Short-term effect of humid airflow on antimicrobial air filters using Sophora flavescens nanoparticles

Bioaerosols have received social and scientific attention because they can be hazardous to human health. Recently, antimicrobial treatments using natural products have been used to improve indoor air quality (IAQ) since they are typically less toxic to humans compared to other antimicrobial substances such as silver, carbon nanotubes, and metal oxides. Few studies, however, have examined how environmental conditions such as the relative humidity (RH), surrounding temperature, and retention time of bacteria on filters affect the filtration and antimicrobial characteristics of a filter treated with such natural products. In this study, we investigated changes in the morphology of the natural nanoparticles, pressure drop, filtration efficiency, and the inactivation rate caused by the short-term effect of humid airflow on antimicrobial fiber filters. Nanoparticles of Sophora flavescens were deposited on the filter media surface using an aerosol process. We observed coalescence and morphological changes of the nanoparticles on fiber filters under humid conditions of an RH > 50%. The level of coalescence in these nanoparticles increased with increasing RH. Filters exposed to an RH of 25% have a higher pressure drop than those exposed to an RH > 50%. In an inactivation test against Staphylococcus epidermidis bacterial aerosol, the inactivation efficiency at an RH of 25% was higher than that at an RH of 57% or 82%. To effectively apply antimicrobial filters using natural products in the environment, one must characterize the filters under various environmental conditions. Thus, this study provides important information on the use of antimicrobial filters made of natural products.

Graphical abstractSEM images of filters. (a) Control without natural product nanoparticles; (b) with antimicrobial particles at an RH of 25%, (c) an RH of 57%, and (d) an RH of 82%.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Antimicrobial treatments using natural products have been used widely to improve indoor air quality. ► This study reported the short term effect of humid air flow on natural product (Sophora flavescens) nanoparticle-deposited filter. ► The results showed that the humid air flow (RH > 50%) caused the morphological change as well as agglomeration of natural product nanoparticles deposited on the surface of the filter. ► These variations in the natural product nanoparticles under the humid air flow could reduce the antimicrobial efficiency of filter.