Photocatalytic reactive oxygen species generation activity of TiO₂ improved by the modification of persistent free radicals

Environmentally persistent free radicals (EPFRs) may help mineral dust to produce more reactive oxygen species (ROS). However, the mechanism of this effect is not yet clear. Therefore, in this study, anatase modified with EPFRs was synthesized via a simple two-step method. The presence of EPFRs was confirmed using a series of characterization techniques, including electron paramagnetic resonance and nuclear magnetic resonance. Herein, we found that EPFRs can improve ˙OH generation via the oxidation reaction between photogenerated holes (h⁺) and OH⁻ (or H₂O). This result was due to two reasons. The first is that the EPFRs construct a built-in electric field, which helps the migration of h⁺ from the bulk to the surface of anatase and then to EPFRs. The other reason is that EPFRs help anatase adsorb more H₂O molecules, which are then oxidized to ˙OH by h⁺. This study will help to understand the photochemical production mechanism of ROS on the surface of mineral dust. Copyright © 2021 The Royal Society of Chemistry.