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

NOx emission heavily affects our environment and human health. Photocatalytic denitrification (deNO(x)) attracted much attention because it is low-cost and nonpolluting, but undesired nitrite and nitrate were produced in reality, instead of harmless N-2. 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(x) 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.