## 4 Efficacy Studies for Water
### Reusability of Synthesized Nano-Silica  
In Table 4, we provided the relevant information for the reusability analysis of nanoparticles. It was critical to articulate how the produced nanoparticles may be used in a sustainable manner. Experiments on reusability were carried out to see how many times each nanoparticle might be reused. When compared to non-reusable sorbents, reusable sorbents offer a much higher economic return value. In our study, the nanoparticles NS and NZ were utilized five times in a row. Nanoparticles were desorbed in n-Hexane after each usage to thoroughly eliminate any petroleum and then rinsed with distilled water before being used again.  
The nanoparticles' effectiveness decreased after the fourth cycle, indicating that they may be safely reused four times. To be categorized as a sustainable material, a material must fulfill certain reusability standards. Reusable sorbents are more cost-effective and easier to use since they may be reused repeatedly [75; 76; 77]. The rate of efficiency of magnetic nano-silica after five uses indicated that the adsorbent remained consistently potent after four uses, but the percentage of sorption reduced after the fifth use.  
Further investigations show that acetic acid is the best solvent for desorption in reusability testing. Desorption studies were carried out by dissolving the depleted NS in acetic acid and stirring the solution for 70 min at 35 \({}^{\circ}\)C in a water bath and this technique  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Nano-Silica** & **First Use** & **Second Use** & **Third Use** & **Fourth Use** \\ \hline Barley-grass-synthesized & 90\% & 90\% & 90\% & 90\% \\ nano-amorphous silica & & & & \\ Wheatgrass-synthesized & 85\% & 85\% & 85\% & 75\% \\ nano-amorphous silica & & & & \\ Barley-husk-grass- & & & & \\ synthesized & 90\% & 90\% & 90\% & 90\% \\ nano-amorphous silica & & & & \\ Barley-grass-synthesized & & & & \\ nano-amorphous silica & 85\% & 85\% & 85\% & 85\% \\ (magnetic) & & & & \\ Rice-husk-synthesized & 90\% & 90\% & 90\% & 85\% \\ nano-amorphous silica & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Reusability results of nanoparticles from different sources.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Nanoparticle** & **Removal Efficiency** & **Equilibrium Time** & **Kinetic Model** & **Isotherm** & **Contaminant** & **Reference** \\ \hline Barley-grass-synthesized & 90\% & 65 min & 1 st Order & Freundlich & Nickel & [19] \\ nano-amorphous silica & & & & & \\ Wheatgrass-synthesized & 85\% & 65 min & 1 st Order & Freundlich & Nickel & [19] \\ barley-husk-grass-synthesized & & & & & \\ synthesized & 90\% & 60 min & 2 nd Order & Langmuir & Diesel oil & [30] \\ nano-amorphous silica (hydrophobic) & & & & & \\ Barley-grass-synthesized & 85\% & 12 min & 2 nd Order & Langmuir & Petrol & [20] \\ nano-amorphous silica (magnetic) & & & & & \\ Rice-husk-synthesized & 90\% & 25 min & - & - & Nickel & [18] \\ nano-amorphous silica & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Results from the applications of nano-silica particles from different sources.  
was repeated after each use of fresh acetic acid. After four cycles, the reusability efficiency declined slightly for wheat- and rice-husk-synthesized nano-silica after the fourth use while remaining the same for nano-silica from other sources. The number of cycles reflects each use after desorption, and the percentage of sorption efficiency for NS-B and NS-W remained impressive from reuse cycles 1 to 8, with 95-91% and 82-77% sorption, respectively.