Catalyst-free synthesis of transparent, mesoporous diamond monoliths from periodic mesoporous carbon CMK-8

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 31; pp. 13593 - 13596
• Main Authors: Zhang, Li, Mohanty, Paritosh, Coombs, Neil, Fei, Yingwei, Mao, Ho-Kwang, Landskron, Kai
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 03.08.2010; National Acad Sciences
• Subjects: Carbon; Chemical synthesis; Diamonds; Electrical phases; Graphite; High pressure; High temperature; Materials; Nanocrystals; Phase transformations; Physical Sciences; Porosity; Porous materials; Pressure; Surface areas
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1006938107

We report on the synthesis of optically transparent, mesoporous, monolithic diamond from periodic mesoporous carbon CMK-8 at a pressure of 21 GPa. The phase transformation is already complete at a mild synthesis temperature of 1,300 °C without the need of a catalyst. Surprisingly, the diamond is obtained as a mesoporous material despite the extreme pressure. X-ray diffraction, SEM, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and Z-contrast experiments suggest that the mesoporous diamond is composed of interconnected diamond nanocrystals having diameters around 5–10 nm. The Brunauer Emmett Teller surface area was determined to be 33 m² g⁻¹ according Kr sorption data. The mesostructure is diminished yet still detectable when the diamond is produced from CMK-8 at 1,600 °C and 21 GPa. The temperature dependence of the porosity indicates that the mesoporous diamond exists metastable and withstands transformation into a dense form at a significant rate due to its high kinetic inertness at the mild synthesis temperature. The findings point toward ultrahard porous materials with potential as mechanically highly stable membranes.