# Nanofiber-Based Materials for Persistent Organic Pollutants in Water Remediation by Adsorption
## 4 Persistent Organic Pollutants
### Aliphatic Organochlorines
#### 4.1.2 Nanofibers for Pesticide Adsorption  
Figure 10 shows the relationship between adsorption capacity and test conditions of initial contaminant concentration and adsorbent dose for Aldrin, Dieldrin, Endrin pesticides plus Heptachlor and its epoxide. Polystyrene (PES) nanofibers decorated with titania nanoparticles showed limited adsorptive performance for these pesticides, as well as against Chlordane, showing a capacity of 0.02 mg/g (Table 11, \(N1\)) [92]. Adsorbent surface properties were not reported, yet the poor affinity of hydrophobic polyester for hydrophobic organochlorines could have impacted the performance, with adsorption reaction localized on the titania surface. In the case of Dieldrin removal, bromopropyl functionalised silica nanofibers revealed an adsorption capacity of 0.19 mg/g for contamination and adsorbent dose of 20 ug/L and 0.1 g/L, respectively (Table 12, \(N1\)). In comparison, untreated silica nanofibers achieved a capacity of 0.014 mg/g (Table 12, \(N2\)). The addition of a dense bromopropyl layer on silica nanofibers produced a hydrophobic adsorbent surface, with chemical affinity with pesticide chlorine groups. Concerning Aldrin removal, vegetal activated carbon showed a relatively high performance with a capacity of 0.38 mg/g for a contamination of 2 mg/L, yet for a relatively large dose of 5 g/L (Table 13, \(N2\)). Vegetal activated carbon performed a similar role in the case of Dieldrin adsorption, in the same conditions (Table 12, \(N8\)). Against Heptachlor epoxide, the vegetal activated carbon was reported to show a capacity of 0.42 mg/g for a contamination of 2.2 mg/L for a similar dose of 5 g/L (Table 14, \(N7\)). Finally, in the case of Endrin, powdered activated carbon was reported to show a capacity of 0.085 mg/g for a contamination of 0.8 ug/L, and a relatively large dose of 0.2 g/L (Table 15, \(N6\)). These results show that although adsorbent specific surface area and pore channels could be adapted to improve the adsorptive performance, activated carbons yield removal efficiencies over 95%. However, compared to nanomaterial adsorbents, a large adsorbent dose is required. Acid-treated date and olive stones showed a significantly improved performance over non-treated biomass adsorbents. For instance, acid-treated date stones showed a capacity of 0.45 mg/g in the removal of Aldrin, while untreated date stones yielded 0.05 ug/g for conditions of contamination and adsorbent dose of respectively 500 ug/L, 1 g/L and 0.5 ug/L and 10 g/L (Table 13, \(N9\), \(N12\)). Date stones were thermally treated with hydrochloric acid, thus creating a hydrophobic layer on the adsorbent surface, and facilitating the anchorage of organochlorines [93]. In the adsorption of Dieldrin and Endrin, acid-treated date stones showed a capacity of 0.44 mg/g and 0.40 mg/g, in the same conditions as Aldrin capture (Table 12, \(N18\) and Table 15, \(N10\)). The lower performance in the adsorption of Endrin compared to Dieldrin can be explained by the spatial organization of