Controlled- and high-ratio of sp3/sp2 carbon of the detonation-synthesized nanodiamond (DND) might play a very important role in many applications. Here, we demonstrate an atmospheric-pressure process of chemical purification using perchloric acid (HClO4) and identify the control parameters including the reaction temperature, ND loading amount, and processing time. The sp3/sp2 carbon ratio was characterized using UV-Raman spectroscopy (325 nm) and is evaluated based on the intensity ratio (IDia/IG) of the diamond peak and G band peak at 1324 cm-1 and 1590 cm-1, respectively. Through the control of process parameters, we successfully fine-tuned the sp3/sp2 carbon ratio with the range from 0.28 to 1.5 and achieved 15.5 % higher sp3 ratio compared with commercial DND. In addition, we also measured electrical conductivity of DND powder as function of the sp3/sp2 carbon ratio and it shown that sp2 carbon ratio directly affects to enhance the electrical conductivity.
Furthermore, we will also demonstrate a new approach for purifying DND using an atmospheric-pressure plasma jet. Oxygen gas is continuously dissociated in the plasma jet and generates reactive oxygen, which plays a key role in removing non-diamond carbon, including graphite and amorphous carbon. The purification process was evaluated by UV-Raman (325 nm) and X-ray photoelectron spectroscopy. This technique was applied to create a high purity nanodiamond pattern in the polymeric system of polyvinyl alcohol (PVA) and nanodiamonds using a localized plasma jet. The plasma-assisted purification of nanodiamonds enabled to the fabrication of patterns with low electrical conductivity and high thermal conductivity.