## 2 Results and Discussion
### Photocatalytic Performance of TiO\({}_{2}\), TC and PPTC
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Photocatalyst**} & **Brunauer Emmett Teller** & **Langmuir** & **Total Pore Volume of** & **Average Adsorption** \\  & **(BET) Multi-Point** & **Single-Point** & **Single-Point** & **Pore Size (nm)** \\  & **Contact (m\({}^{2}\)/g)** & **Contact (m\({}^{2}\)/g)** & **Adsorption (cm\({}^{3}\)/g)** & **Average Adsorption** \\ \hline TiO\({}_{2}\) & 61.9 & 93.7 & 0.3 & 19.5 \\ TC & 385.4 & 594.7 & 0.4 & 4.7 \\ PPTC & 486.7 & 693.6 & 0.5 & 4.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specific surface area of TiO\({}_{2}\), TC, and PPTC. Figure 7: Fluorescence spectra of TiO\({}_{2}\), TC, and PPTC. Usually, the photocatalyst with a high adsorption capacity often has more opportunities to contact the organic pollutant, and the degradation of the organic pollutant is closely related to the adsorption capacity of the photocatalyst. Table 3 summarizes the photocatalytic degradation rates of several organic compounds under the catalysis of TiO\({}_{2}\), TC, and PPTC without illumination and under the irradiation of simulated sunlight (Xe lamp). It can be seen that the three photocatalysts can all photocatalytic the degradation of DMF, methyl orange, methylene blue, and phenol well, and PPTC has better photocatalytic activity than TiO\({}_{2}\) and TC. Particularly, PPTC can adsorb the organic pollutants more efficiently than TiO\({}_{2}\) and TC, which corresponds well to its better photocatalytic activity for the degradation rate of the tested organic pollutants. This could be because PPTC exhibits larger specific surface area and total pore volume than TiO\({}_{2}\) and TC, which corresponds to an increased contact area with the organic pollutants [22; 24]. Further research in this respect is underway. The photocatalytic performance of a photocatalyst is highly dependent on its light response range and adsorption capacity that are related to free radical intensity [25; 26; 27]. Here we measure the ESR spectra of various photocatalysts to estimate the intensities of superoxide free radical (O\({}_{2}\) ), singlet oxygen (\({}^{1}\)O\({}_{2}\)), and hydroxyl radical (OH), hoping to better understand the photocatalytic mechanisms of the as-prepared photocatalysts. As shown in Figure 9, the superoxide free radical intensities of TC and PPTC are nearly identical and higher than that of TiO\({}_{2}\), which indicates that doping Cu\({}^{2+}\) into TiO\({}_{2}\) increases the activity of the photocatalyst and improves its photocatalytic ability for the degradation of the organic pollutants. The H\({}_{2}\)-TPR results of Figure 10 reveal the reduced temperature of the Ti element from TiO\({}_{2}\) by hydrogen is clearly higher than those of TC and PPTC. This could be explained by the supposition that Cu\({}^{2+}\) ions doped into TiO\({}_{2}\) increase the activity of the photocatalyst and produce free radicals, as evidence by relevant ESR results. Moreover, the incorporation of the TC composite into the pores of PP contributes to an increasing contact area between the photocatalyst and organic pollutants, thereby improving the adsorption capacity of the photocatalyst and enhancing the degradation of the organic pollutants (see Table 3). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Photocatalyst**} & \multicolumn{3}{c}{**Degradation Rate of DMF**} \\ \cline{2-4}  & **No Light** & **Xenon Light** & **Sunlight** \\ \hline PPTC & 26.0\% & 73.7\% & 64.0\% \\ TC & 21.2\% & 65.4\% & 57.6\% \\ TiO\({}_{2}\) & 6.5\% & 52.8\% & 48.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Degradation rate of DMF catalyzed by photocatalysts without illumination and under irradiation of simulated sunlight (Xe lamp) or real sunlight. Figure 8: Photocatalytic degradation rate of DMF as a function of recycling number of TiO\({}_{2}\), TC, and PPTC.