Activity and Mechanism Mapping of Photocatalytic NO₂ Conversion on the Anatase TiO₂(101) Surface

NO emission heavily affects our environment and human health. Photocatalytic denitrification (deNO) attracted much attention because it is low-cost and nonpolluting, but undesired nitrite and nitrate were produced in reality, instead of harmless N₂. Unveiling the active sites and the photocatalytic mechanism is very important to improve the process. Herein, we have employed a combinational scenario to investigate the reaction mechanism of NO₂ and H₂O on anatase TiO₂(101). On the one hand, a polaron-corrected GGA functional (GGA + Lany-Zunger) was applied to improve the description of electronic states in photoassisted processes. On the other hand, a reaction phase diagram (RPD) was established to understand the (quasi) activity trend over both perfect and defective surfaces. It was found that a perfect surface is more active via the Eley-Rideal mechanism without NO₂ adsorption, while the activity on defective surfaces is limited by the sluggish recombinative desorption. A photogenerated hole can weaken the OH* adsorption energies and circumvents the scaling relation of the dark reaction, eventually enhancing the deNO activity significantly. The insights gained from our work indicate that tuning the reactivity by illumination-induced localized charge and diverse reaction pathways are two methods for improving adsorption, dissociation, and desorption processes to go beyond the conventional activity volcano plot limit of dark conditions.