Postillumination Activity in a Single-Phase Photocatalyst of Mo-Doped TiO2 Nanotube Array from Its Photocatalytic “Memory”

Several composite photocatalysts with photocatalytic "memory" effect had recently been developed, which could possess postillumination activity for an extended period of time in the dark for many potential applications. Here, a single-phase photocatalyst of Mo-doped TiO2 nanotube array was developed for the first time with the postillumination photocatalytic memory effect, which could eliminate the requirement of building composite photocatalysts with heterojunctions and largely broaden the material selection for this interesting photocatalytic memory effect. Because of the proper electronic band gap structure and variable valences of Mo dopants, photogenerated electrons could transfer from TiO2 to Mo dopants and be trapped there by reducing Mo6+ to Mo5+ under UV irradiation. When UV irradiation was switched off, these trapped electrons could be released from Mo dopants and react with O2 through the two-electron O2 reduction process to produce H2O2 in the dark. Thus, Mo-doped TiO2 nanotube array could remain active in the dark as demonstrated by its effective disinfection of Escherichia coli cells when UV irradiation was turned off. This work demonstrated that photocatalysts with postillumination photocatalytic memory effect were not limited to composite photocatalysts with heterojunctions. Various single-phase photocatalysts could also possess this interesting photocatalytic memory effect through doping metal elements with variable valences.