Two-dimensional polymeric graphitic carbon nitride (g-C3N4) is a low-cost material with versatile properties that can be enhanced by the introduction of dopant atoms and by changing the degree of polymerization/stoichiometry, which offers significant benefits for numerous applications. Herein, we investigate the stability of g-C3N4 under electron beam irradiation inside a transmission electron microscope operating at different electron acceleration voltages. Our findings indicate that the degradation of g-C3N4 occurs with N species preferentially removed over C species. However, the precise nitrogen group from which N is removed from g-C3N4 (C-N-C, [double bond, length as m-dash]NH or -NH2) is unclear. Moreover, the rate of degradation increases with decreasing electron acceleration voltage, suggesting that inelastic scattering events (radiolysis) dominate over elastic events (knock-on damage). The rate of degradation by removing N atoms is also sensitive to the current density. Hence, we demonstrate that both the electron acceleration voltage and the current density are parameters with which one can use to control the stoichiometry. Moreover, as N species were preferentially removed, the d-spacing of the carbon nitride structure increased. These findings provide a deeper understanding of g-C3N4.

Center for Materials Crystallography Department of Chemistry and iNANO Aarhus University DK 8000 Aarhus C Denmark

Department of Chemistry VŠB Technical University of Ostrava Czech Republic and Center for Energy and Environmental Technologies VŠB Technical University of Ostrava 17 Listopadu 15 Ostrava 708 33 Czech Republic

Leibniz Institute for Solid State and Materials Research Dresden Helmholtzstr 20 01069 Dresden Germany

Leibniz Institute for Solid State and Materials Research Dresden Helmholtzstr 20 01069 Dresden Germany and Centre of Polymer and Carbon Materials Polish Academy of Sciences M Curie Skłodowskiej 34 Zabrze 41 819 Poland and Center for Energy and Environmental Technologies VŠB Technical University of Ostrava 17 Listopadu 15 Ostrava 708 33 Czech Republic and Soochow Institute for Energy and Materials Innovations College of Energy Collaborative Innovation Center of Suzhou Nano Science and Technology Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province Soochow University Suzhou 215006 China

Polish Center for Technology Development Ul Stabłowicka 147 Wrocław 54 066 Poland and Centre of Polymer and Carbon Materials Polish Academy of Sciences M Curie Skłodowskiej 34 Zabrze 41 819 Poland

School of Energy and Power Engineering Xi'an Jiaotong University No 28 Xianning West Road Xi'an Shaanxi 710049 China

Soochow Institute for Energy and Materials Innovations College of Energy Collaborative Innovation Center of Suzhou Nano Science and Technology Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province Soochow University Suzhou 215006 China

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Synthesis of vacant graphitic carbon nitride in argon atmosphere and its utilization for photocatalytic hydrogen generation