COMMUNICATION
Surfactant-free hydrothermal synthesis of lithium aluminate
microbricks and nanorods from aluminium oxide nanoparticles{
Upendra. A. Joshi,a Soo Hyun Chungb and Jae Sung Lee*a
Received (in Cambridge, UK) 9th June 2005, Accepted 12th July 2005
First published as an Advance Article on the web 4th August 2005
DOI: 10.1039/b508168h
15). Then the mixture was put into hydrothermal reaction in a
Teflon coated reactor at a constant temperature (150 uC) without
disturbing for 3 days. The as-obtained white product was
separated by centrifugation, washed with distilled water to remove
excess LiOH and then dried in an oven at 100 uC overnight.
Representative scanning electron microscope (SEM) images of
the reaction product are shown in the Fig. 1 and in the Supporting
Information.{ As shown in Fig. 1a, a typical SEM image of the
product obtained by the hydrothermal reaction with Li/Al 5 3
clearly reveals a brick-like morphology. Further, the high
magnification SEM image shown in Fig. 1b clarifies that this
brick-like morphology has an orthorhombic structure with two
edges of 8.45 mm and 8.81 mm respectively, and length of 25 mm;
hence they could be called ‘‘microbricks’’. Similarly, the image in
Fig. 1c of b-LiAlO2 nanorods prepared by the same hydrothermal
reaction with Li/Al 5 15 shows a rod like morphology. Yet, the
cross-section of the nanorods is not circular but rectangular as
shown in Fig. 1d.
b-LiAlO2 microbricks and rectangular nanorods have been
successfully synthesized from Al2O3 nanoparticles by a simple
hydrothermal process without any surfactant or template, by
simply changing the Li/Al molar ratio.
Over the past decade, one-dimensional (1-D) nanosized building
blocks such as nanorods, nanowires, nanotubes and nanobelts
have attracted immense interest because of their distinctive
geometries, novel physical and chemical properties, and potential
applications in nanodevices.1 One-dimensional nanostructures can
be fabricated by template-directed growth methods by using
carbon nanotubes2 or porous alumina templates,3 the vapor–
liquid–solid (VLS) mechanism,4 and the vapor–solid (VS)
mechanism.5 Liquid-phase synthesis could be performed at milder
conditions, yet it requires surfactants as soft templates that have to
be removed afterward by combustion. Thus, a serious challenge
that scientists and engineers have to face to unfold the full
potential of applications and prospects of nanotechnology is the
development of sustainable large-scale manufacturing techniques
for time and cost-effective production.
These nanorods also have an orthorhombic structure with two
edges of 40 nm and 60 nm respectively and lengths of 1–2 mm, and
thus could be called ‘‘rectangular nanorods’’. The uniformity in
morphology and size is impressive for both samples as
demonstrated by SEM images in the Supporting Information
(Fig. S1–S2){. X-ray diffraction patterns in Fig. 1e show that both
microbricks (pattern a) and rectangular nanorods (pattern b) are
composed of highly crystalline orthorhombic b-LiAlO2 structures.
The unit cell parameters for both samples have been determined to
Lithium aluminate (LiAlO2) is a potential candidate for an
electrolyte matrix of molten carbonate fuel cell (MCFC) and a
tritium breeding blanket of fusion reactor due to its chemical and
thermal stability. For these applications, long rod-shaped or
fibrous lithium aluminate forming a fine porous structure is
especially desirable.6,7 Most previous approaches to the prepara-
tion of lithium aluminate employed high temperatures and
expensive precursors.8
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be a 5 5.3 A, b 5 6.3 A and c 5 4.9 A, which are also in
agreement with the corresponding bulk b-LiAlO2 (space group
symmetry Pna21 (33), JCPDS 33-0785) with the structure shown in
Fig. 1f.
We have recently reported the controlled fabrication of
a-LiAlO2 and c-LiAlO2 nanotubes via a surfactant-templated
hydrothermal methods.9 Here, we report for the first time a
surfactant-free hydrothermal synthesis of b-LiAlO2 microbricks
and rectangular nanorods from Al2O3 nanoparticles. Because we
use very mild conditions and all inorganic low-cost raw materials,
scale-up of this procedure for large-scale production should be
very easy.
From the TEM image in Fig. 2a, it is evident that the nanorods
are of fairly uniform lengths of 1–2 mm and diameters of 40–
200 nm. Inset Fig. 2a shows the side view of a tip of a nanorod
which confirms the orthorhombic nature of the rod. In order to
study the lattice structure and to judge the growth direction of
b-LiAlO2 rectangular nanorods, a HRTEM experiment was
carried out. On the basis of the calculation of the lattice spacing
and an analysis of its orientation, it was found that the nanorods
grew perpendicular to [110] as seen in Fig. 2b. Inset Fig. 2b shows
the corresponding selected area electron diffraction (SAED)
pattern.
Detailed experimental and characterization procedure is given in
the Supporting Information.{ In brief, LiOH (98+% Aldrich) and
Al2O3 nanopowder (Aldrich) with sizes of ca. 20–150 nm, were
stirred together with 36 mL distilled water for 1 h (Li/Al 5 3 and
aDepartment of Chemical Engineering, School of Environmental Science
Engineering, Pohang University of Science and Technology
(POSTECH), San 31 Hyoja-dong, Pohang, 790-784, Korea.
E-mail: jlee@postech.ac.kr; Fax: 82-54-279-5528; Tel: 82-54-279-2266
bKorea Institute of Energy Research, Daejeon, 305-343, Korea
{ Electronic supplementary information (ESI) available: detailed experi-
mental procedures, SEM images and XRD pattern for calcined sample.
To investigate the structural information about the environment
of the Al nuclei in the samples, we carried out 27Al MAS NMR.
Mu¨ller et al.10 studied NMR spectra for all the three (a, b, c)
polymorphs of LiAlO2 and concluded that the Al in the b-LiAlO2
was tetrahedrally coordinated confirming an orthorhombic
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 4471–4473 | 4471
Joshi, Upendra A.
