Synergistic Effect of Oxygen Vacancy and High Porosity of Nano MIL-125(Ti) for Enhanced Photocatalytic Nitrogen Fixation.

This work reports that a low-temperature thermal calcination strategy was adopted to modulate the electronic structure and attain an abundance of surface-active sites while maintaining the crystal morphology. All the experiments demonstrate that the new photocatalyst nano MIL-125(Ti)-250 obtained by thermal calcination strategy has abundant Ti3+ induced by oxygen vacancies and high specific surface area. This facilitates the adsorption and activation of N2 molecules on the active sites in the photocatalytic nitrogen fixation. The photocatalytic NH3 yield over MIL-125(Ti)-250 is enhanced to 156.9 µmol g-1 h-1 , over twice higher than that of the parent MIL-125(Ti) (76.2 µmol g-1 h-1 ). Combined with density function theory (DFT), it shows that the N2 adsorption pattern on the active sites tends to be from "end-on" to "side-on" mode, which is thermodynamically favourable. Moreover, the electrochemical tests demonstrate that the high atomic ratio of Ti3+ /Ti4+ can enhance carrier separation, which also promotes the efficiency of photocatalytic N2 fixation. This work may offer new insights into the design of innovative photocatalysts for various chemical reduction reactions.