# Development and Testing of Copper Filters for Efficient Application in Half-Face Masks
## 1 Introduction  
Gold and silver were most likely the first metals that people encountered during evolution. These metals can be found in nature in their pure forms, and in addition to their advantage of being easily processed, they offer not only utility applications but also medical applications. Silver has strong antibacterial effects; it is therefore widely used in contemporary medicine in the production of various medications, ointments, and medical devices. Metals that may be used for medical applications also include copper (Cu) which, unlike silver, is a more accessible and affordable raw material. It is one of a few metals that may be found in its native form, and it is classified as a precious metal. Its medical applications are facilitated by its disinfection properties and effects against bacteria and molds. In a modified form, it is used for the disinfection of premises, surfaces, and clothes, and often as a component of respiratory masks with antiviral effects. An attractive combination of porous copper filters' properties, such as ductility and high thermal and electrical conductivity, makes them excellent candidates for a potential use in a wide range of industrial applications [1]. Copper tends to act as an electron donor and participate in the redox reaction, making it possible to apply copper filters to treat and purify tap water. It can remove several heavy metals, decompose organic pollutants, and has antimicrobial and antiviral properties, which are mainly based on the occurrence of reduction mechanisms. The Copper Development Association (CDA) has reported several independent studies that report the antimicrobial efficacy of uncoated copper and copper alloy surfaces against human-affecting pathogens, including one coronavirus strain(HuCoV-229E), as reported by [PERSON] et al. [2]. Researchers at the National Institutes of Health and the Centers for Disease Control and Prevention (CDC) found that the SARS-CoV-2 virus, which causes COVID-19, remained viable for 2 to 3 days on plastic and stainless-steel surfaces, but only about 4 h on a copper surface. In the first two hours, 96% of the virus particles have been killed, and 99.2% were killed in 5 h [3]. According to the currently available data, it is known that the virus can invade different tissues and the infection can exhibit numerous symptoms [4,5]. The topicality of newly developed Cu filters is supported by the fact that the major copper producer, Chile, recently touted the use of copper in face masks, such as those produced by a U.S.-Chilean company [6]. Pores quality is considered a key factor for sustainable designing of high-performance porous components. These must have a high degree of porosity and arrangement as well as regulated distribution [7, 8, 9]. The combination of metal filters and polymer nanofibers produced by electrospinning (ES) creates new possibilities for increasing the quality of filtration in respirators. In paper [10], ES was used to prepare PVDF (polyvinylidene fluoride) fiber filters, which were subsequently charged with an electrostatic charge. Tests have shown that the preparation of such filter membranes increased the virus filtering efficiency to 90%. Effects of different weight percentage concentrations of polyvinylpyrrolidone in uncalcinated TiO\({}_{2}\) nanofibers were analyzed in connection with the elimination of viruses. The synthesized TiO\({}_{2}\)/polyvinylpyrrolidone nanofibers have a tremendous practical potential in filtration and environmental remediation applications [11]. Electrostatic nanofibers represent another interesting material for fighting against viruses [12]. In this paper, the methods for preparation of high-performance electrospun air filtration membranes (EAFMs), typical surface structures, and the air filtration principles regarding electrospun fibers are reviewed, and the limitations of the use of EAFMs and trends for future developments are presented. Newly developed filter materials can only be commercialized if they are certified and tested in accredited laboratories.