Ag nanoparticles in the cages of MIL-101(Cr) as an efficient and stable photocatalyst for nitrogen reduction reaction

Abstract

The active sites of the catalyst and the charge transfer during the reaction are crucial for the photocatalytic nitrogen reduction reaction (PNRR). Here, ultrafine Ag Nanoparticles (Ag NPs) as the active sites and the electron transporters are successfully fixed in the cavities of the metal–organic frame MIL-101(Cr) by the “double solvent-photoreduction” method. The hydrophilic cages of MIL-101(Cr) could restrict and disperse the growth of Ag NPs, and the windows of the cages prevent them from being detached from the MOF carriers. The Schottky junction between Ag NPs and the MIL-101(Cr) leads to ligand–metal charge transfer (LMCT), while the localized surface plasmon resonance effect (LSPR) possessed by Ag NPs themselves generates hot electrons. Thus, N₂ was converted to NH₃ by the synergistic effect of the two mechanisms, which was 12 times higher than that of pure MIL-101(Cr) and reached 138.81 μmol g⁻¹ h⁻¹. Furthermore, the mechanism of nitrogen fixation and the reason for the stabilization of this catalyst were investigated, and the results were verified by density functional theory calculations.