## 3 Results and Discussion
### Functional Properties Evaluation
#### 3.2.2 Filtration Efficiency  
Filtration efficiency is one of the main concerns regarding the performance of a face-mask. After the evaluation of antibacterial effect, the filtration performance of electrospun membranes was also assessed. The filtration tests were conducted in a filtration chamber using polystyrene particles of 1 mm for 60 s. The obtained results are presented in Table 3 as well as the samples' thickness and basis weight. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{2}{c}{**Mean Diameter of the Halos (mm)**} \\ \cline{2-3}  & _S. aureus_ & _E. coli_ \\ \hline PCL & 0.0 \(\pm\) 0 & 0.0 \(\pm\) 0 \\ PCL/Ag NPs & 18.3 \(\pm\) 0.6 & 16.5 \(\pm\) 0.7 \\ PCL/TiO\({}_{2}\) NPs & 18.7 \(\pm\) 1.2 & 0.0 \(\pm\) 0 \\ PCL/MgO NPs & 25.3 \(\pm\) 0.6 & 13.5 \(\pm\) 0.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Inhibition zone diameter of electrospun membranes (PCL, PCL/Ag NPs, PCL/TiO\({}_{2}\) NPs and PCL/MgO NPs) against _S. aureus_ and _E. coli_ bacteria. Values are represented by mean \(\pm\) standard deviation of triplicates. PCL membranes showed a filtration efficiency of 84.9%. The addition of NPs onto electrospun membranes is expected to improve their adsorption capacity, enhancing the overall filtration performance of the membranes [22; 52]. Nevertheless, the introduction of Ag NPs onto PCL membranes led to a decrease in filtration efficiency to 70.8%. Comparing all samples, the membranes functionalized with Ag NPs presented the lowest filtration efficiency. On contrary to TiO\({}_{2}\) and MgO NPs, Ag NPs were synthetized, and the synthesis solution was used to impregnate PCL membranes. In fact, this result can be related with the synthesis process of these NPs, namely the amount of NPs produced and present at the membrane surface. Although the concentration of AgNO\({}_{3}\) used was estimated to mimic the final concentration of TiO\({}_{2}\) and MgO NPs used, the exact amount of synthetized Ag NPs is unknown. Since the addition of NPs onto the surface of electrospun membranes can increase the adsorption capacity of the system, contributing to the filtration performance, this could be one of the parameters that influence the filtration efficiency [22]. By TGA analysis, it is possible to have an estimation of the amount of NPs present in electrospun membranes, with the PCL/Ag NPs membrane being the one that presented the lowest amount of NPs, which corroborates these findings. Moreover, the impregnation of PCL membranes into the synthesis solution could interfere with the membrane's structure, including its integrity and pore sizes. On the other hand, the incorporation of TiO\({}_{2}\) and MgO NPs promoted an increase in filtration efficiency, presenting values of 86 and 99.4%, respectively. Several parameters regulate the filtration effectiveness, such as fiber diameter, porosity and filter thickness [53]. One possible explanation is due to the changes in diameters of PCL fibers when these NPs are added. In fact, the introduction of TiO\({}_{2}\) NPs led to a slight increase in average diameters of PCL fibers from 1.81 to 2.09 \(\upmu\)m, whereas the addition of MgO NPs increased the diameters to 2.02 \(\upmu\)m. Consequently, a decrease in pore sizes is expected, promoting a higher filtration efficiency of the particles. Therefore, the functionalization of PCL membranes with TiO\({}_{2}\) and MgO NPs was demonstrated to be a promising strategy to efficiently filtrate small particles. [PERSON] et al. reported that the addition of TiO\({}_{2}\) NPs into poly(lactic acid) (PLA) electrospun membranes promoted an increase in the filtration efficiency. This result could be due to the increase in nanometer-scale protrusions induced by the introduction of NPs, which can also enhance the surface roughness and specific surface area. This may dramatically increase the friction coefficient and the effective contact area between the target particles and fibers [22].