## 3 Result and Discussion
### Photocatalytic Results
Otherwise, too high a calcination temperature (600 \({}^{\circ}\)C) reduced the degradation activity significantly, although the photocurrent and the EIS radius were comparable to those of the sample calcined at 400 \({}^{\circ}\)C. A diametral effect of high calcination temperature on photocatalytic activity was reported previously [36]. After calcination at 600 \({}^{\circ}\)C, the BET surface area (17.9 m\({}^{2}\cdot\)g\({}^{-1}\)) and pore volume were significantly smaller than those of the materials calcined at 400 or 500 \({}^{\circ}\)C (see Table 2), which significantly reduces the number of photocatalytically active surface sites. Another reason for the lower rate constant of DCF degradation could be the incipient formation of a rutile phase, which forms from the crystalline anatase phase at 600 \({}^{\circ}\)C and which cannot be detected with XRD due to its low content. In this case, sites of this newly formed phase could act as charge carrier traps and/or recombination centers and thus reduce the photocatalytic activity of the TiO\({}_{2}\) calcined at 600 \({}^{\circ}\)C, despite the high crystallinity of the anatase phase. Figure 7 compares the photocatalytic performance of materials synthesized at different temperatures but calcined under identical conditions at 500 \({}^{\circ}\)C. TiO\({}_{2}\) samples synthesized at 70 \({}^{\circ}\)C or 100 \({}^{\circ}\)C exhibit higher activity after calcination than the sample synthesized at 40 \({}^{\circ}\)C. This confirmed that the formed TiO\({}_{2}\) phase is only one of the factors responsible for the photocatalytic activity. A further important parameter which is used to assess the photocatalytic performance of a photocatalyst is the pollutant mineralization, which describes the total oxidation of the pollutant to CO\({}_{2}\) and H\({}_{2}\)O. The mineralization efficiency was established by comparing the TOC value of the starting solution with the TOC content obtained after 120 min of irradiation. The results presented in Figure 8A-C demonstrate that the DCF mineralization is affected by the synthesis temperature as well as by the applied calcination temperature. For materials which were not calcined, the reduction in TOC content resulted from DCF adsorption as well as from its photocatalytic degradation. Although the calcined materials had largely lost the ability to adsorb DCF, the materials calcined at up to 500 \({}^{\circ}\)C had a  
Figure 6: (**A**) Plot of relative DCF concentration versus time for TiO\({}_{2}\) synthesized at 70 \({}^{\circ}\)C and of samples calcined at 400 \({}^{\circ}\)C, 500 \({}^{\circ}\)C or 600 \({}^{\circ}\)C and (**B**) plot for the estimation of the pseudo-first-order rate constant (for B: c\({}_{0}\) = DCF concentration when turning on the light). higher TOC removal rate than the uncalcined samples, indicating faster mineralization, which is caused by photocatalytically initiated reactions and not by adsorption. When the material was synthesized at 70 \({}^{\circ}\)C, a high mineralization efficiency was observed for the uncalcined sample (95%). The highest mineralization (97%) was observed for TiO2 which was synthesized at 70 \({}^{\circ}\)C or 100 \({}^{\circ}\)C and calcined at 500 \({}^{\circ}\)C. Interestingly, the lower BET surface area of the material calcined at 500 \({}^{\circ}\)C compared to that calcined at 400 \({}^{\circ}\)C (see Table 2) indicates that this parameter alone does not determine the photocatalytic performance of the anatase phase. Independent on the synthesis temperature, a calcination at 600 \({}^{\circ}\)C led to a significant decrease in TOC removal. Finally, the photocatalytic stability of the formed anatase phase for the degradation of DCF was examined using the material synthesized at 70 \({}^{\circ}\)C and calcined at 500 \({}^{\circ}\)C. For this reason, the mineralization was observed in four consecutive runs. Between each run, the catalyst was washed with water.