Nanodiamonds (NDs) are under active investigation for their unique properties and potential applications in energy harvesting, quantum technologies, and nanomedicine. The surface chemistry of diamond nanoparticles strongly modifies their physico-chemical properties (semiconducting behavior, colloidal properties, interaction with water and light). The present study aims to perform a chemical analysis by X-ray photoemission spectroscopy of the ND shallow surface (i. e. the first atomic planes) surrounded with water molecules.
This was achieved on PLEIADES beamline at SOLEIL synchrotron by researchers from NIMBE (CEA-CNRS UMR) on isolated ND in an aerodynamic jet. Results showed for the first time the effect of residual water molecules on different ND surface chemistries.
The electronic properties of diamond nanoparticles (ND) are highly dependent on their surface chemistry (oxidized, hydrogenated). Such ND can be stabilized in water exhibiting different colloidal properties according to their chemistry. These ND colloids can be further used to activate chemical reactions under light: CO2 reduction, hydrogen production, pollutant degradation. The ND / water interface, involved in these reactions, is still under investigation. In this study, the scientists investigated by photoemission the shallow surface chemistry of ND surrounded with water molecules. The synchrotron X-ray beam allowed them to tune the incident photon energy to probe the first atomic layers of ND (here 0.3 nanometer).
These photoemission experiments allowed to build the electronic structure of both hydrogenated and oxidized ND. Obtained results are in fair agreement with the literature. At the same time, a significant signal was collected corresponding to oxidized species whatever the ND surface chemistry. This observation is rather unexpected for hydrogenated ND. Two main hypotheses can explain this result:
- a different spatial location for carbon/oxygen chemical bonds depending on surface chemistry
- labile interactions of the surface with adsorbed water molecules.
Such photoemission measurements required the experimental set-up available on PLEIADES beamline at SOLEIL. It allows first to produce a focused ND beam from a stable aqueous colloid. Then, this beam of isolated ND crosses the soft X-ray beam of tunable energy and the photoemitted electrons are analysed by spectroscopy.
Figure 1: Comparison of conventional and aerosol X-ray photoemission spectrocopies.
These new findings contribute to a better knowledge of the true interface formed with water molecules when ND are in aqueous colloids. This is an important step to further investigate photocatalytic performances of ND under visible light. The next step will be a study of these ND fully solvated in a liquid micro‑jet. The stability of such a jet has already been demonstrated by coupling the PLEIADES dedicated nanoparticle‑injection line with the liquid‑jet setup at the GALAXIES beamline, and the first photoelectron signal has even been recorded.
Consequently, a full research proposal was submitted during the most recent call for proposals, in September 2025.