## 5 Cost Analysis of CNPs and MONPs  
The cost of nanoparticle (NP) preparation is a critical factor in wastewater treatment that requires careful evaluation. The associated cost of applying nanoparticles in wastewater treatment can be classified into three important categories: the cost of raw materials, the scale of production, and the cost of NP synthesis and preparation [10]. The details of nanomaterials cost are shown in Figure 10.  
As recently reviewed by [PERSON] et al. [171], the cost of adsorbent production depends on raw material, transportation, used chemicals, and energy consumption. They found that energy costs contributed to 91% of the total production cost. The cost of producing and utilizing a specific adsorbent is a crucial factor considered by designers and engineers operating large-scale systems. Then, the selection of adsorbents for large-scale applications is based on the overall cost of pollutant removal, not solely on their adsorption capacity.  
Researchers are actively exploring ways to reduce these costs by developing innovative preparation methods or utilizing readily available materials. As reported by [PERSON] and [PERSON] [172], one potential solution is the use of plant-based materials for NP production. This approach highlights the promise of biological methods as a sustainable and cost-effective alternative. In addition, studies indicate that recycling NPs could further lower expenses, offering an economically and environmentally viable solution to minimize reliance on freshly produced nanoparticles.  
Figure 10: Different cost allocations of nanomaterials in the wastewater treatment process.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Nanomaterial** & **Modification** & **Synthesis** & **Pollutant Type** & **Mechanism** & **Removal Time** & **Removal Rate (\%)** & **Ref.** \\ \hline \multirow{3}{*}{\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)} & Hematite was selected & \multirow{3}{*}{Bio-reduction} & \multirow{3}{*}{COD, TDS, TSS} & Photocatalytic degradation & \multirow{3}{*}{8 h} & COD-82.8 & \multirow{3}{*}{[166]} \\  & & over other & & & & & TDS: 47.6 & \\ \cline{1-1} \cline{5-7}  & crystalline structures & & & & & TDS: 75.7 & \\ \hline \multirow{2}{*}{Fe\({}_{2}\)O\({}_{3}\)} & CuO-CeO2-Fe\({}_{2}\)O\({}_{3}\) & \multirow{2}{*}{Reduction} & \multirow{2}{*}{Red 60 textile dye} & \multirow{2}{*}{Adsorption} & \multirow{2}{*}{3 h} & \multirow{2}{*}{77} & [167] \\  & nanocomposite & & & & & & \\ \hline \multirow{2}{*}{\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)} & None & Bio-reduction & Yellow RR dye & Photocatalytic degradation & \multirow{2}{*}{6h} & \multirow{2}{*}{76.6} & [168] \\ \hline \multirow{2}{*}{CMC-Fe\({}_{2}\)O\({}_{4}\)} & Carboxymethyl cellulose-immobilized & One-step & \multirow{2}{*}{Pip\({}^{2}\)-precipitation} & \multirow{2}{*}{Adsorption} & \multirow{2}{*}{12 min} & \multirow{2}{*}{68.4} & [169] \\  & & high-gravity & & & & & \\ \cline{1-1} \cline{5-7}  & & & & & & & \\ \cline{1-1} \cline{5-7}  & & & & & & & \\ \hline \multirow{2}{*}{Fe\({}_{3}\)O\({}_{4}\)} & Sulfur & Micro emulsion & \multicolumn{1}{l}{Pip\({}^{2}\)-} & Adsorption & \multicolumn{1}{l}{24 h} & \multicolumn{1}{l}{-80} & [170] \\ \hline \hline \end{tabular}
\end{table}
Table 8: Application of Fe\({}_{2}\)O\({}_{3}\) NPs in wastewater treatment.