JLMN-Journal of Laser Micro/Nanoengineering Vol. 19, No. 2, 2024

Preparation of Ion-exchanged Zeolite Nanoparticles by Laser Irradiationin Liquid and their Properties
Kishin Konishi and Hiroyuki Wada*
Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan*
Corresponding author’s e-mail: wada.h.ac@m.titech.ac.jp
Zeolite nanoparticles were prepared by laser irradiation of zeolites or ion-exchanged zeolites.
Using ion-exchanged zeolite as a raw material, metal cations introduced into the pores caused local
laser absorption, and zeolite nanoparticles were produced with a minimum size of 50 nm. X-ray
diffraction and transmission electron microscopy images confirmed the crystal structure of the zeolite
nanoparticles. It was found that the crystal structure was maintained up to the nanoparticles’ surface.
By changing the centrifugation intensity, nanoparticles of any size could be selectively recoveredfrom dispersions containing nanoparticles with a wide size distribution. The volume zone of theobtained nanoparticles was estimated by comparing it with the calculated particle size value that all
particles settled using Stokes' law.
DOI: 10.2961/jlmn.2024.02.2003
Keywords: zeolite, nanoparticles, laser, ion exchange, centrifugation
1. Introduction
Zeolites are porous aluminosilicates with a uniform poresize (about 1 nm) and ion exchange capacity. Various zeolite
types with different pore sizes and compositions have been
artificially synthesized for different purposes [1]. Synthesized zeolite is used, for example, as a deodorant [2] or adsorbent to remove emission control substances (such asNOx) contained in exhaust gas from factories and automobiles [3] and to remove impurities from various solvents inchemical plants [4]. It is also used as a catalyst for selective
organic reactions using the molecular sieve effect of pores[5]. Furthermore, studies have been made in recent years todevelop further physical properties by modifying the zeolite
surface [6] and synthesizing metal nanoparticles inside [7].
Nanometer-sized zeolites are attracting attention because of their high specific surface area, and shortening the
diffusion path into pores, which improves the accessibilityof guest molecules into pores and improves dispersibility insolvents [8]. Several major zeolite nanoparticles have beensynthesized by a bottom-up method [9-11]. However, thesynthesis conditions must be a dilute solution, and the heating temperature and time must be appropriately controlled
to suppress the zeolite crystal growth as much as possible.
Moreover, a method of synthesizing by adding an organic
template, such as tetramethylammonium hydroxide, and amethod of synthesizing from an inert medium, such as a gelling polymer, are known to promote nucleation [12-14].
However, these methods have problems in terms of high production costs and wastewater pollution. Although various
kinds of zeolites have been developed currently, the synthesis conditions of each one are different. However, it is moredifficult to synthesize various kinds of zeolite nanoparticles.
A top-down approach using laser ablation in liquid is oneof the promising methods to obtain nanoparticles by dispersing a target substance in a liquid and irradiating it with apulsed laser. Various functional nanoparticles were preparedby laser processing [15-18]. It would be possible to obtainvarious types of zeolite nanoparticles such as A, X, Y, and soon by using commercially available zeolite as a raw material
for laser ablation in liquid. Various types of zeolite nanoparticles can be easily produced in a short time and one step. In
addition, it is possible to prevent the pores from being
clogged by an excessively added organic substance since thenanoparticle-dispersed solution does not contain other organic substances. In the past, nanoparticle production by laser irradiation has been widely performed in producing
metal or metal oxide nanoparticles. A high-temperature andhigh-pressure field are generated by focused irradiation of asolid target, and nanoparticles are produced through melting
and plasma formation [19-21]. In contrast, preparing zeolite
nanoparticles with complex metastable structures remains
challenging. William T Nichols et al [22]. irradiated powdered LTA zeolite with a focused laser and reported that thesize and crystallinity of the nanoparticles produced variedwith the difference in laser power. As the power of laser irradiation was increased, the particle size could be reduced,
but at the same time, zeolite nanoparticles with low crystallinity were produced. This indicates that if the laser power is
too high, the metastable structure will be damaged by forming high-temperature plasma. In their research, the remaining issue was increasing energy absorption and fragment
while avoiding melting and plasma formation due to laser
irradiation.
In this study, ion-exchanged zeolites were used. Metal
cations were introduced into the zeolite pores by performing
ion exchange on the raw material zeolite. By inducing local
laser light absorption into the introduced metal cations, zeolite was fragmented by using unfocused laser light. Topdown approaches are often challenged with maintaining surface crystallinity. The size and crystallinity of the preparednanoparticles were investigated. By centrifuging zeolite nanoparticles with a wide size distribution, nanoparticles withthe desired size were selectively recovered. At that time, thevolume zone of the particle size of the produced zeolite nanoparticles was estimated by comparing it with the particle

JLMN-Journal of Laser Micro/Nanoengineering Vol. 19, No. 2, 2024

size derived from the Stokes' equation, which all sedimented
when the centrifugation conditions were changed.
2. Experimental
HSZ-320-HOA (SiO2⁄Al2O3) = 5.6, Na2O 4.0 wt%) was
purchased from Tosoh Corporation as the raw material zeolite. The raw material was washed with ultrapure water 10times (ultrasonic dispersion in ultrapure water followed bycentrifugation at 500 rpm for 20 minutes to recover the precipitate). As a procedure for ion exchange, after dispersing
the starting zeolite in ultrapure water, CuCl2, AgNO3, andFeSO4 were added so that the supported metal cation amountwas 1 wt%, and the mixture was stirred for 2 days. The resulting zeolite was dried in an oven at 120°C for 3 hours andstored as a powder sample. Diffuse reflectance ultravioletvisible absorption spectra of raw material zeolites and ionexchanged zeolites were measured using a spectrophotometer (DR UV–vis, JASCO, V-670).
0.02 g of a powdered zeolite sample was added to 20 mLof ultrapure water and dispersed using ultrasonic waves. The
dispersion was irradiated with a nonfocused Nd:YAG laser(Spectron Laser system, SL8585G, SHG, wavelength of 532
nm, pulse duration of 13 ns, repetition frequency of 10 Hz)
for 30 minutes. The irradiation area was measured in eachexperiment, and the laser power was adjusted so that the fluence was 3000 mJ/cm2. Centrifugation was performed for 20
minutes while changing the rotation speed (500, 1000, 2000,
3000 rpm) because the raw material zeolite and nanoparticles were mixed in the dispersion after laser irradiation. 3 µLof the nanoparticle dispersion was dropped onto the elastic
carbon support film on the copper grid and observed with ascanning electron microscopy (SEM, Hitachi High-technologies, S-4800, acceleration voltage of 5 kV, working distance of 8 mm). The secondary particle size (particle size inthe aggregated state) of the dispersion was measured using
dynamic light scattering (DLS, Sysmex, Zetasizer Nano, laser wavelength of 633 nm, and detection angle of 173°). The
crystal structures of the powdered raw zeolite, Fe3+-zeolite,
and the obtained Fe3+-zeolite nanoparticles were analyzed
using X-ray diffraction method (XRD, Rigaku, Mini Flex
600, Cu-Kα radiation (λ0 = 0.15418 nm), scan range of
5.0000–100.0000 deg.). Since the nanoparticles’ yield was
extremely small, the nanoparticle dispersions obtained in 10
experiments under the same conditions were combined anddried at 120°C to obtain a powder sample for measurement.
Furthermore, for samples containing Fe3+, it was necessary
to measure them in the fluorescent X-ray reduction mode tosuppress the background increase, which is a problem whenmeasuring iron-based samples with a Cu-ray source. Accordingly, the scan speed was changed for the raw material
zeolite powder and the others (scan speed at raw material
zeolite: 2.0000 deg./min, at Fe3+-zeolite and Fe3+-zeolite nanoparticle: 1.0000 deg./min). Therefore, instead of simply
comparing the intensities, we normalized the three samples
and evaluated the changes in the crystal structure based on
the peak positions and intensity ratios. The crystallite sizesof the three samples were calculated from the Full Width atHalf Maximum (FWHM) at the first peak (2θ = 23.8°) using
the following Scherrer's equation.
K𝜆𝜆0
𝐷𝐷 =
(1)
𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵

where, D is the crystallite size, K=1.0747 is the Scherrer
constant when the crystallite is assumed to be a sphere, andB is the FWHM. Furthermore, the field-emission transmission electron microscopy (FE-TEM, JEM-2100F, JEOL, acceleration voltage 200 kV) was used to evaluate the nanoparticles’ crystallinity of about 50 nm. Moreover, elemental
mapping was performed by transmission scanning electron
microscopy–energy dispersive X-ray spectroscopy (STEM–EDS, JED-2300T) to investigate the composition.
3. Results and discussion
SEM images are shown for samples irradiated with a laser at varying fluences to zeolite that had not been ion-exchanged (Fig. 1). It was observed that the particles were finer
than the raw material zeolite, and the particle size was about
200 nm to 500 nm regardless of the fluence. A possible zeolite fragmentation mechanism is energy storage through local absorption. Zeolite is a material with a large bandgap,
and most of the laser light incident on the raw material zeolite is thought to pass through without being absorbed. Furthermore, laser ablation occurs by two-photon absorption,
and as will be shown later in Figure 2, non-doped zeolite has
no absorption at 266 nm. Therefore, laser ablation by twophoton absorption rarely occurred. However, a study by
Nichols et al [22]. pointed out the possibility that crystal defects produced during zeolite synthesis and impurity metal
cations, such as iron ions that are unintentionally incorporated, may lead to local energy storage by absorbing light.
No significant change was observed due to fluence in therange of this experiment, and it was thought that further fragmentation and higher yield would be difficult in the laser irradiation of raw material zeolite. The local absorption points
were increased by introducing metal cations into the poresby performing ion exchange on the raw zeolite.

Fig. 1 SEM images of zeolite nanoparticles at each laser
fluence: (a) 325 mJ/cm2, (b) 750 mJ/cm2, (c) 1500 mJ/cm2,(d) 3000 mJ/cm2.

Figure 2 shows the DR UV–vis spectra of ion-exchanged
zeolites ion-exchanged with each metal cation. A change in
the absorption spectrum shape and an absorbance increase
were observed in the ion-exchanged zeolite compared to theraw material zeolite. Fe3+-zeolite showed a broad absorption
band from 200 to 400 nm. Peaks near 200 and 280 nm areassigned to isolated Fe3+ with tetrahedral and octahedral coordination, respectively [23-24]. The 300–400 nm absorption band was derived from oligonuclear Fe3+xOy clusters inside the zeolite [25]. For Cu2+-zeolite, a strong peak was observed near 200 to 250 nm. This peak originated from the

JLMN-Journal of Laser Micro/Nanoengineering Vol. 19, No. 2, 2024
Cu2+ ← O2− charge transfer transition due to the coordinationbond of the ion-exchanged Cu2+ with the surrounding oxygen atoms [26]. Regarding Ag+-zeolite, although there wasno significant absorbance increase, peaks were observed
near 240 and 280 nm, which are considered to be Ag+-derived peaks [27]. On the other hand, none of the ion-exchanged zeolites had an absorption band at the laser wavelength of 532 nm. All metal cations in the zeolite would not
directly absorb the laser light irradiated at 532 nm this time.
The absorption at 266 nm showed a large difference between
non-doped zeolite and metal ion-doped zeolite. Through theabsorption at 266 nm observed only in doped zeolites, laser
ablation due to two-photon absorption occurred only in
doped zeolites. In non-doped zeolite, there was noabsorption at 266 nm and laser ablation due to two-photon
absorption did not occur.

Fig. 2 Diffuse reflectance UV-vis spectrum for each ionexchanged zeolite.

Figure 3 shows the SEM image of the sample irradiatedwith laser for each ion-exchanged zeolite. Fe3+-zeolite (b),Cu2+-zeolite (c), and Ag+-zeolite (d) laser-irradiated samples
showed smaller zeolite nanoparticles than the laser-irradiated samples of raw material zeolite (a). This suggests thatthe intentional metal cation introduction by ion exchange
was effective for efficient fragmentation. On the other hand,
however, the yield was extremely low and was below thedetection limit of the electronic balance, so a quantitative increase in yield could not be confirmed. Considering the results in conjunction with the results in Fig. 2, multiphoton
laser light absorption by metal cations or ion exchange ofsome metal cations to special positions is thought to be thecause of further fragmentation despite the absorption band
increase, which is not at the laser wavelength. First, about
the multiphoton laser light absorption, a bandgap that cannot
be overcome with the energy of a single photon can be excited by irradiating a high-fluence laser light with the energyof multiple photons [28]. Since this study used 532 nm laser
light, it is possible that the energy of the two photons could
cause the excitation of an energy band corresponding to half
the wavelength. It is necessary to use a laser light sourcewith a small pulse width that is more likely to induce multiphoton absorption to expect a higher yield in the future.
Alternatively, it may be necessary to introduce metal cations
into more unstable positions by changing the amount or
method of ion exchange. Rapid heat transfer occurs frommetal cations that absorb energy locally within the pores tothe surrounding lattice through electron-phonon coupling.
As a result of the stress accumulated in the crystal lattice dueto the lattice vibration, it was presumed that the bond breakage occurred and led to the miniaturization.

Fig. 3 SEM images of each ion-exchanged zeolite: (a)Zeolite, (b) Fe3+-Zeolite, (c) Cu2+-Zeolite, (d) Ag+-Zeolite.

Figure 4 shows the XRD measurement results of the entire Fe3+-zeolite nanoparticles obtained. These three data
were normalized. All the peaks seen in the graph are attributed to Y-type zeolite (space group 227: Fd-3m, crystal
phase name Sodium Aluminum Silicon Oxide). It was confirmed that there was no change in peak positions and intensity ratios in the three samples. It is known that the crystalline structure of zeolites does not change before and after ion
exchange in small, well-dispersed quantities [29]. So, it canbe inferred that Fe3+ was also sufficiently dispersed in thisexperiment. In addition, no change in peak position or intensity ratio was observed after laser irradiation, and no increase in baseline due to amorphous scattering was confirmed. This suggests that the crystallinity of the nanoparticles was maintained after laser irradiation. When the crystallite size was calculated using Scherrer's equation at 2θ =23.8°, which is the first peak, for the raw material zeolite, it
was 71.2 nm, for the Fe3+-zeolite was 73.4 nm, and for the
Fe3+-zeolite nanoparticles were 69.5 nm. A slight decrease
was observed after laser irradiation, but there was almost nochange in the three samples. It can be inferred that fragmentation by laser irradiation does not cause significant damage
to the crystallites themselves. In this study, it was not possible to experiment on the crystallite size effect of the starting
zeolite. However, the small crystallite size of the raw material zeolite may be advantageous in producing nanoparticles
by laser irradiation from the viewpoint of easily inducing
fractures at crystal interfaces.

Fig. 4 XRD patterns of the products: (a) Raw material zeolite, (b) Fe3+-Zeolite, (c) Fe3+-Zeolite nanoparticles.

JLMN-Journal of Laser Micro/Nanoengineering Vol. 19, No. 2, 2024

Fig. 5 STEM images and EDS elemental mapping of Fe3+Zeolite nanoparticles.

Figure 5 shows the STEM–EDS elemental mapping of
the obtaine d small Fe3+-zeolite nanoparticles. The nanoparticles confirmed in the STEM image were composed of zeolite constituent elements Si, O, Al, and Na, and it was verified that the obtained fine nanoparticles were zeolite nanoparticles. On the other hand, ion-exchanged Fe was hardly
mapped. In this study, the supported metal cation amount
was not large, and the metal cations dispersed in the fine nanoparticles may be difficult to detect by EDS. Since Fe was
not detected in this study, it can be inferred that the iron ionsdispersed in the zeolite did not change into aggregates suchas FeO within the pores after laser irradiation.
TEM images of small Fe3+-zeolite nanoparticles areshown in Figs. 6(a) and (b). Lattice fringes were also observed at the edges of the nanoparticles in the TEM images.
This indicates that the Fe3+-zeolite nanoparticles refined by
local absorption by the laser retained their crystallinity on
the crystal surface. Zeolite is a material exhibiting its function by introducing molecules into its pores [30,31] or thathas excellent adsorption properties in its pores [32,33]. The
nanoparticle surface crystallinity is very important in termsof pore accessibility [34]. FFT power spectra of the obtained
TEM images were observed. Three strong points were confirmed in the spectrum of (c). Since points A and B are at thesame distance from the center point, it was confirmed thatlattice fringes spread in different directions with the sameplane spacing in (a). Point C exists in the same direction as
point B and at a different distance from the center. In the
spectrum of (d), ring-shaped weak points were found here
and there, indicating that the nanoparticles had a polycrystalline structure. It was suggested that fragmentation due tolaser irradiation was not biased toward a specific crystal
plane because there was no bias toward a specific planethrough the two patterns. If melting nanoparticles occurred,
crystallinity would be decreased, and amorphous would becreated. However, the observation of the lattice fringes in
Figs. 6(a) and (b) and points at the FFT power spectrum in
Fig. 6(c) would imply the retention of crystallinity and theexistence of pores of zeolite.
Figure 7 shows SEM images of the samples with different centrifugal strengths for the Fe3+-zeolite nanoparticle
dispersion. It was observed that only smaller particles remained as the revolution number increased. As for the shape,
it was observed that the smaller particles had more anisotropy. Those with an irregular surface structure have a larger
specific surface area than spherical particles. This change inshape was thought to be desirable when considering the application to catalytic reactions, in which the accessibility ofguest molecules to pores is important.

Fig. 6 (a) (b) TEM images of Fe3+-Zeolite nanoparticles.
(c) FFT pattern of (a). (d) FFT pattern of (b).

Fig. 7 SEM images of Fe3+-Zeolite nanoparticles at eachcentrifugation speed: (a) 500 rpm, (b) 1000 rpm, (c) 2000
rpm, (d) 3000 rpm.

Fig. 8 DLS frequency distribution of secondary particle
size of Fe3+-Zeolite nanoparticles at each centrifugation
speed.

Figure 8 shows the secondary particle size distribution
by DLS. As for the secondary particle size, it was observedthat only the smaller particle size remained by increasing therevolution number in the same manner as the primary particle size. As for the secondary particle size, it was observedthat only the smaller particle size remained by increasing therevolution number in the same manner as the primary particle size. From these, zeolite nanoparticles of any particle
size can be selectively recovered by changing the rotation
speed during centrifugation. By combining laser irradiationand centrifugation, we easily prepared nanoparticles of the
optimum size according to the purpose. In addition, since theprimary particle size analyzed from the SEM image and thesecondary particle size measured by DLS were almost the

JLMN-Journal of Laser Micro/Nanoengineering Vol. 19, No. 2, 2024
same, it was found that the nanoparticles were not aggregated in the supernatant liquid and were in a dispersed state.
Figure 9 shows the primary particle size distribution as
measured by SEM and the particle size that was completely
precipitated, which was derived from the Stokes equation.
The calculation was performed according to the following
procedure. First, the sedimentation velocity of spherical nanoparticles in a stationary solution can be expressed by thefollowing equation according to Stokes' law.
4(𝑃𝑃𝑠𝑠 − 𝑃𝑃𝑤𝑤 )g𝑑𝑑
𝑣𝑣 = �
3𝑃𝑃𝑤𝑤 𝐶𝐶𝑑𝑑(2)

where, Ps is particle density (kg/m3), Pw is dispersion medium density (kg/m3), g is the gravitational acceleration(9.81 m/s2), d is particle size (m), and Cd is the drag coefficient. The drag coefficient can be approximated by the following formula when the particles settle quietly without disturbing the dispersion medium.
24
𝐶𝐶𝑑𝑑 =(3)
𝑅𝑅𝑒𝑒 ∗*
where Re is the particle Reynolds number, expressed by thefollowing equation.
𝑣𝑣𝑣𝑣
𝑅𝑅𝑒𝑒 ∗ =(4)
𝜂𝜂/𝑃𝑃𝑤𝑤where η is the viscosity (Pa·s) of the dispersion medium.
During centrifugation, nanoparticles can be expressed as follows using the rotation radius r (m) and the rotation angularvelocity ω proportional to the rotation speed N instead of thegravitational acceleration g [35].
(𝑃𝑃𝑠𝑠 − 𝑃𝑃𝑤𝑤 )𝑑𝑑 2
𝑣𝑣 =× 𝑟𝑟𝜔𝜔2
(5)
18𝜂𝜂
and
𝑁𝑁
𝜔𝜔 = 2𝜋𝜋(6)60During centrifugation, the particle velocity v can be expressed as the change in the radius of gyration with respect
to time, so it is dr⁄dt. From here, the sedimentation time T (s)can be expressed as follows by performing integration from
Rmin → Rmax (liquid surface → centrifugal tube bottom) withthe radius of gyration as a variable [36].
18𝜂𝜂(ln 𝑅𝑅𝑚𝑚𝑚𝑚𝑚𝑚 − ln 𝑅𝑅𝑚𝑚𝑚𝑚𝑚𝑚 )𝑇𝑇 =(7)(𝑃𝑃𝑠𝑠 − 𝑃𝑃𝑤𝑤 )𝑑𝑑 2 𝜔𝜔 2

Fig. 9 Relationship between centrifugal speed and particle
size: (a) Maximum fully precipitated particle size (calculated value), (b) Primary particle size distribution (SEM).

This sedimentation time varies depending on the particle
size of the nanoparticles and the centrifugation speed. In thisstudy, centrifugation was carried out for 20 minutes, so we

calculated the particle size that would sediment in just 20
minutes at each rotation speed and compared it.
The primary particle size distribution was below the calculated fully precipitated particle size. It showed that the theoretical calculation using Stokes' law which assumes spherical nanoparticles, can be applied to separating anisotropic
zeolite nanoparticles fragmented by laser irradiation. As thecentrifugation rotation speed decreased, a larger divergence
was observed between the total sedimentation particle size
and the particle size. It is considered that this is because few
nanoparticles were produced by laser irradiation in the dissociated particle size range. This suggests that the volume
zone of nanoparticles produced by laser irradiation in thisstudy was about 300 ~ 400 nm.
4. Conclusions
In this study, nanoparticles were produced by unfocusedirradiation of a commercially available zeolite with ananosecond laser with a wavelength of 532 nm. It was
speculated that the refinement was caused by local energy
accumulation due to impurity metal cations and crystal
defects in the raw material zeolite. In addition, thefragmentation progressed by introducing metal cations suchas Fe3+ into the pores. The diffuse reflectance UV–vis
spectrum of the ion-exchanged zeolite showed noabsorbance increase at 532 nm. This suggests thatmultiphoton excitation by laser light and the metal cation
arrangement at irregular positions may greatly affectfragmentation. It is necessary to devise ways to efficiently
induce these absorptions to improve the yield in future
research. It was confirmed by XRD measurement that the
crystal structure did not change in all three samples, raw
zeolite, ion-exchanged zeolite, and laser-irradiated zeolite
nanoparticles. Crystallite size calculation using Scherrer's
equation suggested that zeolite produced for industrial use
has a small crystallite size, which may work favorably in the
production of nanoparticles by laser irradiation. Latticefringes in the TEM image revealed that the crystal structure
was maintained up to the surface of the zeolite nanoparticles.
This shows great potential for surface damage, which has
been viewed as a problem in previous top-down approaches.
By using centrifugal separation, zeolite nanoparticles with awide size distribution were selectively recovered.
Comparison with the sedimentation particle size obtained
from Stokes' law suggested that many nanoparticles with aparticle size of about 400 nm were produced by laser
irradiation.
Acknowledgments
The authors wish to thank M. Hara, Y. Kitamoto and K.
Nakamura at Tokyo Tech for laser process and measurements. This study was supported by the Collaborative Research Project of Materials & Structures Laboratory (Tokyo
Tech.) and Suzukakedai Materials Analysis Division (Tokyo
Tech.).
References[1] C. Baerlocher, L.B. McCusker, and D.H. Olson: “Atlas
of Zeolite Framework Types” ed. by W.M. Meier (Elsevier, Amsterdam, 2007).
[2] I. Masakado and M. Akihiro: JP Patent 2002248317 A(2001).

JLMN-Journal of Laser Micro/Nanoengineering Vol. 19, No. 2, 2024

[3] L. Yuejin and W. K. Hall: J. Phys. Chem., 94, (1990)
6145.
[4] D. Thomas: Top. Catal., 13, (2000) 349.
[5] M. Koji, H. Yuichiro, O. Kaito, U. Yoshiaki, T. Shunsuke, and N. Norikazu: J. Catal., 342, (2016) 63.
[6] N.M. Mahmoodi and M.H.S. Dastgerdi, Microchem. J.,
145, (2019) 74.
[7] P.W. Andrey, F. Davide, K. Oliver, and B.A. Jeroen:
ACS. Catal., 9, (2019) 2303.
[8] T. Lubomira, V.P. Valentin, Nanozeolites: Chem. Mater., 17, (2005) 2494.
[9] I. Lama, B.N. Krassimir, C. Guillaume, D. Luc, and V.
Valentin: Chem. A. Eur. J., 17, (2011) 2199.
[10] W. Toru, I. Akio, I. Satoshi, T. Junichi, S. Kaku, K.
Katsutoshi, M. Takeshi, K. Yoshihiro, and N. Atsushi:
Cryst. Growth. Des., 11, (2011) 5153.
[11] L. Qinghua, M. Boriana, C. Derek, and S. Johan: Micropor. Mesopor. Mater., 43, (2001) 51.
[12] H. Limin, W. Zhengbao, S. Jinyu, M. Lei, L. Quanzhi,
Y. Yushan, and Z. Dongyuan: J. Am. Chem. Soc., 122,
(2000) 3530.
[13] W. Huanting, H. A. Brett, and Y. Yushan: J. Am. Chem.
Soc., 125, (2003) 9928.
[14] M. Svetlana, O. H. Norman, V. Valentin, and B.
Thomas: Sci., 283, (1999) 958.
[15] Haibo Zeng,Xi-Wen Du,Subhash C. Singh, Sergei A.
Kulinich, Shikuan Yang, Jianping He, and Weiping Cai:Adv. Func. Mater., 22, (2012) 1333.
[16] Dongshi Zhang, Bilal Goekce, and Stephan Barcikowski: Chem. Rev., 117, (2017) 3990.
[17] Yaohui Zhan, Lei Zhang, Mohsen Rahmani, Vincenzo
Giannini, Andrey E. Miroshnichenko, Minghui Hong,
Xiaofeng Li, Stefan A. Maier, and Dangyuan Lei, ACS
Photonics, 8, (2021) 166.
[18] Lianwei Chen, and Minghui Hong: Opto-Electr. Sci., 1(2022) 210007.
[19] T. Takeshi, I. Kenzo, W. Norihisa, and T. Masaharu:
Appl. Surf. Sci., 202, (2002) 80.
[20] T. Yoshihiro and M. Fumitaka: Chem. Phys. Lett., 599,
(2014) 110.
[21] J. Jin-Woo, Y. Sangwoo, C.W. Hae, K. Joohan, F. Dave,and C. Sung-Hak: Appl. Sci., 8, (2018) 112.
[22] N. T, William, K. Tetsuya, S. Yukichi, S. Yoshiki, S.
Takeshi, and K. Naoto: J. Phys. Chem. B, 110, (2006)
83.
[23] M. S. Kumar, M. Schwidder, W. Grünert, and A. Brückner: J. Catal., 227, (2004) 384.
[24] L. Čapek, V. Kreibich, J. Dědeček, T. Grygar, B. Wichterlová, Z. Sobalík, J.A. Martens, R. Brosius, and V. Tokarová: Micropor. Mesopor. Mater., 80, (2005) 279.
[25] P. Marturano, L. Drozdová, G.D. Pirngruber, A. Kogelbauer, and R. Prins: Phys. Chem. Chem. Phys., 3,(2001) 5585.
[26] A. Kharchenko, V. Zholobenko, A. Vicente, C. Fernandez, H. Vezin, V. D. Waele, and S. Mintova: Phys.
Chem. Chem. Phys., 20, (2018) 2880.
[27] C. Shi, M. Cheng, Z. Qu, and X. Bao: J. Mol. Catal. A:
Chem., 235, (2005) 35.
[28] K.P. Aicher, U. Wilhelm, and J. Grotemeyer: J. Am.
Soc. Mass. Spectrom., 6, (1995) 1059.
[29] L. Li, Q. Shen, J. Li, Z. Hao, Z.P. Xu, and G.Q.M. Lu:
Appl. Catal. A. Gen., 344, (2008) 131.

[30] M. Pauchard, A. Devaux, and G. Calzaferri: Chem. Eur.
J., 6, (2000) 3456.
[31] G. Calzaferri, D. Brühwiler, S. Megelski, M. Pfenniger,
M. Pauchard, B. Hennessy, H. Maas, A. Devaux, and U.
Graf: Solid State. Sci., 2, (2000) 421.
[32] N. Patdhanagul, T. Srithanratana, K. Rangsriwatananon,and S. Hengrasmee: Micropor. Mesopor. Mater., 131,(2010) 97.
[33] O.O. Ltaief, S. Siffert, S. Fourmentin, and M. Benzina:
Comptes Rendus Chimie, 18, (2015) 1123.
[34] Y. Hiroki, I. Takayuki, L. Zhendong, N. Yusuke, O.
Koji, K. Shinji, O. Tatsuya, and W. Toru: Cryst. Growth.
Des., 16, (2016) 3389.
[35] B.D. Hames: “Centrifugation: a practical approach” ed
by D. Rickwood, (IRL Press, Oxford, 1984).
[36] T. Svedberg and J. B. Nichols: J. Am. Chem. Soc., 45,(1923) 2910.

(Received: March 19, 2023, Accepted: May 2, 2024)