Ca2+ doped metal organic frameworks for enhanced photocatalytic ammonia synthesis

Photocatalytic NH3 synthesis from N2 is a clean and sustainable approach, however, the efficiency of this process is low due to the difficult activation of NN triple bonds. Herein, we propose a metal-doping strategy to facilitate the interfacial charge transfer for promoting the photocatalytic NH3 yield. Ca2+ with low electronegativity was doped in UiO-66-NH2, a kind of Zr-based MOFs, to increase the electron donor capacity of Zr active sites. The X-ray photoelectron spectroscopy (XPS) spectra and density functional theory (DFT) calculations show that the Ca2+ doping enhances the electron density of Zr active sites. Moreover, the diamino ligand is incorporated to tune the bandgap structure of MOFs to expand its light absorption range. By adjusting the ratio of metals and organic ligands, the optimal photocatalyst UN(Zr-0.30Ca)-4 reaches a high NH3 evolution rate of 759.3 μmol g−1 h−1 under full spectrum. This study may provide some inspiration for the design of advanced photocatalysts for diverse chemical reduction reactions.