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  • ReceivedApr 22, 2018
  • AcceptedApr 24, 2018
  • PublishedJun 15, 2018

Abstract

Atomically dispersed metal has gained much attention because of the new opportunities they offer in catalysis. However, it is still crucial to understand the mechanism of single-atom catalysis at molecular level for expanding them to other more difficult catalytic reactions, such as ammonia synthesis from nitrogen. In fact, developing ammonia synthesis under ambient conditions to overcome the high energy consumption in well-established Haber-Bosch process has fascinated scientists for many years. Herein, we demonstrate that single Cu atom yields facile valence-electron isolation from the conjugated π electron cloud of p-CN. Electron spin resonance measurements reveal that these isolated valence electrons can be easily excited to generate free electrons under photo-illumination, thus inducing high efficient photo-induced ammonia synthesis under ambient conditions. The NH3 producing rate of copper modified carbon nitride (Cu-CN) reached 186 μmol g−1 h−1 under visible light irradiation with the quantum efficiency achieved 1.01% at 420 nm monochromatic light. This finding surely offers a model to open up a new vista for the ammonia synthesis at gentle conditions. The introduction of single atom to isolate the valence electron also represents a new paradigm for many other photocatalytic reactions, since the most photoinduced processes have been successfully exploited sharing the same origin.


Funded by

the National Key R&D Program of China(2017YFA0207301)

the National Natural Science Foundation of China(21622107,11621063,U1532265)

the Key Research Program of Frontier Sciences(QYZDY-SSW-SLH011)

the Youth Innovation Promotion Association CAS(2016392)

the Fundamental Research Funds of Central University(WK2340000075)

and the Major Program of Development Foundation of Hefei Center for Physical Science and Technology(2017FXZY003)


Acknowledgment

This work was supported by the National Key R&D Program of China (2017YFA0207301), the National Natural Science Foundation of China (21622107, 11621063, U1532265), the Key Research Program of Frontier Sciences (QYZDY-SSW-SLH011), the Youth Innovation Promotion Association CAS (2016392), the Fundamental Research Funds of Central University (WK2340000075), and the Major Program of Development Foundation of Hefei Center for Physical Science and Technology (2017FXZY003). We thank Prof. J.H. Su from the University of Science and Technology of China for his helpful discussion of the ESR results. The computational center of USTC is acknowledged for computational support.


Interest statement

The authors declare that they have no conflict of interest.


Supplement

Supporting Information

The supporting information is available online at http://chem.scichina.com and http://link.springer.com/journal/11426. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.


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  • Figure 1

    (a) XRD patterns for p-CN and Cu-CN. (b) HRTEM and (c) HAADF-STEM image of Cu-CN. (d) FT-EXAFS curves of Cu foil and Cu-CN. (e) FT-EXAFS curves of the experimental data and the fit of Cu-CN. (f) Proposed configuration of Cu-CN in a T-defect (color online).

  • Figure 2

    (a) Quantitative determination of NH3 generated under visible light. (b) Photocatalytic ammonia-production rate under different atmospheres. (c) Photoluminescene spectra of p-CN and Cu-CN. (d) Photocurrent performance of p-CN and Cu-CN (−0.4 V vs. Ag/AgCl, pH=6.6) (color online).

  • Figure 3

    Photocatalytic synthesis of ammonia over the as-prepared Cu-CN. (a) In situ FTIR spectra recorded during the photocatalytic synthesis of ammonia over Cu-CN. (b) and (c) Amplified selected areas in Figure 3(a). The black dashed boxes indicate the changes during the procedure (color online).

  • Figure 4

    ESR of p-CN and Cu-CN (a) before and (b) during light irradiation. (c) Top view of the electron density distribution. (d) Side view of the electron density distribution. The yellow and green isosurfaces correspond to an increase in the number of electrons and the depletion zone, respectively. The isosurfaces are 0.003 e Å−3. (e) Projected density of states of C and N atoms around the T-defect. (f) Projected density of states of Cu atoms, donor N atoms, and C atoms bound with the donor N atoms (color online).

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