Synthesis of zinc glycerolate microstacks from a ZnO nanorod sacrificial template

Article abstract of DOI:10.1002/ejic.200900308

We synthesized zinc glycerolate (ZnGly) microstacks by treating ZnO with glycerol at 100°C under reflux. We observed that the morphology of the ZnO source has a pronounced effect on the appearance of the ZnGly product. In the absence of structure-directin

Full text of DOI:10.1002/ejic.200900308

FULL PAPER
DOI: 10.1002/ejic.200900308
Synthesis of Zinc Glycerolate Microstacks from a ZnO Nanorod Sacrificial
Template
Róbert Rémiás,[a] Ákos Kukovecz,*[a] Mária Darányi,[a] Gábor Kozma,[a] Szilvia Varga,[a]
Zoltán Kónya,[a] and Imre Kiricsi[a]
Keywords: Electron microscopy / Zinc / Nanostructures / Chelates / Sacrificial templating
We synthesized zinc glycerolate (ZnGly) microstacks by
treating ZnO with glycerol at 100 °C under reflux. We ob-
served that the morphology of the ZnO source has a pro-
nounced effect on the appearance of the ZnGly product. In
the absence of structure-directing effects the product ZnGly
is obtained as a random heap of hexagonal prisms with an
average diameter and thickness of ca. 2.5 µm and ca. 350 nm,
respectively. However, bundles of nanorod-shaped ZnO ob-
tained by the thermal decomposition of zinc oxalate nano-
rods could readily be transformed into 2–4 µm long zinc glyc-
erolate microstacks in which 6–12 hexagonal prisms are
aligned face-to-face. We present evidence that the ZnGly
plates in the microstacks are bound together by forces strong
enough to withstand mechanical deformation exercised by a
contacting AFM tip. The ZnGly microstacks appear to
emerge from the ZnO nanorod bundles in an approx. 1:1 ratio
in the reactive template synthesis.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
ber compounds.[22] The general public is regularly exposed
to ZnGly as it is effective against oral herpetic sores[23] and
serves as the active component of the product “GlyZinc.”
It belongs to the monoclinic crystal system, space group
P21/c and exhibits a strong tendency towards forming plate-
like hexagonal crystals with a prismatic habit.[24] Until now,
no attempt was made to direct the growth of zinc glycer-
olate into any morphology other than a random assembly
of hexagonal prisms. It should be noted though that Mole-
ski et al. have recently succeeded in the controlled conver-
sion of ZnGly into ZnO nanoparticles.[25]
Zinc, cobalt, manganese, and iron monoglycerolates all
have a similar structure and can be synthesized by using
the same reaction.[26–29] Cobalt glycerolate appears to be
particularly important today as it is a layered antiferromag-
netic material, which was recently shown by Pratt et al.[30]
to exhibit a chiral-like critical behavior. Nontransition-
metal glycerolates like calcium glycerolate[31] and lead glyc-
erolate[32] have also attracted some attention in the past.
Gaining more control over the nanoscale morphology of
zinc glycerolate is expected to advance the evolution of
these related fields as well.
Bottom-up methods are used extensively for the synthesis
of several nanostructured materials including for example
biological nanomaterials,[33] self-assembled monolayers,[34]
and nanoelectronics components.[35] Their common advan-
tage is that they exploit the natural shape and pattern for-
mation drive of materials and therefore, they are generally
cheaper and more scalable then top-down approaches. On
the other hand, the lack of a suitable structure-directing
agent or template can hinder the development of a bottom-
Introduction
Cosmetic and dermatological applications of nanotech-
nology have attracted considerable attention recently.[1] In
fact, the pharmaceutical and the cosmetics industry are
among the largest commercial benefactors of nanotechnol-
ogy today.[2] Advances related to personal care products as
well as therapeutic materials including novel nanosized car-
riers[3,4] or metallic[5,6] and semiconducting[7] nanoparticles,
polymers[8] and magnetic materials[9] as active components
appear with increasing frequency. The last few years have
also seen an increased awareness[10] of the potential health
hazards of nanomaterials,[8,11,12] their toxicity[13–15] and the
necessity to study their interaction with living tissue in de-
tail.[16,17] However, studies focused on controlling the mor-
phology of health-agent nanoparticles are not evenly dis-
tributed among the potential materials, even though such
advances could certainly contribute to the success of the
emerging nano-cosmetology and nano-dermatology disci-
plines.
Zinc glycerolate (ZnGly) is a typical example of such a
material. It is a slow-release nontoxic source of therapeutic
zinc[18] with antiarthritic,[19] antiulcer,[20] and antiinflamma-
tory[21] activity. Recently, Heideman et al. have reported on
the applicability of ZnGly for replacing ZnO in various rub-
[a] Department of Applied and Environmental Chemistry, Univer-
sity of Szeged,
Rerrih Béla tér 1, 6720 Szeged, Hungary
Fax: +36-62-544-619
E-mail: kakos@chem.u-szeged.hu
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900308.
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Zinc Glycerolate Microstacks
up method considerably. Ideally, the morphology of the re-
The morphology of the ZnO nanorods can be assessed
actants should be mirrored in the structure of the product in Figure 2. Individual zinc oxalate nanorods (Figure 2a)
to give the most feasible bottom-up synthesis. In some reac- are typically over 1 µm long and measure less than 100 nm
tion types (e.g. calcination of oxalate precursors[36] or the in diameter. They are organized into bundles over 3 µm
conversion of titanate nanowires into anatase nanowires[36]
)
long and over 500 nm in diameter. This structure is mir-
this is readily achieved, whereas other reactions – especially rored in the ZnO nanorods (Figure 2b) prepared from zinc
the ones involving the complete chemical restructuring of oxalate. Here the individual rods are close to 2 µm in length
both reactants – are generally not available for reactive tem- and less than 100 nm in diameter, whereas the ZnO bundles
plating.[37]
(microrods) are longer than 3 µm, and their diameter is ap-
In the present contribution we give a working example prox. 500 nm. Thus, the morphology of the synthesized rod-
for a complete bottom-up synthesis with sacrificial templat- like ZnO agrees well with results published earlier[38,39] and
ing: first, we exploit a natural pattern formation tendency demonstrates the success of the first reactive templating
of nonstructured starting materials to obtain zinc oxalate step. In Figure 2c the morphology of the commercial ZnO
nanorods, then we use a well-known reactive templating re- powder used as a reference is shown. The ZnO particles
action to transform these into ZnO nanorods, and finally, have a broad diameter distribution with a mean particle size
we copy the rodlike structure of ZnO into a completely dif- of 1100 nm and random particle alignment.
ferent material, zinc glycerolate by sacrificial templating.
Results and Discussion
In Figure 1 we present the XRD profiles of the materials
discussed. The characteristic wurtzite ZnO reflections inde-
xed in curve (a) are present both in the diffractogram of the
commercial ZnO source (a) and the profile of the nanorods
(b) synthesized according to Ha et al.[38] For reference, the
profile of the zinc oxalate intermediate is also shown as
curve (c) and indexed on a basis of a monoclinic cell of zinc
oxalate dihydrate. Profiles (d) and (e) are characteristic of
zinc glycerolate synthesized from commercial ZnO powder
and ZnO nanorods, respectively. The signature reflections
of zinc glycerolate are found at 11.1° (100), 17.2° (011),
20.7° (111), 23.8° (102), 24.8° (012), and 27.6° (020) with
several minor peaks in the 28–50° range. It can be seen that
(i) both ZnO sources could be transformed into zinc glycer-
olate, and (ii) zinc glycerolate synthesized from ZnO nano-
rods appears to contain less ZnO impurities than its com-
mercial ZnO-based counterpart.
Figure 2. SEM images of hydrothermally synthesized zinc oxalate
nanorods (a), ZnO nanorods obtained from these by calcination
(b), and a reference commercial ZnO powder (c).
Zinc glycerolate synthesized from this commercial ZnO
powder (Figure 3a) consists of a random assembly of hex-
agonal crystals averaging ca. 2.5 µm in diameter and ca.
350 nm in thickness. Since no structure-directing effects
were at work in the reaction mixture, there is no preferential
crystal-face alignment. This finding is in agreement with
the work of Hambley and Snow[24] who did not note any
orientation effects in ZnGly prepared from commercial
Figure 1. XRD profiles of commercial ZnO powder (a), ZnO nano-
ZnO. In Figure 3b we present the image of the same mate-
rods (b) prepared from zinc oxalate nanorods (c), unaligned zinc
rial after sonicating it in ethanol in a low-energy ultrasonic
bath for 20 min and then allowing the suspension to settle
glycerolate prepared from commercial ZnO powder (d), and zinc
glycerolate microstacks prepared from ZnO nanorods (e).
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Á. Kukovecz et al.
FULL PAPER
gently without mechanical disturbances. This experiment
was performed in order to loosen up the zinc glycerolate
crystals and see if stacking interactions alone could re-as-
semble the hexagonal platelets on top of each other. Fig-
ure 3b clearly proves this hypothesis void: the alignment of
the crystals remained random after sonication. Therefore,
we may conclude that spontaneous stacking forces acting
between the zinc glycerolate crystals are inadequate to exer-
cise any orientation effect on the material.
Figure 4. Typical SEM images of zinc glycerolate microstacks.
Figure 3. SEM images of zinc glycerolate as-synthesized from com-
mercial ZnO powder (a) and the same material after being soni-
cated for 20 min and allowed to settle down (b).
oxygen atom is involved in an O–H···O hydrogen bond,
respectively. Spectral changes all originate from the confine-
ment of the glycerato ligands into well-defined 5-member-
ring structures in the zinc glycerolate chelate compound as
described in the original report of Radoslovich et al.[41] The
spectra of the two ZnGly phases – curves (a) and (b) – are
almost identical; therefore, the structure of the randomly
aligned material and the microstacks can be considered the
same on the molecular level as well.
Zinc glycerolate prepared from ZnO microrods consists
of hexagonal crystals with a mean diameter and thickness
of ca. 1400 nm and ca, 330 nm, respectively (Figure 4a).
However, the particles are well oriented in this case. Align-
ment is ensured by the stacking basal planes of the hexago-
nal prisms and results in an irregularly shaped ZnGly
microstack with a long axis perpendicular to the crystallo-
graphic bc plane of the crystals. Typically, one microstack
consists of 6–12 zinc glycerolate prisms and has a total
length of 2–4 µm (Figure 4b, c). The excellent match be-
tween the XRD profiles of the randomly aligned zinc glyc-
erolate phase and the microstacks (Figure 1) indicates that
their crystal structures are identical.
Infrared spectra (Figure 5) were recorded to assess the
similarity on the molecular scale. Spectra (a) and (b) belong
to the randomly oriented and the microstack-structured
ZnGly, respectively. Curve (c) is the reference spectrum of
glycerol. The characteristic ν(O–H), ν(C–H), and (νC–O)
vibrations of glycerol are observable at 3360, 2910, 1124,
and 1046 cm–1.[40] The narrowing of the glycerol bands in
ZnGly is due to the crystalline nature of the material. The
formation of the zinc glycerolate phase is indicated by the
shifting of certain glycerol bands (e.g. from 676 cm–1 in
glycerol to 653 cm–1 in ZnGly and from 1046 cm–1 in glyc-
erol to 1065 cm–1 in ZnGly) and the appearance of the
Figure 5. Infrared spectra of zinc glycerolate prepared from com-
mercial ZnO powder (a) and zinc glycerolate microstacks (b). The
spectrum of liquid glycerol is shown in curve (c) as a reference.
A close-up view of the prism–prism interface (Figure 4c)
bands at 2500 cm–1 and 1940 cm–1. These can be assigned in the microstacks suggests that 3–5 prisms may be grown
to OH stretching and CO stretching vibrations where the together because even at high magnification no gap is vis-
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Zinc Glycerolate Microstacks
ible between them. However, it is not possible to decide on
The most peculiar finding of our work is that ZnO nano-
the basis of the SEM images alone if this really is the case rod bundles can serve as sacrificial templates and give an
or if the ZnGly prisms are merely stacking together. organometallic reaction product. This is the inverse of the
In Figure 6 an AFM image of the zinc glycerolate micro- more common path of converting a shape-controlled hy-
stacks is presented. Letters A–E mark five different ZnGly droxide[43,44] or organic salt[39,45] into an oxide nanorod. Ex-
microstack examples, and several more unmarked ones are amples of similar conversions are scarcely found in the lit-
also visible. The physical dimensions and the stacked hexag- erature. Besides the mentioned oxide production reactions,
onal-prism structure of the microstacks determined from reactive templating is mostly used for the preparation of
the AFM measurement agree well with the SEM observa- low-dimensional electroceramic nanostructures[46–48] today.
tions. In order to test the validity of the assumption that
Concerning the mechanism of the zinc glycerolate micro-
the ZnGly hexagons are attached to each other, we lowered stack formation it seems evident that the ZnO microrod can
the AFM probe to the top left corner of the ZnGly as- not dissolve fully in the first reaction step because in that
sembly marked F and moved the tip back and forth 2 µm case the structure-directing phenomenon would not be ob-
in the sample plane. This method is based on the work of servable. It is also clear that ZnO microrods are consumed
Biro et al. who used a similar technique to prove the pres- in the reaction, which makes the synthesis a working exam-
ence of chemical linkage between functionalized carbon ple of a reactive templating bottom-up method. However,
nanotubes by STM.[42] The image on the right-hand side in it is an open question if the ZnO Ǟ ZnGly conversion pro-
Figure 6 depicts the studied area after the manipulation. gresses from one end of the ZnO rod to the other or takes
The damage caused by the AFM tip to the ZnGly object F place along the whole length simultaneously. It has been
is observable as a white spot. Moreover, it is also visible reported earlier that the ZnO surface can interact with
that the F assembly has flipped over the top left/bottom –OH groups through hydrogen bonds[49] and that different
right diagonal of the image. Since neither the A–E micro- ZnO facets exhibit different affinities towards interaction
stacks nor the unmarked ZnGly units changed their relative with polyethylene glycol.[50] Combining these findings with
positions, the movement of F can only be assigned to the our experience in diffusion-limited hydrothermal growth in
agitation effect of the tip. Let us now observe that object F static autoclaves we suggest that the former option has a
consisted of two hexagonal prisms originally. This structure higher probability.[51]
is completely preserved: both prisms appear to have moved
That is, the end of the ZnO microrod is more likely to be
together, without changing their relative position even attacked by the chelating agent glycerol. Since the autoclave
though the force exercised by the AFM tip was large is not agitated, the volume near the end of the nanorod
enough to damage the ZnGly crystal itself. This finding could become locally oversaturated for zinc glycerolate,
complements the SEM results (Figure 4c) and suggests that which will spontaneously crystallize in hexagonal prisms.
the hexagonal ZnGly prisms in one microstack not only The close proximity (there is no convection in the system
appear to be very close but they are indeed bound together. because the autoclave is static) of the previously formed
It is not yet possible to determine if this is through a pri- ZnGly prisms will then allow the system to minimize its
mary chemical bond (that is, ZnGly prisms grown together) surface energy by the attachment of the prisms to a ZnGly
or van der Waals forces, but the attachment is certainly microstack (Figure 7). A similar explanation has recently
strong enough to preserve the microstack structure even been offered to explain the formation of ZnO doughnuts by
when subjected to a considerable deformation force. Fur- Ghoshal et al.[52] On the other hand, when the synthesis is
ther studies are required to uncover the exact role of the done from randomly oriented commercial ZnO particles the
noncrystalline material visible (Figure 4c) between the indi- ZnGly prisms are not aligned well enough to allow proxim-
vidual ZnGly prisms in the structural integrity of the micro- ity-induced surface-energy minimalization (Figure 3), and
stacks.
therefore ZnGly microstack formation does not take place.
Figure 6. AFM images of zinc glycerolate microstacks before (left) and after (right) flipping the hexagonal prism assembly “F” over by
an AFM tip. Positions A–E mark some typical ZnGly microstacks unaffected by the AFM manipulation.
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We suggest that the glycerolate microstack preparation
principle reported here could easily be extended to cover the
preparation of microstacks from other glycerolate-forming
metal oxide nanorods, e.g. iron, cobalt, and manganese ox-
ides. Although some questions concerning the exact forma-
tion mechanism of ZnGly microstacks are still open, we
expect that with the expansion of the nano-dermatology
field and the recent interest in layered magnetic materials,
answers will come soon.
Experimental Section
Synthesis of ZnO Nanorods: Zn(NO3)2·6H2O (10 mmol, Reachim)
and oxalic acid (10 mmol) were dissolved in absolute ethanol (40–
40 mL, Molar) and mixed together thoroughly at room tempera-
ture. The resulting mixture was transferred into a Teflon-lined
stainless steel autoclave and kept at 130 °C for 10 h. The product
mixture was filtered, washed with distilled water and ethanol, and
dried at 80 °C in air overnight. Finally, the synthesized zinc oxalate
was decomposed to ZnO by calcination at 420 °C in an N2 flow
for 2 h (heating temperature ramp was set to 2.5 °Cmin–1).
Figure 7. Illustration of the conversion of a ZnO nanorod bundle
(on the left) into a ZnGly microstack (on the right) upon the attack
of chelating agent glycerol. When the same reaction takes place in
an agitated vessel, the ZnGly hexagonal prisms cannot attach to
each other to form a microstack.
The diameter difference between the ZnO microrods and
the ZnGly microstacks could be related to the different
structure (wurtzite crystal vs. chelato complex) of the mate-
rials. Whereas the density of wurtzite ZnO[53] is 5.6 gcm–3,
the density of zinc glycerolate is 2.2 gcm–3 according to
Synthesis of Zinc Glycerolate (ZnGly): ZnO (0.25 g, either a com-
mercial product from Reanal or the nanorods described above) was
mixed with glycerol (25 mL, Molar) at 100 °C under reflux for 4 h.
The resulting mixture was transferred into a Teflon-lined stainless
steel autoclave and kept at 150 °C for 24 h. The product mixture
Hambley and Snow.[24] This ca. 250% density difference was filtered, washed with distilled water, and dried at 80 °C in air
overnight.
matches the observed mean diameter difference (ca. 500 nm
for a ZnO nanorod bundle vs. ca. 1400 nm for a ZnGly
microstack, see Figures 2 and 4) well. Combined with the
fact that the mean length of a ZnO nanorod bundle and
that of a ZnGly microstack are similar we may assume that
on average, one ZnO nanorod bundle is converted into one
ZnGly microstack during the hydrothermal treatment. The
reason for the heterogeneous size distribution of the ZnGly
prisms within one microstack is still unclear; one may hy-
pothesize that it is related to the nonuniform cross-section
(Figure 2b) of the ZnO nanorods or to local concentration
fluctuation effects.
Characterization: X-ray diffraction profiles were recorded with a
Rigaku Miniflex 2 instrument by using Cu-Kα radiation. Scanning
electron microscopy (SEM) was performed with a Hitachi S-4700
Type II cold field-emission microscope. Samples were sputter-
coated by an approx. 5 nm thick Au/Pd layer before measurement
to avoid charging effects. Infrared (IR) spectra were recorded in a
KBr matrix with a Bruker Vertex 70 FT-IR instrument under ambi-
ent conditions averaging 64 scans at a resolution of 4 cm–1. Atomic
force microscopy images were recorded with an NT-MDT Smena
A unit on HOPG substrate in semi-contact mode by using
TAP300GD tips with a resonance frequency of 300 kHz and force
constant 40 N/m.
Supporting Information (see footnote on the first page of this arti-
cle): Reverse scan direction image of Figure 6.
Conclusions
Acknowledgments
We synthesized zinc glycerolate (ZnGly) by treating ZnO
with glycerol. We observed that the morphology of the ZnO
source has a large effect on the appearance of the ZnGly
product. In the absence of structure-directing effects the
product ZnGly is obtained as a random heap of hexagonal
The financial support of the Hungarian Scientific Research Fund
(OTKA) through projects NNF-78920 and 73676 is acknowledged.
prisms. Their alignment remains random even if subjected [1] S. J. Choi, J. M. Oh, J. H. Choy, J. Mater. Chem. 2008, 18, 615–
620.
to ultrasonic perturbation and subsequent relaxation. How-
[2] M. Goldberg, R. Langer, X. Q. Jia, J. Biomater. Sci., Polym.
ever, nanorod-shaped ZnO could readily be transformed
Ed. 2007, 18, 241–268.
into zinc glycerolate microstacks in which 6–12 hexagonal
[3] R. H. Muller, M. Radtke, S. A. Wissing, Adv. Drug Delivery
prisms are aligned face-to-face. We presented evidence that
the ZnGly plates in the microstacks are bound together by
forces strong enough to withstand mechanical deformation
exercised by a contacting AFM tip and suggested a forma-
tion scheme to explain the main features of the ZnO micro-
rod to ZnGly microstack conversion.
Rev. 2002, 54, S131–S155.
[4] R. H. Muller, R. D. Petersen, A. Hornmoss, J. Pardeike, Adv.
Drug Delivery Rev. 2007, 59, 522–530.
[5] K. C. Bhol, P. J. Schechter, Br. J. Dermatol. 2005, 152, 1235–
1242.
[6] L. S. Nair, C. T. Laurencin, J. Biomed. Nanotechnol. 2007, 3,
301–316.
3626
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Zinc Glycerolate Microstacks
[7] T. Maier, H. C. Korting, Skin. Pharmacol. Physiol. 2005, 18,
253–262.
[8] P. Somasundaran, S. Chakraborty, Q. Qiang, P. Deo, J. Wang, [31] R. M. Taylor, P. G. Slade, G. L. Aldous, I. R. Wilding, O. Sid-
[30] F. L. Pratt, P. J. Baker, S. J. Blundell, T. Lancaster, M. A.
Green, M. Kurmoo, Phys. Rev. Lett. 2007, 99, 017202.
R. Zhang, J. Cosmet. Sci. 2004, 55, S1–S17.
[9] I. Perelshtein, N. Perkas, S. Magdassi, T. Zioni, M. Royz, Z.
Maor, A. Gedanken, J. Nanopart. Res. 2008, 10, 191–195.
[10] O. Renn, M. C. Roco, J. Nanopart. Res. 2006, 8, 153–191.
[11] G. J. Nohynek, J. Lademann, C. Ribaud, M. S. Roberts, Crit.
Rev. Toxicol. 2007, 37, 251–277.
diqui, M. W. Whitehouse, Aust. J. Chem. 1992, 45, 1179–1185.
[32] H. L. Keller, H. J. Riebe, Z. Anorg. Allg. Chem. 1987, 550, 102–
108.
[33] S. W. Lee, W. J. Chang, R. Bashir, Y. M. Koo, Biotechnol. Biop-
rocess Eng. 2007, 12, 185–199.
[34] J. J. Gooding, F. Mearns, W. R. Yang, J. Q. Liu, Electroanalysis
2003, 15, 81–96.
[12] R. Brayner, Nano Today 2008, 3, 48–55.
[13] J. W. Seo, A. Magrez, M. Milas, K. Lee, V. Lukovac, L. Forro,
J. Phys. D: Appl. Phys. 2007, 40, R109–R120.
[14] A. Magrez, S. Kasas, V. Salicio, N. Pasquier, J. W. Seo, M.
Celio, S. Catsicas, B. Schwaller, L. Forro, Nano Lett. 2006, 6,
1121–1125.
[15] A. Nel, T. Xia, L. Madler, N. Li, Science 2006, 311, 622–627.
[16] G. Jia, H. F. Wang, L. Yan, X. Wang, R. J. Pei, T. Yan, Y. L.
Zhao, X. B. Guo, Environ. Sci. Technol. 2005, 39, 1378–1383.
[17] C. Kirchner, T. Liedl, S. Kudera, T. Pellegrino, A. M. Javier,
H. E. Gaub, S. Stolzle, N. Fertig, W. J. Parak, Nano Lett. 2005,
5, 331–338.
[35] W. Lu, C. M. Lieber, Nat. Mater. 2007, 6, 841–850.
[36] J. Y. Fang, J. Wang, S. C. Ng, C. H. Chew, L. M. Gan, Nanos-
truct. Mater. 1997, 8, 499–505.
[37] G. Z. Cao, D. W. Liu, Adv. Colloid Interface Sci. 2008, 136, 45–
64.
[38] Z. G. Ha, L. H. Yue, Y. F. Zheng, Z. D. Xu, Mater. Chem.
Phys. 2008, 107, 137–141.
[39] T. Ahmad, S. Vaidya, N. Sarkar, S. Ghosh, A. K. Ganguli,
Nanotechnology 2006, 17, 1236–1240.
[40] A. Mudalige, J. E. Pemberton, Vib. Spectrosc. 2007, 45, 27–35.
[41] E. W. Radoslovich, M. Raupach, P. G. Slade, R. M. Taylor,
Aust. J. Chem. 1970, 23, 1963–1971.
[42] A. A. Koos, Z. E. Horvath, Z. Osvath, L. Tapaszto, K. Niesz,
Z. Konya, I. Kiricsi, N. Grobert, M. Ruhle, L. P. Biro, Mater.
Sci. Eng., C 2003, 23, 1007–1011.
[18] D. P. Fairlie, M. W. Whitehouse, R. M. Taylor, Agents Actions.
1992, 36, 152–158.
[19] M. W. Whitehouse, K. D. Rainsford, R. M. Taylor, B. Vernon-
roberts, Agents Actions. 1990, 31, 47–58.
[20] K. D. Rainsford, M. W. Whitehouse, J. Pharm. Pharmacol.
1992, 44, 476–482.
[21] M. W. Whitehouse, D. P. Fairlie, Y. H. Thong, Agents Actions.
1994, 42, 123–127.
[43] B. Liu, S. H. Yu, F. Zhang, L. J. Li, Q. Zhang, L. Ren, K.
Jiang, J. Phys. Chem. B 2004, 108, 4338–4341.
[44] L. Yan, R. B. Yu, G. R. Liu, X. R. Xing, Scr. Mater. 2008, 58,
707–710.
[22] G. Heideman, J. W. M. Noordermeer, R. N. Datta, KGK,
Kautsch. Gummi Kunstst. 2006, 59, 178–183.
[23] A. Apisariyakulm, D. Buddhasukh, S. Apisariyakul, B. Ternai,
Med. J. Aust. 1990, 152, 54–54.
[24] T. W. Hambley, M. R. Snow, Aust. J. Chem. 1983, 36, 1249–
1253.
[45] S. H. Yu, M. Yoshimura, Adv. Mater. 2002, 14, 296.
[46] T. Sato, Y. Yoshida, T. Kimura, J. Am. Ceram. Soc. 2007, 90,
3005–3008.
[47] Y. A. Chung, C. Y. Lee, C. W. Peng, H. T. Chiu, Mater. Chem.
Phys. 2006, 100, 380–384.
[48] T. Kimura, J. Ceram. Soc. Jpn. 2006, 114, 15–25.
[49] S. Liufu, H. Xiao, Y. P. Li, Powder Technol. 2004, 145, 20–24.
[50] X. M. Liu, Y. C. Zhou, J. Cryst. Growth 2004, 270, 527–534.
[51] A. Kukovecz, N. Hodos, E. Horvath, G. Radnoczi, Z. Konya,
I. Kiricsi, J. Phys. Chem. B 2005, 109, 17781–17783.
[52] T. Ghoshal, S. Kar, S. Chaudhuri, Cryst. Growth Des. 2007, 7,
136–141.
[25] R. Moleski, E. Leontidis, F. Krumeich, J. Colloid Interface Sci.
2006, 302, 246–253.
[26] L. Rodrique, G. Delvaux, A. Dardenne, Powder Technol. 1978,
19, 93–101.
[27] P. Bruylants, A. Munaut, G. Poncelet, J. Ladriere, J. Meyers, J.
Fripiat, J. Inorg. Nucl. Chem. 1980, 42, 1603–1611.
[28] E. Mendelovici, A. Sagarzazu, R. Villalba, J. Therm. Anal.
1993, 40, 1115–1122.
[29] E. Mendelovici, R. Villalba, A. Sagarzazu, J. Mater. Sci. Lett.
1990, 9, 28–31.
[53] D. R. Lide (Ed.), CRC Handbook of Chemistry and Physics,
CRC Press, Boca Raton, FL, 2005.
Received: April 2, 2009
Published Online: July 14, 2009
Eur. J. Inorg. Chem. 2009, 3622–3627
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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