Biomedical Engineering Reference
In-Depth Information
The obtained results give strong evidence that the final chemical
state of extracted nanodiamond grains depends on the type of raw
soot, which in turn differs according to the details of detonation
synthesis. This can be caused by the difference in the chemical
activity of detonation nanodiamond in carbon soot synthesized
in different conditions, which revealed in the reactions with the
substances during the extraction from the soot. The chemical
activity of the surface of diamond in different media depends on the
atomic structure (crystalline orientation) of the surface [73, 74].
The conditions of detonation synthesis have a strong influence on
the shape of diamond nanocrystals [75] and the structure of their
surface shell [67, 76]. One could suggest therefore to consider the
surface crystal structure as a “hereditary” feature affecting the
chemical reactivity of nanodiamond surface toward environmental
conditions (both during synthesis and extraction).
Thus, even with the identical procedure of extraction the surface
properties of the final nanodiamond product are in many respects
determined by the properties of initial detonation soot, which in
turn depend on the conditions of the explosive synthesis.
Modification of Nanodiamond Surface by
Thermal Oxidation
6.3.7
As has been demonstrated earlier [58], the thermal treatment of
UDDs in air at temperatures up to 450°C is a simple and effective
method of modification of the composition and structure of oxygen-
containing surface groups. This procedure was applied to the UDD
of different types, and the surface chemistry of modified UDD was
characterized by TDMS.
The TDMS profiles of CO and CO
for UDD samples CH-7 and
K-2 preheated in air at 370°C for 60 minutes are shown in Fig. 6.5
(curve 3). In contrast to the case of acid treatment (Fig. 6.5, curves 1
and 2) the mild oxidation by air oxygen leads to a better “unification”
of structure and content of the oxygen-containing groups, revealed
by the similarity of the profiles of thermal desorption including the
peak temperatures and the amounts of evolved carbon oxides.
This possibility of unification of the oxidation state of UDD surface
by heat treatment in air was confirmed by the data of IR spectroscopy
for the different samples, heated in air atmosphere during 5-10
minutes at 440-460°C [26]. The absorption band of C-O bond is
positioned in the range from 1720 cm
2
-1
-1
(sample CH-7) to 1850 cm
