Chemical functionalization of nanodiamond by amino groups: an X-ray photoelectron spectroscopy study

Utilizing Constant Energy Difference between sp-Peak and C 1s Core Level in Photoelectron Spectra for Unambiguous Identification and Quantification of Diamond Phase in Nanodiamonds

The modification of nanodiamond (ND) surfaces has significant applications in sensing devices, drug delivery, bioimaging, and tissue engineering. Precise control of the diamond phase composition and bond configurations during ND processing and surface finalization is crucial. In this study, we conducted a comparative analysis of the graphitization process in various types of hydrogenated NDs, considering differences in ND size and quality. We prepared three types of hydrogenated NDs: high-pressure high-temperature NDs (HPHT ND-H; 0-30 nm), conventional detonation nanodiamonds (DND-H; ~5 nm), and size- and nitrogen-reduced hydrogenated nanodiamonds (snr-DND-H; 2-3 nm). The samples underwent annealing in an ultra-high vacuum and sputtering by Ar cluster ion beam (ArCIB). Samples were investigated by in situ X-ray photoelectron spectroscopy (XPS), in situ ultraviolet photoelectron spectroscopy (UPS), and Raman spectroscopy (RS). Our investigation revealed that the graphitization temperature of NDs ranges from 600 °C to 700 °C and depends on the size and crystallinity of the NDs. Smaller DND particles with a high density of defects exhibit a lower graphitization temperature. We revealed a constant energy difference of 271.3 eV between the sp-peak in the valence band spectra (at around 13.7 eV) and the sp3 component in the C 1s core level spectra (at 285.0 eV). The identification of this energy difference helps in calibrating charge shifts and serves the unambiguous identification of the sp3 bond contribution in the C 1s spectra obtained from ND samples. Results were validated through reference measurements on hydrogenated single crystal C(111)-H and highly-ordered pyrolytic graphite (HOPG).

Nanodiamond (ND)-based polyamide (PA) 66 nanocomposite studied with infrared (IR) microscopy and time-domain nuclear magnetic resonance (TD-NMR) combined with two-trace two-dimensional (2T2D) correlation analysis

Nanodiamond/polyamide (ND/PA) nanocomposite was examined with infrared (IR) microscopy and time-domain nuclear magnetic resonance (TD-NMR) to elucidate in detail the interphase between amino functionalized ND (ND-NH₂) and PA 66. An IR image of the ND/PA nanocomposite suggested the uniform nanoscale distribution of the ND-NH₂ particles thanks to the spherical shape and accessible external surface of ND terminated with reactive amino groups. On the other hand, a substantial level of change was observed in T₂ decay curves when the ND-NH₂ particles were incorporated in the PA 66. The fine features of the thermally induced changes in the decay curves were readily analyzed with the two-trace two-dimensional (2T2D) correlation method. The variation in the asynchronous correlation intensity indicated that the changes observed in the mechanical properties of the ND/NH₂ may be attributed to the development of crosslinking between tie chains in the amorphous region via the interaction between the ND-NH₂ and PA 66. Accordingly, such firm links have a substantial effect in preventing the displacement of the amorphous domain, which eventually increases the Young's modulus but reduces the ductility of the PA.