Article
pubs.acs.org/Langmuir
Photochemical Preparation of Silver Nanoparticles Supported on
Zeolite Crystals
Moussa Zaarour,† Mohamad El Roz,† Biao Dong,† Richard Retoux,‡ Roy Aad,§ Julien Cardin,§
Christian Dufour,§ Fabrice Gourbilleau,§ Jean-Pierre Gilson,† and Svetlana Mintova*,†
†
LCS, ‡CRISMAT, and §CIMAP, ENSICAEN, Université de Caen, CNRS, 6 bd du Maréchal Juin, 14050 Caen, France
S Supporting Information
*
ABSTRACT: A facile and rapid photochemical method for preparing supported silver nanoparticles (Ag-NPs) in a suspension
of faujasite type (FAU) zeolite nanocrystals is described. Silver cations are introduced by ion exchange into the zeolite and
subsequently irradiated with a Xe−Hg lamp (200 W) in the presence of a photoactive reducing agent (2-hydroxy-2methylpropiophenone). UV−vis characterization indicates that irradiation time and intensity (I0) influence significantly the
amount of silver cations reduced. The full reduction of silver cations takes place after 60 s of a polychromatic irradiation, and a
plasmon band of Ag-NPs appears at 380 nm. Transmission electron microscopy combined with theoretical calculation of the
plasmon absorbance band using Mie theory shows that the Ag-NPs, stabilized in the micropores and on the external surface of
the FAU zeolite nanocrystals, have an almost spheroidal shape with diameters of 0.75 and 1.12 nm, respectively. Ag-NPs, with a
homogeneous distribution of size and morphology, embedded in a suspension of FAU zeolites are very stable (∼8 months), even
without stabilizers or capping agents.
molecules or metals with interesting properties for optical
applications.9−14 In fact, the use of zeolites for optical
applications has already attracted the attention of researchers
because of their diverse structures, high porosity, high thermal
stability, and availability in different sizes and morphologies.10
The incorporation of zeolites into an optical device offers the
possibility of stabilizing and organizing the photoactive guests
as well as preventing intermolecular interactions that reduce or
even quench their photophysical properties.11 As a result,
several studies reported the use of zeolites as suitable supports
for Ag-NPs.12−14
Ag-NPs are generally prepared by either thermal reduction,15
microwave reduction,16 sonochemical reduction,17 chemical
reduction,18 or photoreduction of silver cations (Ag+) in
solution.19−21 Thermal treatment is a classical way to prepare
Ag-NPs: the solution containing silver cations is heated in the
presence of a reducing agent such as H2 or CO, introduced
INTRODUCTION
Silver nanoparticles are currently the focus of intensive research
because of their catalytic, antibacterial, and optical properties.1
Their interesting optical properties, more precisely, their
plasmonic properties, make them highly desirable in various
applications like sensors,2 OLEDs,3 and photovoltaic solar
cells.4−6 Their plasmonic properties depend strongly on their
size, morphology, and density.7 Therefore, a systematic
modification of these parameters allows the tuning of their
plasmonic response over the whole visible spectrum.
In solution, silver nanoparticles agglomerate to form clusters
or even large particles and hence lose their optical properties.
To prevent this and maintain the plasmonic properties, Ag-NPs
are usually charged or dispersed in media such as noble gases,
organic scaffolds, or a porous matrix (zeolites).7
Zeolites are crystalline aluminosilicates with a framework
made of SiO4 and AlO4 tetrahedra, in which the negatively
charged Al sites are neutralized by the charge-balancing extraframework cations, such as K+, Li+, Na+, etc.8 These charge
compensating cations are noncovalently bonded to the zeolite
and offer the possibility of replacing them with organic
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© 2014 American Chemical Society
Received: February 19, 2014
Revised: May 7, 2014
Published: May 8, 2014
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directly into the reaction mixture, or generated in situ.15
Microwave-assisted reduction presents several advantages like a
more homogeneous heating, a shorter reaction time, and an
easier nucleation of Ag-NPs.16 The sonochemical process is
used for the preparation of Ag-NPs when the particle size
strongly depends on the type of reducing agent applied.17
Using sodium borohydride, a strong reducing agent, results in
spherical Ag-NPs 10 nm in size, while with a weak reducing
agent, such as sodium citrate, the formation of Ag-NPs ∼3 nm
in size is observed.17 Moreover, chemical treatment is an
efficient process for preparing Ag-NPs in solution with good
control of their size and shape. The key to a rational design is to
find the proper combination of silver precursors, a reducing
agent, stabilizers, and reaction conditions (rate and pH).18 The
drawback of these methods is the use of relatively large
amounts of reducing agents and their subsequent elimination in
an additional step. Furthermore, Ag-NPs are generally sensitive
to heat and oxygen; the addition of capping and stabilizing
agents is usually recommended to preserve their structure and
prevent their aggregation in solution.
The photoassisted synthesis (photoreduction) of silver is
another method used for the preparation of Ag-NPs, albeit less
practiced. It allows the preparation of stable nanoparticles of
Ag-NPs by irradiation of a reaction mixture with a light source
(laser or lamp) in the presence of photoreducing agents
without the need to introduce stabilizers or surfactants.19−21
Their size and the time needed for their preparation are directly
proportional to the irradiation power of the light source. For
example, with a low-power lamp (4 W), irradiation for 9 h is
needed to produce 19 nm diameter Ag-NPs,21 while with a
stronger source (150 W), the reaction takes only 45 min.
However, in the latter case, the Ag-NPs are polydisperse and
smaller than when they are prepared using a lower-energy
lamp.21
In this work, we report a facile and rapid preparation of AgNPs, supported on FAU type zeolite crystals, using a
photochemical reduction method. The silver cations are
introduced into the FAU zeolite nanocrystals (Si/Al = 1.2)
by ion exchange and subsequently reduced (to Ag0) by
irradiation with a Xe−Hg lamp (200 W) for 5−60 s. The
irradiation intensity and time have a direct influence on the Ag
nanoparticles and their plasmonic properties. The microstructure and optical properties of the Ag-NPs are monitored
by high-resolution transmission electron microscopy
(HRTEM) and UV−vis spectroscopy, respectively.
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conventional oven. The zeolite nanocrystals were purified by
centrifugation (25000 rpm for 4 h) and dispersed in doubly distilled
water (dd H2O) until the pH of the decanted suspension reached 7.
Finally, the purified FAU zeolite sample was centrifuged and decanted;
the resulting FAU slurry is further ion-exchanged as described below.
Ion Exchange of FAU Zeolites. The FAU slurry (100 mg) was
sonicated in a 10 mL aqueous solution of AgNO3 (0.1 M) for 6 h, and
the product was purified by centrifugation and washed three times
with doubly distilled water to remove any excess of silver. The ionexchanged FAU zeolite in a water suspension will hereafter be termed
FAU-Ag+. The as-prepared suspension was freeze-dried; the color of
the FAU-Ag+ sample prior reduction is white. The FAU-Ag+ powder
sample was redispersed in water (0.25 g/L in H2O). One milliliter of
this FAU-Ag+ suspension containing 2.64 × 10−4 mg of Ag+ was then
added to 0.1 mL of 2-hydroxy-2-methylpropiophenone (0.096 M in
ethanol, 99%). This mixture was stirred while being irradiated with a
Xe−Hg polychromatic lamp with an intensity varying from 20 to 100%
for 5−60 s.
Preparation of Ag-NPs in FAU Zeolites. UV irradiation of the
FAU-Ag+ suspension (1 mL) was conducted with a polychromatic
Xe−Hg lamp (LC8-01A spot light, Hamamatsu, L10852, 200 W)
using a UV light guide (model A10014-50-0110). This device was
mounted at the entrance of the reactor containing the zeolite
suspensions to establish a “homogeneous” irradiation. The UV
irradiation intensity (I0) at full capacity of the lamp measured with a
light power meter (from Hamamatsu) was 55 mW/cm2 at 366 nm. All
samples were stirred in the reactor during the reduction process. The
Xe−Hg polychromatic lamp intensity varied from 20 to 100% for 5−
60 s. The FAU suspensions containing Ag-NPs will hereafter be
termed FAU-Ag.
Characterization of Ag-NPs in FAU Zeolite Suspensions. The
UV−vis absorption spectra of the zeolite suspensions containing AgNPs were recorded on a Thermo-electron evolution 500 UV−vis
spectrometer working in transmission and in quartz cuvettes with a 1
cm path length. The zeolite suspension prior to ion exchange was used
as a reference for all UV−vis measurements.
Dynamic Light Scattering (DLS) Analysis. The hydrodynamic
diameters of the as-prepared suspensions of zeolite nanoparticles and
those containing Ag-NPs were determined with a Malvern Zetasizer
Nano instrument using a backscattering geometry (scattering angle of
173°, He−Ne laser with a 3 mW output power at a wavelength of
632.8 nm). The DLS analyses were performed on samples with a solid
concentration of 1 wt %.
High-Resolution Transmission Electron Microscopy (HRTEM). The
crystal size, morphology, crystallinity, and chemical composition of
suspensions of FAU-containing Ag-NPs were characterized using
HRTEM coupled with an energy dispersive analysis (EDS) on a 200
kV JEOL 2010 FEG STEM electron microscope (tilt of ±42°)
equipped with an EDS (energy dispersive spectrometer, Si/Li
detector; a double tilt sample holder was used). The suspensions
were sonicated for 15 min prior to their deposition on a holey carbon
supported on a nickel grid.
Theoretical Modeling of the Ag Plasmon Band. The
simulation of the UV−vis absorbance spectra was performed using
the Mie theory.22 Simulations were conducted using the refractive
index of water taken from the IAPWS23 or an adjustable constant
refractive index for the surrounding medium. The refractive index of
silver was taken from ref 24. The refractive index of silver was sizecorrected to take into account the reduction of the electron mean free
path in nanoparticles. The size correction was conducted by
introducing an additional surface contribution into the electronic
scattering to retain the Drude part of the dielectric function using the
electron scattering rate given by Kriebig:25
EXPERIMENTAL SECTION
Raw Materials. Silver nitrate (AgNO3) was purchased from Alfa
Aesar, and 2-hydroxy-2-methylpropiophenone [C 6 H 5 COC(CH3)2OH], benzophenone (C13H10O), and benzaldehyde (C7H6O)
were purchased from Sigma-Aldrich. Aluminum hydroxide [Al(OH)3,
Sigma-Aldrich], sodium hydroxide (NaOH, Sigma-Aldrich, 97%), and
colloidal silica (SiO2, Ludox-HS 30, 30 wt % SiO2, pH 9.8, Aldrich)
were used to prepare FAU type zeolite crystals (zeolite X) according
to the procedure below; these reagents were used without further
purification.
Preparation of a FAU Type Zeolite Suspension. The FAU
nanocrystals were synthesized from a clear precursor suspension with a
9:0.9:10:200 Na2O:Al2O3:SiO2:H2O ratio. The suspension was
prepared by mixing Al(OH)3, NaOH, and SiO2 with doubly distilled
water and subjected to vigorous stirring at room temperature until a
clear suspension was obtained. Then the resulting clear suspension was
aged for 24 h at room temperature prior to the hydrothermal
synthesis. The crystallization was performed at 150 °C for 45 min in a
γ = γ0 + 2g
νF
D
(1)
where γ0 is the bulk scattering rate and νF is the Fermi velocity of
silver. The nanoparticle diameter (D) and a phenomenological
dimensionless parameter (g) are related to the shape of the particles
as well as the material properties and the surrounding dielectric host
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Scheme 1. Preparation of Ag-NPs by Photogeneration of Free Radicals in Suspension
Figure 1. Evolution of the Ag plasmon band in FAU zeolite suspensions after UV treatment (H2O suspension) (A) at 60 s at (a) an I0 of 20% or (b)
an I0 of 100% and (B) at 15 s at (a) an I0 of 20% or (b) an I0 of 100%.
matrix. For spherical nanoparticles, g is estimated to be ∼0.7 ± 0.1.26
The values of γ0 and νF for silver were taken from ref 27.
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homolytic C−C bond scission (α-cleavage) upon exposure to
UV irradiation giving rise to a pair of radicals28 (Scheme 1).
After the radical formation, the following processes are
possible: (1) recombination of radicals going back to the
original compound or (2) deactivation of radicals by dissolved
oxygen present in the reaction medium (Scheme 1). (3) In the
presence of silver cations, the radicals can undergo a redox
process giving rise to silver nanoparticles (Ag-NPs) in addition
to the cationic form of the radicals that rearrange to form their
corresponding ketones. At the end of the reaction, the reducing
agent is fully dissociated and will be no longer available to
stabilize the produced Ag-NPs.
Influence of Irradiation Intensity on the Formation of
Ag-NPs. Because the light source used is of adjustable
intensity, the FAU-Ag+ suspension is irradiated with different
intensities (I0). At I0 values of <20%, few and nonreproducible
reactions are triggered because of a nonstable irradiation at such
low intensities. Upon irradiation with an I0 of 20% for 60 s, a
plasmon absorbance band at 375 nm appears in the UV−vis
spectrum of the FAU-Ag+ suspension and is associated with a
green coloration, indicative of the generation of Ag-NPs.
Interestingly, a further increase in I0 induces a progressive
hyperchromic shift of the plasmon absorbance band as well as a
slight bathochromic (red) shift. The sample irradiated with an
I0 of 100% presents an absorbance twice that at an I0 of 20%,
and the peak position shifts from 375 to 380 nm (Figure 1A).
This implies that more silver cations are reduced.19 The
reaction rate is directly proportional to the irradiation intensity
RESULTS AND DISCUSSION
The photochemical treatment of materials is a fast and efficient
method for producing electrons. It requires the use of a photoreducing agent or a photoactive species that becomes
electronically excited and rapidly transfers electrons to the
Ag+ cations (reducing them into Ag0), upon irradiation at a
specific wavelength. The compatibility between the photoreducing agent and the irradiation source is of prime
importance because the catalyst should absorb in the same
range as the light excitation to generate the free electrons.
Besides the reducing activity, the catalyst is used as a stabilizing
agent for the produced species.
In this work, three photoreducing agents, benzophenone,
benzaldehyde, and 2-hydroxy-2-methylpropiophenone, are used
as photocatalysts. The first two show a very low reactivity in the
FAU-Ag+ suspension, while the last one is the most compatible
with the zeolite suspension and consequently used in all
experiments. To ensure the miscibility between the zeolite
suspension and the reducing agent, 2-hydroxy-2-methylpropiophenone was first dissolved in ethanol and subsequently added
to the FAU-Ag+ suspension (in water); the mixture was stirred
vigorously during the reaction to ensure homogeneous
suspensions free of sedimentation.
The photo-reducing agent used is from the family of
hydroxyl-methylphenone, which is well-known to undergo a
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the Supporting Information)]. Besides, an additional amount of
reducing agent is added to the samples and then subjected to
irradiation. No notable change in the plasmon band is observed
under these conditions; thus, we conclude that the silver
cations are fully reduced after treatment for only 1 min. Instead,
a decrease in plasmon band intensity takes place at a long
irradiation time (5 min), probably because of a partial
destruction of the zeolite nanoparticles caused by the harsh
conditions used. Interestingly, no change in the absorbance
wavelength is noticed; this indicates that the reaction does not
occur via the formation of small Ag seeds growing into larger
particles during the reaction.21 Because of the fast reaction
process, Ag-NPs of a similar size are progressively produced.
The DLS study of the FAU-Ag suspensions obtained under
different irradiation conditions shows a monomodal particle
size distribution of particles with an average diameter of 70 nm
(Figure 3), matching the DLS from a pure FAU zeolite
used. At a low intensity, a small number of radicals are
generated, because of the competing deactivation process
(Scheme 1); only a few radicals are available for the reduction
of silver cations, explaining the low intensity of the plasmon
absorbance band. At a high irradiation intensity (I0 = 100%),
many free radicals are generated and are rapidly consumed.
This favors the reduction of silver over the deactivation of free
radicals and leads to the full reduction of silver cations after
only 60 s. This assumption is confirmed by running the
reaction for a shorter time (15 s) (Figure 1B). At a low
irradiation intensity (I0 = 20%), a very low intensity band
appears at 355 nm with no change in the color of the
suspension. This suggests that the number of free radicals
generated is not enough to reduce the silver cations. With an I0
of 100%, an intense absorption at 375 nm is associated with the
appearance of a dark green color, indicating that the reaction is
almost complete after irradiation for 15 s. For comparison, the
UV−visible spectra of the FAU-Ag+ suspension without and
with a photoreducing agent (2-hydroxy-2-methylpropiophenone) at time zero are taken and presented in Figure S1 of the
Supporting Information. It is clearly seen that after mixing, no
absorption band is observed in the spectrum, while the plasmon
band appears after 15 s (Figure 1). These results demonstrate
that the photoreducing agent upon exposure to UV irradiation
is giving rise to a pair of radicals, and the sequential processes
are followed as presented in Scheme 1.
Influence of Irradiation Time on the Formation of AgNPs. The irradiation of a silver-containing zeolite suspension is
conducted for different times while fixing the intensity of the
light source at 100%. As observed in Figure 2, a plasmon band
Figure 3. DLS curves of FAU-Ag suspensions after irradiation with an
I0 of 100% for (a) 5, (b) 10, (c) 15, and (d) 60 s.
suspension (Figure S3 of the Supporting Information). This
indicates that the silver nanoparticles are completely associated
with the zeolite crystals and no evidence of separate Ag-NPs is
observed in the suspensions.
The DLS results are confirmed by a HRTEM study (Figure 4
and Figure S4 of the Supporting Information). The zeolite
crystals contain silver nanoparticles predominantly located in
the channels of FAU crystals; however, several Ag-NPs are seen
on the zeolite surface. At high magnifications, the zeolite
nanoparticles show a high degree of crystallinity and wellaligned crystal fringes. As previously mentioned, because of the
short reaction period, the Ag nanoparticles are of similar size
and shape and appear as spheres with a diameter in the range of
0.7−1.1 nm. More than 80% of the Ag-NPs are located in the
super cages (1.1 nm) and some in the sodalite cages (0.7 nm)
of the FAU zeolite crystals. The entire FAU zeolite crystal
containing Ag-NPs at high magnification is shown in Figure
4C; the homogeneous distribution of Ag-NPs all over the
zeolite crystal can be seen. The regular distribution of Ag-NPs
in the zeolite crystals is observed at high magnifications, as
shown as an inset of the enlarged selected area in Figure 4B.
However, some Ag-NPs with a size of 5−6 nm can be seen on
the zeolite external surface (Figure 4A).
The zeolite crystals containing Ag-NPs are further
characterized by EDS-TEM (Figure 5).
Figure 2. Evolution of the Ag plasmon band in FAU suspensions after
UV treatment at 100% for (a) 5, (b) 10, (c) 15, and (d) 60 s.
appears at 365 nm, associated with a pale green coloration of
the suspension after irradiation for 5 s. This highlights the high
efficiency of this mode of reduction, i.e., formation of Ag-NPs
after irradiation for only 5 s instead of several hours for the
chemical reduction method.21 Increasing the reaction time
leads to a continuous hyperchromic shift of the plasmon band
and a darkening of the zeolite suspension, indicative of the
progressive formation of Ag-NPs. On the basis of the band
intensity, more than 75% of the silver cations are reduced after
only 15 s. Furthermore, all silver cations are reduced after
irradiation for 60 s with no increase in the plasmon band
intensity with longer irradiation times [2 or 3 min (Figure S2 of
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Figure 4. HRTEM images of FAU crystals containing Ag-NPs. (A) Ag-NPs within the cages and on the external surface of the zeolite crystals
(arrows). (B) Ag-NPs in the zeolite cages only. The inset shows an enlarged selected area showing the silver nanoparticle in the zeolites. (C) Ag-NPs
homogeneously distributed in the entire crystalline FAU zeolite particle. This sample was obtained after UV treatment at 100% for 60 s.
Figure 5. Elemental composition of the FAU-Ag sample measured by EDX-HRTEM (C corresponds to the holey carbon film, and Ni is coming
from the grid used in the TEM experiment). The inset shows the elemental analysis of the FAU-Ag sample expressed in weight and atomic percent.
Figure 6. (A) Plasmon band of Ag-NPs in (a) a FAU-Ag suspension and (b) pure Ag-NPs in water (I0 = 100% for 10 s). (B) Evolution of the
plasmon band for (a) FAU-Ag and (b) pure Ag in water after 60 min.
The zeolite main components, i.e., Al, Si, and Na, are
measured and presented in Figure 5. A Si:Al ratio of ∼1.2,
which is characteristic of the FAU type zeolite (X), is measured.
Additionally, the partial ion exchange of sodium for silver is
evidenced. Besides, the chemical composition of the ionexchanged (FAU-Ag+) and reduced (FAU-Ag) zeolite samples
is determined and presented in Table S1 of the Supporting
Information. The results confirm that the silver content does
not change; thus, only reduction of the silver cations occurred,
leading to the formation of Ag-NPs, which is proven by UV−vis
measurements.
Stability of Ag-NPs. The stability of Ag-NPs in the FAU
zeolite is of prime importance. It is expected that the
photoreductant has a dual action during the photoreduction
process: (1) reducing the silver cations and simultaneously (2)
stabilizing the Ag-NPs from further oxidation. However, we
have already mentioned that, in our case, the reducing agent is
fragmented during the reaction and so produces free radicals.
Hence, it is not capable of ensuring the stability of the reaction
products. The zeolite is therefore used as an inorganic matrix to
stabilize the Ag-NPs.10 In Figure 6A, the plasmon band of AgNPs stabilized in the FAU zeolite, and a control test with the
same amount of nonsupported and reduced silver in a water
solution is presented. It is clearly seen that the Ag-NPs in FAU
zeolite exhibit an intense and nearly symmetrical band
reflecting their high degree of monodispersity, already shown
by HREM. Moreover, the Ag-NPs in a water solution have a
very broad and weak band extending from 365 to 800 nm
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particle diameters, show that the experimental results are best
fit with a unique diameter. While it is difficult to ponder the
relative weight of both diameters, the simulations unambiguously show that silver nanoparticles with sizes ranging between
0.74 and 1.12 nm are at the origin of the absorption peak at 380
nm. The ratio of the two sizes of Ag-NPs (D = 0.735 nm, and D
= 1.124 nm) with different damping factors could be further
investigated to determine the ratio of the opening of the super
cage (sodalite cage) over the super cage.
(Figure 6A, black line). This band indicates the presence of AgNPs of different sizes. Hence, the first role of the zeolite crystals
is to induce a homogeneous formation of Ag-NPs with a
defined location within the zeolite pores, and on the zeolite
surface. One hour after irradiation, the plasmon band of AgNPs supported on FAU zeolite crystals is unchanged (Figure
6B), while the corresponding band for free Ag-NPs in a water
solution totally disappears. This evolution is accompanied by
the discoloration of the suspension, from light brown to
colorless. For the FAU-Ag suspension, no change in suspension
color, plasmon band position, or intensity is observed after
several months, while in the absence of zeolite, the Ag-NPs
start to be oxidized after reduction for only a few minutes
(Figure S5 of the Supporting Information).
Theoretical Calculations of Ag-NPs Based on the
Plasmon Band. A comparative study between the experimental and calculated plasmon bands for Ag-NPs stabilized in
FAU zeolites is presented in Figure 7. Simulations of Ag-NPs in
CONCLUSIONS
A facile and rapid preparation of silver nanoparticles supported
on FAU zeolite crystals (zeolite X) based on UV irradiation is
reported and analyzed. A silver ion-exchanged FAU zeolite
suspension is irradiated with a Xe−Hg lamp (200 W) in the
presence of a photoactive reducing agent (2-hydroxy-2methylpropiophenone). Silver nanoparticles are prepared after
a very short irradiation time (5−60 s), and a faster reduction is
achieved after optimizing the process conditions at higher
irradiation intensities. The optimal conditions for fully reducing
the silver cations are a lamp intensity (I0) of 100% for 60 s.
The size, morphology, and distribution of Ag-NPs in the
FAU zeolite crystals are characterized by HRTEM. The Ag-NPs
are located predominantly inside the micropores and to a lesser
extent on the external surface of the FAU zeolite crystals. The
Ag-NPs have an almost spheroidal shape with a diameter of
0.74−1.124 nm, which corresponds to the size of the cage
opening (sodalite cage) and super cage of FAU type zeolite.
This is further confirmed by a theoretical modeling of the
plasmon band. The Ag-NPs in the FAU zeolite crystals without
stabilizers or capping agents exhibit high stability and, after
several months, do not change, again because of the stabilizing
role of the zeolite nanocrystals.
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Figure 7. Experimental plasmon band of Ag-NPs in a FAU zeolite
suspension irradiated with an I of 100% after 60 s (black line) and
calculated plasmon band for Ag spheres with diameters (d) of 0.74 and
1.12 nm [parameter g = 0.62 and g = 0.96, N_m = 1.28 (red dotted
line)] and calculated plasmon band for the Ag sphere with diameters
of 0.74 and 1.12 nm (parameter g = 0.55 and g = 0.85, N_m = 1.28).
ASSOCIATED CONTENT
S Supporting Information
*
UV−vis spectra of the FAU-Ag+ suspension without and with a
photoreducing agent (2-hydroxy-2-methylpropiophenone) at
time zero (Figure S1), evolution of the Ag plasmon band in the
FAU-Ag suspension after UV treatment at an I0 of 100% for 1,
2, and 3 min (Figure S2), DLS curve of the FAU zeolite
suspension with a solid content of 1 wt % (Figure S3), TEM
picture of the FAU-Ag sample (M = 100 nm) (Figure S4),
evolution of the plasmon band of Ag-NPs with time after
irradiation of AgNO3 in water (Figure S5), modeling of Ag NPs
based on the UV−vis spectra, and elemental analysis of the
FAU-Ag sample before and after reduction expressed in weight
and atomic percent (Table S1). This material is available free of
charge via the Internet at http://pubs.acs.org.
water are first conducted. The simulations are performed for
two spheres with diameters of 0.74 nm (opening of the
supercage) and 1.12 nm (diameter of the supercage, dotted
blue line), using an adjustable damping parameter (g),
determined using a fitting algorithm. As shown in Figure 7,
the D = 0.74 nm, g = 0.55 case and the D = 1.12 nm, g = 0.85
case result in similar absorption spectra. In fact, the
experimental absorption spectrum can be reproduced with
various values of D and g. However, larger nanoparticle
diameters would be best fit using a “g” value of >0.85, and
smaller nanoparticle diameters would be best fit with a “g” value
of <0.55. Thus, the values shown in Figure 7 present the best
agreement between the diameters expected for the silver
nanoparticles and the g value, reported in the literature for
spherical particles (i.e., 0.7 ± 0.1). The fits can be improved by
changing the refractive index of the surrounding medium to a
value of 1.28. Again, the experimental data can be best fit with
the D = 0.74 nm, g = 0.62 case and the D = 1.12 nm, g = 0.96
case, as shown in Figure 7. Although both diameters can explain
the experimental absorption spectra, additional Mie theory
simulations, using adjustable Gaussian distributions of nano-
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AUTHOR INFORMATION
Corresponding Author
*E-mail: svetlana.mintova@ensicaen.fr.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The financial support from the SOLAIRE Emergent Region
Project of Lower Normandy and the MEET, INTERREG EC
project is acknowledged. We acknowledge Hussein Awala for
the preparation of FAU zeolite crystals.
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