Improved visible light photocatalytic nitrogen fixation activity using a Fe II -rich MIL-101(Fe): breaking the scaling relationship by photoinduced Fe II /Fe III cycling.

The scaling relations between nitrogen adsorption and NH x destabilization are key challenges to the widespread adoption of the photocatalytic synthesis of ammonia. In this work, a Fe II -rich MIL-101(Fe) (MIL-101(Fe II /Fe III )) was synthesized using a one-step solvent thermal method with ethylene glycol (EG) as a reducing agent, which can break the scaling relationship by photoinduced Fe II (high nitrogen adsorption ability) and Fe III (high NH z destabilization ability) cycling. XPS was used to detect the change in iron valence state in the MIL-101(Fe II /Fe III ) material. The photocatalytic nitrogen fixation efficiency of MIL-101(Fe II /Fe III ) under visible light without any sacrificial agent was 466.8 μmol h -1 g -1 , five times that of MIL-101(Fe). After photocatalytic experiments, MIL-101(Fe II /Fe III ) retained an unchanged Fe II /Fe III rate, indicating that this Fe II /Fe III cycling can be maintained. DFT modeling of the Fe II -rich MOF material showed that a FeII1 FeIII2 system has a higher N 2 activation capacity than a FeIII3 system. The catalytic mechanism was further proved by in situ infrared spectra and N 15 isotopic tracers. Therefore, the improvement of photocatalytic activity was mainly attributed to the change in the nitrogen adsorption capacity during the photoinduced Fe II /Fe III cycling.