Antibacterial Efficiency of Stainless-Steel Grids Coated with Cu-Ag by Thermionic Vacuum Arc Method

P Dinca,M Lungu,I Cretescu,C Staicu,B Butoi,M Diaconu,I Burducea,C.P Lungu,A Niculescu,G Soreanu,C Porosnicu,O Trusca,I Jepu

doi:10.3390/coatings10040322

Abstract

Autonomous smart natural ventilation systems (SVS) attached to the glass façade of living quarters and office buildings can help reducing the carbon footprint of city buildings in the future, especially during warm seasons and can represent an alternative to the conventional mechanical ventilation systems. The work performed in this manuscript focuses on the investigation of bacteria trapping and killing efficiency of stainless steel grids coated with a mixed layer of Cu-Ag. These grids are to be employed as decontamination filters for a smart natural ventilation prototype that we are currently building in our laboratory. The tested grids were coated with a mixed Cu-Ag layer using thermionic vacuum arc plasma processing technology. The fixed deposition geometry allowed the variation of Cu and Ag atomic concentration in coated layers as a function of substrate position in relation to plasma sources. The test conducted with air contaminated with a pathogen strain of staphylococcus aureus indicated that the filtering efficiency is influenced by two parameters: the pore size dimension and the coating layer composition. The results show that the highest filtering efficiency of 100% was obtained for fine pore (0.5 × 0.5 mm) grids coated with a mixed metallic layer composed of 65 at% Cu and 35 at% Ag. The second test performed only on reference grids and Cu-Ag (65–35 at%) under working conditions, confirm a similar filtering efficiency for the relevant microbiological markers. This particular sample was investigated from morphological, structural, and compositional point of view. The results show that the layer has a high surface roughness with good wear resistance and adhesion to the substrate. The depth profiles presented a uniform composition of Cu and Ag in the layer with small variations caused by changes in deposition rates during the coating process. Identification of the two metallic phases of the Cu and Ag in the layers evidences their crystalline nature. The calculated grain size of the nanocrystalline was in the range 14–21 nm.

Highlights

The air has an extremely important epidemiological role, representing a way of transmission for a large number of pathogens
In the current work we explore the possibility of employing Cu-Ag coated stainless steel grids into the air filtration module, considering that based on airflow simulation we conducted previously we determined that both pores dimension
The stainless-steel grids used for air filtering in an smart natural ventilation systems (SVS) prototype currently built in our laboratory were successfully coated with Cu-Ag layers with various concentrations using thermionic vacuum arc method (TVA) plasma processing technology

Summary

Introduction

The air has an extremely important epidemiological role, representing a way of transmission for a large number of pathogens. Individuals in large urban agglomerations have a tendency to spend most of their time indoors. In this context ventilating and air conditioner systems are essential to create and provide stable and comfortable climate conditions in confined spaces especially in homes, offices, schools, hospitals, and other public buildings. In order to avoid circulating large volumes of air contaminated with micro-organisms indoors these installations require efficient air filtering solutions. In particular because of moisture and poor maintenance, conventional air filters tend to become fertile breeding surfaces for microbes and bacteria, resulting in biologically contaminated low-quality indoor air that can affect the population health [1]

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Results

Conclusion