The exfoliation of bulk graphitic carbon nitride (g-C3N4) into monolayer has been intensively studied to induce maximum sur?face area for fundamental studies, but ended in failure to realize chemi?cally and physically well-defined monolayer of g-C3N4 mostly due to the difficulty in reducing the layer thickness down to an atomic level. It has, therefore, remained as a challenging issue in two-dimensional (2D) chemistry and physics communities. In this study, an "atomic monolayer of g-C3N4 with perfect two-dimensional limit" was successfully prepared by the chemically well-defined two-step routes. The atomically resolved monolayer of g-C3N4 was also confirmed by spectroscopic and micro?scopic analyses. In addition, the experimental Cs-HRTEM image was collected, for the first time, which was in excellent agreement with the theoretically simulated; the evidence of monolayer of g-C3N4 in the perfect 2D limit becomes now clear from the HRTEM image of orderly hexagonal symmetry with a cavity formed by encirclement of three adjacent heptazine units. Compared to bulk g-C3N4, the present g-C3N4 monolayer showed significantly higher photocatalytic gen?eration of -H2O2 and -H2, and electrocatalytic oxygen reduction reaction. In addition, its photocatalytic efficiency for -H2O2 production was found to be the best for any known g-C3N4 nanomaterials, underscoring the remarkable advantage of monolayer formation in optimizing the catalyst performance of g-C3N4.

Intelligent Nanohybrid Materials Laboratory(INML),Institute of Tissue Regeneration Engineering(ITREN),Dankook University,Cheonan 31116,Republic of Korea;College of Science and Technology,Dankook University,Cheonan 31116,Republic of Korea;Department of Nanobiomedical Science and BK21 PLUS NBM Global Research Center for Regenerative Medicine,Dankook University,Cheonan 31116,Republic of Korea;Department of Materials Science and Engineering,College of Engineering,Yonsei University,Seoul 03722,Republic of Korea;SKKU Advanced Institute of Nanotechnology(SAINT),Sungkyunkwan University(SKKU),Suwon 440?746,Republic of Korea;Department of Nano Engineering,Sungkyunkwan University(SKKU),Suwon 440?746,Republic of Korea;National Center for Inter?University Research Facilities(NCIRF),Seoul National University,Seoul 08826,Republic of Korea;Graphene Research Center,Advanced Institute of Convergence Technology,Suwon 16229,Republic of Korea;Department of Pre?Medical Course,College of Medicine,Dankook University,Cheonan 31116,Republic of Korea;0Tokyo Tech World Research Hub Initiative(WRHI),Institute of Innovative Research,Tokyo Institute of Technology,Yokohama 226?8503,Japan

[1]Huiyan Piao;Goeun Choi;Xiaoyan Jin;Seong?Ju Hwang;Young Jae Song;Sung?Pyo Cho;Jin?Ho Choy-.Monolayer Graphitic Carbon Nitride as Metal?Free Catalyst with Enhanced Performance in Photo? and Electro?Catalysis)[J].纳微快报（英文）,2022(03):308-321

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