Crystallization of well-defined anatase nanoparticles in SBA-15 for the photocatalytic decomposition of acetic acid

Article abstract of DOI:10.1039/d0ra04528d

Anatase nanoparticles with a size ofca.5 nm were prepared in mesoporous silica (SBA-15 with the pore diameter of 6 nm) by impregnation of the precursor derived from titanium tetraisopropoxide and subsequent heat treatment in air. The mesoporous structure of the anatase-silica hybrid and the size of the anatase particles were kept unchanged during the crystallization of anatase at 200-600 °C. The hybrids were applied as a photocatalyst for the decomposition of acetic acid in water under UV irradiation to find the heat treatment over 400 °C led to higher efficiency of the reaction (45-55 μmol h^?1of carbon-dioxide production) over the samples heated at temperatures lower than 300 °C (3-14 μmol h^?1of carbon-dioxide production).

Full text of DOI:10.1039/d0ra04528d

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PAPER
Crystallization of well-defined anatase
nanoparticles in SBA-15 for the photocatalytic
Cite this: RSC Adv., 2020, 10, 32350
decomposition of acetic acid†
a
b
and Makoto Ogawa *a
Kasimanat (Guy) Vibulyaseak,
Bunsho Ohtani
Anatase nanoparticles with a size of ca. 5 nm were prepared in mesoporous silica (SBA-15 with the pore
diameter of 6 nm) by impregnation of the precursor derived from titanium tetraisopropoxide and
subsequent heat treatment in air. The mesoporous structure of the anatase–silica hybrid and the size of
ꢀ
the anatase particles were kept unchanged during the crystallization of anatase at 200–600 C. The
Received 21st May 2020
Accepted 30th July 2020
hybrids were applied as a photocatalyst for the decomposition of acetic acid in water under UV
ꢀ
irradiation to find the heat treatment over 400 C led to higher efficiency of the reaction (45–55 mmol
DOI: 10.1039/d0ra04528d
ꢁ1
ꢀ
h
of carbon-dioxide production) over the samples heated at temperatures lower than 300 C (3–14
ꢁ1
rsc.li/rsc-advances
mmol h of carbon-dioxide production).
uses as photocatalysts, while the sizes and the locations of the
anatase particles in the pores/on the external surface of the MPS
Nanoparticles supported in porous solids are an important class particles are not precisely control resulting the broad particle
1
Introduction
1
7
of materials especially for application in catalysts. Mesoporous size distribution of the anatase particles. The optimization of
silicas (MPSs) have been used as the supports to immobilize the crystallization temperature of anatase in MPS have been
various kinds of nanoparticles to construct hybrid catalysts, reported where the size of the anatase particle and the porosity
taking advantage of such characteristic features of MPSs, such as of the hybrids changed by increasing the crystallization
well-dened and variable pore shape and size, chemical and temperature, which were probably due to the growth of the
thermal stability, and surface reactivity due to silanol groups on anatase particles located on the external surface of the MPS
1
8–21
the pore surface for the concentration and diffusion of particles during the heat treatment.
The changes in the size
2,3
substrates. Titanium dioxide (TiO ) is the species studied most of the anatase and the porosity of the hybrids makes the
2
extensively to be immobilized in MPSs and the catalysts' appli- comparative evaluation of the photocatalysts' performances
4,5
cations of the TiO
shape and size of the particles as well as their location in MPSs are suppressed by the decrease of the surface area of the anatase
key factors, so that the TiO
species have been immobilized in nanoparticles due to the particles' aggregation/fusion, which
MPSs in such different states as isolated molecular species and block the pore entrance for the adsorption/diffusion of the
2
–MPS hybrids have been reported so far. The difficult. The photocatalytic performance of the hybrids is
2
6–21
oxide nanoparticles in the silica wall and on the mesopores.
Though the size-controlled synthesis of TiO particles has been
reactants in the pore channels.
In the present paper, we report a precise syntheses of hybrids
2
a topic of interest in materials chemistry to adapt the wide range composed of a MPS, SBA-15, and well-dened anatase nano-
of applications of TiO2 and to optimize the materials' perfor- particles exclusively in the mesopores and the application of the
mances, size-controlled synthesis of TiO
templates is still challenging.
2
using MPSs as hybrids as photocatalysts using the decomposition of acetic
acid as a model reaction. The size of the anatase nanoparticles
Well-dened anatase nanoparticles (precise size-control and (5 nm) was controlled by the pore size (6 nm) of the SBA-15. The
narrow particle size distribution) are expected to obtain from size distribution of the anatase nanoparticles was discussed
the well-dened porous structure of the MPS template. There from the UV-vis diffuse reectance spectra to be narrower than
are many papers on the preparation of anatase in MPSs and the the anatase particles prepared in SBA-15 reported so far. The
role of a mesoporous silica to suppress the aggregation/fusion
of the anatase particles during the crystallization at high
temperatures was examined. Thanks to the precise immobili-
zation of the anatase nanoparticles in the mesopores, the size of
the anatase particles and the porosity of the SBA-15–anatase
hybrids were keeping unchanged by increasing the crystalliza-
tion temperature.
a
School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and
Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
E-mail: makoto.ogawa@vistec.ac.th
b
Institute for Catalysis, Hokkaido University, Sapporo 001-0021, Japan
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/d0ra04528d
1
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lower than the TiO
TTIP (2 mL). The result suggested that a half portion of the
added TTIP precursor was inltrated in the mesopores and was
2
content (50 wt%) derived from the used
2
Experimental details
2.1 Materials
Tetraethyl orthosilicate (TEOS), titanium tetraisopropoxide converted to TiO
TTIP), poly(ethylene glycol)-block-poly(propylene glycol)-block- treatment.
poly(ethylene glycol) (Pluronic P123), and isopropyl alcohol
IPA) were purchased from Aldrich. Hydrochloric acid (HCl) was
aer the reaction with HCl vapor and the heat
2
(
(
purchased from Tokyo Chemical Industry Co. All of the reagents
were used without further purication. Water was puried by
using the Milli-Q system (>18 MU cm, Millipore).
2
.4 Characterization of the SBA-15–anatase hybrids
Nitrogen (N
2
) adsorption/desorption isotherms were obtained
ꢀ
at ꢁ196 C on a Yuasa-Quantachrome NOVA 1200e surface and
pore size analyzer. Prior to the measurement, the samples were
2
.2 Synthesis of SBA-15
ꢀ
ꢁ6
dehydrated at 120 C under vacuum (6.7 ꢂ 10 bar) for 2 h. The
SBA-15 was synthesized by the reported method. Deionized surface area was calculated by the Brunauer–Emmett–Teller
22
ꢁ1
water (30 g) was mixed with 2 mol L aqueous solution of HCl (BET) method using a linear plot over the range of P/P ¼ 0.05–
0
25
(120 g) in the screw Pyrex glass container (250 mL) with the 0.20. Pore size distribution was derived from the N adsorp-
2
26
plastic cap, then Pluronic P123 (4.0 g) was added. The mixture tion isotherm by the Barrett–Joyner–Halenda (BJH). Scanning
ꢀ
was magnetically stirring at 35 C until the clear solution was Electron Micrography (SEM) was performed on a JEOL JSM-
obtained. Then, TEOS (8.5 g) was added into the solution under 7610F eld-emission scanning electron microscope. Prior to
ꢀ
magnetic stirring at 35 C and stirred furtherly for 20 h. The the measurements, the samples were coated with a platinum
mixture was transfer to the teon-lined autoclave (250 mL) and layer (4 nm). Transmission Electron Microscope (TEM) images
ꢀ
ꢁ1
ꢀ
heated at the heating rate of 10 C min to 100 C and kept for were obtained with a JEOL JEM ARM200F operated at 200 kV.
4 h without stirring. The solid product was collected by The X-ray powder diffraction (XRD) patterns of the products
2
centrifugation at 4000 rpm for 15 min and washed with the were recorded using Cu Ka radiation in a Rigaku RINT 2500
deionized water. The washing process was repeated for 5 times equipped with a carbon monochromator. Raman spectra was
ꢀ
and the product was air dried at 25 C overnight. The sample recorded using Confocal Raman Microscope SENTERRA II
ꢀ
was calcined by heating from 25 to 500 C for 8 h and kept at (Bruker Corporation) with an excitation wavelength of 532 nm.
ꢀ
5
00 C for 6 h to remove P123 completely.
The composition was determined on a wavelength-dispersive X-
ray uorescence spectrometer (XRF, Bruker S8 Tiger). UV-vis
diffuse reectance spectra were recorded on a PerkinElmer
Lambda 1050 (PerkinElmer, U.S.A.) using integrated sphere and
polytetrauoroethylene as the reference. The size of the anatase
nanoparticles was estimated from the shi of the band gap
2
.3 Preparation of anatase in the mesopore
The incorporation of anatase in the mesopore of SBA-15 is
based on the preferential impregnation of TTIP into the pore
and subsequent heat treatment as reported previously.
was mixed with IPA and the mixture was sonicated for 15 min by
to obtain the homogenous transparent solution. The volume
ratio of TTIP:IPA was designed as 1 : 8 to keep the remaining
23,24
TTIP
g
energy (E ) of the anatase nanoparticles, derived for the UV-vis
diffuse reectance spectra of the SBA-15–anatase by Tauc plat
and the linear interpolation, from bulk anatase (3.2 eV) using
27
the following equation,
24
pore space aer the removal of IPA aer the heat treatment.
2
2
2
SBA-15 was added in a 2-neck round bottom ask where the
neck was connected to an oil-sealed rotary vacuum pump
through a glass valve and another neck was closed with a rubber
4h p
3:6e
3d
DE
g
¼
ꢁ
2md2
where h is the Planck constant, e is the elementary charge, 3 is
ꢀ
septum. The SBA-15 was dehydrated at 120 C for 3 h under the
the dielectric constant of TiO
2
ꢁ1
, d is the diameter of the TiO
2
ꢁ6
ꢀ
reduced pressure (6.7 ꢂ 10 bar) and cooled down to 25 C
under the reduced pressure. Aer that, the valve was closed and
TTIP solution (18 mL) was added to the dehydrated SBA-15 (1 g)
by using syringe injected through the rubber septum, then the
mixture was magnetically stirred for 24 h at 25 C under the
reduced pressure. The volume of TTIP solution (18 mL) was
ꢁ1
ꢁ1
particle and m is dened as m ¼ m
e
+ m
h
, where m
e
and m
h
2
are the electron and hole effective masses of TiO .
ꢀ
2.5 Photocatalytic decomposition of acetic acid
designated to excess the amount of SBA-15 powder (1 g). The The photocatalyst (50 mg) was dispersed in an aqueous solution
solid product was collected by centrifugation at 4000 rpm for of acetic acid (5 mL with 5 vol% of acetic acid). A glass tube (35
15 min. The product was exposed to hydrogen-chloride (HCl) mL) was used as the reactor and the volume of the head space
vapor for 1 day in a closed container, where silica gel was used was 30 mL. A high-pressure mercury arc (400 W) was used as
to adsorb the excess moisture. The sample is designated as SBA- a light source. The decomposition of acetic acid was followed by
1
5–TTIP. For the crystallization of anatase, the samples were the amount of carbon-dioxide (CO
heated at 200, 300, 400, 500 and 600 C for 3 h in air. The in the head space was collected and injected to a gas chro-
2
) produced. The gas (0.2 mL)
ꢀ
samples are designated as SBA-15–anatase-X, where X is the matograph (Shimadzu GC-8A, porapak
Q
column, TCD
heat treatment temperature. TiO content in the SBA-15– detector) to determine the amount of CO
2
2
produced for every
anatase was measured by XRF to be ca. 25 wt%. The value is 20 min for 120 min.
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3
Results and discussion
3.1 Characteristics of SBA-15–anatase hybrids
The porosity and the morphology of SBA-15–anatase before and
aer the crystallization of anatase at the temperature of 200 to
ꢀ
6
00 C were followed by N
2
adsorption/desorption isotherms
and SEM. The N
2
adsorption/desorption isotherms were type IV
and the BJH pore size was 6 nm for SBA-15 and SBA-15–anatase
hybrids (Fig. 1(A), (B) and (C)). The BET surface area and the
2
ꢁ1
pore volume of the SBA-15 decreased from 668 to 469 m g
3
ꢁ1
and from 1.0 to 0.54 cm g of SBA-15–TTIP. From the pore
3
ꢁ1
volume of the SBA-15 (1 cm g ) and the TTIP content in IPA
TTIP : IPA ¼ 1 : 8), the volume of TTIP lled the pores was
(
3
ꢁ1
derived to be 0.11 cm g . The amount of TiO
2
was derived
from the volume of the inltrated TTIP and the density of
ꢁ
3
anatase (3.78 g cm ) to be ca. 0.4 g, which was converted to
0 wt% of TiO . The value was consistent with the TiO content
3
2
2
of the sample derived from XRF. The result suggested the
formation of anatase particles from the inltrated TTIP in the
mesopores. The BET surface areas and the pore volumes were Fig.
slightly higher for the samples heated at the higher temperature
1
(A and B) N2 adsorption (filled circle)/desorption (cross)
isotherms and (C) BJH pore size distribution derived from the N
2
adsorption isotherms of SBA-15, SBA-15–TTIP, SBA-15–anatase-200,
SBA-15–anatase-300, SBA-15–anatase-400, SBA-15–anatase-500
and SBA-15–anatase-600, respectively. (D) The correlation of the BET
surface areas/the pore volumes and the heat treatment temperatures,
(Fig. 1(D)). Bulk density of the SBA-15–TTIP, derived from the
volume of the sample (10 mg) in the capillary tube (diameter of
1
ꢁ3
0
.018 cm), aer heating decreased from 0.15 to 0.11 g cm for
SBA-15–anatase-200 probably due to the evaporation of IPA, and and the inset shows the appearance of the samples (10 mg) in the
capillary tubes.
the bulk density of the SBA-15–anatase did not change upon
heating at 200 to 600 C (Fig. 1(D), the inset). As the shrinkage of
ꢀ
the immobilized TiO
2
from non-crystalline phase to anatase,
the porosity increased. From the pore volume of the SBA-15 (1 The size and the size distribution of the anatases particle are
3
ꢁ1
ꢁ3
27
cm g ) and the density of anatase (3.78 g cm ), the amount of discussed using UV-vis absorption spectra. The sharpness,
the anatase required to ll the pores was calculated to be 3.78 g, dened as the width between the maximum and the edge of the
which was converted to 79 wt% of TiO . The pore lling was UV-vis absorption spectra, presented the size distribution of the
2
calculated from the TiO content of the hybrids (25 wt%) to be anatase particles. The absorption edge of SBA-15–anatase shif-
2
3
2% of pore volume. The value was consistent with the decrease ted to the shorter wavelength region and the size of the anatase
of pore volume (30% of pore volume), derived from the pore particle, derived from the shi of the band gap energy from
3
ꢁ1
27
volume of SBA-15 (1.0 cm g of silica) and SBA-15–anatase-600 a bulk anatase particle (3.2 eV), decreased slightly for the
(
3
ꢁ1
0.7 cm g of silica), which suggested the formation of the samples heated at the higher temperatures (Fig. 3(B) and (C)).
anatase in the mesopores. As shown in the SEM images The result is consistent with the increasing porosity of the SBA-
Fig. 2), no change in the particle morphology of the SBA-15 was
23
(
seen aer the immobilization of TiO and the heat treatment at
2
ꢀ
6
00 C and no anatase particles were observed in the external
surface of the SBA-15–anatase particles.
Spherical particles with the diameter of ca. 5 nm were
observed in the pore channels of the SBA-15 (Fig. 3(A)). The
particles were isolated from each other, which was probably due
to the interaction between the surfaces of anatase particles and
silica from the dehydroxylation of Ti–OH and Si–OH during the
heat treatment. The d(101) value of 0.35 nm of anatase was seen
in the TEM image. The result conrmed the crystallization of
the anatase nanoparticles in the pore channels of the SBA-15.
No absorption was observed for the SBA-15 and the absorp-
2
tion of TiO was observed at the wavelength of 300–320 nm for
SBA-15–TTIP (Fig. 3(B)). The result suggested that SBA-15 does
not absorb UV light. The absorption edge of the SBA-15–TTIP
shied from 320 nm to 330 nm aer the heat treatment sug-
gested the crystallization of the non-crystalline TiO to anatase. Fig. 2 SEM images of SBA-15 (A and B) and SBA-15–anatase-600 (C
2
and D).
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Fig. 4 (A) The correlation between the particle sizes of the anatase/
2 2
BET surface areas of SBA-15–TiO hybrids, zeolite–TiO hybrids and
clay–TiO hybrids and the heat treatment temperatures.
2
The optimization of the crystallization temperature for
1
8–21
anatase in SBA-15
zeolites
and other porous supports such as
had been reported for the uses as
38–40
41–46
and clays
photocatalysts. The correlation of the particle sizes of the
anatase and the BET surface areas of the hybrids with the
crystallization temperatures is shown in Fig. 4 and the reported
values of the size of the anatase particles and the porosity of the
hybrids at the optimized heat treatment temperatures are
summarized in Table S2.† The BET surfaces and the pore
volumes of the SBA-15–TiO hybrids decreased and the sizes of
2
the anatase particles increased when increased the crystalliza-
ꢀ
18,20
tion temperature from 300 to 600 C (Fig. 4 and Table S2†).
The collapse of SBA-15–TiO
2
hybrid by the heat treatment at
ꢀ
600 C suppressed the photocatalytic activity of the hybrid for
Fig. 3 (A) TEM image of SBA-15–anatase-600. (B) UV-vis absorption
spectra of SBA-15, SBA-15–TTIP, SBA-15–anatase-200, SBA-15– the decompositions of organic compounds (phenol, MB, methyl
20
anatase-300, SBA-15–anatase-400, SBA-15–anatase-500 and SBA- orange and rhodamine B). The size of the anatase particle
5–anatase-600. (C) The correlation between the particle sizes,
1
38,40
44,45
immobilized on zeolites
and clays
were also increased
calculated from the shift of the absorption from a bulk anatase, and the
heat treatment temperatures.
and the porosities of the hybrids were changed by increasing
the crystallization temperature (Fig. 4 and Table S2†).
In the present study, thanks the well-dened porous struc-
ture of a mesoporous silica, the exclusive immobilization as well
as the regular special distribution/isolation of the anatase
1
5–anatase aer the crystallization at the higher temperature
(Fig. 1(D)). The size (5 nm) of the anatase nanoparticles derived
23,24
particles in the mesopore,
the size of the anatase particles
from TEM image and UV-vis absorption spectra and the
consistent between the decrease of the pore volume of SBA-15
and the TiO content together with the SEM observation that
2
no observation of anatase particles in SEM image conrmed the
formation of the anatase nanoparticles in the mesopores (6 nm)
of the SBA-15.
was maintained keeping the narrow particle size distribution
and the porosity of the hybrid was also kept for the crystalliza-
ꢀ
tion of anatase from 200 to 600 C. The crystallization of the
anatase in the pores of mesoporous silicas with varied compo-
sitions and mesostructures are worth investigating to
The size, the band gap energy and the sharpness of the re-
13–20,28–37
ported anatase particles prepared in SBA-15
as well as
their photocatalytic reactions are summarized in Table S1.† The
sharpness for SBA-15–anatase hybrids were relatively narrow
compared with the values derived from the reported UV-vis
absorption spectra of the anatase particles prepared in SBA-
15, conrmed the narrow particle distribution of the anatase
particles. The size of the reported anatase particles, derived
from the shi of the band gap, prepared in SBA-15, was larger
than the pore diameter of the pristine SBA-15, even the crys-
tallization of anatase had been done at the temperature bellow
ꢀ
13,17–20,24,33–37
6
00 C (Table S1†).
In this study, the size of the Fig. 5 (A) The relationship between the amount of CO
and the irradiation time of SBA-15–TTIP, SBA-15–anatase-200, SBA-
5–anatase-300, SBA-15–anatase-400, SBA-15–anatase-500 and
2
production
anatase particles was within the BJH pore diameter of the SBA-
5 (6 nm) keeping narrow particle size distribution even aer
the crystallization from 200 to 600 C (Fig. 3(B)).
1
1
SBA-15–anatase-600. (B) The correlation of the photocatalytic activ-
ꢀ
ities/particle sizes with the crystallization temperatures.
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+
48
oxidation of the acetic acid by the photogenerated hole (h ) or
the oxidation of the acetic by the superoxide anion radical from
the reaction of the molecular oxygen and the photogenerated
49
electron. Another possible mechanism is production of peroxy
radical, as a carrier for a radical chain reaction (RCR), through
reaction with radical species generated by the oxidation of
+
50
acetic acid and h . It is difficult to clarify that the acetic acid
was decomposed through which mechanism, because the
ꢁ
intermediates ($CH
3
, $CH
2
COOH, $OH, HOOc, O
2
c ) are not
stable and can be further reacted without the light irradiation.
Fig. 6 (A) X-ray powder diffraction patterns and (B) Raman spectra of
SBA-15–TTIP, SBA-15–anatase-200, SBA-15–anatase-300, SBA-15– For the photodecomposition of acetic acid by SBA-15–anatase,
anatase-400, SBA-15–anatase-500 and SBA-15–anatase-600.
the acetic acid molecule was diffused into the mesopores and
had the reaction with the anatase nanoparticles located in the
mesopores. The slow diffusion of the acetic acid (the molecular
size of 0.5 nm) through the space (1 nm) between the anatase
nanoparticles (5 nm) and the pore walls in the pore channel (6
nm) may have induced the direct reduction of the acetic acid by
understand the role of the embedded TiO
mesostructure and the role of mesoporous silica on the crys-
tallization and phase transformation of the embedded TiO
2
on the stability of the
2
.
+
the h on the surface of the anatase nanoparticles.
3.2 Photocatalytic activity of SBA-15–anatase hybrids
The photocatalytic activity of the SBA-15–anatase was
The photocatalytic decomposition of acetic acid of SBA-15– compared with the commercial TiO
anatase is summarized in Fig. 5, and the crystallization of the been used for the photocatalytic decomposition of acetic acid
nanoparticles, which have
2
51
anatase in the hybrids was followed by XRD and Raman as under the same conditions of this study. The photocatalytic
shown in Fig. 6. SBA-15–TTIP was active for the photodecom- activities together with the sizes of the anatase nanoparticles
position of acetic acid, while the reaction efficiency was low (3 are summarized in Table 1, where the reaction efficiency of the
ꢁ
1
ꢀ
ꢁ1
mmol h of CO
efficiency upon heating the samples were observed in 2 steps production) was high compared with the commercial anatase
2
production). The improvements of the reaction SBA-15–anatase heated over 400 C (45–55 mmol h of CO
2
ꢁ
1
(
Fig. 5(B)). The reaction efficiency of SBA-15–TTIP increased 5 particles (10–53 mmol h of CO production). The high crys-
2
ꢀ
ꢁ1
times when heated the sample at 200 C (14 mmol h of CO
2
tallinity as well as the isolation of the anatase nanoparticles in
production for SBA-15–anatase-200). A part of the immobilized
TiO was thought to be crystallized to anatase. However, the
2
Table 1 Summary of the crystallite sizes and the photocatalytic
amount of the anatase is too small to be detected by XRD and
Raman (Fig. 6). Raman signal ascribable to anatase was
observed for SBA-15–anatase-300 (Fig. 6(B)), while the diffrac-
tion due to anatase was not observed in the XRD pattern
activity for the decomposition of acetic acid of the commercial TiO
nanoparticles
2
Activity/
mmol h of CO
2
ꢁ
1
Crystallite
(
Fig. 5(A)), due to the higher sensitivity of Raman to detect
f
47
Sample
size /nm
production
anatase crystal compared with XRD. However, no improve-
ment in the reaction efficiency was seen when the crystallization
a
TIO-7a
8
4
10
6
5
8
9
8
21
31
20
28
28
43
13
33
30
53
14
14
45
50
55
ꢀ
temperature was 300 C. Non-crystalline TiO , which is thought
2
TIO-8a
to be less active as photocatalyst, remained in the SBA-15– TIO-9
a
b
ꢀ
TIO-12
anatase even aer the heat treatment at 300 C.
ꢁ
1
VP-P90c
The reaction efficiency of SBA-15–anatase-400 (45 mmol h
PC-101
of CO
2
production) was higher than SBA-15–anatase-300 for 4
d
Hombikat
e
times. The 101 diffraction peak of anatase was clearly observed
in the XRD patterns of SBA-15–anatase-400, SBA-15–anatase-500 P25
and SBA-15–anatase-600 (Fig. 5(A)). The intensity of the Raman
signals increased with the higher crystallization temperature of
anatase, suggesting that the anatase content increased
ST-01
b
g
SBA-15–anatase-200
SBA-15–anatase-300
SBA-15–anatase-400
SBA-15–anatase-500
SBA-15–anatase-600
No peak (5.6)g
No peak (4.9)
g
Too broad (4.9)g
Too broad (4.9)
g
(Fig. 5(B)). No substantial improvement of the reaction effi-
Too broad (4.3)
ciency was observed when the hybrid was heated at 500 and
a
Commercial TiO
2
nanoparticles were obtained from Catalysis Society
nanoparticles were obtained from
nanoparticles were obtained from
nanoparticles were obtained from
nanoparticles were obtained from
Ishihara Sangyo. The crystallite size of the anatase particle derived
ꢀ
600 C. The weak intensity of the diffraction peaks may be
b
of Japan. Commercial TiO
2
c
probably due to the scattering contrast between the anatase Nippon Aerosil. Commercial TiO
particles and the pore wall. The isolation of the anatase nano-
particles from SBA-15 and the characterization of the isolated
2
d
Tayca.
Commercial TiO
2
e
Hombikat. Commercial TiO
2
f
particles are being done in our laboratory and the results will be from the 101 diffraction of anatase from XRD pattern using Scherrer
g
equation. The crystallite size of the anatase particles was derived
reported separately.
from the shi of the band gab energy from band gap energy of a bulk
anatase particle (3.2 eV).
The possible mechanism of the photodecomposition of
2
acetic acid by TiO particles has been proposed as the direct
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and Technology Development Agency (NSTDA), Thailand, and
the Cooperative Research Program of Institute for Catalysis,
Hokkaido University. One of the authors (K. G. V.) acknowl-
edges Vidyasirimedhi Institute of Science and Technology
(VISTEC) for the scholarship to his PhD study.
Notes and references
Fig. 7 Photographs of the suspensions of SBA-15–anatase-600 and
ST-01 in aqueous solutions of acetic acid (A) and the suspensions after
the centrifugation at 4000 rpm for 15 min (B). The concentrations of
SBA-15–anatase-600 and ST-01 in the water is 1.5 g L . The
suspension was centrifuged at 4000 rpm for 15 min.
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Acknowledgements
This work was supported by the Research Chair Grant 2017 23 K. Vibulyaseak, S. Bureekaew and M. Ogawa, Langmuir, 2017,
grant number FDA-CO-2560-5655) from the National Science 33, 13598.
(
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