Sub-4 nm Nanodiamonds from Graphene-Oxide and Nitrated Polycyclic Aromatic Hydrocarbons at 423 K

Abstract

Nanodiamonds are interesting materials from the point of view of their biocompatibility and their chemical, spectroscopic, and mechanical properties. Current synthetic methods for nanodiamonds involve harsh environments, which are potentially hazardous in addition to being expensive. We report a low-temperature (423 K) hydrothermal approach to form nanodiamonds by using graphene-oxide or nitrated polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, or pyrene) as a starting material. The reaction products contain single-crystalline or twinned nanodiamonds with average diameters in the 2–3 nm range. Theoretical calculations prove that, at the nanoscale, sub-4 nm nanodiamonds may adopt a structure that is more stable than graphene-oxide and nitrated polycyclic aromatic hydrocarbons. Our findings show that sp 2 carbon in the polycyclic aromatic precursor can be converted to sp 3 carbon under unexpectedly moderate temperature conditions by using nanoscale precursors and thus offer a low-temperature approach for the synthesis of sub-4 nm nanodiamonds.

Ultrasmall Nanodiamonds: Perspectives and Questions

“…58,99 Further theoretical and experimental efforts are needed to fully understand the role of electron-withdrawing (nitro-) groups of the polyaromatic precursors in their conversion to diamond. 29 The effects of the environment (or catalysis) on this conversion also need a better understanding. In general, a variety of "chemical" aspects of diamond synthesis discussed above need more attention in the future.…”

“…One interesting example is a recent publication, 29 where the authors emphasize the importance of the right choice of precursor (a nitrated polyaromatic compound in this case) based on mainly "chemical" considerations; i.e., the functional group induced partial rehybridization of sp 2 to sp 3 carbon has lowered the bond strength in the precursor structure, in this way facilitating the conversion of a polyaromatic compound to USND. Many different chemical vapor deposition (CVD) diamond film synthesis techniques are another example.…”

“…This is important for particles embedded in a matrix as one can selectively record the signal from a nanoparticle. 29,68 Hence, TEM is an indispensable characterization tool for USNDs. Figure 5a−c shows high-resolution TEM (HRTEM) images of single DNDs ranging from 1.8 to 4 nm in size and exhibiting well-resolved atomic columns of the diamond core and a single layer of atoms constituting reconstructed surfaces resembling fullerene-like structures.…”

“…An interesting recent study has reported a synthesis of sub-4 nm NDs from graphene oxide and nitrated polycyclic aromatic hydrocarbons at 423 K and ambient pressure. 29 Below, we discuss this and other approaches to synthesize USNDs, some of their properties and potential applications, as well as related advantages and challenges. Of particular interest for this perspective are the bottom-up synthesis methods of diamonds, NDs, and USNDs, while the readers interested in details of the top-down techniques are referred to the corresponding publications cited throughout this perspective.…”

“…Filling the ∼4 nm gap in size between the largest presently synthesizable diamondoid and a typical DND particle (Figure ) invites further efforts. An interesting recent study has reported a synthesis of sub-4 nm NDs from graphene oxide and nitrated polycyclic aromatic hydrocarbons at 423 K and ambient pressure . Below, we discuss this and other approaches to synthesize USNDs, some of their properties and potential applications, as well as related advantages and challenges.…”