Photocatalytic performance and mechanism of nitrate resource utilization on Ag single atoms anchored on UiO-66-NH2

Photocatalytic nitrate (NO3-) reduction reaction (NITRR) is a sustainable route for value-added ammonia (NH3) production, which can realize the resource utilization of nitrate in wastewaters. Although transition metals show great promise in photocatalytic NITRR, the precise control of their interactions with supports remains a major challenge, which profoundly affects their catalytic properties. Herein, we rationally design Ag single atoms (SAs) on a UiO-66-NH2 support (Ag SAs/UiO) by photoinduction method, where the Ag-N4 catalytic sites dominantly promote photocatalytic NO3- reduction to NH3 at ambient conditions with yield rate of 14.0 mmol gcat -1 h-1, nearly 100 % selectivity, and apparent quantum efficiency of 4.8 % at 650 nm. The yield rate is significantly higher than those of UiO-66-NH2 and Ag nanoparticles/UiO with Ag-Ag catalytic sites. In situ characterization and theoretical calculations demonstrate that Ag-N4 catalytic sites effectively reduce the adsorption energy of NO3-, facilitate the conversion of NO3-* to NO2-* and NH3*, and prevent the formation of N2 and N2O via N-N coupling step. In simulated wastewaters, our study demonstrates the reliable activity of Ag SAs/UiO highlights its enormous potential for industrial application.