## 4 Conclusions  
Fly ash is a solid waste generated in the combustion of coal. A strategy proposed to prevent environmental pollution is to use FA in wastewater environmentally friendly applications, such as photocatalysis. The majority of raw FA consists of numerous metal oxides such as silica (SiO\({}_{2}\)), alumina (Al\({}_{2}\)O\({}_{3}\)), calcium oxide (CaO), magnesium oxide (MgO), iron oxide (Fe\({}_{2}\)O\({}_{3}\)), and titania (TiO\({}_{2}\)) with good photocatalytic activity. In this work, considering the intelligent management of fly ash, this raw material was used in ternary TiO\({}_{2}\)-Cu\({}_{x}\)S-FA heterostructure with application in advanced wastewater treatment. The TiO\({}_{2}\)-Cu\({}_{x}\)S-FA heterostructures give the possibility to get simultaneous adsorption and photocatalytic unit operations in a single reactor. The modelling of such a system must adequately take into account the dual functionality of materials, to set linking between adsorption and photodegradation mechanisms. The comparison between the adsorption and photodegradation tests performed with TiO\({}_{2}\)-Cu\({}_{x}\)S-FA with different TiO\({}_{2}\) ratios showed that in dark conditions, the methylene blue removal was 75% after 360 min, while in the presence of UV light, the efficiency was 96% after the same treatment period. The degradation rate of MB, when H\({}_{2}\)O\({}_{2}\) is used as an electron acceptor, could reach 90% in adsorption and 99% in combined adsorption/photocatalysis processes. The adsorption isotherm was found to follow the [PERSON] and Freundlich models. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Adsorbat**} & \multirow{2}{*}{\begin{tabular}{c} **adsorbent** \\ **System** \\ \end{tabular} } & \multicolumn{4}{c}{**Langmuir Adsorption Isotherm**} & \multicolumn{4}{c}{**Freundlich Adsorption Isotherm**} \\ \cline{3-10}  & & \begin{tabular}{c} **qmax** \\ **(mg/g)** \\ \end{tabular} & \begin{tabular}{c} **K\({}_{\rm L}\)** \\ **(I/mg)** \\ \end{tabular} & \begin{tabular}{c} **Correlation** \\ **Coefficient (R\({}^{2}\))** \\ \end{tabular} & \begin{tabular}{c} **Separation** \\ **Factor (S\({}_{\rm F}\))** \\ \end{tabular} & \
\begin{tabular}{c} **(I/n)** \\ **(mg/g)/(mg/L)** \\ \end{tabular} &
\begin{tabular}{c} **K\({}_{\rm F}\)** \\ **R\({}^{2}\)** \\ \end{tabular} \\ \hline \multirow{10}{*}{\(\text{TiO}_{2}\):FA} & Fly 1 & 0.34316 & 0.95091 & 0.81714 & 0.20859 & 1.008 & 1.752 & 0.84752 \\ \cline{2-10}  & Fly1/H\({}_{2}\)O\({}_{2}\) & 0.61348 & 1.64123 & 0.93782 & 0.13248 & 1.551 & 1.488 & 0.93372 \\ \cline{2-10}  & Fly 2 & 0.36597 & 8.31400 & 0.96815 & 0.02926 & 0.805 & 1.502 & 0.97459 \\ \cline{2-10}  & Fly2/H\({}_{2}\)O\({}_{2}\) & 0.46289 & 5.31114 & 0.87451 & 0.04506 & 1.426 & 3.464 & 0.81278 \\ \cline{2-10}  & Fly 3 & 0.39512 & 1.10957 & 0.85531 & 0.18426 & 1.113 & 2.543 & 0.88178 \\ \cline{2-10}  & Fly3/H\({}_{2}\)O\({}_{2}\) & 0.43805 & 0.90199 & 0.87311 & 0.21744 & 1.272 & 2.456 & 0.87442 \\ \hline \multirow{2}{*}{Sample A10} & Fly1-Cu\({}_{x}\)S & 0.29346 & 0.76514 & 0.89664 & 0.24674 & 0.746 & 1.906 & 0.92464 \\ \cline{2-10}  & Fly1-Cu\({}_{x}\)S/H\({}_{2}\)O\({}_{2}\) & 0.79888 & 2.75445 & 0.94830 & 0.08340 & 2.458 & 3.824 & 0.88054 \\ \hline \multirow{2}{*}{Sample B10} & Fly2-Cu\({}_{x}\)S & 0.21061 & 2.19786 & 0.95273 & 0.10236 & 0.516 & 2.016 & 0.97168 \\ \cline{2-10}  & Fly2-Cu\({}_{x}\)S/H\({}_{2}\)O\({}_{2}\) & 0.47047 & 0.44766 & 0.94939 & 0.35892 & 1.071 & 6.958 & 0.95102 \\ \hline \multirow{2}{*}{Sample C10} & Fly3-Cu\({}_{x}\)S & 0.36371 & 1.20442 & 0.90034 & 0.17225 & 0.928 & 2.196 & 0.9175 \\ \cline{2-10}  & Fly3-Cu\({}_{x}\)S/H\({}_{2}\)O\({}_{2}\) & 1.02334 & 0.35541 & 0.97737 & 0.41355 & 3.303 & 2.939 & 0.91938 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Isotherm data for the adsorption of methylene blue (MB) on the ternary heterostructures (TiO\({}_{2}\)–Cu\({}_{x}\)S–FA) and TiO\({}_{2}\):FA composites.