Directional Shunting of Photogenerated Carriers in POM@MOF for Promoting Nitrogen Adsorption and Oxidation

• Published in: Advanced materials (Weinheim) 2023-11, Vol.35 (44), p.e2304532-n/a
• Main Authors: Li, Xiaohong, Yang, Lan, Liu, Qilong, Bai, Wei, Li, Huiyi, Wang, Mengxiang, Qian, Qizhu, Yang, Qinghua, Xiao, Chong, Xie, Yi
• Format: Article
• Language: English
• Subjects: Adsorption; Catalysis; directional shunting; Electrons; Materials science; Metal clusters; Metal-organic frameworks; Nitrogen; Nitrogenation; Oxidation; photocatalytic nitrogen fixation; polyoxometalates; Polyoxometallates
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202304532

The efficient catalysis of nitrogen (N2) into high‐value N‐containing products plays a crucial role in the N economic cycle. However, weak N2 adsorption and invalid N2 activation remain two major bottlenecks in rate‐determining steps, leading to low N2 fixation performance. Herein, an effective dual active sites photocatalyst of polyoxometalates (POMs)‐based metal–organic frameworks (MOFs) is highlighted via altering coordination microenvironment and inducing directional shunting of photogenerated carriers to facilitate N2/catalyst interaction and enhance oxidation performance. MOFs create more open unsaturated metal cluster sites with unoccupied d orbital possessing Lewis acidity to accept electrons from the 3σg bonding orbital of N2 for storage by combining with POMs to replace bidentate linkers. POMs act as electron sponges donating electrons to MOFs, while the holes directional flow to POMs. The hole‐rich POMs with strong oxidation capacity are easily involved in oxidizing adsorbed N2. Taking UiO‐66 (C48H28O32Zr6) and Mo72Fe30 ([Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O) as an example, Mo72Fe30@UiO‐66 shows twofold enhanced adsorption of N2 (250.5 cm3 g−1) than UiO‐66 (122.9 cm3 g−1) at P/P0 = 1. And, the HNO3 yield of Mo72Fe30@UiO‐66 is 702.4 µg g−1 h−1, ≈7 times and 24 times higher than UiO‐66 and Mo72Fe30. This work provides reliable value for the storage and relaying artificial N2 fixation. The Mo72Fe30@UiO‐66 composite is prepared by a one‐step hydrothermal reaction, which realizes an effective photocatalyst for storing and relaying oxidation N2 by inducing directional shunting of photogenerated carriers under mild conditions. The Mo72Fe30@UiO‐66 exhibits the high N2 adsorption capacity (250.5 cm3 g−1, at P/P0 = 1) and superior N2 oxidation performance to produce HNO3 (702.4 µg g−1 h−1).