## 3 Results and Discussion
### Physical and Chemical Properties
The result of EDS showed that TiO\({}_{2}\) had deposited on the surface of PCS successfully. BET was applied to explore the specific surface area of samples. As shown in Table 3, the specific surface area of CS and mortars are 0.0770 m\({}^{2}\)/g and 0.0013 m\({}^{2}\)/g, respectively. The specific surface area of CS is much higher than that of mortars. Figure 3: X-ray diffraction patterns of CS, TiO\({}_{2}\) (P25), 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). Figure 5 and Table 4 showed the pore size distribution, total porosity and available pore volume for all PCS samples. Figure 5a revealed that PCS exhibited a pore size distribution mostly in the range of 1-100 \(\upmu\)m, with a small amount of pores from 10 to 1000 nm. The pores distributed in the range of 10-1000 nm increased with the increase of the PCS particle size while the pores distributed in the range of 1-100 \(\upmu\)m decreased with the increase of the PCS particle size. In other words, when CS was crushed into smaller pieces, many small pores of CS were lost but the amount of larger pores increased. This might be because some small pores at section were destroyed through the crushing, while some larger closed pores turned to open. Therefore the CS with small particle size had higher total porosity and pore volume than larger ones (as shown in Table 4). More big pores, higher porosity and pore volume might cause the waste of TiO\({}_{2}\) particles, because the TiO\({}_{2}\) particles at the bottom of the pores could not accept the light. In addition, big pores were nearly useless to gas diffusion compared with small ones. Figure 5b showed the similar pore distribution curves for the samples prepared with different TiO\({}_{2}\) coating concentrations. The pore volumes of PCS with different TiO\({}_{2}\)  
Figure 4: Surface morphology and EDS of CS and PCS; (**a,b**) surface morphology of CS-1.25-2.35; (**c,d**) surface morphology of PCS (4 PCS-1.25-2.35); (**e**–**g**) surface morphology and EDS patterns of PCS (1 PCS-1.25-2.35); EDS: energy dispersive spectrometer. \begin{table}
\begin{tabular}{c c} \hline \hline
**CS (m2/g)** & **Mortars (m2/g)** \\ \hline
0.0770 & 0.0013 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: BET results of CS and mortars. coating concentrations had few changes, corresponding to the results of Figure 5b. With the increasing of TiO\({}_{2}\) coating concentrations, the pores between 90 \(\upmu\)m and 100 \(\upmu\)m reduced slightly while the pores in the range of 1-1000 nm increased. This phenomenon can be attributed to the formation of TiO\({}_{2}\) layer provided many small pores and reduced the pore size of some big pores. According to the above results, it can be inferred that PCS-1.25-2.35 might possess more excellent photocatalytic performance due to appropriate pore structure (more pores in the range of 10-1000 nm, relatively lower total porosity and pore volume), which could provide an excessive exposure of TiO\({}_{2}\) and more gas diffusion channels. Figure 5: The pore distribution of all PCS samples; (**a**) 1 PCS-n, (n = 0.1\(\sim\)0.6, 0.6\(\sim\)1.25, 1.25\(\sim\)2.35 mm); (**b**) mPCS-1.25–2.35, (m = 1, 2, 3, 4, 5 g/L). In order to further identify the chemical composition of PCS before and after TiO\({}_{2}\) loading, XPS analysis was carried out. The XPS spectra survey patterns of Mg, Fe, O, Ti, C, Si, and Al peaks are showed in Figure 6a, indicating the elemental components and their chemical states of PCS, which are consistent with the XRD results. The C1s peak correspond to organic and inorganic carbon, which represent the pollution peak. The O1s characteristic peaks can be deconvoluted into four peaks at 529.6, 530.8, 531.9 and 532.5 eV, which can be assigned to Ti-O-Ti, Al-O-Al, Ti-O-Si and Si-O-Si, respectively [26]. The Al-O-Al bonds might be caused by the calcination of CS [27]. The bonding of titanium and silicon (Ti-O-Si) is supported by peaks centered at 531.6 eV, formed by the combination of Ti-O-H bond and Si-O-H bond.