## 3 Results and Discussion
### Photocatalytic Activity Tests
#### 3.3.2 BTEX Decomposition  
The photocatalytic activity was evaluated during BTEX decomposition. The mixture of benzene, toluene, ethyl benzene and xylenes were used. The obtained results in Figure 5 were presented. Initially, the gas mixture was passed through the reactor for 10 min to achieve the complete filling of the reactor space with the gas. After 10 min, the outlet and inlet of the gases was closed. A Smart SPME Arrow was introduced into the gas reactor and for 2 min the gases were sorbed on the bed. After 2 min, the Smart SPME Arrow was  
Figure 4: The final setting time of the modified clinkers.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multicolumn{3}{c}{**NO Decomposition [\%]**} \\ \cline{2-3}  & **1 ppm** & **0.2 ppm** \\ \hline Clinker & 2.0 & 2.7 \\
300/1 & 3.7 & 5.9 \\
300/3 & 5.2 & 7.0 \\
300/5 & 3.0 & 7.8 \\
600/1 & 5.0 & 6.0 \\
600/3 & 7.4 & 7.8 \\
600/5 & 8.3 & 9.5 \\
700/5 & 6.0 & 14.4 \\
800/1 & 4.8 & 7.6 \\
800/3 & 5.5 & 5.0 \\
800/5 & 5.1 & 10.9 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Photocatalytic decomposition of NO with an initial concentration of 1 and 0.2 ppm under UV light irradiation.  
inserted into the chromatograph injector and subjected to 1 min of desorption. The mass detector was used to measure gases concentration, obtained values were marked as the initial concentration, marked on the graph as 100%. Then, two plates made of unmodified clinker were placed in the reactor and the procedure of filling the reactor with gases and the procedure of determining the concentration with Smart SPME Arrow were repeated. As can be seen in Figure 5, ethyl benzene and xylenes have been adsorbed on the surface of the unmodified clinker in the amount of 7% and 13%, respectively. After adsorption studies, studies on photolysis in the presence of unmodified clinker and photocatalysis in the presence of modified clinker were started. After 10 min of UV light irradiation, as it can be seen in Figure 5, there was a partial desorption of gases from the clinker surface, which is particularly visible in the case of ethyl benzene, whose concentration increased by 4%. In addition, it can be noted that after switching on UV radiation, partial photolysis of gases (ethyl benzene and xylenes were decomposed) occurred, as there was a clear increase in the concentration of benzene (by 21%) and toluene by (27%). Since research on the breakdown of BTEX is expensive, only one material has been selected for these tests, which has the highest applicability. It is a material that was created because of the addition of 5 wt% amorphous TiO\({}_{2}\) to cement clinker at a temperature of 700 \({}^{\circ}\)C. As can be seen in Figure 5, after 10 min of irradiation, the level of ethyl benzene (by 37%) and xylene (by 62%) was significantly reduced. There was an increase in benzene concentration (by 25%), the level of toluene remained unchanged. These results mean that in the process of photocatalysis, the ethyl group of ethyl benzene and methyl group of xylenes broke off, which resulted in an increase in the concentration of benzene. The increase in benzene concentration is not proportional to the decrease in ethylbenzene and xylenes concentrations. Benzene can be oxidized, the formation of phenol, benzoquinone, and hydroquinone certainly also occurred. When the benzene ring is decomposed the formation of such products as CO\({}_{2}\) and CO occurs [13; 14].