Hydrogen plasma treated nanodiamonds lead to an overproduction of hydroxyl radicals and solvated electrons in solution under ionizing radiation

Abstract

In numerous fields of application (environmental remediation, catalysis, nanomedicine), production of hydroxyl radicals and solvated electrons by nanomaterials is a cornerstone. Through a very sensitive, nanoparticle-compatible, coumarin-based protocol, we quantified hydroxyl radicals in solution when hydrogenated (H-ND) and oxidized (Ox-ND) detonation nanodiamonds were irradiated by MeV photons. We highlighted a blatant difference between the two surface chemistries as only H-ND led to 50% more radicals, for irradiation doses and ND concentrations relevant in nanomedicine. For the first time, we also quantified solvated electrons after keV irradiation of both suspensions and showed that in the presence of H-ND, hydroxyl radicals and solvated electrons were available in solution in equivalent and higher amounts than in water only. This asks the question of the mechanisms at stage and beside the negative/positive electron affinity hypothesis usually mentioned, we proposed, as for other nanomaterials, that interfacial water could play an essential role in radicals’ production in solution when detonation H-ND are irradiated.