ARTICLE IN PRESS
D. Mu n˜ oz-Rojas et al. / Journal of Solid State Chemistry 178 (2005) 295–305
299
On the other hand, the diffraction patterns of the
products obtained when Ag Cu2O3 was treated with dry
gaseous ozone. Such radical may not be able to
decompose the Ag Cu2O4 formed, while the active
2
2
ozone are shown in Fig. 3C and D. The behavior of
Ag Cu2O3 in this case is similar to that treated with wet
species present in gaseous ozone could be responsible for
the Ag Cu2O4 decomposition/amorphization observed
2
2
ozone. After 16 h the peaks that appear correspond to
Ag Cu O ; but in this case the crystallinity of the
with no solvent present. On the other hand, kinetic
factors could also affect the reaction outcome when
comparing dry and wet ozone. Thus, it could be induced
that the oxidation may proceed by different mechanisms
in ozone oxidation or by traditional electrochemical
methods in aqueous solutions, and also when oxidation
is performed in water or in solid state.
2
2
4
product is even worse than before, and when the
treatment is kept for longer times, Ag Cu2O4 tends to
2
decompose and become amorphous even faster than
when wet ozone is used. Peaks corresponding to AgO
can also be identified after 66.5 h of treatment. In all
cases the presence of Ag Cu2O4 can be considered a
2
In order to see whether the ozone treatment would
affect the electrochemically synthesized phase
Ag Cu O ; a sample of it was also treated with dry
proof that the transformation of Ag Cu O to
2
2
3
Ag Cu O occurs in solid state as a rather special
4
2
2
2
2
4
‘
‘corrosion reaction’’.
Finally, when an aqueous Ag Cu2O3 suspension is
and wet ozone. In this case, electrochemical Ag Cu2O4
2
shows no sings of amorphization/decomposition after
long exposures to ozone (31 h). It seems then that well
crystallized Ag Cu2O4 is not affected by the higher
2
bubbled with ozone, the result is quite different (Fig. 4).
Again the peaks that appear correspond to Ag Cu2O4;
2
2
but in this case, the oxidation product is better crystal-
lized, and as opposed to what happens in the previous
two cases, the longer the treatment with ozone the better
the crystallinity of the oxidation product. After 60 h of
ozone potential, proving a larger stability vs. ozone than
its precursor Ag Cu2O3:
2
Both electrochemical synthesized Ag Cu O and the
2
2
4
product resulting of ozonization of Ag Cu O in
2
2
3
ozonization, only the peaks corresponding to Ag Cu2O4
2
suspension were analyzed by SEM, to compare their
morphology (see Fig. 5). Fig. 5A corresponds to the
electrochemical route phase, while Fig. 5B corresponds
to the sample ozonized in suspension for 4.5 h (pattern
A in Fig. 4). As in the diffractogram, unreacted needle-
can be seen and there are no sign of loss of crystallinity
or decomposition. Nevertheless, in all cases, even this
last one, the crystallinity obtained for Ag Cu2O4 is far
2
less than that of the electrochemically synthesized one
(
Ref. in Fig. 4) [4,5].
The fact that better crystallinity, and no decomposi-
like crystals of Ag Cu2O3 are detected in the last, along
2
with much smaller plate-like crystals which would
correspond to the Ag Cu O being formed. Fig. 5C
2
2 4
tion/amorphization, is achieved when there is a large
amount of water present during the reaction, would
imply that the oxidation of Ag Cu2O3 to form
corresponds to a sample treated longer time (powder
diffraction pattern is shown in Fig. 4B, when all
2
Ag Cu2O4 may be proceeding through the formation
2
Ag Cu2O3
Ag Cu2O4). The particle size obtained in this case
shows a higher dispersion and is smaller on average
has already reacted and formed
2
of an oxygen oxidizing aqueous species, like an oxy-or
hydroxyl radical, less reactive than the species found in
2
Fig. 4. Ag Cu2O3 suspension treated with ozone for different times. Bottom: XRD pattern of pure Ag Cu2O3(n). Top: electrochemically synthesized
2
2
Ag Cu2O4 as Refs. [4,5].
2