Fig. 3.

Time-resolved photoluminescence (TRPL) measurements of N-doped TiO₂ photocatalysts under different conditions. a N-doped P25 treated by ammonia at different temperatures and promoted by Au. b N-P25-620 after being soaked in acidic solutions with different pH. c N-P25-620 after being soaked in alkaline solutions with different pH. d Au/N-P25-620/MgO(111), Au/N-P25-620/MgO(110) and Au/N-P25-620/MgO(100) with Au/N-P25-620 included as a reference (exciton lifetimes and errors are shown in Supplementary Table 4). e Schematic illustration of the local electric field of polar MgO(111) nanocrystals with negative and positive ion-terminated surfaces can assist the photocatalytic water splitting to H₂/O₂ via H⁺ and OH⁻ surrounding the N-doped TiO₂ catalyst particle