The issue to achieve efficient nitrogen (N 2 ) reduction to ammonia (NH 3 ) has posed a significant challenge for decades as the inert N≡N bond could be hardly broken because of the extremely large bond energy of 940.95 kJ mol –1 . To date, the industrial fixation of N 2 to NH 3 is monopolized by the energy-intensive Haber-Bosch process (673-873 K and 15-25 MPa), which unsustainably employs natural gas to make the hydrogen (H 2 ) feedstock with enormous energy consumption from fossil fuels, leading to a large amount of carbon dioxide (CO 2 ) emission. In this context, photocatalytic N 2 reduction is regarded as a sustainable alternative way for NH 3 synthesis from N 2 and water under ambient conditions.
However, the efficiency of most traditional photocatalysts is still far from satisfactory mainly due to the hard bond dissociation of the inert N 2 , which results from the weak binding of N 2 to the catalytic material and further inefficient electron transfer from photocatalyst into the antibonding orbitals of N 2 . In order to promote efficiency of N 2 photofixation, introducing the electron-donating centers as the catalytic activation sites for optimizing the N 2 adsorption properties and improving the photoexcited charge transport in the catalysts is a promising strategy.
Oxygen vacancy (OV) represents the most widely and prevalent studied type of surface defect for N 2 fixation. On one hand, OV can be facilely created for its relatively low formation energy; on the other hand, OV can assist photocatalysts to gain exciting N 2 fixation photoactivity by virtue of its superiority in N 2 capture and activation. Therefore, a semiconductor with sufficient OVs may be favorable to improve their N 2 fixation performance. Transition metal (TM) doping is another widely investigated effective method to improve the photoactivity of N 2 fixation, because the TM species possess the advantageous ability of binding (and even functionalizing) with inert N 2 at low temperatures due to their empty and occupied d-orbitals, which can achieve the TM-N 2 interaction via “acceptance-donation” of electrons. Mo, as a critical element of the catalytic center in mysterious Mo-dependent nitrogenase, has attracted a lot of attention for the N 2 fixation. To this end, OVs-rich and Mo-doped materials would be ideal candidates for N 2 photofixation. In addition, layered bismuth oxybromide (BiOBr) materials have attracted numerous attentions because of their suitable band gaps and unique layer structures. For BiOBr-based semiconductors, such as Bi 3 O 4 Br and Bi 5 O 7 Br, it has been revealed that OV with sufficient localized electrons on their surface facilitates the capture and activation of inert N 2 molecules.
Recently, a research team led by Prof. Yi-Jun Xu from Fuzhou University, China reported that the introduction of OVs and Mo dopant into Bi 5 O 7 Br nanosheets can remarkably improve the photoactivity of N 2 fixation. The modified photocatalysts have showed the optimized conduction band position, the enhanced light absorption, the improved N 2 adsorption and charge carrier separation, which jointly contribute to the elevating N 2 fixation photoactivities. This work provides a promising approach to design photocatalysts with light-switchable OVs for N 2 reduction to NH 3 under mild conditions, highlighting the wide application scope of nanostructured BiOBr-based photocatalysts as effective N 2 fixation systems. The results were published in Chinese Journal of Catalysis (https://doi.org/10.1016/S1872-2067(21)63837-8) .
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About the Journal
Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top six journals in Applied Chemistry with a current SCI impact factor of 8.271. The Editors-in-Chief are Profs. Can Li and Tao Zhang.
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Chinese Journal of Catalysis