摘要
The effi ciency of photocatalytic ammonia(NH_(3))synthesis is severely limited by the extremely diffi cult activation of N_(2) owing to its high N≡N triple bond energy.To address this challenge,we propose an N-doping strategy to facilitate the N_(2) activation.Our strategy involves optimizing the electronic structure of the metal active sites by modulating the coordination element.First,we introduce fi ve diff erent N-coordination ligands with distinct steric hindrances and N electron densities(2-methyl-imidazole(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),NH_(2)-MIL-68(NM),to construct the N-coordination via the partial replacement of the O-coordination in the metal clusters.Electrochemical impedance spectroscopy and photocur-rent 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 eff ectively boosts the carrier separation efficiency than incorporating small(MI)or large(TA)ligands.Furthermore,the N-doped MOF modifi ed with BIT(in which N exhibits a moderate electron density)exhibits the strongest carrier separation capability.Concurrently,the X-ray photoelectron spec-troscopy,density functional theory,and N_(2) temperature-programmed desorption results confi rm that the established low-electronegativity N-coordination elevates the electron density of the metal active sites,which consequently enhances the N_(2) activation process.The systematic optimization of the N-coordinating ligand species and doping concentrations allows the optimal NM-0.5BIT to achieve a NH 3 production rate of 175.5μmol/(g·h).The proposed N-doping strategy off ers several insights into the activation of inert molecules and the development of organic framework photocatalysts.
基金
the National Natural Science Foundation of China(Nos.21621004,22478295,and 22122809)
the National Key Research and Development Program of China(Nos.2022YFC2105902 and 2024YFB4206301)
Young Scientifi c and Technological Talents(Level One)in Tianjin(No.QN20230103)
Program of Introducing Talents of Discipline to Universities(No.BP0618007)
Haihe Laboratory of Sustainable Chemical Transformations.
