Raman spectroscopy study of the nanodiamond-to-carbon onion transformation

Abstract

Here, we present a comprehensive study analyzing early stages of the transformation of detonation nanodiamond (ND) powder to graphitic carbon onions via thermal annealing in argon atmosphere. Raman spectroscopy was employed to monitor this transformation, starting with the sp³-to-sp² conversion of the ND surface at the onset of the graphitization process. Additionally, transmission electron microscopy, x-ray diffraction, and thermogravimetric analysis were used to supplement the structural information obtained from Raman spectroscopy and allow for an accurate interpretation of the obtained Raman data. The effect of the annealing time on the transformation process was also studied to determine the kinetics of the conversion at low temperatures. The results presented in this study complement previous work on ND annealing and provide deeper insight into the nanodiamond-to-carbon onion conversion mechanism, in particular the time and size dependence. We present further evidence for the existence of a disordered sp² phase as an intermediate step in the transformation process.

Surface Modifications of Nanodiamonds and Current Issues for Their Biomedical Applications

“…The selective synthesis of a thin graphitic layer on the ND surface by annealing under vacuum at temperature lower than 900°C gives rise to hybrid nanocarbons combining the intrinsic core properties of diamond with the surface reactivity of sp 2 -based nanomaterials. These results were recently confirmed by a Raman study of the sp 3 to sp 2 conversion for detonation NDs [160]. NMR and EPR investigations detect the early stages of graphitization for annealing temperatures included between 600 and 800°C [161].…”

“…Recently, several groups focused on the early stages of surface graphitization of detonation NDs using XPS, HRTEM, Raman or NMR characterizations [55,75,99,160,161]. The aim is to control the formation of hybrid nanoparticles with a sp 2 organized surface covering a sp 3 core, thus avoiding the graphitization of the diamond core.…”

Understanding structure and porosity of nanodiamond-derived carbon onions

“…The Ferrari and Robertson model assumes two regions: below 2 nm, the I D /I G ratio increases with domain size approximately quadratic; only for values above 2 nm, the I D /I G ratio of nanocrystalline graphite decreases with the reciprocal domain size according to the correlation first established by Tuinstra and Koenig [60]. The latter is also observed in the case of OLC: at temperatures of or above 1100°C, the I D /I G ratio decreases constantly with annealing temperature [40,41,[61][62][63][64]. These findings and conclusions are in agreement with the evolution of the full-width at half maximum (FWHM) of the D-and G-mode (Fig.…”

“…Nitrogen gas sorption was performed at À196°C in the relative pressure range from 5 AE 10 À7 to 1.0 in 68 steps. The pore size distribution (PSD) between 0.56 and 37.5 nm was derived using the quenched-solid density functional theory (QSDFT) [39,40] supplied by Quantachrome assuming a slit shape pore geometry. The latter has recently been shown to be the most appropriate model for carbon onions [49].…”

“…As shown by X-ray diffraction (XRD) and Raman spectroscopy studies, the degree of graphitization increases with higher temperatures due to the higher ordering of the carbon shells into graphitic carbon [17,[39][40][41]]. On a single particle level, the transformation causes a significant increase in volume because of the much larger (0 0 2)-plane spacing of graphitic carbon (0.344 nm; extending radially from the center of the onions) compared to the initial CAC bonding distance of diamond (0.154 nm).…”