Last Update
December 4, 2008 |
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Current Research
During his stay in Potsdam, he started to develop, together with Dr. Niederberger, several non-aqueous sol-gel
routes for the synthesis of a large variety of metal oxide nanoparticles [1-3]. These new
approaches resulted in a generalized synthesis strategy to inorganic nanomaterials. Hence, a toolbox
of well-known chemical reactions was gathered, allowing to prepare the targeted nanoparticles by
following a sequence of predictable synthesis steps. These new routes imply many important
advantages over traditional aqueous sol-gel chemistry and other recent approaches that require large
amount of surfactants for a good control of the particle growth. In fact, the main advantages of the
developed routes are: high purity, high crystallinity, large yield, and well-defined and uniform
particle sizes and morphologies.
Transmission electron micrographs of typical examples of nanocrystals
synthesized in organic solvents but, principally in benzyl alcohol
are displayed in figure 1: HfO2 (Fig 1a), Nb2O5
(Fig 1b), Ga2O3 (Fig 1c), In2O3
(Fig 1d), Sn0.90In0.10Ox (Fig 1e),
Fe3O4 (Fig 1f).
In the most cases, the crystallites exhibit a spherical morphology
with uniform shapes, small size distributions and good
dispersibility. However, the examples of Nb2O5 and
WO3-H2O which present a platelet like
morphology or nanorods and nanowires of ZnO
already point to the
possibility to get anisotropic particle morphologies without the use
of any additional surfactant.
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Figure 1) TEM images of selected nanoparticle assemblies. a) HfO2,
b) Nd2O5, c) Ga2O3, d)
In2O3, e) Sn0.90In0.10Ox,
f) Fe3O4
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High resolution transmission microscopy (HRTEM) studies have been
performed in each system. As a general trend it was found that the
as-synthesized nanoparticles present good crystallinity even for such
moderate reaction temperatures. In figure 2 selected HRTEM examples
together with their respective power spectrum (PS) are displayed.
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Figure 2) a) HRTEM image of a part of an In2O3
cubic nanoparticle, b) 2nm nanoparticle Sn0.95In0.05Ox,
c) a 16 nm nanoparticle of Fe3O4, d) a part of
a Nb2O5 nanoplatelet. Inserts show respective
PS.
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Furthermore, it was shown that these new materials posses new
and highly demanded properties. As an example semi-conducting metal oxide nanoparticles
revealed extremely good performances in gas sensing [4]. They are thus highly suitable for the
production of cheap and portable sensing devices for the detection of toxic gases at sub-ppm level.
Figure 3 depitcs an example of dynamic response of a think layer of In2O3 nanoparticles
subjected to different NO2 concentrations in dry air. The extrapolated sensitivity of this sensor was 1ppb.
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Figure 3) Dynamic response of the In2O3-based sensor to different NO2 concentrations
in dry air.
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More recently it was shown that nonhydrolitic sol-gel reactions are not only suitable for the
formation of highly crystalline pure inorganic nanoparticles but also
for organic-inorganic hybrid nanoparticles [5].
The reaction of rare earth (RE) alkoxides with benzyl alcohol or a
derivative thereof (e.g. 4-byphenylmethanol,
4-tert-butylbenzylalcohol) results in the direct formation of
ordered lamellar organic-inorganic hybrid materials based on RE2O3
oxides. The material consists of very thin
crystalline oxide layers of general formula RE2O3
regularly separated from each other by organic layers.
Figure 4 depicts typical examples of such hybrid nanostructures.
Then doped with emitting ions, typically other lanthanides, these hybrid materials show good
photoluminescent performances and interesting new optical features compared to standard pure inorganic phosphors.
In fact, they show the following advantages: i) higher radiance and luminance values, ii) larger excitation
range with the maximum shifted toward the red, and iii) the possibility to tune the emission
chromaticity simply by varying the excitation wavelength.
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Figure 4) TEM overview images of the a) neodymium
oxide and b) samarium oxide based benzoate hybrid materials. c)
Gadolinium oxide and d) neodymium oxide based biphenolate hybrid
materials.
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Actually, Nicola Pinna is interested in the application of the nonaqueous
sol-gel routes, he recently developed, for the deposition of well calibrated
and highly crystalline thin films by Atomic Layer Deposition. First results are very
promising, in fact at very low temperature many oxides were deposited onto several substrates.[6]
References
[1] Surfactant-Free Nonaqueous Synthesis of Metal Oxide Nanostructures
Nicola Pinna, Markus Niederberger
Angew. Chem. Int. Ed. 2008, in print
[2] Nonaqueous Routes to Crystalline Metal Oxide Nanoparticles: Formation Mechanisms and Applications
Markus Niedereberger, Georg Garnweitner, Nicola Pinna, Giovanni Neri
Prog. Sol. State Chem. 2005, 33, 59
[3] Nonaqueous Synthesis of Metal Oxide Nanoparticles: Review and Indium Oxide as Case Study for the Dependence of Particle Morphology on Precursors and Solvents
Markus Niederberger, Georg Garnweitner, Jelena Buha, Julien Polleux, Jianhua Ba, Nicola Pinna
J. Sol-Gel Sci. Technol. 2006, 40, 259
[4] Nonaqueous synthesis of nanocrystalline semi-conducting metal oxides for gas sensing
Nicola Pinna, Giovanni Neri, Markus Antonietti, Markus Niederberger
Angew. Chem. Int. Ed. 2004, 43, 4345
[5] The "benzyl alcohol route": an elegant approach towards organic-inorganic hybrid nanomaterials
Nicola Pinna
J. Mater. Chem. 2007, 17, 2769
[6] Non-Aqueous Routes to Metal Oxide Thin Films by Atomic Layer Deposition
Erwan Rauwel, Guylhaine Clavel, Marc-Georg Willinger, Protima Rauwel, Nicola Pinna
Angew. Chem. Int. Ed. 2008, 47, 3592
For more details see the complete list of Publications
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