Photo-Regenerable Antimicrobial Air Filter Using Monolithic Cu-Grafted TiO₂ Nanotube Mesh

Airborne transmission of pathogens has emerged as a significant public health concern amid recurring pandemics. While conventional air filtration can capture bioaerosols, it poses risks of re-emitting pathogens, necessitating long-term air sterilization. Here, we developed a photo-regenerable antimicrobial air filter by grafting Cu clusters onto a titanium dioxide nanotube mesh (Cu_xO/mTNT, 1 < x < 2). The in situ grown tubular nanotubes on the mesh support provide a high surface area, and the dispersed Cu clusters exhibited superior disinfection activity. The filter achieved rapid inactivation of Gram-negative Escherichia coli (4.80-log reduction) and Gram-positive Staphylococcus aureus (2.58-log reduction) and respiratory viruses including Influenza A virus (H1N1) and Human coronavirus 229E within minutes. While Cu-based nanomaterials induce antimicrobial effects through direct contact, they gradually lose efficiency as Cu^(I) species oxidize to Cu^(II). When Cu clusters are grafted onto TiO₂, the interfacial charge transfer (IFCT) allows for the absorption of visible light and the formation of charge carriers. The Cu clusters dispersed onto the TNT continuously regenerate Cu^(I) under mild visible light through IFCT, achieving sustained recovery of the antimicrobial efficiency. Integrated into a commercial air purifier, the Cu_xO/mTNT filter achieved efficient space disinfection of bioaerosols, showed reversible photo-regeneration over 10 cycles, and maintained durability for over six months. Field tests demonstrated that this filter achieved disinfection efficiency, whereas conventional filtration-based filters left microbial residuals, which could pose hazards to human health.