compared to the photocatalytic effect of samples. It was demonstrated that the surface pores of PCS played an important role in photocatalytic reaction. The presence of PCS increased the reaction area and the loading contents of TiO\({}_{2}\) particles, which were beneficial to improve the photocatalytic efficiency. The photocatalytic activity of PCM increased with the increase of PCS on the surface of PCM from 1 g to 5 g because the photocatalysts on the surface of PCSs were not covered by cement materials and hydration products and had no agglomeration problem. The PCM still remained high photocatalytic activities after exposure to the natural environment for 6 months (which is marked by PCM-5-6 months) which is more stable than Surface coating. It is because that the chemical bond (Si-O-Ti) between TiO\({}_{2}\) and CS could prevent TiO\({}_{2}\) particles from peeling from PCS. On the other hand, TiO\({}_{2}\) coated on the surface of CS was influenced slightly by the envelope of cement hydration products and the carbonation of cement. However, the prepared PCM was washed and brushed repeatedly for 6 months, and the slight coverage of macro-particles was unavoidable in atmospheric environment exposure, which could slightly decrease the photocatalytic activity of specimen [30]. The resusability performance of catalyst is also an important parameter to evaluate the long-term catalytic performance of photocatalytic material in practical application. Figure 10 showed that time of fully degradation of 2 \(\upmu\)L benzene by PCS with different TiO\({}_{2}\) concentrations and control group. All PCSs still presented excellent photocatalytic activity after being reused for 10 cycles. This might be due to the good stability of substrate and the large bonding force between TiO\({}_{2}\) and CS. The control group (Surface coating) showed decreased photocatalytic effects during the cycle experiment. This might be because that high surface energy of TiO\({}_{2}\) and low specific surface area of mortar caused the agglomeration of TiO\({}_{2}\) particles, which could lead to more recombination of electron-hole and difficulties for TiO\({}_{2}\) particles to be exposed to the photocatalytic reaction. Comparing with the previous studies [22; 31], our material had an excellent long-term photocatalytic performance with higher retention rate for photocatalytic activity. The reason was that the structures of porous PCS provided higher specific surface area and more gas diffusion channels than cementitious materials and prevented TiO\({}_{2}\) particles from being affected seriously by the envelope of cement hydration products  
Figure 9: Photocatalytic activity of PCM and mortars without photocatalysts to benzene; PCM-1, 3, 5 (photocatalytic cement materials with 1, 3, 5 g 4 PCS-1.25–2.35). and the carbonation of cement [32], which improved the reacting areas, utilization rate of catalysts, and enhanced the photocatalytic activity effectively.