Bactericidal–Bacteriostatic Foam Filters for Air Treatment

A highly loaded porous polyimide (PI) foam type air filter has been fabricated by incorporating antimicrobial active metals to prevent microbial growth and kill microbes, and so to provide health benefits for people in enclosed spaces. PI foams containing antibacterial agents, such as PCu80 (PI (20 wt %)/copper (80 wt %)), PNi80 (PI (20 wt %)/nickel (80 wt %)), and copper-nickel composites, were synthesized and tested against model bacterium, Erwinia carotovora (Gram negative) to determine the antibacterial efficacy of the air filter. Scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) confirmed the distribution of copper and nickel throughout PCu80 and PNi80, where concentrations between 70% and 75% were detected. The copper: nickel ratio was consistent throughout the foam for PCu64Ni16 (PI (20 wt %)/copper (64 wt %)/nickel (16 wt %)). PCu80 displayed a high log reduction value (LRV) of 99.996% and, thus, exhibited a bactericidal effect. PNi80 displayed a lower LRV of 99.4%. However, a higher LRV value was observed compared to the control, 95.5% (PI foam without antibacterial agent), and thus, demonstrated a bacteriostatic effect. PCu64Ni16 exhibited and sustained exceptional microbe removal efficiencies of 99.9997% for 24 h at high humidity levels and demonstrated the highest zone of inhibition (ZOI) value of 33.90 +/- 0.16 mm compared to PCu80 (27.5 +/- 1.1 mm). Nickel strongly inhibited the proliferation of bacteria, while copper destroyed the bacteria on the foam filters. Therefore, such functionalized filters can potentially overcome the inherent limitation in conventional filters and imply their superiority for controlling indoor air quality.