# An Overview of Nanofiltration and Nanoadsorption Technologies to Emerging Pollutants Treatment
## 4 Synthesis and Fabrication of Nanomaterials for the Remediation of Emerging Pollutants
### Nanofiltration Membranes  
Wastewater filtration processes using nanofiltration membranes are considered effective in the effluent treatment because they have high density and small pores (less than 2 nm) that allow the application in the retention of small molecules and multivalent ions [45; 90]. Nonofiltration polymeric membranes can be manufactured by different methods, including interfacial polymerization, surface modification, and phase inversion. In interfacial polymerization, condensation occurs between the monomers at the interface of two immiscible phases. In this way, the monomer is placed in contact with the porous support, removing the remainder of the aqueous solution. Subsequently, the organic phase is added to the support, forming a layer at the interface [91]. Among the monomers that can act in the formation of the surface barrier, it is worth mentioning tannic acid, phenyl-diamine, and bisphenol A [92]. Nanofiltration membranes produced by the interfacial polymerization method are usually negatively charged, which interferes with the crosslinking process of the material due to charge repulsion [93]. In this sense, positively charged membranes can be obtained through the in-situ introduction or grafting of electropositive monomers [94; 95; 96]. In interfacial polymerization, surface, plasma, and layer-by-layer treatments can also be applied, enhancing membrane action [91; 97]. Membranes incorporated by nanoparticles gained prominence for being able to increase membrane permeability, in addition to contributing to mechanical properties, hydrophilicity, and selectivity. Titanium dioxide, silica, silver, and zinc oxide nanoparticles are commonly reported in the fabrication of nanofiltration membranes [92]. [PERSON] et al. [98] evaluated the ability to remove small-sized cationic contaminants by nanocomposite membranes added with quarternized carbon-based nanoparticles. The incorporation of the nanoparticles in the membranes reached the ideal permeate flux (23.8 L m\({}^{-2}\) h\({}^{-1}\) bar\({}^{-1}\)), high rejection rates (around 95%) for the contaminants (cationic trimethyloprim, atenol, rhodamine B, methylene blue and MgCl\({}_{2}\)), and flow rate and recovery 85.5% compared to the pure membrane. In this context, [PERSON] et al. [99] studied the incorporation of Au/TiO\({}_{2}\) (gold and titanium dioxide) and Y\({}_{2}\)(CO\({}_{3}\))\({}_{3}\) (Yttrium carbonate) nanoparticles in poly (vinylidene-hexafluoropropylene fluoride) nanomembranes to contaminant removal. The materials added with nanoparticles showed 57% degradation of the nonfloxacin. Regarding surface modification strategies, UV-assisted graft polymerization, electron beam irradiation, plasma, and layer-by-layer approach can be performed. The UV-assisted graft polymerization process occurs due to a chemical reaction involving the active film and  
Figure 2: Schematic illustration of the synthesis of nanomaterials for application in the remediation of emerging pollutants. substrate present in the membrane [100]. High-energy electron beam irradiation penetrates the polymer layer and contributes to the reduction of membrane pores [101]. In plasma surface modification, nitrogen functional groups increase the hydrophobic characteristic of the membrane [102]. The alternating incorporation of polyelectrolytes (cationic and anionic) occurs in the layer-by-layer method. In the phase inversion, the thermodynamically stable polymer solution is separated into two phases, the first with a high concentration of polymer and the other with a smaller amount of the material [91]. Phase inversion can be used to prepare ceramic nanofiltration membranes for removing emerging pollutants. These ceramic membranes have high thermal, mechanical, and chemical stability, well-defined pore size distribution, and high flux [103]. High dye rejections were achieved with ceramic nanofiltration membrane (>98%) [104, 105]. Moreover, [PERSON] et al.