Photocatalytic inactivation of airborne bacteria in a polyurethane foam reactor loaded with a hybrid of MXene and anatase TiO2 exposing {0 0 1} facets

Abstract

A hybrid of TiO2 exposing {001} facets and monolayer Ti3C2Tx nanosheet (MXene) was synthesized, characterized and used as a photocatalyst in this study. The introduction of MXene (3.4 wt%) helped to reduce the recombination of photo-induced electrons and holes, and thus enhanced the photocatalytic activity by 30%. A continuous flow-through reactor loaded with the as-prepared photocatalyst coated onto polyurethane foam was developed to inactivate airborne bacteria. The photocatalytic inactivation efficiency of airborne Escherichia coli (E. coli) achieved 3.4 lg order under ultraviolet (UV) irradiation at 254 (UV254), which was superior to that using UV254-only treatment with 2.5 lg order under the same operating condition (95% relative humidity and retention time of 4.27 s). The effect of humidity and bacteria species on inactivation performance was also investigated. The thick cell membrane could protect bacteria from photocatalytic oxidation while high humidity increased the photocatalytic inactivation efficiency by generating more reactive oxygen species. The phenomena of photo reactivation and dark repair of airborne E. coli using UV254-only treatment was observed. However, no reactivation occurred after UV photocatalytic inactivation, and even a continuous decline under visible light. These results suggested a different inactivation mechanism between UV irradiation and UV photocatalysis that the former inactivated bacteria by damaging their DNA, whereas photocatalysis physically damaged their cell structure.