Iron oxide nanowire-based filter for inactivation of airborne bacteria

Heating, ventilation, and air conditioning (HVAC) systems are among the most common methods to improve indoor air quality. However, after long-term operation, the HVAC filter can result in a proliferation of bacteria, which may be released into the filtered air subsequently. This issue can be addressed by designing antibacterial filters. In this study, we report an iron oxide nanowire-based filter fabricated from commercially available iron mesh through a thermal treatment. Under optimal conditions, the filter demonstrated a log inactivation efficiency of >7 within 10 seconds towards S. epidermidis (Gram-positive), a common bacterial species of indoor bioaerosol. 52% of bioaerosol cells can be captured by a single filter, which can be further improved to 98.7% by connecting five filters in tandem. The capture and inactivation capacity of the reported filter did not degrade over long-term use. The inactivation of bacteria is attributed to the synergic effects of hydroxyl radicals, electroporation, and Joule heating, which disrupt the cell wall and nucleoid of S. epidermidis, as verified by model simulations, fluorescence microscopy, electron microscopy, and infrared spectroscopy. The relative humidity plays an important role in the inactivation process. The filter also exhibited satisfactory inactivation efficiency towards E. coli (Gram-negative). The robust synthesis, low cost, and satisfactory inactivation performance towards both Gram-positive and Gram-negative bacteria make the filter demonstrated here suitable to be assembled into HVAC filters as an antibacterial layer for efficient control of indoor bioaerosols.