Colloidal dispersion is essential for most nanodiamond applications, but its
influence on nanodiamond electronic properties remains unknown. Here we have
probed the electronic structure of oxidized detonation nanodiamonds dispersed
in water by using soft X-ray absorption and emission spectroscopies at the
carbon and oxygen K edges. Upon dispersion in water, the π* transitions from
sp2-hybridized carbon disappear, and holes in the valence band are observed.