## 4 Conclusions  
In this work, biodegradable antibacterial PCL/NPs electrospun membranes were produced to act as a filter layer of a facemask. Defect-free PCL membranes were developed by electrospinningning, showing average diameters of 1.81 \(\upmu\)m. Subsequently, PCL electrospun membranes were functionalized with Ag, TiO\({}_{2}\) and MgO NPs, being the Ag NPs firstly synthetized using a green methodology, where PEG was used as a reducing, dispersant and stabilizing agent. The average diameters of the fibers changed to 1.78, 2.09 and 2.02 \(\upmu\)m, with the impregnation of Ag, TiO\({}_{2}\) and MgO NPs, respectively. FESEM, EDS, ATR-FTIR and GSDR confirmed the impregnation of NPs onto PCL membranes. Moreover, TGA analysis revealed that PCL electrospun membranes contained an estimated percentage of Ag, TiO\({}_{2}\) and MgO NPs of 0.512, 3.09 and 3.79%, respectively.  
PCL/Ag NPs membranes exhibited an inhibition zone with diameters of 18.3 \(\pm\) 0.6 against _S. aureus_ and 16.5 \(\pm\) 0.7 against _E. coli_, whereas PCL/TiO\({}_{2}\) NPs membranes only demonstrated antibacterial effect against Gram-positive bacteria, with an inhibition zone of 18.7 \(\pm\) 1.2 mm. Finally, PCL functionalized with MgO NPs showed halos with a size of 25.3 \(\pm\) 0.6 and 13.5 \(\pm\) 0.7 for _S. aureus_ and _E. coli_ bacteria, respectively, demonstrating the highest antibacterial effect against Gram-positive bacteria. The filtration performance of PCL membrane was 84.9%, which reduced to 70.8% with the addition of Ag NPs. This could be due to the synthesis process of these NPs. This decrease was not observed when using commercial NPs. The impregnation of TiO\({}_{2}\) and MgO NPs led to a filtration efficiency of 86.0 and 99.4%, respectively. The highest filtration efficiency was detected for the membrane with the lowest thickness and basis weight (PCL/MgO NPs).  
PCL/MgO NPs membranes were selected to act as the filter layer of the facemask prototypes. The addition of the filter layer in the middle of the cotton outer and inner layers significantly enhanced the filtration efficiency from 15.6 to 96.2%, which increased even more with the incorporation of two electrospun membranes (99.1%). These results were accompanied with a decrease in air permeability. Thermal management analysis revealed that the incorporation of PCL/MgO NPs electrospun membrane in the middle of the cotton layers promoted an increase in thermal comfort.  
This research work reports the development of an eco-friendly active facemask. Joining the properties of electrospun membranes with the NPs, it was possible to achieve filter layers with high filtration performance and excellent antibacterial effect against both Gram-positive and Gram-negative bacteria.  
Conceptualization, investigation, writing--original draft preparation, S.M.C.; investigation, methodology, writing--original draft preparation, L.P.; conceptualization, writing--review and editing, supervision, D.P.F.; supervision, R.F.; investigation, methodology, review and editing, P.T.; methodology, review and editing, W.A., R.V. and N.B. All authors have read and agreed to the published version of the manuscript.  
The authors are thankful to project UID/CTM/00264/2021 of 2 CZT--Centro de Ciencia e Tecnologia Textil, funded by National Founds through FCT/MCTES- Fundacao para a Ciencia e a Tecnologia. [PERSON] is thankful to CEECIND/02803/2017 and [PERSON] for the FCT PhD Scholarship (SFRH/BD/147517/2019), founded by National Founds through FCT/MCTES. [PERSON] is thankful to the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit.  
Not applicable.  
The authors declare no conflict of interest.