Environmental Engineering Reference
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(002)
(11-1)
(111)
(111)
(11-1)
(002)
(111)[-110]
CeO
2
// (111)[-110]
Au
(
a
)
(
b
)
Figure 8.21
HRTEM micrographs of gold islands deposited on CeO
2
nanoparticles
following the deposition-precipitation and coprecipitation methods respectively. Dislocation
networks are highlighted in the insets. Reproduced with permission from [109].
discontinuity in the region close to the metal-nonmetal transitions in gold,
as the melting point collapses.
h e dependency of catalytic activity on noble metal catalysis mainly
originates from the dif erent crystal planes exposed on the nanocrystal
surface (Figure 8.21). h ere are two types of crystal planes: (i) high-index
facets, low catalytic activity during catalytic cycle due to high surface
energy, leading to possible structural instability [106], and (ii) low-index
facets, including {111}, {100} and {110} planes with both high activity and
good stability [107, 108].
Very recently, Wang
et al.
[110] reported the shape-dependent catalytic
activities of Au nanocrystals toward electrooxidation of glucose in alkaline
medium. h ey found that {100}-bounded cubic Au nanocrystals are sig-
nii cantly more active than the {110}-bounded rhombic dodecahedral and
{111}-bounded octahedral Au nanocrystals.
It is generally accepted that AuOH sites on the Au surfaces act as the
active species for glucose oxidation (11) and the oxidation of glucose is
strongly dependent on the number of AuOH sites. Among the three types
of Au nanocrystals (Figure 8.22, let ), the cubic ones have the highest cur-
rent densities at all three oxidation peaks (Figure 8.23, right). h e current
densities at -0.40 V (oxidation of glucose to gluconolactone and a very lim-
ited number of AuOH sites on the nanocrystal surfaces due to the reduc-
tive nature of the electrodes) for the cubic Au nanocrystals are 6.5 and
2.6 times those of the octahedral and rhombic dodecahedra Au nanocrys-
tals, respectively. A similar comparison shows this to be 1.5 and 1.7 times
higher at 0.25 V (further oxidation of gluconolactone and the population
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