Important contributions of in-situ produced H2O2 during photocatalytic sterilization of air by self-doped Bi2.15WO6

Abstract

Photocatalytic generation of oxidative free radicals is an effective method to eliminate viruses and bacteria in air. Nevertheless, the underlying mechanisms governing the gas-phase sterilization remain unclear. In this study, the self-doped Bi_2.15WO₆ was synthesized to prepare the Bi_2.15WO₆ coating. In the presence of Bi_2.15WO₆ coating, the average logarithmic degradation efficiencies (LDEs) are 3.82 and 3.07 for E. coli and S. aureus, respectively under UV illumination for 12.9 s, indicating its desirable sterilization efficiencies. In addition, the sterilization rates of E. coli and S. aureus slightly decrease by 3 % and 6 % after 30-repeated cycles, indicating the high stability of this catalytic coating. The 2,7-dichlorofluorescein (DCF) fluorescence experiments and SEM analysis indicate that reactive oxygen species (ROS) produced by Bi_2.15WO₆ have effectively destroyed cell structure to achieve the complete inactivation. The N,N-diethyl-p-phenylenediamine sulfate (DPD) and radical trapping experiments further reveal that H₂O₂ is the primary oxidizing species, and its yields are linearly proportional to the LDE values. The produced H₂O₂ is further decomposed to •OH under UV irradiation to kill bacteria. Raman analysis confirms the presence of the intermediate species of surface ≡Bi-OO• superoxo and/or ≡Bi-OOH peroxo groups on Bi_2.15WO₆, which are the precursors of H₂O₂. In addition, the 3-D filter facilitates sterilization by the Bi_2.15WO₆ in that it prolongs the duration of free radical via physically intercepting bioaerosols, thus apparently improving the degradation rate. This study provides new insights on the sterilization mechanism involved in the gas-phase photocatalytic processes.