Nanodiamonds or Ultra Dispersed
Diamonds (UDD) or Ultra-Nano-Crystalline Diamonds (UNCD) belong to the carbon
nanomaterials, which, along with graphene, fullerene and nanotubes, have
attracted great interest in recent years due to their unique physical and
chemical properties. Nanodiamond is a carbon nano-crystallite with a cubic
diamond structure and a size of less than 100 nm.
Two types of nanodiamonds produced in commercial
scale are available today in the market: detonation nanodiamonds (DND) having
an average size of 4-5 nm and nanodiamonds obtained by crashing of
microdiamonds produced by high pressure high temperature (HPHT) having an
average size of more than 30 nm.
Each ND particle has cubic diamond lattice when
each carbon atom is bonded covalently with four other carbon atoms inside the
crystalline (Fig. 1), while surface atoms, in contrast to internal ones, have
less than four neighbor atoms; unpaired electrons provide bonding with diverse
functional groups on crystalline surface or form non-diamond bonds with
neighbor surface atoms.
(4-5 nm) ND crystallites, unlike big once, around 15-18 % of carbon atoms are
located on the surface, have unpaired electrons responsible for a high and
variable chemical activity of crystallites surface. Controlling the surface
chemistry of nanodiamonds defines the possibility to provide their desired
interaction with molecules of other materials and objects.