## 3 Results and Discussion
### Photocatalytic Activity
However, in the case of photocatalysts of the PtO/g-C\({}_{3}\)N\({}_{4}\) series, the concentration of hydrocarbons increases with the concentration of CO\({}_{2}\), which leads to a significant decrease in the selectivity of the photocatalytic H\({}_{2}\) production process. For both series of photocatalysts, the amount of ethane released after 90 min increases with cocatalyst loading. At the same time, the amount of ethylene is generally reduced compared to unmodified g-C\({}_{3}\)N\({}_{4}\). During the photocatalytic process, at the first stage, ethanol is oxidized on the photocatalyst surface to acetaldehyde (Equation (2)), which then, under the action of light, decomposes into methane and CO (Equation (3)) [63; 64]. \[\text{C}_{2}\text{H}_{5}\text{OH}+2\text{h}+=\text{CH}_{3}\text{CHO}+2\text{H}^ {+} \tag{2}\]  
\[\text{CH}_{3}\text{CHO}=\text{CH}_{4}+\text{CO} \tag{3}\]  
Simultaneously, on the surface of the photocatalyst, the H\({}^{+}\) reduction process occurs with the formation of H\({}_{2}\). Dehydration of ethanol leads to the formation of a small amount of ethylene (Equation (4)), which is then hydrogenated to form ethane (Equation (5)):  
\[\text{C}_{2}\text{H}_{5}\text{OH}=\text{C}_{2}\text{H}_{4}+\text{H}_{2}\text{O} \tag{4}\]  
\[\text{C}_{2}\text{H}_{4}+\text{H}_{2}=\text{C}_{2}\text{H}_{6} \tag{5}\] \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Photocatalyst**} & \multicolumn{6}{c}{**Product Amount, \(\mu\)mol**} & \multirow{2}{*}{**S (H\({}_{2}\)), \%**} \\ \cline{2-2} \cline{5-8}  & **H\({}_{2}\)** & **CO** & **CO\({}_{2}\)** & **CH\({}_{4}\)** & **C\({}_{2}\)H\({}_{4}\)** & **C\({}_{2}\)H\({}_{6}\)** & **C\({}_{2}\)H\({}_{6}\)** \\ \hline g-C\({}_{3}\)N\({}_{4}\) & 0.19 & 0.03 & 0.23 & 0.01 & 0.05 & 0 & 36.3 \\
0.5\% Pt/g-C\({}_{3}\)N\({}_{4}\) & 18.6 & 0.02 & 0.15 & 0.01 & 0.01 & 0.01 & 98.9 \\
2\% Pt/g-C\({}_{3}\)N\({}_{4}\) & 17.1 & 0.01 & 0.14 & 0.06 & 0 & 0.02 & 98.7 \\
5\% Pt/g-C\({}_{3}\)N\({}_{4}\) & 18.8 & 0.02 & 0.12 & 0.19 & 0 & 0.06 & 98.0 \\
0.5\% PtO/g-C\({}_{3}\)N\({}_{4}\) & 12.6 & 0.01 & 0.25 & 0.04 & 0.01 & 0.05 & 97.2 \\
2\% PtO/g-C\({}_{3}\)N\({}_{4}\) & 10.3 & 0.01 & 0.29 & 0.08 & 0 & 0.10 & 95.5 \\
5\% PtO/g-C\({}_{3}\)N\({}_{4}\) & 6.6 & 0 & 0.38 & 0.08 & 0.06 & 0.17 & 90.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Reaction products in the gas phase after 90 minutes of the light irradiation. It should be noted that the rate of hydrogen formation on composite photocatalysts significantly exceeds the rate of formation of hydrocarbons. Thus, it can be concluded that the decomposition of acetaldehyde and the dehydration of water occur to a small extent. The rate of H\({}_{2}\) evolution as well as of selectivity in the presence of the photocatalysts considered in this work, compared to some platinized ones reported in the literature, are shown in Table 3.  
The activity of the photocatalysts synthesized in this work does not exceed the values reported in the literature for CdS and TiO\({}_{2}\)-based photocatalysts; however, it is at the level of Nb\({}_{2}\)O\({}_{5}\) and WO\({}_{3}\)-based photocatalysts. It is also worth noting that the selectivity of the hydrogen evolution process exceeds the value presented in the literature for platinized TiO\({}_{2}\).