The thermal property of an as-synthesized black powder,a detonation nanodiamond (DND) product,was first analyzed,followed by thermal oxidation to modify its surface.During the thermal treatment,the non-diamond carbonaceous shell of the black powder was oxidized,with the likelihood of forming a C-O-C bonding between carbon atoms on the particle surface.This new structure may rupture with intensified oxidation through increasing the heating temperature and prolonging the process duration.As more oxygen-containing functional groups form on the particle surface,the particle surface becomes negatively charged,and the powder turns to be more hydrophilic.