## 4 Conclusions  
The sustainable, eco-friendly, cost-effective, and magnetic responsive nanocomposite was synthesized to remove dissolved oil in wastewater. Hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)) nanoparticles were incorporated into rGO to prepare the magnetic nanohybrid composite. The magnetic nanocomposite (rGO-Fe\({}_{2}\)O\({}_{3}\)) was developed using a one-step hydrothermal method with 47 wt.% iron oxides. The batch and column adsorption tests were carried out under different industrial conditions to evaluate the adsorption capacity of the prepared nanocomposite \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Cycle (n)**} & \multicolumn{2}{c}{**rGO-Fe\({}_{2}\)O\({}_{3}\)-NC**} & \multicolumn{2}{c}{**GO [9]**} \\ \cline{2-5}  & **q\({}_{e,n}\) (mg/g)** & **q\({}_{e,n}\)/q\({}_{e,1}\) (\%)** & **q\({}_{e,n}\) (mg/g)** & **q\({}_{e,n}\)/q\({}_{e,1}\) (\%)** \\ \hline
1 & 1279 & 100\% & 1140 & 100\% \\
2 & 1208 & 94\% & 1138 & 99.8\% \\
3 & 1002 & 83\% & 904 & 79\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Regeneration effects on adsorption capacity of rGO-Fe\({}_{2}\)O\({}_{3}\)-NC in comparison to GO. Figure 5: Breakthrough curves for oil adsorption on rGO-Fe\({}_{2}\)O\({}_{3}\). Initial concentration = 100 ppm, flowrate = 200 mL/h, bed volume = 10 mL, adsorbent mass = 1 g.  
for dissolved oil removal. rGO-Fe\({}_{2}\)O\({}_{3}\) exhibited extremely fast (within 30 min) and 90% removal of dissolved oil from its solution, having 100 mg/L concentrations with 3 mg of rGO-Fe\({}_{2}\)O\({}_{3}\). The nanocomposite showed a maximum Langmuir adsorption capacity of 1301 mg/g using 200 mg/L of dissolved oil solution and 1 mg of rGO-Fe\({}_{2}\)O\({}_{3}\). The adsorption capacity improved substantially when the wastewater salinity was increased compared to the 0 mg of NaCl/L solution. The adsorption kinetics followed the pseudo-second-order model and provided the best mathematical fit to the experimental data, and a good correlation was achieved with the intraparticle diffusion model. The fixed-bed prototype with 0.2 g of rGO-Fe\({}_{2}\)O\({}_{3}\) was used in a breakthrough experiment that confirmed its ability to treat 12 L of a 100 mg/L emulsion. The removal efficiency was ~90%, which is very promising because the residence time of the 3.3 mL/min emulsion stream was very short (<1 min). The nanocomposite was regenerated with ethanol and went through three cycles of adsorption-regeneration, with more than 80% retention of the adsorption capacity and near 100% retention of the removal efficiency. Overall, this nanocomposite had superior adsorption performance to other graphene nano-adsorbents, making rGO-Fe\({}_{2}\)O\({}_{3}\) an optimum choice for dissolved oil removal from high-salinity wastewater as the cost of large-scale GO production continues to decrease. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app12199414/s1](https://www.mdpi.com/article/10.3390/app12199414/s1)]([https://www.mdpi.com/article/10.3390/app12199414/s1](https://www.mdpi.com/article/10.3390/app12199414/s1)). Supplementary Information: Analysis of the adsorption data using different isotherm models. References [42; 43; 45; 54] are cited in the supplementary materials. [PERSON] was responsible for data curation, visualization, analysis, and writing the first draft; [PERSON] was responsible for analysis, writing, review, and editing; [PERSON] was responsible for analysis, writing--review, and editing; [PERSON] was responsible for conceptualization, methodology, analysis, supervision resources, writing--review and editing. All authors have read and agreed to the published version of the manuscript. This research was funded by Qatar National Research Fund (QNRF) through a QRLP postgraduate award granted to Mr. [PERSON]. The APC was funded by Qatar National Library (QNL). Not applicable. Data Availability Statement: Data can be obtained via a request to the corresponding author ([PERSON]).