Synthesis of sub-10 nm Nanodiamonds via Hydrothermal Synthesis Route

Abstract

Nanodiamonds are fascinating allotropes of Carbon that have been recently added to the carbon family, they offer unique mechanical, optical, and chemical properties. In recent years, there have been widespread studies on various synthesis strategies of nanodiamonds (top-down and bottom-up approaches) which in turn will be applied to various industrial and biomedical applications. The contemporary methods of synthesis that are being employed lack chances of scalability, are expensive due to their high post–production and purification cost, and, are certainly perilous. We have developed a one-step hydrothermal synthesis approach to produce nanodiamonds by using citric acid and sodium hydroxide as primal reaction materials. The specific choice of our precursor materials played a critical role that made the diamond synthesis possible at low temperature and pressure conditions. TEM and XRD analysis were used to investigate the phase composition and crystal size of the synthesized product. The product formed via this route has confirmed the presence of single-crystal nanodiamonds with particle sizes less than 10nm. These synthesized nanodiamonds had d-spacing values that were in harmony with previously reported values of lab-grown nanodiamonds. The XPS survey scan exhibited all the photoelectrons and Auger-electron lines of our envisioned elements in our lab-grown nanodiamonds. Functional group analysis by FTIR confirmed the presence of the diamond peak at around 1332 cm-1. The optical properties of the synthesized nanodiamonds were investigated by photoluminescence studies that showed the presence of NV0 and NV- color centers under 533nm laser excitation. UV/Vis spectroscopy also revealed the presence of the intrinsic diamond peak at around 225nm, upon excitation. Nanodiamonds tend to emit a fluorescence which was also explored using confocal microscopy. Our proposed method of nanodiamond synthesis relies on the fact that sodium must have acted as a reductant and helped in the organization of the carbon atoms into a sp 3 network by means of covalent bonding and assisted in diamond formations.