8
J. Oliver–Meseguer and A. Leyva–Pérez
I 2
I 2
Fig. 1.7 Disaggregation of supported metal nanoparticles to clusters with iodine
Following top–down approaches (Fig. 1.7), redox active halogen species can be
used to dislodge metal nanoparticles into sub-nanometer clusters. For instance, I 2
solutions broke Au NPs supported on charcoal, Al 2 O 3 , TiO 2 and ZnO, into subnanometric Au clusters and isolated atoms [50, 62, 63].
1.2.3 Metal Cluster Characterization Techniques
1.2.3.1 UV–Vis and Fluorescence
Ultraviolet-visible (UV–vis) spectrophotometric analysis is probably the easiest and
fastest characterization method to determine the presence or absence of metal clusters in solution and also when supported on solids (diffuse reflectance mode). The
appearance of absorption bands in the UV–A and blue visible regions (250–400 nm)
can be indicative of the presence of metal clusters, which have defined valence
orbitals, in clear contrast with metal nanoparticles which present plasmon bands in
a different and non-interfering area, around 550 nm (Fig. 1.8). Based on the Jellium
model presented above, the number of atoms of the clusters, N, can be calculated
by the simple Eq. 1 (E F = 5.32 eV for bulk Au) and Eg the HOMO–LUMO energy
band gap, respectively (HOMO 1/4 highest occupied molecular orbital, LUMO 1/4
Fig. 1.8 Experimental
absorption UV/Vis and the
corresponding emission
(inset) spectra for the
AuIPrCl-catalyzed hydration
of 1–octyne just after the
induction time, where the
formation of Au clusters (is
completed) [53]. Copyright
© 2013 by John Wiley &
Sons, Inc.
J. Oliver–Meseguer and A. Leyva–Pérez
I 2
I 2
Fig. 1.7 Disaggregation of supported metal nanoparticles to clusters with iodine
Following top–down approaches (Fig. 1.7), redox active halogen species can be
used to dislodge metal nanoparticles into sub-nanometer clusters. For instance, I 2
solutions broke Au NPs supported on charcoal, Al 2 O 3 , TiO 2 and ZnO, into subnanometric Au clusters and isolated atoms [50, 62, 63].
1.2.3 Metal Cluster Characterization Techniques
1.2.3.1 UV–Vis and Fluorescence
Ultraviolet-visible (UV–vis) spectrophotometric analysis is probably the easiest and
fastest characterization method to determine the presence or absence of metal clusters in solution and also when supported on solids (diffuse reflectance mode). The
appearance of absorption bands in the UV–A and blue visible regions (250–400 nm)
can be indicative of the presence of metal clusters, which have defined valence
orbitals, in clear contrast with metal nanoparticles which present plasmon bands in
a different and non-interfering area, around 550 nm (Fig. 1.8). Based on the Jellium
model presented above, the number of atoms of the clusters, N, can be calculated
by the simple Eq. 1 (E F = 5.32 eV for bulk Au) and Eg the HOMO–LUMO energy
band gap, respectively (HOMO 1/4 highest occupied molecular orbital, LUMO 1/4
Fig. 1.8 Experimental
absorption UV/Vis and the
corresponding emission
(inset) spectra for the
AuIPrCl-catalyzed hydration
of 1–octyne just after the
induction time, where the
formation of Au clusters (is
completed) [53]. Copyright
© 2013 by John Wiley &
Sons, Inc.