## 3 Results and Discussion
### Photocatalytic Activity Evaluation
#### 3.5.2 Composition of the Rice Husk Extract after the Photocatalytic Reaction  
Figure 8 displays the TIC obtained for the rice husk extract sample after the photocatalytic reaction. A major portion of the organic compounds consisted mainly of long-chain alkanes molecules and some alcohols. Hence, the photocatalytic reaction promoted biomass conversion and value addition to the rice husk extract by transforming organic compounds present before the reaction, i.e., carboxylic acids, phenols, amines, aldehydes, and ketones, to long-chain alkanes and some alcohols. Figure 8b presents the enlarge view of TIC. Table 2 presents the percentage areas for organic compounds formed after the photocatalytic reaction (1 h) of the rice husk extract with Zn-Fe LDH. Figure 8: (**a**) Total ion chromatogram of the rice husk extract after the photocatalytic reaction and (**b**) enlarged view of (**a**). Figure 9 presents the bar chart of the organic compounds in the rice husk extract after the photocatalytic reaction. These compounds are indicated according to their parental compound. Hence, GC-MS showed that, after the photocatalytic reaction, the rice husk contained 82.62% of long-chain alkanes, 7.83% of alcohols, 0.38% of ketones, 9.17% of other compounds. These compounds were the outcome of many interconnected reactions that took place during the photocatalytic conversion. **Alkanes after the photocatalytic reaction:** Table 2 displays the data relevant to the peaks of alkane-containing compounds after the photocatalytic reaction. The amount of aliphatic compounds was high as compared to that of other compounds detected in the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **RT (min)** & **Name of Compounds Found after Its Photocatalytic Reaction** & **Area (\%)** \\ \hline \multicolumn{4}{c}{**Alkanes after Photocatalytic Reaction**} \\ \hline
1 & 2.18 & 2-methyl Pentane & 12.27 \\ \hline
2 & 2.32 & 3-methyl Pentane & 15.50 \\ \hline
3 & 2.51 & n-Hexane & 30.92 \\ \hline
4 & 2.94 & Methyl Cyclopentane & 15.69 \\ \hline
5 & 3.53 & Cyclohexane & 3.37 \\ \hline
6 & 5.02 & 3,3-Dimethyl-1,2-epoxybutane & 4.87 \\ \hline \multicolumn{4}{c}{**Alcohols after Photocatalytic Reaction**} \\ \hline
7 & 3.06 & 2-methyl 1-Propanol & 2.96 \\ \hline
8 & 4.89 & Tri methyl silyl methanol & 3.49 \\ \hline
9 & 5.08 & 2-methyl 1-Butanol & 1.38 \\ \hline \multicolumn{4}{c}{**Other Compounds in Smaller Quantity after Photocatalytic Reaction**} \\ \hline
10 & 2.27 & Allyl fluoride & 6.43 \\ \hline
11 & 2.77 & Ethyl Acetate & 2.19 \\ \hline
12 & 6.42 & Dihydro-2-methyl 3(2H)-Furanone & 0.38 \\ \hline
13 & 6.55 & Acetic acid, butyl ester & 0.55 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Compounds in the rice husk extract after the photocatalytic reaction. Figure 9: Compounds in the rice husk extract after the photocatalytic reaction. sample after the photocatalytic reaction. Aromatic compounds present in the rice husk extract before the photocatalytic reaction were converted in aliphatic compounds due to the high accessibility of hydrogen radicals [H+] present there [41]. The reactions involved in the photocatalytic conversion are condensation, hydration, dehydration [33], absorption, desorption, recombination, oxidation, reduction, polymerization of compounds, and repolymerization of compounds, as reported by [42]. Here, we observed that, due to the complex reactions in the photocatalytic process within the rice husk extract, it was quite challenging to infer a reaction mechanism that clearly explained all the conversion reactions occurring in photocatalytic reaction of the rice husk extract. However, based on the reported literature [4, 5, 43, 44, 45], it can be presumed herein that a series of reactions involving Bronsted and Lewis acids occurred, resulting in a variety of key products. A proposed mechanism is shown in Figure 10, in which major compounds present in the rice husk extract, are associated with photocatalytic conversion mechanisms in the presence of Zn-Fe LDH.