Constructing Mimic-Enzyme Catalyst: Polyoxometalates Regulating Carrier Dynamics of Metal–Organic Frameworks to Promote Photocatalytic Nitrogen Fixation
Xiaohong Li, Hui Li, Shenlong Jiang, Lan Yang, Huiyi Li, Qilong Liu, Wei Bai, Qun Zhang, Chong Xiao, Yi Xie
Abstract
In nature, nitrogenase can achieve efficient environmental fixation of nitrogen (N 2 ) molecules through π-backbonding mechanism, which inspires us to simulate the N 2 fixation process of nitrogenase to overcome the bottleneck in existing artificial synthetic ammonia (NH 3 ), so as to achieve efficient artificial conversion of N 2 to NH 3 under mild conditions. Herein, we highlight a strategy of constructing a mimic-enzyme catalyst for photocatalytic N 2 fixation based on metal–organic frameworks (MOFs) and polyoxometalates (POMs) in which POMs can efficiently regulate carrier dynamics of MOFs to simulate the π-backbonding mechanism of nitrogenase. Oxygen-rich group POMs with strong electronegativity attract electrons from transition-metal atom in MOFs, thus reducing the 3d orbitals’ electron density of transition-metal atom and enhancing unoccupied d-orbitals in favor of adsorbing N 2 . Simultaneously, the photoexcited electrons in MOFs are efficiently transferred by POMs into the N–N π* antibonding system to activate N 2 via π-backbonding mechanism. Taking MIL-88A (C 12 H 6 O 13 Fe) and PMo 10 V 2 (H 5 PMo 10 V 2 O 40 ) as an example, we have obtained a significantly enhanced NH 3 production rate of 50.82 μmol g –1 h –1, which is enhanced by 6 times for MIL-88A and 14 times for PMo 10 V 2 . Our results make an important contribution to further guidance for artificial N 2 fixation under mild conditions.