How g-C3N4 Works and Is Different from TiO2 as an Environmental Photocatalyst: Mechanistic View

  • Jonghun Lim
    Jonghun Lim
    Division of Environmental Science and Engineering and Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea
    More by Jonghun Lim
  • Hyejin Kim
    Hyejin Kim
    Division of Environmental Science and Engineering and Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea
    More by Hyejin Kim
  • Jihee Park
    Jihee Park
    Division of Environmental Science and Engineering and Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea
    More by Jihee Park
  • Gun-Hee Moon
    Gun-Hee Moon
    Division of Environmental Science and Engineering and Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea
    More by Gun-Hee Moon
  • Junie Jhon M. Vequizo
    Junie Jhon M. Vequizo
    Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511, Japan
  • Akira Yamakata
    Akira Yamakata
    Graduate School of Engineering, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511, Japan
  • Jinwoo Lee
    Jinwoo Lee
    Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
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  • , and 
  • Wonyong Choi*
    Wonyong Choi
    Division of Environmental Science and Engineering and Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea
    *E-mail: [email protected]. Phone: +82-54-279-2283. Fax: +82-54-279-8299.
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Cite this: Environ. Sci. Technol. 2020, 54, 1, 497–506
Publication Date (Web):December 3, 2019
https://doi.org/10.1021/acs.est.9b05044
Copyright © 2019 American Chemical Society
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Abstract

Graphitic carbon nitride (CN) as a popular visible light photocatalyst needs to be better understood for environmental applications. The behaviors of CN as an environmental photocatalyst were systematically studied in comparison with a well-known TiO2 photocatalyst. The two photocatalysts exhibit different photocatalytic oxidation (PCO) behaviors and dependences on the experimental conditions (e.g., pH, Pt loading, and the kind of organic substrate and scavenger). The PCO of organic substrates was significantly enhanced by loading Pt on TiO2 under UV light (λ > 320 nm), whereas Pt–CN exhibited a lower PCO activity than bare CN under visible light (λ > 420 nm). While the presence of Pt enhances the charge separation in both TiO2/UV and CN/visible light systems (confirmed by transient IR absorption spectroscopic analysis), the opposite effects of Pt are ascribed to the different mechanisms of OH generation in the two photocatalytic systems. The negative effect of Pt on CN is ascribed to the fact that Pt catalytically decomposes in situ-generated H2O2 (a main precursor of OH radical), which hinders OH production. The production of OH radicals on CN is favored only at acidic pH but 1O2 generation is dominant in alkaline pH. The pH-dependent behaviors of reactive oxygen species generation on CN were confirmed by electron paramagnetic resonance spin trap measurements.

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.9b05044.

  • List of chemicals and materials, Mott−Schottky plots of bare and platinized TiO2 and CN (Figure S1), Pt 4f XPS spectra of various Pt−CN samples and the photocatalytic activity (Figures S2, S3), N2 adsorption-desorption isotherms and SEM images of CN and Pt-CN (Figure S4), XPS and XRD spectra of CN_lsa and CN (Figure S5), photocatalytic activities of bare- and Pt−CN (Figures S6−S8), photocatalytic degradation rates and the apparent quantum efficiencies (Tables S1, S2) (PDF)

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