Chemistry Reference
In-Depth Information
1.4
Hydrothermal/Solvothermal Route
The hydrothermal/solvothermal synthesis is typically carried out in
autoclaves, where the superheated solvents and the autogenerated
high pressure provide a microenvironment distinctly different
from those in common synthetic systems. As a result, the products
usually exhibit few defects, high crystallinity, fine homogeneity,
and sometimes special morphologies and thermodynamically
metastable phases, especially when appropriate chelating reagents
or mineralizers are employed.
Cerium hydroxyl carbonate (Ce(OH)CO
) can be readily produced
by hydrothermal reactions and thus frequently used as intermediates
for CeO
3
through hydrothermal route
using cerium oxalate as the Ce source, and ceria was obtained by
subsequent sintering [59]. Similarly, Lu
. Li
et al
. obtained Ce(OH)CO
2
3
et al
. prepared spindle-like
nanocrystals through a hydrothermal
synthesis with urea at 100
orthorhombic Ce(OH)CO
3
°
C [60]; Han
et al
. prepared flower-like
nanorod bundles of hexagonal Ce(OH)CO
at 200
°
C [61]; Chen
et
3
al
. reported the solvothermal synthesis of Ce(OH)CO
and CeO
in
3
2
mixed solvents of water and ethanol [62]. Du
. reported the
hydrothermal synthesis of uniform triangular plate-like and shuttle-
like Ce(OH)CO
et al
assisted by different surfactants (CTAB or PVA) [63,
64]. The intermediates were converted into ceria by calcination in
air. Sun
3
et al
. reported the synthesis of nearly monodisperse flower-
like CeO
microspheres consisting of nanosheet as petals [65].
Ce(OH)CO
2
spheres with similar morphology were prepared first as
an intermediate, using glucose, acrylamide, and ammonia to form a
gel, which was then subjected to hydrothermal treatment at 180
3
C.
An ensuing two-step calcination procedure affords the final products
(Fig. 1.6).
Chen
°
. developed an EDTA-assisted hydrothermal route for
the selective preparation of submicrorods of CeO
et al
via an incomplete
reaction [66]. They also found that uniform nanoparticles were
formed through a complete reaction between NaClO
2
and Ce-
3
EDTA complexes. Yan
et al
. used Na
PO
·6H
O as a mineralizer in
3
4
2
a hydrothermal process at 170
C to synthesize ceria nanocrystals
[67]. During the reaction, octahedral-shaped ceria particles formed
first, and then underwent a phosphate-ion-related dissolution-
recrystallization process to form nanorods.
°
