## 3 Results and Discussion
### Proposed Mechanism of Oxidative Degradation of Ethanol Under Simulated Solar Light  
Light-activated photocatalysts generate electrons and holes that, after reaching the catalyst surface, can display a variety of photoredox reactions [35; 37; 38; 79; 80; 81]. In our case, the photocatalytic oxidative degradation of ethanol produces intermediates (acetaldehyde and formic acid) and end-products (carbon dioxide). The ability of the investigated materials to produce reactive oxygen species (specifically hydroxyl radical -OH and superoxide anion radical -O\({}_{2}\)\({}^{-}\)) was checked, with only the presence of superoxide anion radical being confirmed (Figure 14). A significant number of photocatalysts, including those based on TiO\({}_{2}\), are active, especially under UV or near-UV light irradiation [37; 38; 82], with their efficiency also being decreased by charge recombination [83]. In order to increase the photocatalyst activity and extend the absorption wavelength range, noble metal doping was performed. In the present experiment, the oxidative degradation of ethanol (CH\({}_{3}\)CH\({}_{2}\)OH) under AM1.5 irradiation on pure and Pt-modified La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) follows a photocatalytic mechanism involving the generation of electron-hole pairs. The reaction pathway includes the oxidation of ethanol to acetaldehyde (CH\({}_{3}\)CHO) followed by further oxidation to carbon dioxide (CO\({}_{2}\)), with formic acid (HCOOH) detected as a minor intermediate. Below is the detailed mechanism:  
1. The process of photon absorption and charge separation (Equation (1)), according to the literature [18; 84], can be described as follows: \[\text{La}_{2}\text{Ti}_{2}\text{O}_{7}+\text{h}\text{v}\rightarrow\text{e}^{-} +\text{h}^{+}\] (1)
2. Pt-modifying role--Platinum (Pt) enhances charge separation by trapping electrons and reducing recombination (Equation (2)), leading to more efficient ethanol oxidation and CO\({}_{2}\) formation [35; 86; 85] and promoting the adsorption and reduction of the oxygen (Equation (3)). \[\text{Pt}+\text{e}^{-}\rightarrow\text{Pt}^{-}\] (2) \[\text{O}_{2}+\text{e}^{-}\rightarrow\text{O}_{2(\text{ads})}^{-} \rightarrow[\text{O}](\text{activeoxygen})\] (3)
3. Oxidative degradation of ethanol by photogenerated holes--ethanol is oxidized by holes (h\({}^{+}\)) to form the ethoxy radical (CH\({}_{3}\)CH\({}_{2}\)O-) (Equation (4)) and this undergoes further oxidation, yielding acetaldehyde (CH\({}_{3}\)CHO) (Equations (4)-(6)). Acetaldehyde is also oxidized by holes to generate formic acid (HCOOH) in trace amounts, finally leading to CO\({}_{2}\) (Equations (7) and (8)) [37; 87; 88; 89; 90; 91]. \[\text{CH}_{3}\text{CH}_{2}\text{OH}+\text{h}^{+}\rightarrow\text{CH}_{3}\text{CH }_{2}\text{O}\cdot+\text{H}^{+}\] (4) \[\text{CH}_{3}\text{CH}_{2}\text{O}\cdot+[\text{O}]\rightarrow\text{CH}_{3} \text{CH}_{2}\text{O}\cdot\] (5) \[\text{CH}_{3}\text{CH}_{2}\text{O}\cdot+\text{h}^{+}+\text{e}^{-} \rightarrow\text{CH}_{3}\text{CHO}+\text{H}_{2}\text{O}\] (6) \[\text{CH}_{3}\text{CHO}+[\text{O}]\rightarrow\text{HCOOH}+\text{H}_{2}\text{O}\] (7) \[\text{HCOOH}+[\text{O}]\rightarrow\text{CO}_{2}+\text{H}_{2}\text{O}\] (8) \[\text{CH}_{3}\text{CH}_{2}\text{OH}\xrightarrow{\text{slowly}}\text{CH}_{3} \text{CHO}\rightarrow\text{HCOOH}\xrightarrow{\text{rapidly}}\text{CO}_{2}\] (d) Photogenerated electrons (e\({}^{-}\)) can reduce protons (H\({}^{+}\)) to form molecular hydrogen (H\({}_{2}\)) (Equation (9)) [92]. \[2\mathrm{H}^{+}+2\mathrm{e}^{-}\to\mathrm{H}_{2} \tag{9}\]  
This mechanism demonstrates how ethanol undergoes oxidative degradation in the gaseous phase when exposed to simulated solar light. The literature data present the use of La\({}_{2}\)Ti\({}_{2}\)O\({}_{7}\) mostly for a liquid phase reaction targeting the hydrogen evolution and water depollution by organic compound degradation, especially for dyes [93; 94]. [PERSON] et al.