## 3 Results and Discussion  
### Physical and Chemical Properties  
Figure 2 showed the surface morphology of CS and PCS with different particle sizes. The samples were denoted as CS-n and mPCS-n, where m was the coating concentration of TiO\({}_{2}\) absolute alcohol dispersion (m = 1, 4 g/L), n was the particle size of CS (n = 0.1-0.6, 0.6-1.25, 1.25-2.35 mm). No apparent color differences were observed between CS-0.1-0.6 and 1 PCS-0.1-0.6. In addition, 1 PCS-0.6-1.25 was a little whiter than samples without coating. Nevertheless, all PCS of the particle size 1.25-2.35 mm were obviously whiter compared with the control samples without coating, which was consistent with [PERSON]'s study [17]. The change of color was attributed to the light absorption and reflection of TiO\({}_{2}\) particles [22]. As we can see, PCS with TiO\({}_{2}\) dispersion solution concentrations 4 g/L were significantly whiter than that of 1 g/L, which was related to more TiO\({}_{2}\) coating areas and thicker TiO\({}_{2}\) coating layer. The surface topography of PCM with 1, 3, 5 g PCS loaded and interface between PCS and matrix are shown in Figure 2 as well. Figure 2: Surface morphology of photocatalytic ceramics sand and photocatalytic cement materials and the interface of PCS and cement; CS-n and mPCS-n (m was the coating concentration of TiO\({}_{2}\) absolute alcohol dispersion, m = 1–4 g/L, n was the particle size of CS, n = 0.1–0.6, 0.6–1.25, 1.25–2.35 mm); PCM-1, 3, 5 (photocatalytic cement materials with 1, 3, 5 g PCS); PCS: photocatalytic ceramics sand; CS: ceramicside; PCM: Photocatalytic cement material. XRD patterns were applied to explore the crystalline structure of samples. Figure 3 showed the XRD patterns of CS, TiO\({}_{2}\) (P25) and 1 PCS-1.25-2.35 with ultrasonic activation (1 PCS-1.25-2.35-UA) and alkali activated (1 PCS-1.25-2.35-AC). It can be seen that the main components of CS were SiO\({}_{2}\) and Mg\({}_{0.7}\)Fe\({}_{0.23}\)Al\({}_{1.97}\)O\({}_{4}\). Comparing with the XRD pattern of TiO\({}_{2}\), the characteristic peaks of 1 PCS-1.25-2.35-UA occurred at about 20 = 27\({}^{\circ}\) and 44.3\({}^{\circ}\) can be assigned to the Rutile [23]. The characteristic peaks at 20 = 25.3\({}^{\circ}\) can be assigned to the Anatase. The peak of TiO\({}_{2}\) could also be found in 1 PCS-1.25-2.35-AC, but weaker than 1 PCS-1.25-2.35-UA. The XRD suggested that TiO\({}_{2}\) particles were successfully coated on the surface of CS and ultrasonic activation could get more actives sites for combination of CS and TiO\({}_{2}\). SEM images in Figure 4 presented the morphological structure of CS, 4 PCS-1.25-2.35, and 1 PCS-1.25-2.35, respectively. From Figure 4a,b, it can be seen that the pore size of CS mainly ranged from 5 to 50 \(\upmu\)m and there are some small pores under 1 \(\upmu\)m. Some inter-connecting pores were also observed clearly, which could facilitate the coating of TiO\({}_{2}\) and the absorption of gas pollutants. Figure 4c,d showed that TiO\({}_{2}\) was coated on the surface of CS successfully. It can be found TiO\({}_{2}\) was layered homogeneously on the surface of CS and there were abundant small holes among TiO\({}_{2}\) layers, which could contribute to the absorption of gas pollutants. There are three factors to form those structures, including silica-based CS, ultrasonic activation and negative pressure preparation method. These factors were helpful to produce hydroxyl groups on the surface of CS and therefore lead to the formation of Ti-O-Si bonds and the accumulation of TiO\({}_{2}\) particles [24; 25]. TiO\({}_{2}\) particles on the surface of 1 PCS-1.25-2.35 were observed in Figure 4e, which were seen as bright spots. It was confirmed that TiO\({}_{2}\) particles loaded on the surface of CS agglomerated rarely. The observation in Figure 4e was in agreement with the results of EDS in Figure 4f,g. Element Ti could be identified at Area 1 where many bright spots could be observed. Meanwhile, Area 2 contained no Ti had no bright spot.