# Nanofiber-Based Materials for Persistent Organic Pollutants in Water Remediation by Adsorption
## 4 Persistent Organic Pollutants
### Polychlorinated Biphenyls (PCBs) and Polyaromatic Hydrocarbons (PAHs)
#### 4.2.2. Nanofibers for Pesticide Adsorption  
Figure 11 shows the adsorption capacity related to the adsorbent dose and initial contamination for adsorbents of PCBs and Phenantrene. Oriented porous magnetite nanofibers were tested in the adsorption of PCB 77 and showed a capacity of 0.18 mg/g in hexane for a contamination of 30 \(\mu\)g/L and a dose of 0.15 g/L (Table 19, \(N8\)). However, activated carbon showed the largest adsorption capacity of 649 mg/g for a contamination of 4 mg/L and a relatively small dose of 0.015 g/L (Table 19, \(N1\)). To study the influence of the adsorbate aromatic structure on the adsorption performance, Phenantrene, with three aromatic cycles, has been considered here. Cellulose acetate unmodified \begin{table}
\begin{tabular}{c c c c c} \hline
**Name** & **Formula** & **M (g/mol)** & **Log K\({}_{\rm{ow}}\)** & **Solubility in Water** (mg/L, 25\({}^{\circ}\)C) & **Structure** \\ \hline
**Phenantrene** & C\({}_{14}\)H\({}_{10}\) & 178.234 & 4.46 & 1.15 \\ \hline \end{tabular}
\end{table} 
Table 18: Characteristics of Phenantrene (obtained from PubChem). \begin{table}
\begin{tabular}{c c c c c} \hline
**Name** & **Formula** & **M (g/mol)** & **Log K\({}_{\rm{ow}}\)** & **Solubility in Water** (mg/L, 25\({}^{\circ}\)C) & **Structure** \\ \hline
**Phenantrene** & C\({}_{14}\)H\({}_{10}\) & 178.234 & 4.46 & 1.15 \\ \hline \end{tabular}
\end{table} 
Table 19: Characteristics of Phenantrene (obtained from PubChem). nanofibers showed limited performance in the capture of Phenantrene, which could be due to the hydrophilic nature of cellulose acetate; they are thus poorly adapted for the adsorption of apolar compounds [112]. Cyclodextrin-grafted cellulose acetate nanofibers were tested for the capture of Phenantrene via molecular filtration, by inclusion-complexation of the hydrophobic contaminants in the apolar cyclodextrin cavity [112]. Hydrophobic interactions led to a contaminant removal of 97% (Table 20, \(N2\)). Cross-linking of cellulose acetate nanofibers with benzene rings by polybenzoxazine provided a hydrophobic adsorptive structure [113]. The adsorbent benzene rings further enabled \(\pi\)-\(\pi\) interactions with Phenantrene aromatic rings, thus leading to 98.5% contaminant removal (Table 20, \(N1\)). Activated carbons and carbon nanotubes however, demonstrated an adsorption capacity of 85 mg/g for a dose of 4 mg/L (initial concentration was not reported) (Table 20, \(N7\)). It can be suggested that \(\pi\)-\(\pi\) electron interaction between the unsaturated Phenantrene aromatics and the carbon adsorbent surface is the predominant reaction mechanism; in that sense, a higher carbon content and full crystalline structure would lead to an increased specific surface area and, for a large pore volume of adapted size, Phenantrene adsorption. Among the reported carbon-based materials, granular activated carbon possessed a BET of 706 m\({}^{2}\)/g and a pore volume of 0.711 cm\({}^{3}\)/g, yielding the highest performance. On the other hand, carbon nanotubes with a higher pore volume of 0.818 cm\({}^{3}\)/g but a lower BET of 537 m\({}^{2}\)/g showed a capacity of 75 mg/g (Table 20, \(N4\)). Furthermore, activated carbon fibers with the highest BET of 949 m\({}^{2}\)/g but the lowest pore volume of 0.381 cm\({}^{3}\)/g yielded a lower capacity of 60 mg/g (Table 20, \(N6\)), indicating a synergetic effect of pore volume and surface area (BET). Figure 11: Graphs showing the proportion between adsorbent dose (blue column, left scale), initial pesticide concentration (green column, middle right scale) and adsorption capacity (red scatter, far left scale) in the adsorption of PCBs (**A**) and Phenantrene (**B**).