Understanding the Surfaces of Nanodiamonds

Abstract

Functional groups and their associated charges are responsible for the binding and release of molecules from the surfaces of particles in nanodiamond colloids. In this work, we describe a combined set of experimental and computational techniques that are used to characterize these functional groups quantitatively. The surfaces of the particles examined during this study are amphoteric, as one would expect for surfaces made of carbon, with high concentrations of phenols, pyrones, and sulfonic acid groups; the average 50-nm-diameter nanodiamond aggregate has approximately 22000 phenols, 7000 pyrones, and 9000 sulfonic acids. The aggregates also have at least 2000 fixed positive charges, stabilized within pyrones and/or chromenes. No evidence for a significant concentration of carboxylic acid groups was found, although some are probably present. Hydroxyl and epoxide groups are present on some areas of the surfaces. The surfaces are graphitized, so the presence of phenols and pyrones is not surprising because such groups are common on graphitic surfaces. The sulfonic acid is due to the sulfuric acid treatment used to remove amorphous carbon and graphite during particle cleaning. The fixed charges are also due to the cleaning procedure that includes the use of KMnO 4 with the sulfuric acid.Based on titration and zeta potential experiments, elemental and particle size analyses, and modeling using semiempirical quantum mechanics, a model is proposed for the types and concentrations of surface groups. The modeling shows how functional groups form during the bead milling and cleaning used in the preparation of the colloid. It also shows that the pK a associated with the phenols and pyrones that are formed (pK a = 7.6−10.0) is consistent with that predicted using titration experiments (pK a ≥ 7.3). The positive surface potential means that the latter pK a value is significantly larger than a Henderson− Hasselbalch-based estimate. The model is shown to be useful in explaining a number of recent experiments in which nanodiamonds were used to bind and release therapeutic drug and polymer molecules.

Laser induced fluorescence spectroscopy of various carbon nanostructures (GO, G and nanodiamond) in Rd6G solution

“…7(c) indicates no significant spectral shift for the Rd6G solution with nanodiamond additives (ND + Rd6G). This nano carbon structure exhibits a loose affinity of transferring electron to Rd6G molecules [54]. Notice that the fluorescence emission intensity due to the addition of ND is relatively higher than that of G/GO.…”

“…It is likely due to the fact that increasing Rd6G concentration, leads to the reduction of PH and subsequently the enhancement of hydrogen bonding. The latter is known as one of the main loading mechanisms [7,54]. In summary, when spectral overlap sensibly exists mainly due to large S-parameter (Huang-Rhys factor) for a certain fluorophore such as Rd6G, then the dye concentration C dye and nanoscatterer density ρ s affect competitively to induce blue or red spectral shifts.…”

Iron embedded magnetic nanodiamonds for in vivo MRI contrast enhancement

“…Both Fe-NDs and NDs were purified and carboxylated to remove the surface graphite fractions and impurities with similar previously described methods 28 . The as received…”

Raman microspectroscopy of nanodiamond-induced structural changes in albumin

“…[7][8][9] The bioconjugation can be facilitated with the aid of functionalization of the ND surface (e.g., by means of carboxylation). [10][11][12] The absence of toxicity of carboxylated NDs (cNDs) has been demonstrated in Refs. 8 and 13 for in vitro interaction with various cells of human organisms.…”