## 3 Results
### Mechanism of Photocatalytic Degradation  
Experiments were also performed to gain a detailed understanding of the degradation mechanism of TMP during photocatalytic degradation. To achieve this, three different series of experiments were conducted with the lamp switched on:  
1. experiments with the addition of isopropanol to verify the role and action of hydroxyl radicals (\({}^{\bullet}\)OH);
2. experiments with the addition of ammonium oxalate to verify the role and action of superoxide radicals (\({}^{\bullet}\)O\({}_{2}^{-}\));
3. experiments with the addition of triethanolamine to verify the role and action of positive holes (\(h^{+}\)). It was assumed that isopropanol acts as a scavenger of \({}^{\bullet}\)OH radicals, ammonium oxalate acts as a scavenger of superoxide radicals, and triethanolamine acts as a positive hole (\(h^{+}\)) scavenger [41; 42]. The influence of these radical scavengers is shown in Figures 5-7. Additionally, experiments were conducted in the dark, with the lamp switched off, to confirm that the adsorption process of TMP on the film was negligible. Figure 4: Degradation/formation profiles of TMP and its degradation products. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Compound** & **Chemical Formula** & **Chemical Structure** \\ \hline TMP & & \\
[M+H]\({}^{+}\) & C\({}_{14}\)H\({}_{19}\)N\({}_{4}\)O\({}_{3}\) & \\ \(m/z\) 261 & C\({}_{12}\)H\({}_{13}\)N\({}_{4}\)O\({}_{3}\) & \\ \(m/z\) 230 & C\({}_{12}\)H\({}_{14}\)N\({}_{4}\)O & \\ \(m/z\) 123 & C\({}_{5}\)H\({}_{7}\)N\({}_{4}\) & \\ \(m/z\) 109 & C\({}_{4}\)H\({}_{5}\)N\({}_{4}\) & \\ \hline DP-1 & & \\
[M+H]\({}^{+}\) & C\({}_{14}\)H\({}_{19}\)N\({}_{4}\)O\({}_{4}\) & \\ \(m/z\) 289 & C\({}_{14}\)H\({}_{17}\)N\({}_{4}\)O\({}_{3}\) & \\ \(m/z\) 259 & C\({}_{13}\)H\({}_{15}\)N\({}_{4}\)O\({}_{2}\) & \\ \(m/z\) 243 & C\({}_{12}\)H\({}_{11}\)N\({}_{4}\)O\({}_{2}\) & \\ \hline DP-2 & & \\
[M+H]\({}^{+}\) & C\({}_{14}\)H\({}_{17}\)N\({}_{4}\)O\({}_{4}\) & \\ \(m/z\) 289 & C\({}_{13}\)H\({}_{13}\)N\({}_{4}\)O\({}_{4}\) & \\ \(m/z\) 137 & C\({}_{5}\)H\({}_{8}\)N\({}_{4}\)O & \\ \hline DP-3 & & \\
[M+H]\({}^{+}\) & C\({}_{13}\)H\({}_{17}\)N\({}_{4}\)O\({}_{3}\) & \\ \(m/z\) 261 & C\({}_{13}\)H\({}_{17}\)N\({}_{4}\)O\({}_{2}\) & \\ \(m/z\) 246 & C\({}_{13}\)H\({}_{16}\)N\({}_{3}\)O\({}_{2}\) & \\ \(m/z\) 216 & C\({}_{12}\)H\({}_{14}\)N\({}_{3}\)O & \\ \hline DP-4 & & \\
[M+H]\({}^{+}\) & C\({}_{5}\)H\({}_{7}\)N\({}_{4}\)O\({}_{2}\) & \\ \(m/z\) 137 & C\({}_{5}\)H\({}_{5}\)N\({}_{4}\)O & \\ \hline DP-5 & & \\
[M+H]\({}^{+}\) & C\({}_{5}\)H\({}_{7}\)N\({}_{4}\)O & \\ \(m/z\) 96 & C\({}_{4}\)H\({}_{6}\)N\({}_{3}\) & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Tentative structures of photolytic and photocatalytic degradation products of TMP. Figure 5: Degradation of TMP with and without isopropanol. In Figure 5, a significant scavenging effect of isopropanol was observed, as shown by the high C/C\({}_{0}\) ratio. The C/C\({}_{0}\) ratio represents the ratio of the current chromatographic peak area of TMP (which changes over time) to the initial peak area, obtained by the HPLC system with PDA detector, with an initial concentration of 10 mg/L. This ratio is also shown in other Figures 5-7. When ammonium oxalate was added (Figure 6), the degradation mechanism changed, resulting in an accelerated rate of degradation. It seems that superoxide radicals are not the mechanism of TMP degradation. It is possible that the pH increase caused by the addition of ammonium oxalate to the solution led to an increase in the degradation rate, as supported by a 33% increase in the degradation rate constant. Figure 7 shows that the addition of triethanolamine led to a significantly slower reaction, suggesting a significant dependence of the degradation mechanism on the positive holes. According to the data shown in Figures 5-7, it can be concluded that it seems the main mechanisms of the TMP degradation are the acting of \({}^{\bullet}\)OH radicals and oxidizing  
Figure 6: Degradation of TMP with and without ammonium oxalate.