# Nanofiber-Based Materials for Persistent Organic Pollutants in Water Remediation by Adsorption
## 2 Moderately Hydrophobic Pesticides
### Nanofibers for Pesticide Adsorption
#### 2.2.3 Nanofiber Performance Comparison Regarding Initial Pesticide Concentration and Adsorbent Dose  
Figure 4 shows bar charts representing the adsorption capacity with the corresponding tests conditions of initial pesticide concentration and adsorbent dose for each pesticide, nanofiber adsorbent and selected benchmark adsorbents. It can be noticed from all the charts that nanofibers delivered an adsorption performance on average in the range of other benchmarked adsorbents. Indeed, nanofiber adsorption capacities ranged from 5.8 to 19.5 mg/g (Table 2, \(N1\) and Table 4, \(N6\)), for a similar range of initial dye concentration around 10 mg/L compared to benchmark materials, yet for an adsorbent dose on average below 1 g/L. Other macro-adsorbents were reported for a dose on average over 3 g/L. The lower adsorbent dose required for nano-adsorbents compared to macrostructures should be taken into consideration when calculating the material fabrication cost and regeneration volumes. In the case of organochlorines, Organo-layered double hydroxide nanohybrids and single walled carbon nanotubes showed the highest adsorption capacities of 113 mg/g and 130 mg/g against Alachlor and Atrazine, respectively (Table 2, \(N2\) and Table 4, \(N9\)). However, other ceramic and carbon adsorptive nanostructures showed a lower performance for the same adsorbate respectively. Indeed, organosilane/alumina nanofibers demonstrated a capacity of 5.8 mg/g against Alachlor (Table 2, \(N1\)), and carbon nanofiber/carbon nanotube composites showed a capacity of 19.5 mg/g against Atrazine (Table 4, \(N6\)). Other than the action of other adsorption mechanisms, these performance differences for similar adsorbent sizes and compositions may also be explained by a different adsorbent pore structure that is hindering the diffusion of the pesticides, as in the case of modified alumina nanofibers, for example. Nevertheless, the predominant efficiency of carbon and metal oxide adsorbent surfaces suggests that \(\pi\)-\(\pi\) electron and electrostatic interactions are the most efficient adsorption mechanisms towards selected pesticides, compared to hydrophobic interactions, which by comparison reached average performance when serving as the predominant mechanism at stake [29]. Furthermore, carbon nanofibers were reported to show adsorptive affinity for other contaminants, such as sulfamethoxazole, in a multi-contaminant flow through adsorption test, demonstrating the versatility of carbonaceous adsorbents towards organic molecules with unsaturated bonds such as aromatic rings [39]. Polystyrene molecular imprinted nanofibers showed limited performance against Atrazine and Chlorpyrifos (Table 4, \(N2\) and Table 5, \(N1\)). Although polyester is a hydrophobic polymer and is thus supposed to show affinity to the pesticides studied here, it is suggested that adsorption may be limited by an unsuitable solution pH, conferring on both adsorbent and adsorbate a similar surface charge [40]. Nylon-Poly(pyrrole) core-shell nanofibers showed an adsorption capacity of 2.77 mg/g, corresponding to an efficiency of 27% (Table 4, \(N3\)). The aromatic ring of Poly(pyrrole) enables \(\pi\)-\(\pi\) interaction with the Atrazine triazine ring, while nylon does not have unsaturated bonds [41]. Experiments here were reported for a neutral solution pH. However, the Poly(pyrrole) isoelectric point has been reported around 10, meaning that at neutral pH both adsorbent and atrazine exhibited a positive surface charge [41]. It was concluded that a pH slightly above 10 would favour adsorption with a negative Poly(pyrrole) surface and still slightly protonated atrazine [41]. In the case of organophosphates, benchmark adsorbents tested in similar conditions to nanofiber adsorbents could rarely be found. For instance, activated carbon nanofibers modified with either magnesium or aluminium oxide nanoparticles showed a capacity of 0.1 mg/g against Diazinon (Table 3, \(N1\), \(N2\)).