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

Abstract

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 m 2 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.high pressure | nano

Synthesis and characterization of a nanocrystalline diamond aerogel

“…S1) and were found to be similar to prior reports on amorphous carbon aside from pressure-induced shifts. This observation rules out the possibility of a superhard graphite phase helping to prevent pore collapse, which has been hypothesized for mesoporous carbon (17) given that the spectrum still appears amorphous after pressurizing. Spectra obtained following laser heating (Fig.…”

“…Impressive advances have been made in the case of polycrystalline aerogels through the oxidative aggregation of chalcogenide quantum dots that preserve spectral signatures of quantum confinement (14). Furthermore, recent high-pressure, high-temperature (HPHT) experiments with mesoporous silica and periodic carbon have been employed to produce mesoporous coesite (15,16) and diamond (17) structures.…”

Photothermal effects during nanodiamond synthesis from a carbon aerogel in a laser-heated diamond anvil cell

“…The EELS spectra also contain a dip at 302.5 eV, characteristic of cubic diamond's second gap. The minimum conditions (16.3 GPa and ~1800 K) to drive the phase change of carbon aerogel to nanodiamond are among the lowest reported, as illustrated in Figure 1a [22,25,27,40]. In a separate experiment at 12.0 GPa and identical irradiances, there was no evidence of phase conversion, suggesting that the carbon aerogel-nanodiamond phase line sits between 12.0 and 16.3 GPa and 1340 and 1800 K. These relatively mild conditions are likely due to the amorphous carbon starting material and the rapid heating conditions.…”

“…In fact, during the first successful HPHT experiments in the 1960's, nanodiamonds were an unexpected byproduct during the first successful production of bulk diamond at an industrial scale. The direct HPHT synthesis of nanodiamonds was not pursued again until recently [20][21][22][23][24]. Research on bulk HPHT diamond during this 50-year hiatus realized a range of important discoveries including the use of catalysts to decrease the pressures and temperatures required for diamond production, the observation that different carbon precursors can form diamond at less extreme conditions, and the ability to incorporate dopants into diamond by simply mixing them into the carbon precursor [20,22,[25][26][27][28].…”

Missing-atom structure of diamondΣ5 (001) twist grain boundary

“…1 Moreover, in the past few years, it has been possible to produce materials with very small diamond crystals, with particle sizes in the order of a few nm. 2 Indeed, the synthesis of nanocrystalline films of diamondlike carbon, polycrystalline cubic diamond, and aggregated diamond nanorods has been reported in literature [3][4][5][6][7][8][9] Importantly, polycrystalline diamond, reported to consist of very fine granular crystals, was found to be as hard or even harder than single-crystal diamond, with constant hardness throughout the sample. 3 The aggregated diamond nanorods, and mesoporous diamond composed of interconnected nanocrystals, were found to be the densest among all carbon materials and had the lowest experimentally determined compressibility.…”