Thiol-terminated nanodiamond powders for support of gold nanoparticle catalysts

Abstract Surface-functionalized nanodiamond (ND) is a promising material for nanomedicine and nanotechnology applications. Among the surface functionalizations developed for ND, thiol-termination has received relatively little attention. Here we describe a new method of thiolating the surface of detonation and high-pressure high-temperature ND by treatment with elemental sulfur at 450 °C, followed by reduction of surface-bound sulfur moieties. The surface composition of the functionalized ND was characterized using X-ray photoelectron spectroscopy and transmission electron microscopy. Analysis revealed the presence of both sulfur in the thiol oxidation state and oxygen, indicating that the surface was partially modified with thiols with no graphitization of the diamond surface detected. The surface thiols participated in a thiol-Michael addition with fluorescein-5-maleimide, demonstrating the utility of the thiols for conjugation of molecules to the diamond surface. Thiolated detonation ND was used as a support for gold (Au) nanoparticles (NPs) formed by in situ reduction of Au salt at 250 °C. The thiol-terminated ND stabilized the Au NPs, maintaining the small (~4 nm) size, whereas aggregates formed on ND powder with an oxygenated surface. The supported Au NPs catalyzed the reduction of resazurin, indicating that the active sites were not passivated by interaction with the ND surface thiols.