Surface properties of hydrogenated nanodiamonds: a chemical investigation

Abstract

Hydrogen terminations (C-H) confer to diamond layers specific surface properties such as a negative electron affinity and a superficial conductive layer, opening the way to specific functionalization routes. For example, efficient covalent bonding of diazonium salts or of alkene moieties can be performed on hydrogenated diamond thin films, owing to electronic exchanges at the interface. Here, we report on the chemical reactivity of fully hydrogenated High Pressure High Temperature (HPHT) nanodiamonds (H-NDs) towards such grafting, with respect to the reactivity of as-received NDs. Chemical characterizations such as FTIR, XPS analysis and Zeta potential measurements reveal a clear selectivity of such couplings on H-NDs, suggesting that C-H related surface properties remain dominant even on particles at the nanoscale. These results on hydrogenated NDs open up the route to a broad range of new functionalizations for innovative NDs applications development.

Surface Modifications of Nanodiamonds and Current Issues for Their Biomedical Applications

“…In addition, a new component appears in the XPS C1s core level [93]. A similar modification of the C1s peak was reported for a diamond surface after UV oxidation [117].…”

“…The spontaneous grafting of a diazonium salt on hydrogenated HPHT NDs was also demonstrated [93]. On a diamond surface, this arises from specific electronic properties conferred by C-H terminations [122].…”

“…The surface reactivity of HPHT H-NDs (50 nm) was investigated applying several surface modifications [93]: a selective oxidation under UV exposure and functionalization with alkenes and diazonium moieties. These reactions are common on hydrogenated diamond films towards efficient biological functionalizations (DNA, proteins grafting) [113][114][115] so their use on NDs may also lead to promising developments.…”

“…Third, a significant amount of hydroxyl groups can be generated during milling [69] or BASD [84] of NDs in water. More recently, a photochemical oxidation under UV was performed on NDs previously hydrogenated [93].…”

“…The origin of this positive ZP is not yet clearly understood. In the literature, colloidal aqueous suspensions of positively charged NDs (ZP > 30 mV) were also reported after different surface modifications: reduction with borane or LiAlH 4 [18,129], UV hydroxylation [93], annealing under hydrogen flow [88], plasma hydrogenation [86] or surface graphitization [75]. These charge modifications may be related to graphitic carbon surrounding NDs core or to protonation of some chemical functional groups or lastly to intrinsic properties of hydrogenated diamond surface.…”