# TiO2 Modified Geopolymers for the Photocatalytic Dye Decomposition
## 3 Results and Discussion
### Photocatalytic Activity
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Peak Area**} & \multicolumn{3}{c}{**Area Ratio**} & \multirow{2}{*}{**Amorphous**} \\ \cline{2-2} \cline{4-6}  & **(101)** & **(101)** & **(104)** & **Anatase/** & **Anatase/** & **Phase Proportion, wt.\%** \\ \hline GP & 2.2 & 1.7 & 3.3 & 1.3 & 0.7 & 66–69 \\ \hline GP-P25 & 10.3 & 2.4 & 3.8 & 4.3 & 2.7 & 63–65 \\ \hline GP-CG100 & 10.5 & 2.2 & 3.1 & 4.8 & 3.4 & 62–64 \\ \hline GP-CG300 & 2.6 & 2.1 & 3.1 & 1.2 & 0.8 & 67–69 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The peak areas and the peak-area ratios in powder X-ray diffraction patterns for the parent geopolymer matrix and the incorporated photocatalysts. The decomposition rate (calculated in the similar way as X) as-measured and corrected by the absorption of the RhB dye by the geopolymer porous structure difference for the GP-P25 photocatalyst during the illumination is shown in Figure 7. After 120 min of illumination, the as-measured and corrected decomposition rate for the GP-P25 photocatalyst were 22.5 and 18%, respectively. The text below discusses only the corrected decomposition rate of the photocatalysts marked with the photocatalytic activity X, evaluated for pure TiO\({}_{2}\) or the counterparts incorporated into the parent GP as in the case of GP-P25. Figure 8A summarizes the photocatalytic activity X (%) during the illumination for as-supplied pure TiO\({}_{2}\) photocatalysts (P25, CG100, CG300), the parent geopolymer matrix (GP) and a mechanical mixture of the parent geopolymer with the addition of 3 wt.% of TiO\({}_{2}\) P25 (MM-GP-P25). The photocatalytic activity of the parent geopolymer matrix (Figure 8A) is much lower in comparison with the other materials, of only X \(\approx\) 1.4 % after 120 min of illumination. This is in accordance with the literature as the photocatalytic mechanism in geopolymers is usually extrinsic [59]. On the other hand, the commercially used pure TiO\({}_{2}\) P25 photocatalyst reached X = 98.6% within as early as 15 min under the given illumination conditions (see Figure 8A). Furthermore, pure CG100 and CG300 photocatalysts reached the comparable photocatalytic activity (X) of 87.0 and 82.5%, respectively, but only after 120 min of illumination. The reasons for the different photocatalytic activity of the pure photocatalyst may be as follows: (i) even though CG100 and CG300 photocatalysts consist of only pure anatase, P25 also contains 13 wt.% of the rutile phase (see Figure 1 and the corresponding text); and (ii) there are significant differences in the average particle size and the specific surface area between individual photocatalysts (see Table 4A). According to the literature data [9; 10; 11; 60; 61], all of these properties could have an effect on the photocatalytic activity of the photocatalyst. The different manufacturing method for the pure TiO\({}_{2}\) P25 in  
Figure 6: The change of RhB dye absorbance spectra during (**A**) the illumination by UV photons generated at \(\lambda\) = 360 nm (using a filter transmitting in the range of 320–410 nm) and 50% of total light source intensity or (**B**) without the illumination in the presence of the GP-P25 photocatalyst. Figure 7: The time dependence of the as-measured/corrected decomposition rate for the GP-P25 photocatalyst. The lines are included as a mere eye guide. comparison with CG100 and CG300 photocatalysts (see Table A1 and the results of LOI) could also influence their photocatalytic activity. Furthermore, the mechanical mixture (MM-GP-P25) of the parent geopolymer with the addition of 3 wt.% of TiO\({}_{2}\) P25 also had an almost comparable X, of 77.0% after 120 min of illumination. This mechanical mixture (MM-GP-P25) was prepared for comparison as the pure TiO\({}_{2}\) P25 powder exhibited the highest photocatalytic activity.