Microwave-induced polyol-process synthesis of copper and copper oxide nanocrystals with controllable morphology

Article abstract of DOI:10.1002/ejic.200400258

Different morphologies of copper and copper oxide nanocrystallites, including radially arrayed whiskers, cubic particles and sphere particles, have been successfully synthesized by a microwave-induced method under ambient conditions. In aqueous solution containing different ethylene glycol concentrations, copper acetate hydrate produces different reduction products. The as-prepared copper and copper oxide crystallites were characterized by various techniques, including X-ray powder diffraction, transmission electron microscopy, selected-area electron diffraction and UV/Vis absorption spectroscopy. It was found that microwave irradiation plays a critical role in the formation of the products; temperature was also found to be important in the reaction. The irradiation time and copper acetate concentration also affect the morphology of the products. The possible formation mechanism is also discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400258

FULL PAPER
Microwave-Induced Polyol-Process Synthesis of Copper and Copper Oxide
Nanocrystals with Controllable Morphology
Yu Zhao,[a] Jun-Jie Zhu,*[a] Jian-Min Hong,[a] Ningsheng Bian,[a] and Hong-Yuan Chen[a]
Keywords: Copper / Copper oxides / Microwaves / Nanostructures / UV / Vis spectroscopy
Different morphologies of copper and copper oxide nanocry- scopy, selected-area electron diffraction and UV/Vis absorp-
stallites, including radially arrayed whiskers, cubic particles
and sphere particles, have been successfully synthesized by
a microwave-induced method under ambient conditions. In
aqueous solution containing different ethylene glycol con-
centrations, copper acetate hydrate produces different reduc-
tion spectroscopy. It was found that microwave irradiation
plays a critical role in the formation of the products; temper-
ature was also found to be important in the reaction. The
irradiation time and copper acetate concentration also affect
the morphology of the products. The possible formation
tion products. The as-prepared copper and copper oxide mechanism is also discussed.
crystallites were characterized by various techniques, includ-
((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ing X-ray powder diffraction, transmission electron micro- Germany, 2004)
Introduction
translation motions of free or bound charges such as elec-
trons or ions and rotate charged complexes such as di-
poles.[43] The resistance of these induced motions due to
inertial, elastic, and frictional force, which are frequency
dependent, causes losses and attenuates the electric field.
Compared to ultrasonic irradiation, there is no similar bub-
ble formation during microwave heating, although super-
heating occurs in localized spots. The main advantages of
microwave-assisted reactions over conventional methods in
synthesis are: (a) the kinetics of the reaction are increased
by one to two orders of magnitude, (b) novel phases are
formed, (c) the initial heating is rapid, which can lead to
energy savings, and (d) selective formation of one phase
over another often occurs.[44Ϫ46] One possible hypothesis
for these microwave-induced effects is the generation of lo-
calized high temperatures at the reaction sites to enhance
reaction rates in an analogous manner to that of ultrasonic
waves,[47] where both high temperatures and pressures have
been reported during reactions. The enhanced kinetics of
crystallization can lead to energy savings of up to 90%.[48]
Nanometer-sized metals, semiconductors, and oxides are
of great interest because they can have physical and chemi-
cal properties that are not characteristic of the atoms or of
their bulk counterparts. The large surface area to volume
ratio can contribute to some of the unique properties of
nanoparticles.[1Ϫ5] Among them, Cu, Cu2O and CuO are
industrially important materials that are widely used in fi-
elds such as magnetic storage media, solar energy trans-
formation, electronics, sensors, catalysis, batteries, reson-
ance imaging and so forth.[6Ϫ12] In the past, some successful
attempts have been made to synthesize nanoparticles of
copper and copper oxides, such as sonochemical
methods,[13Ϫ15] microwave irradiation,[16] photochemical
methods,[17Ϫ20] hydrothermal and solvothermal meth-
ods,[21,22]
electrochemical
methods,[23Ϫ31]
sol-gel
methods,[32Ϫ35] solid-state reactions,[36] chemical reduction
and decomposition route[37Ϫ42] and so on.
Microwaves are a portion of the electromagnetic spec-
trum with frequencies in the range of 300 MHz to 300 GHz.
The corresponding wavelengths of these frequencies are 1 m
to 1 mm. The most commonly used frequency is 2.45 GHz.
The degree of interaction of microwaves with a dielectric
medium is related to the materialЈs dielectric constant and
dielectric loss.[43] When microwaves penetrate and propa-
gate through a dielectric solution or suspension, the internal
electric fields generated within the affected volume induce
The polyol method is a low-temperature process that is
environmentally benign because the reactions are carried
out under closed-system conditions. It was first introduced
to produce metal submicron-sized powders.[49Ϫ51] In this
method, a suitable solid metal salt is suspended in a liquid
polyol. The suspension is stirred and heated to a certain
temperature; the reduction of the starting compound yields
fine metal powders. The polyol itself acts not only as a sol-
vent in the process but also as a stabilizer, limiting particle
growth and prohibiting agglomeration.[52Ϫ54] Recently, this
method has also been extended to the preparation of metal
oxides[55Ϫ57] and metal chalcogenides.[58Ϫ60] Tarascon and
co-workers have demonstrated that in these reactions the
[a]
State Key Laboratory of Coordination Chemistry, Department
of Chemistry, Nanjing University,
Nanjing, 210093, P. R. China
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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temperature is a dominant factor in affecting the reactivity. ure 1. Figure 2 (e) depicts Cu particles, the size of which
Three factors are influenced by the temperature: (1) the re- ranges from 100Ϫ120 nm. The SEAD pattern of these cop-
duction potential of ethylene glycol, (2) the rupture and cre- per particles is inset.
ation of chemical bonds, and (3) diffusion.[61] All these fac-
tors make microwave-heating techniques favorable for the
fabrication of metal and metal oxides by using ethylene gly-
col as a solvent. The ethylene glycol is an excellent suscep-
tor for the microwave radiation because of its high perma-
nent dipole. The metallic particles produced as intermedi-
ates in the polyol reaction are also good for this purpose.
In this paper, we present a novel microwave-induced po-
lyol route to synthesize different morphologies of Cu, Cu2O
and CuO nanoparticles. Ethylene glycol (EG) aqueous solu-
tions with different concentration were used in order to
control the reaction temperature during the microwave
heating. Cu, Cu2O or CuO were formed in the different
conditions. The effect on the morphology of the nanopart-
icles was also investigated. It was found to be a fast, con-
venient, mild, energy efficient and environmentally friendly
route to produce nanoparticles of Cu, Cu2O and CuO.
Figure 1. XRD patterns of: (a) CuO; (b) CuO mixed with Cu2O;
(c) Cu2O; (d) Cu2O mixed with Cu; (e) Cu
Results and Discussion
In order to elucidate the mechanism of temperature con-
trol in the EG aqueous solution, we first supposed that the
ethylene glycol and water mixture is an ideal binary system,
which therefore behaves according to Raoults Law
In order to study the nature and morphology of the prod-
ucts, various techniques such as X-ray diffraction (XRD),
transmission electron microscopy (TEM), selected-area
electron diffraction (SAED) and UV/Vis absorption spec-
troscopy were employed.
yA ϭ xA·P*A/P
with yA ϭ mol fraction of substance A in the vapor phase
equilibrium with the solution, XA ϭ mol fraction of sub-
stance A in the solution; P*A ϭ equilibrium vapor pressure
of substance A; P ϭ vapor pressure of the whole system.
We calculated the theoretical boiling point of the system
at different water volume ratios; the results are depicted in
Figure 3. In our microwave dielectric heating process, the
system temperature elevates rapidly. The reaction tempera-
tures measured fit well with the theoretical values. As a re-
sult, an accurate and average temperature can be controlled
in our microwave dielectric heating system.
As far as we know, when the solvent is pure ethylene
glycol copper acetate is only partly dissolved and no chemi-
cal reaction occurs at 108 °C; when the solvent is water,
copper acetate is completely soluble. On the contrary, in the
EG aqueous solution, when the reaction temperature varies
between 90 and 108 °C, CuO can be produced. We propose
the process of producing CuO as follows: first, copper acet-
ate hydrate dissolves in the solution; then EG esterifies with
OAcϪ to produce ethylene glycol monoacetate and OHϪ;
finally OHϪ and Cu2ϩ ion combine in solution and then
dehydrate to form CuO. The reaction can be schematized
as follows:
The results of the powder XRD analysis are shown in
Figure 1 (see aϪe). The diffraction peaks correspond to the
reflection of: (a) CuO (CCID file no. 801916 monoclinic),
(b) CuO mixed with Cu2O, (c) Cu2O (CCID file no. 782076
cubic), (d) Cu2O mixed with Cu, and (e) Cu (CCID file no.
040836 cubic). In all the reactions, highly crystalline prod-
ucts were obtained. The positions of the peaks are in good
agreement with literature values.
TEM images of the products are presented in Figure 2
(see aϪe), where the different morphologies that be
achieved simply by changing the water/EG ratio of the sol-
vent can be clearly observed. Figure 2 (a) depicts the mor-
phology of CuO, which shows radially arrayed whiskers. In
this image, a single whisker is calculated to be about 80 nm
in length and less than 10 nm in diameter; the SAED pat-
tern of the products is shown in the inset. Figure 2 (b)
shows a mixture of whiskers and cubic particles. Two differ-
ent phases can be observed clearly in this picture. Accord-
ing to the SEAD images, and compared with the other
SEAD patterns shown in Figure 2 (see a and c), it can be
concluded that the whiskers are CuO of monoclinic phase
[SAED pattern inset top right in Figure 2 (b)], and the
cubes are Cu2O in the cubic phase (SAED pattern inset
bottom left). Cu2O particles are observed as shown in Fig-
ure 2 (c); they are around 50 nm cubic nanoparticles. The
SAED pattern of a single crystal of one of these particles
is shown in the inset. Figure 2 (d) depicts Cu mixed with
Cu2O particles; the products are not clearly separated. We
conclude it to be mixture only by the XRD pattern in Fig-
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Figure 2. The TEM images of as-prepared: (a) CuO (inset: SEAD of CuO); (b) CuO mixed with Cu2O (inset bottom left: SAED of the
whiskers; top right: SAED of a single cube); (c) Cu2O (inset: SEAD pattern of Cu2O) (d) Cu2O mixed with Cu; (e) Cu (inset: SAED
pattern of Cu particles)
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Microwave-Induced Synthesis of Copper and Copper Oxide Nanocrystals
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Figure 3. Theoretical boiling points with different EG volume ratios in the EG aqueous system
Figure 4. The UV/Vis absorption spectra of a suspension of copper acetate (0.03 g/40 mL) suspended in 49% EG aqueous solution after
different microwave irradiation times; the numbers on the spectra indicate the time of irradiation; path length ϭ 1 cm
To prove the reaction mechanism, we removed the water fast, so the formation of CuO nanocrystals is determined
from the solvent for GC-MS detection after removing the by reaction 1. In this process, the single whiskers prepared
precipitate by centrifugation. The results show that ethylene from different copper acetate concentration have the same
glycol monoacetate is the only reaction product remaining size.
in solution.
Figure 5 (see aϪd) shows the change in morphology of
To demonstrate the formation process of CuO nanocrys- as-prepared CuO as a function of time. The growth of CuO-
tals, we recorded UV/Vis absorption spectra at different re- whisker arrays can be described by three steps. First, crystal
action times (Figure 4). There is no absorption present at seeds of CuO are formed. These seeds then grown into
the beginning of the reaction (0 min). As the reaction pro- whiskers, and, in the end, the CuO whiskers assemble into
ceeds, however, an absorption shoulder appears at around radially arrayed whiskers.
310 nm. After 15 minutes irradiation, the suspension
The concentration of copper acetate also plays a dra-
becomes dark-brown, and a broad absorption peak cen- matic role in determining the morphology (Figure 6). In the
tered at 310 nm can be observed. There is no obvious shift case of a single whisker of the CuO nanocrystals, the crystal
of the absorption peak with time. This means that the crys- size is almost the same for all copper acetate concentration,
tal size changes very little during the whole precipitation but the morphology varies: the higher the concentration is,
process. As an ionic reaction, reaction 2 is comparatively the denser the radial arrays will be. As we can see, when the
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Figure 5. TEM images of CuO as a function of reaction time: a)
3 min; b) 6 min; c) 10 min; d) 15 min (0.03 g/40 mL copper acetate
in 49% EG aqueous solution)
Figure 6. TEM images of CuO at various copper acetate concen-
trations: a) 0.03 g; b) 0.30 g; c) 0.70 g; d) 1.00 g (in 40 mL 49% EG
aqueous solution)
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Microwave-Induced Synthesis of Copper and Copper Oxide Nanocrystals
copper acetate concentration increases to 0.70 g/40 mL, the
FULL PAPER
Figure 8 (aϪd) depict the change in morphology of cop-
CuO radical arrays are so dense that they look like a sphere per as a function of time. After six minutes, Cu2O cubic
(see d in Figure 6). Interestingly we also found that the particles of about 300 nm have formed. This Cu2O is con-
growth of the radial whisker arrays is directed mainly along tinuously being reduced to give dispersedCu particles with
the axes of a tetrahedron.
a dispersed particle size of about 15 nm in diameter (c in
Cu and Cu2O nanocrystals can also be prepared by this Figure 8). However, after reaction for 15 minutes, the Cu
method; they follow a reduction mechanism. At 197 °C, the aggregates into particles of about 60 nm.
reduction product is Cu. Fievet et al.[2] have proposed that
Cu2O is obtained at 140 °C. UV/Vis absorption spectra
the metal particles are formed by nucleation and growth were recorded after different reaction times to investigate
from the solution. According to this mechanism, we have the reaction (Figure 9). Only after 12 minutes did the ab-
proposed a formation process for the Cu nanoparticles: sorption shoulder at around 460 nm appear. This peak can
first, under dielectric heating, copper acetate hydrate dis- be attributed to Cu2O, and corresponds well with the ab-
solves completely in ethylene glycol, and then the inter- sorption band of the intermediate phase in the preparation
mediate solid phase between the starting material and the of Cu nanoparticles.
final metal powder is formed; during the second stage of
The growth of Cu2O nanoparticles was also investigated
the reaction the re-dissolution of the intermediate solid (Figure 10). As can be seen from the morphology of Cu2O
phase takes place. The reduction action of ethylene glycol after different reaction times, the Cu2O is formed as cubes
is due to diacetyl, which is formed by a duplicative oxi- of about 40 nm (Figure 10, a). As the reaction proceeds the
dation of acetaldehyde previously produced by dehydration particles grow further. It is interesting that hexagons [Fig-
of ethylene glycol.
The reaction can be schematized as follows:
ure 10 (d)] and truncated cubes [Figure 10 (e)] are also
found in the reaction products; they can be regarded as in-
termediate morphologies en route to cubic particles. An
SEAD pattern was also measured. As calculated, the in-
serted SEAD pattern of a truncated cube in Figure 10 (d)
shows the (001) face and the hexagon in Figure 10 (e) shows
the (111) face; they are both Cu2O of primitive cubic phase.
As the reaction time is prolonged to 30 minutes, we can get
cubic Cu2O as large as 500 nm. It is therefore possible to
control the size of the Cu2O crystals.
UV/Vis spectra were taken as a function of time (Fig-
ure 7). After six minutes irradiation, an absorption shoulder
appears at around 490 nm, which indicates an intermediate
phase. The phase will be shown to be Cu2O later. After nine
minutes, colloidal copper has formed with an absorption
peak at 580 nm. This absorption can be attributed to the
Conclusion
Using a novel microwave-induced polyol process, we have
plasma resonance absorption of the copper particles. As the successfully synthesized copper, cuprites and copper() ox-
reaction progresses, the copper colloid aggregates and pre- ides systematically. The EG aqueous solution was heated
cipitates. As a result, after 15 minutes the absorption peak by microwave irradiation, easy and precise control on the
at 580 nm has almost disappeared.
temperature was realized. By varying the conditions we
Figure 7. The UV/Vis absorption spectra of a suspension of copper acetate (0.03 g/40 mL) in pure EG solution as a function of irradiation
time; the numbers on the spectra indicate the time of irradiation; path length ϭ 1 cm
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Y. Zhao, J.-J. Zhu, J.-M. Hong, N. Bian, H.-Y. Chen
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Figure 9. The UV/Vis absorption spectra of a suspension of copper
acetate (0.03 g/40 mL) in 90% EG aqueous solution after different
irradiation times; the numbers on the spectra indicate the ir-
radiation time; path length ϭ 1 cm
were able to prepare products with different morphology
and particle sizes. A formation mechanism of the as-pre-
pared products was proposed and the effects on the mor-
phology and size were investigated. This kind of method is
advantageous as it is a one-step reaction that occurs at rela-
tively mild temperatures and gives well-dispersed products.
Its extension to the preparation of other materials is cur-
rently being investigated.
Experimental Section
General: All the experiments were performed in a modified
National frequency-convertible microwave oven (NN-S570MFS).
A reflux system was connected to the microwave oven. X-ray pow-
der diffraction (XRD) measurements were performed on a Philips
XЈpert X-ray diffractometer at a scanning step of 0.03°, continue
time 10 seconds, in the 2q range from 20° to 80°, with graphite
monochromated Cu-Ka radiation (l ϭ 0.15418 nm) and a nickel
filter. Transmission electron microscopy (TEM) images and selec-
ted-area electron diffraction (SAED) images were recorded on a
JEOL-JEM 200CX transmission electron microscope, at an acce-
lerating voltage of 200 kV. The samples used for TEM observations
were prepared by dispersing some products in ethanol followed by
ultrasonic vibration for 30 min, then placing a drop of the disper-
sion onto a copper grid coated with a layer of amorphous carbon.
A Shimazu UV-2401PC photospectrometer was used to record the
UV/Vis absorption spectra of the as-prepared samples dispersed
in water.
Synthesis of Copper and Copper Oxides: In a typical procedure, the
appropriate amount of Cu(OAc)2·H2O was added into an 80 mL
round-bottomed flask, and then 40 mL of EG aqueous solution
was added into the same flask. The mixture was placed into the
microwave reflux system and the reaction was carried out under
ambient conditions for 15 minutes at a power of 365 W. The de-
tailed reaction conditions in various EG aqueous solutions are
listed in Table 1. The reactants dissolved in the EG aqueous solu-
tion after irradiating for 3 min. As the reaction progressed a large
amount of precipitate formed (dark-brown for CuO, reddish yellow
for Cu2O, and red for Cu). After the reaction, the suspension was
Figure 8. The TEM images in the formation of Cu as a function
of reaction time: a) 6 min; b) 8 min; c) 9 min; d) 15 min (0.03 g/40
mL copper acetate in pure EG solution)
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Microwave-Induced Synthesis of Copper and Copper Oxide Nanocrystals
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Figure 10. The TEM images of Cu2O as a function of reaction time: a) 3 min; b) 6 min; c) 9 min; d) and e) 15 min; f) 30 min (0.03 g/40
mL copper acetate in 90% EG aqueous solution)
Table 1. The reaction conditions in various EG aqueous solutions
and products via Microwave dielectric heating
were collected for characterizations. The products of the different
reactions are also listed in Table 1.
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (No.20325516, 90206037) and the Research
Foundation for the Doctoral Program of the Ministry of Education
of China (Grant No. 20020284022). The authors also thank Prof.
Xinhua Xia and Mr. Zhengwei Shi for allowing us to use their
facilities.
[1]
cooled to room temperature and the precipitate was centrifuged,
washed with distilled water, absolute ethanol and acetone in se-
quence and dried in vacuo at room temperature. The final products
M. D. Morse, Chem. Rev. 1986, 86, 1049Ϫ1109.
[2]
W. P. Halperin, Rev. Mod. Phys. 1986, 58, 533Ϫ603.
[3]
A. Henglein, Chem. Rev. 1989, 89, 1861Ϫ1873.
Eur. J. Inorg. Chem. 2004, 4072Ϫ4080
www.eurjic.org
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[4]
[33]
[34]
[35]
[36]
G. D. Stucky, J. E. MacDougall, Science 1990, 247, 669Ϫ678.
V. V. Kresin, Phys. Rep. 1992, 220, 1Ϫ52.
A. Inoue, B. L. Shen, J. Mater. Res. 2003, 18, 2799Ϫ2806.
S. Krongelb, L. T. Romankiw, J. A. Tornello, IBM J. Res. Dev.
L. Armelao, D. Barreca, M. Bertapelle, G. Bottaro, C. Sada,
E. Tondello, Thin Solid Films 2003, 442, 48Ϫ52.
J. C. S. Wu, I. H. Tseng, W. C. Chang, J. Nanopart. Res. 2001,
3, 113Ϫ118.
M. Epifani, G. T. De, A. Licciulli, L. Vasanelli, J. Mater. Chem.
2001, 11, 3326Ϫ3332.
W. H. Wang, Y. J. Zhan, G. H. Wang, Chem. Commun. 2001,
727Ϫ728.
M. Yang, J. J. Zhu, J. Cryst. Growth 2003, 256, 134Ϫ138.
W. Wang, Z. Liu, Y. Liu, C. Xu, C. Zheng, G. Wang, Appl.
Phys. A, Mater. Sci. Process. 2003, 76, 417Ϫ420.
C. K. Xu, Y. K. Liu, G. D. Xu, G. H. Wang, Mater. Res. Bull.
2002, 37, 2365Ϫ2372.
W. Z. Wang, G. H. Wang, X. S. Wang, Y. J. Zhan, Y. K. Liu,
C. L. Zheng, Adv. Mater. 2002, 14, 67Ϫ69.
L. F. Gou, C. J. Murphy, Nano. Lett. 2003, 3, 231Ϫ234.
M. H. Cao, C. W. Hu, Y. H. Wang, Y. H. Guo, C. X. Guo, E.
B. Wang, Chem. Commun. 2003, 1884Ϫ1885.
W. H. Sutton, Am. Ceram. Soc. Bull. 1989, 68, 376.
H. Katsuki, S. Komarneni, J. Am. Ceram. Soc. 2001, 84,
2313Ϫ2317.
S. Komarneni, R. Roy, Q. H. Li, Mater. Res. Bull. 1992, 27,
1393Ϫ1405.
S. Komarneni, Ionics 1995, 21, 95.
K. S. Suslick, Science 1990, 247, 1439Ϫ1445.
Brochure on AultraCLAVE by Milestone, Microwave Labora-
tory Systems (Monroe, CT).
M. Figlarz, F. Fievet, J. P. Lagier, Europe patent no. 0113281;
USA no. 4539041; Japan: application no. 24303783, 1985.
F. Fievet, J. P. Lagier, B. Bin, Solid State Ionics 1989, 32,
198Ϫ205.
[5]
[6]
[7]
1998, 42, 575Ϫ585.
T. Mitsuyu, O. Yamakazi, K. Ohji, K. Wasa, Ferroelectrics
[8]
1982, 42, 233Ϫ240.
M. M. Viitanen, W. P. A. Jansen, R. G. van Welzenis, H. H.
[9]
[37]
[38]
Brongersma, D. S. Brands, E. K. Poels, A. Bliek, J. Phys. Chem.
B 1999, 103, 6025Ϫ6029.
U. Bjoerksten, J. Moser, M. Graetze, Chem. Mater. 1994, 6,
858Ϫ863.
[10]
[39]
[40]
[11]
J. Tamaki, K. Shimanoe, Y. Yamada, Y. Yamamoto, N. Miura,
N. Yamazoe, Sens. Actuat. B 1998, 49, 121Ϫ125.
Y. Jiang, S. Decker, C. Mohs, K. J. Klabunde, J. Catal. 1998,
180, 24Ϫ35.
[12]
[41]
[42]
[13]
R. V. Kumar, Y. Mastai, Y. Diamant, A. Gedanken, Chem.
Mater. 2000, 12, 2301Ϫ2305.
R. V. Kumar, Y. Mastai, Y. Diamant, A. Gedanken, J. Mater.
[43]
[44]
[14]
Chem. 2001, 11, 1209Ϫ1213.
N. A. Dhas, C. P. Raj, A. Gedanken, Chem. Mater. 1998, 10,
1446Ϫ1452.
[15]
[45]
[16]
H. Wang, J. Z. Xu, J. J. Zhu, H. Y. Chen, J. Cryst. Growth
[46]
[47]
[48]
2002, 244, 88Ϫ94.
G. G. Condorelli, L. L. Costanzo, I. L. Fragala, S. Giuffrida,
[17]
G. Ventimiglia, J. Mater. Chem. 2003, 13, 2409Ϫ2411.
S. Kapoor, T. Mukherjee, Chem. Phys. Lett. 2003, 370, 83Ϫ87.
A. V. Loginov, V. V. Gorbunova, T. B. Boitsova, J. Nanopart.
[18]
[49]
[50]
[19]
Res. 2002, 4, 193Ϫ205.
T. B. Boitsova, A. V. Loginov, V. V. Gorbunova, Russ. J. Appl.
[20]
Chem. 1997, 70, 1507Ϫ1512.
Z. Liu, Y. Yang, J. Liang, Z. Hu, S. Li, S. Peng, Y. J. Qian, J.
[51]
[52]
[53]
C. Feldmann, Adv. Funct. Mater. 2003, 13, 101Ϫ107.
Y. G. Sun, Y. N. Xia, Adv. Mater. 2002, 14, 833Ϫ837.
S. Komarneni, D. Li, B. Newalkar, H. Katsuki, A. S. Bhalla,
Langmuir 2002, 18, 5959Ϫ5962.
[21]
Phys. Chem. B 2003, 107, 12658Ϫ12661.
S. J. Chen, X. T. Chen, Z. L. Xue, L. H. Li, X. Z. You, J. Cryst.
[22]
Growth 2002, 246, 169Ϫ175.
M. G. Shumsky, J. A. Switzer, Chem. Mater. 1999, 11,
2289Ϫ2291.
[54]
[55]
[56]
C. Feldmann, H. O. Jungk, Angew. Chem. Int. Ed. 2001, 40,
[23]
359Ϫ362.
O. Palchik, J. J. Zhu, A. Gedanken, J. Mater. Chem. 2000, 10,
1251Ϫ1254.
[24]
J. K. Barton, A. A. Vertegel, E. W. Bohannan, J. A. Switzer,
Chem. Mater. 2001, 13, 952Ϫ959.
L. Huang, H. Wang, Z. Wang, A. Mitra, D. Zhao, Y. Yan,
T. Yamamoto, Y. Wada, H. B. Yin, T. Sakata, H. Mori, S.
Yanagida, Chem. Lett. 2002, 10, 964Ϫ965.
F. Kooli, V. Rives, W. Jones, Chem. Mater. 1997, 9, 2231Ϫ2235.
R. Harpeness, O. Palchik, A. Gedanken, V. Palchik, S. Amiel,
M. A. Slifkin, A. M. Weiss, Chem. Mater. 2002, 14,
2094Ϫ2102.
H. Grisaru, O. Palchik, A. Gedanken, M. A. Slifkin, A. M.
Weiss, V. Palchik, Inorg. Chem. 2003, 42, 7148Ϫ7155.
H. Grisaru, O. Palchik, A. Gedanken, V. Palchik, M. A. Slif-
kin, A. M. Weiss, Y. R. Hacohen, Inorg. Chem. 2001, 40,
4814Ϫ4815.
[25]
Chem. Mater. 2002, 14, 876Ϫ880.
S. Kenane, L. Piraux, J. Mater. Res. 2002, 17, 401Ϫ406.
M. E. T. Molares, V. Buschmann, D. Dobrev, R. Neumann, R.
[57]
[58]
[26]
[27]
Scholz, I. U. Schuchert, J. Vetter, Adv. Mater. 2001, 13, 62Ϫ65.
I. Enculescu, Z. Siwy, D. Dobrev, C. Trautmann, M. E. T. Mo-
[28]
[59]
[60]
lares, R. Neumann, K. Hjort, L. Westerberg, R. Spohr, Appl.
Phys. A, Mater. Sci. Process. 2003, 77, 751Ϫ755.
Y. Konishi, M. Motoyama, H. Matsushima, Y. Fukunaka, R.
[29]
Ishii, Y. Ito, J. Electroanal. Chem. 2003, 559, 149Ϫ153.
T. Gao, G. W. Meng, Y. W. Wang, S. H. Sun, L. Zhang, J.
[30]
[61]
F. Bonet, C. Guery, D. Guyromard, R. Herrera Urbina, K.
Tekaia-Elhsissen, J. M. Tarascon, Int. J. Inorg. Mater. 1999,
1, 47Ϫ51.
Phys.: Condens. Matter 2002, 14, 355Ϫ363.
D. K. Sarkar, X. J. Zhou, A. Tannous, M. Louie, K. T. Leung,
[31]
Solid State Commun. 2003, 125, 365Ϫ368.
C. L. Kitchens, M. C. McLeod, C. B. Roberts, J. Phys. Chem.
Received March 30, 2004
[32]
Early View Article
B 2003, 107, 11331Ϫ11338.
Published Online August 26, 2004
4080
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