Nitrogen-Doped Metal–Organic Frameworks for Boosting Photocatalytic Ammonia Synthesis

Yonghui Shi; Yongqi Liu; Qian Li; Hongxiang Liu; Dong Yang; Zhongyi Jiang

doi:10.1007/s12209-025-00451-3

Transactions of Tianjin University ›› 2025, Vol. 31 ›› Issue (6) :567 -578. DOI: 10.1007/s12209-025-00451-3

Research Article

research-article

Nitrogen-Doped Metal–Organic Frameworks for Boosting Photocatalytic Ammonia Synthesis

Yonghui Shi ¹^,²
, Yongqi Liu ¹^,²
, Qian Li ¹^,²
, Hongxiang Liu ¹^,²
, Dong Yang ³^,⁴^,^a
, Zhongyi Jiang ¹^,²^,³^,⁵^,^b

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¹Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, 300072, Tianjin, China

²Haihe Laboratory of Sustainable Chemical Transformations, 300192, Tianjin, China

³State Key Laboratory of Synthetic Biology, Tianjin University, 300072, Tianjin, China

⁴School of Environmental Science and Engineering, Tianjin University, 300072, Tianjin, China

⁵Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, 350207, Binhai New City, Fuzhou, China

^a dongyang@tju.edu.cn

^b zhyjiang@tju.edu.cn

Dong Yang

Dong Yang Dong Yang is an Associate Professor at School of Chemical Engineering and Technology of Tianjin University. He obtained a PhD at Northeast Forestry University in 2001 under the guidance of Professor Lijia An. After a stint with Professor Limin Qi as a Postdoctoral at Peking University, he joined the faculty of Tianjin University in 2004. His research interests encompass functional nanomaterials, biocatalysis, and photocatalysis.

Zhongyi Jiang

Zhongyi Jiang Zhongyi Jiang is a Professor at School of Chemical Engineering and Technology of Tianjin University, Changjiang Scholars, the winner of National Science Fund for Distinguished Young Scholars. He received his PhD from Tianjin University in 1994. He served as a visiting scholar of University of Minnesota in 1996–1998 and California Institute of technology in 2009. His research interest includes membranes and membrane processes, enzymatic catalysis, and photocatalysis.

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Abstract

The efficiency of photocatalytic ammonia (NH₃) synthesis is severely limited by the extremely difficult activation of N₂ owing to its high N≡N triple bond energy. To address this challenge, we propose an N-doping strategy to facilitate the N₂ activation. Our strategy involves optimizing the electronic structure of the metal active sites by modulating the coordination element. First, we introduce five different N-coordination ligands with distinct steric hindrances and N electron densities (2-methylimidazole (MI), isoindolin-1-one (II), 1,2-benzisothiazolin-3-one (BIT), benzo[d]isoxazol-3-ol (BIX), and terephthalamide (TA)) into an amino-functionalized metal–organic framework (MOF), NH₂-MIL-68 (NM), to construct the N-coordination via the partial replacement of the O-coordination in the metal clusters. Electrochemical impedance spectroscopy and photocurrent analysis demonstrate that N-doping enhances electron transfer and carrier separation. Moreover, incorporating ligands with moderate sizes and steric hindrances (II, BIT, and BIX) more effectively boosts the carrier separation efficiency than incorporating small (MI) or large (TA) ligands. Furthermore, the N-doped MOF modified with BIT (in which N exhibits a moderate electron density) exhibits the strongest carrier separation capability. Concurrently, the X-ray photoelectron spectroscopy, density functional theory, and N₂ temperature-programmed desorption results confirm that the established low-electronegativity N-coordination elevates the electron density of the metal active sites, which consequently enhances the N₂ activation process. The systematic optimization of the N-coordinating ligand species and doping concentrations allows the optimal NM-0.5BIT to achieve a NH₃ production rate of 175.5 μmol/(g·h). The proposed N-doping strategy offers several insights into the activation of inert molecules and the development of organic framework photocatalysts.

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Keywords

Photocatalysis / Ammonia synthesis / N-doped / Metal–organic framework / Active site regulation

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Yonghui Shi, Yongqi Liu, Qian Li, Hongxiang Liu, Dong Yang, Zhongyi Jiang. Nitrogen-Doped Metal–Organic Frameworks for Boosting Photocatalytic Ammonia Synthesis. Transactions of Tianjin University, 2025, 31(6): 567-578 DOI:10.1007/s12209-025-00451-3

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