Preparation of monodispersed spherical titania-octadecylamine particles containing silane-coupling reagents

Article abstract of DOI:10.1246/bcsj.20120013

Well-defined spherical titania-octadecylamine (titania-ODA) (titania: titanium dioxide) hybrid particles containing silane-coupling reagents including aminopropyl, sulfanylpropyl, octadecyl, and phenyl groups (molar Ti:silane-coupling reagent ratio of 50:1) were prepared by sol-gel reaction of titanium tetraisopropoxide with the aid of a flow reactor. Average particle sizes were 520, 380, 540, and 510 nm for aminopropyl, sulfanylpropyl, octadecyl, and phenyl group containing particles, respectively. ODA was removed by washing the as-synthesized products with acidic EtOH, resulting in the formation of organosilyl group containing nanoporous titania. The porosity was investigated by the nitrogen adsorption/desorption isotherms (BET surface area of 250 to 400 m²g^-1) and the surface hydrophilicity/hydrophobicity is discussed based on the water and benzene vapor adsorption/desorption isotherms. Crystallization of anatase within the spherical particles is possible by postsynthetic hot water or hydrothermal treatment.

Full text of DOI:10.1246/bcsj.20120013

1040 Bull. Chem. Soc. Jpn. Vol. 85, No. 9, 1040-1047 (2012)
© 2012 The Chemical Society of Japan
Preparation of Monodispersed Spherical Titania-Octadecylamine
Particles Containing Silane-Coupling Reagents
Kota Shiba,1,³ Soh Sato,1 and Makoto Ogawa*1,2
1Graduate School of Creative Science and Engineering, Waseda University,
1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050
2Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169-8050
Received January 11, 2012; E-mail: makoto@waseda.jp
Well-defined spherical titania-octadecylamine (titania-ODA) (titania: titanium dioxide) hybrid particles containing
silane-coupling reagents including aminopropyl, sulfanylpropyl, octadecyl, and phenyl groups (molar Ti:silane-coupling
reagent ratio of 50:1) were prepared by sol-gel reaction of titanium tetraisopropoxide with the aid of a flow reactor.
Average particle sizes were 520, 380, 540, and 510 nm for aminopropyl, sulfanylpropyl, octadecyl, and phenyl group
containing particles, respectively. ODA was removed by washing the as-synthesized products with acidic EtOH, resulting
in the formation of organosilyl group containing nanoporous titania. The porosity was investigated by the nitrogen
adsorption/desorption isotherms (BET surface area of 250 to 400 m2 g¹1) and the surface hydrophilicity/hydrophobicity
is discussed based on the water and benzene vapor adsorption/desorption isotherms. Crystallization of anatase within the
spherical particles is possible by postsynthetic hot water or hydrothermal treatment.
Immobilization of various organosilyl groups onto the
surface of titania and titanate is a promising way to obtain
titania and titanate with modified surface properties such as
selective adsorption,1-3 improved dispersibility into solvents or
polymers,4-7 suppressed photocatalytic activity,8 variable swel-
ling behavior,9,10 metal nanoparticle immobilization,11,12 and so
on. Although the amount and distribution of grafted organosilyl
groups probably affect the properties,3 it is not clear whether
all the silane-coupling reagents evenly distribute in the titania
particles. When the hierarchical design of hybrid particles
(shape, size, and monodispersity) is achieved, quantitative and
detailed discussion as well as precise tailor-made materials
design will become possible.
In this paper, we report the preparation of silane-coupling
reagent containing titania-octadecylamine (titania-ODA) hy-
brid spherical particles. Our recent successes in the introduction
of heteroelements (Zr and Si) into monodispersed titania-ODA
spherical particles13,14 which was achieved by using a flow
reactor, motivated us to prepare well-defined organosilyl group
containing titania particles with various potential applications.
Uniform size and shape of particles help with discussion of the
distribution of components (homogeneity/heterogeneity), relat-
ing to the properties of resultant materials. One of the merits of
flow reactors, where efficient mixing is possible,15-17 has been
utilized for the preparation of monodispersed particles, while a
part of the starting materials is likely to remain due to the
insufficient residence time in the flow reactor. It indicates that
the preparation of monodispersed particles, which requires long
aging period, is difficult to be achieved by using flow reactors.
In our previous work, the flow reactor was successfully applied
to prepare uniform size nanoparticles which might be nuclei
(first step) and the nanoparticles were subsequently grown in
an open vessel (second step). In addition to titania-ODA,18,19
monodispersed silica-hexadecyltrimethylammonium (silica:
silicon dioxide) hybrid spherical particles, where longer time
was required for the formation of the particles than for titania-
ODA, were prepared by the two-step procedure using the flow
reactor to achieve better reproducibility and monodispersity.20
In the present study, titania-ODA hybrid spherical particles
were prepared in the presence of silane-coupling reagents
(aminopropyl, sulfanylpropyl, octadecyl, and phenyl) to exam-
ine possible incorporation of organic functionality within the
products while retaining the well-defined shape to extend the
materials’ variation obtained by the flow reactor assisted sol-
gel reactions.
Experimental
Materials.
Titanium tetraisopropoxide (abbreviated as
TTIP), trimethoxy(octadecyl)silane (abbreviated as TMODS),
3-aminopropyltriethoxysilane (abbreviated as APTES), and
triethoxy(phenyl)silane (abbreviated as TEPS) were purchased
from Tokyo Chemical Industry Co., Ltd. Tetraethoxysilane
(abbreviated as TEOS) and 2-propanol (abbreviated as IPA)
were purchased from Kanto Chemical Co., Ltd. Octadecylamine
(abbreviated as ODA) and trimethoxy(3-sulfanylpropyl)silane
(abbreviated as TMSPS) were purchased from Sigma-Aldrich,
Inc. All the reagents were used without further purification.
Preparation of Titania-Octadecylamine Particles Con-
taining Silane-Coupling Reagents. The titania-ODA hybrid
spherical particles precipitated with silane-coupling reagents
were synthesized based on a procedure reported previously.18
The synthetic procedure is schematically shown in Scheme 1.
IPA (9.44 g) solution containing TTIP (0.458 mL) and silane-
³ Present address: World Premier International (WPI) Research
Center, International Center for Materials Nanoarchitectonics
(MANA), National Institute for Materials Science (NIMS), 1-1
Namiki, Tsukuba, Ibaraki 305-0044
Published on the web September 8, 2012; doi:10.1246/bcsj.20120013

K. Shiba et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012) 1041
Syringe pump
Flow reactor with Y type junction
3 cm
H2O
IPA
ODA
Stirring
Reaction within the flow reactor
Batch reaction
TTIP
IPA
H2O
IPA
APTES, TMSPS, TMODS, TEPS
Scheme 1. Schematic illustration of the experimental setup used in this study.
coupling reagent (APTES: 0.0080 mL, TMSPS: 0.0050 mL,
TMODS: 0.0113 mL, TEPS: 0.0066 mL) and aqueous IPA
solution (IPA 9.74 g, deionized water 0.077 mL) were flowed
within the tube made of PFA (with a diameter of 1 mm) with a
syringe pump (MR2 Pump, provided by YMC, Inc.) at 20
mL min¹1 and were mixed within a flow reactor made of PTFE
and with a flow channel of Y-type junction (KeyChem mixer,
Hadar, provided by YMC, Inc.). The channel cross section was
ca. 1 mm2. The molar ratio of TTIP:H2O after the mixing was
1:2.7 and the molar ratio of TTIP:silane-coupling reagent was
1:0.02. The mixture was further flowed within a PFA tube of
70 cm in length and 1 mm in diameter. Then, the solution was
mixed with a solution containing deionized water (0.30 mL),
IPA (49.32 g), and ODA (0.0684 g, molar ODA/TTIP ratio was
0.18) under magnetic stirring until the addition of the mixture
was completed (it took 40 s). After aging the solution at room
temperature for 24 h, the product was collected by vacuum filtra-
tion with a membrane filter (cellulose acetate, pore size of 0.2
¯m), washed with IPA, and then dried at 60 °C in air for a day.
In order to remove ODA for the formation of nanoporous
particles, 150 mg of as-synthesized titania-silica-ODA were
washed with a mixture of 12 M HCl(aq) and EtOH with a
volume ratio of 0.125/25 for 1 h under magnetic stirring and
were collected by vacuum filtration with a membrane filter
(cellulose acetate, pore size of 0.2 ¯m). This washing-collect-
ing cycle was repeated twice. Finally, the HCl/EtOH washed
products were dried at 60 °C in air for a day. The products
were named as titania-C3NH2, titania-C3SH, titania-C18H37,
and titania-C6H5 for APTES, TMSPS, TMODS, and TEPS
coprecipitated products, respectively. For comparison, titania
particle was also prepared according to the reported proce-
dure,18 and named as titania.
the following conditions: magnetic stirring at room temper-
ature, 80 °C for 5 h, hydrothermal reaction at 150 °C for 5 h.
The products were then collected by vacuum filtration with a
membrane filter (cellulose acetate, pore size; 0.2 ¯m). Finally,
the products were dried at 60 °C in air for a day.
Characterization. Scanning electron microscope (SEM)
images were obtained on a Hitachi S-2380N scanning elec-
tron microscope. Prior to the measurements, the samples were
coated with 20 or 30 nm gold layer. Average particle size and
coefficient of variation (CV) were obtained from the SEM
images by counting 50 particles. Thermogravimetric-differ-
ential thermal analysis (TG-DTA) curves were recorded on a
¹1
Rigaku TG-8120 instrument at a heating rate of 10 °C min
under air flow and using ¡-alumina as a standard material. X-ray
diffraction (XRD) patterns of products were recorded on a
Rigaku RAD IB powder diffractometer equipped with mono-
chromatic Cu K¡ radiation operated at 20 mA and 40 kV. The
size of crystallites was calculated using the Scherrer’s equation
based on the full width at half maxima of anatase (101) reflec-
tion at 2ª = 25.176°. Nitrogen adsorption/desorption isotherms
of the HCl/EtOH washed products were measured at ¹196 °C
on a Belsorp Mini instrument (Bel Japan, Inc.). Prior to the
measurements, the samples were dried at 140 °C under nitrogen
atmosphere for 3 h. The surface area was calculated using the
Brunauer-Emmett-Teller (BET) method21 using a linear plot
over the range of P/P0 = 0.05-0.20. Pore size distributions
of the HCl/EtOH washed products were derived from the
nitrogen adsorption isotherms by the Barrett-Joyner-Halenda
(BJH) method22 and the t-plot method.23 Water vapor and
benzene adsorption/desorption isotherms of the HCl/EtOH
washed products were measured at 25 °C on a Belsorp Max
instrument (Bel Japan, Inc.). Prior to the measurements, the
samples were dried at 140 °C under nitrogen atmosphere for 3 h.
Heat Treatment of Aqueous Dispersion of Nanoporous
Titania Spherical Particles and Nanoporous Titania Spher-
ical Particles Precipitated with Silane-Coupling Reagents.
120 mg of the particles after removing ODA was dispersed into
50 mL of water by ultrasonication and then heat treated under
Results and Discussion
SEM images of the titania-based particles and particle size
distributions derived from the SEM images are shown in

1042 Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012)
Organosilylated Monodispersed Titania
titania-C3NH2
titania-C3SH
titania-C18H37
titania-C6H5
Flow
reactor
1 μm
1 μm
1 μm
1 μm
Without
flow
reactor
1 μm
1 μm
1 μm
1 μm
800
600
400
d = 519 nm
CV = 6.7 %
d = 377 nm
CV = 7.6 %
d = 536 nm
CV = 7.1 %
d = 514 nm
CV = 5.2 %
200
0
Number of particles
Figure 1. SEM images of organosilyl groups containing titania-ODA hybrid spherical particles prepared using (upper) and without
using the flow reactor (lower). Particle size distributions of organosilyl groups containing titania-ODA hybrid spherical particles
prepared using the flow reactor are also shown.
Table 1. Summary of Yield, Dissolved Amount and Residual Amount of Organosilyl Groups of Products
Dissolved amount
of products/%
Residual amount of
silyl groupsb)
/wt %
BET surface area
Yielda)
/%
¹1
/m2 g
HCl/EtOH
Hydrothermal
Titania
600
420
370
240
350
91
97
92
99
95
19
8
13
6
Not measured
®
Titania-C3NH2
Titania-C3SH
Titania-C18H37
Titania-C6H5
26
31
27
35
3.2 (1.4)
3.3 (1.8)
5.8 (5.1)
3.8 (2.1)
4
a) The values were roughly determined based on the collected amount of the products considering the
composition determined from the amount of ash after the TG analysis up to 600 °C. b) The values were
determined based on the weight loss in the TG curves in the temperature range from 200 to 600 °C where the
organosilyl groups thermally decomposed. The values in the parenthesis were calculated based on the formula
weight of each organosilyl group in the corresponding silane coupling reagents.
Figure 1. Monodispersed spherical particles (with the size of
519, 377, 536, and 514 nm for titania-C3NH2, titania-C3SH,
titania-C18H37, and titania-C6H5, respectively) were formed by
the present synthesis using a flow reactor. Although the reason
for the smaller particle size of titania-C3SH is not clear,
products with a narrow particle size distribution were obtained
irrespective of the type of silane-coupling reagents (CV was 5-
7%, which is almost the same as that of titania-ODA reported
previously18). As a comparison, the same sol-gel reaction
was conducted without using the flow reactor. SEM images of
the products are shown in Figure 1. Consequently, not only
spherical particles but also irregular shaped particles were seen
and the particle size distribution was broader. This indicates
that the present two-step synthesis using the flow reactor,
i.e., nucleation within the flow reactor and growth by batch
reaction, was successfully applied to the coprecipitation of
titania with silane-coupling reagents. The product yield was
roughly determined based on the collected amount of the
products considering the composition which was determined
from the amount of ash after the TG analysis up to 600 °C. The
yields were over 90% for all the products (Table 1), indicating
most of the starting materials were solidified under the experi-
mental conditions employed in the present study.
The spherical shape was maintained after removing ODA by
washing with acidic EtOH (Figure 2). In the case of titania
particles without coprecipitation, ca. 20% of titania dissolved
during the washing process. On the other hand, only 10% or
less of titania dissolved when the silane-coupling reagent con-
taining products were washed with acidic EtOH, indicating
the surface of the titania particles was modified while the
same washing procedure should be conducted under different
temperature, pH, sample amount as well as using particles with
various amounts of organosilyl groups in order to further
discuss the dissolved amount of products. The exothermic

K. Shiba et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012) 1043
titania
titania-C3NH2
titania-C3SH
titania-C18H37 titania-C6H5
500 nm
500 nm
500 nm
500 nm
500 nm
Figure 2. SEM images of organosilyl groups containing nanoporous titania spherical particles after removing ODA.
titania
titania-C3NH2 titania-C3SH titania-C18H37 titania-C6H5
0
5
100
80
60
40
20
0
10
15
20
25
30
35
-20
100 300 500 700 100 300 500 700 100 300 500 700 100 300 500 700 100 300 500 700
Temperature / °C
Figure 3. TG-DTA curves of organosilyl groups containing nanoporous titania spherical particles after removing ODA.
titania
titania-C3NH2
titania-C3SH
titania-C18H37
titania-C6H5
250
200
150
100
50
500 m2 g-1
420 m2 g-1
370 m2 g-1
240 m2 g-1
350 m2 g-1
0
0 0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
1
Relative pressure
160
120
80
40
0
2.5 nm
1.8 nm
2.0 nm
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
10
Pore size / nm
Figure 4. Nitrogen adsorption/desorption isotherms of organosilyl groups containing nanoporous titania spherical particles after
removing ODA. : adsorption, ©: desorption. BJH pore size distributions are also shown below each adsorption/desorption
isotherm.
reaction, which did not accompany any weight loss, was seen
in the DTA curves (Figure 3) at around 410 °C for the silane-
coupling reagent containing particles. This indicates that
silane-coupling reagents were incorporated into titania, as
judged based on the previous report where the crystal phase
transition of amorphous titania into anatase occurred at around
500 °C for titania-silica particles (Si/Ti = 0.19).14
The absorption bands attributable to C-H stretching vibra-
tion (around 2920 and 2850 cm¹1) and Si-C(phenyl) vibration
(around 1130 cm¹1) were seen for the IR spectra of the prod-
ucts (Figure S1).24-26 On the other hand, absorption bands of
aminopropyl and sulfanylpropyl groups were not seen possibly
because the absorption was weak and/or the absorption bands
of water (around 1620 and 3000 cm¹1) overlapped with those
of aminopropyl and sulfanylpropyl groups. The presence
of aminopropyl and sulfanylpropyl groups was confirmed by
TG-DTA (Figure 3). Exothermic reactions, which accompanied
weight losses of 12-14 wt % in the corresponding TG curves,
were seen at 200-300 °C in the DTA curves. Titania showed
weight loss of ca. 11 wt % in the same temperature range,

1044 Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012)
Organosilylated Monodispersed Titania
suggesting dehydration and thermal decomposition of organo-
silyl groups occurred in the same temperature range to give
larger mass loss. The added amount of aminopropyl and
sulfanylpropyl groups was 1.5-2.0 wt %, showing quantitative
incorporation of organosilyl groups. Although the introduction
of organosilyl groups into titania particles was indicated, the
detailed state of the organosilyl groups was not characterized.
In order to discuss the state, we will further proceed to the
characterization as well as the investigation of the properties of
the present silane-coupling reagent containing titania particles.
Nitrogen adsorption/desorption measurements were per-
formed to examine BET surface area of the products. All the
titania-silane-coupling reagent coprecipitated particles were
converted to nanoporous particles by acidic EtOH washing
as revealed by the nitrogen adsorption/desorption isotherms
(Figure 4). BET surface area was around 400 m2 g¹1 for titania-
vapor at the initial stage of the measurement, suggesting silane-
coupling reagent containing particles possessed hydrophilic
surface due to the surface hydroxy groups. The relative BET
surface area (benzene/nitrogen) for silane-coupling reagent
containing particles was also larger than that for titania. On the
other hand, benzene adsorption/desorption isotherms of the
products showed that the shape of hysteresis was different
160
titania-C3NH2
140
120
100
80
60
40
20
0
titania-C6H5
titania-C3SH
¹1
C3NH2, titania-C3SH, and titania-C6H5, and 240 m2 g for
titania-C18H37
titania-C18H37, while nanoporous titania particles possessed
¹1
BET surface area of 500 m2 g (Table 1). The smaller surface
area of silane-coupling reagent containing products is possibly
due to the presence of organosilyl groups in the pores: because
octadecyl group occupies the largest volume among the four
organosilyl groups, titania-C18H37 showed the smallest BET
surface area. BJH pore sizes were 2.5, 1.8, and 2.0 nm for
titania, titania-C3SH, and titania-C6H5, respectively, and there
were no peaks in the BJH pore size distributions of titania-
C3NH2 and titania-C18H37. t-Plot analyses revealed that all the
organosilyl group containing products possessed micropores
(Figure 5). It is pointed out that the interaction between titania
and alkylamine (such as hydrogen bonding) played a signifi-
cant role in forming precursors of nanoporous titania par-
ticles.27-29 In this study, organosilyl groups present on the
surface of titania when titania particles, which formed in the
flow reactor, were mixed with ODA to grow as titania-ODA.
Therefore, the interaction between titania and ODA was differ-
ent than the case without organosilyl groups, although the
amount of incorporated ODA was almost the same among all
the products (titania and organosilyl group containing titania).
The adsorbed amount of water vapor for silane-coupling
reagent containing particles was larger than that for titania,
as judged from the relative BET surface area (water/nitrogen)
between nitrogen adsorption and water vapor adsorption
(Figure 6 and Table 2), while BET surface area of titania
derived from nitrogen adsorption isotherm was the largest. All
the silane-coupling reagent containing particles adsorbed water
2t / nm
0.80
0.90
0.83
1.0
titania-C3NH2
titania-C3SH
titania-C18H37
titania-C6H5
0
0.5
1
1.5
t (pore radius) / nm
Figure 5. t-Plots of organosilyl groups containing nano-
porous titania spherical particles after removing ODA. The
2t values (pore diameter) are shown in the inset.
Table 2. Summary of BET Surface Area Derived from
Nitrogen, Water, and Benzene Adsorption Isotherms of
Organosilyl Groups Containing Products, and Relative
BET Surface Area
BET surface area
Relative
BET surface area
¹1
/m2 g
Nitrogen Water Benzene Nitrogen Water Benzene
Titania
Titania-C3NH2 420
Titania-C3SH 370
Titania-C18H37 240
Titania-C6H5 350
500
450
610
540
470
560
170
330
230
180
200
0.90
1.45
1.46
1.96
1.60
0.34
0.79
0.62
0.75
0.57
0.38
0.54
0.43
0.38
0.36
titania
titania-C3NH2
titania-C3SH
titania-C18H37
titania-C6H5
500
400
300
200
100
0
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 1
Relative pressure
Figure 6. Water adsorption/desorption isotherms of organosilyl groups containing nanoporous titania spherical particles after
removing ODA. : adsorption, ©: desorption.

K. Shiba et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012) 1045
titania
titania-C3NH2
titania-C3SH
titania-C18H37
titania-C6H5
100
80
60
40
20
0
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8
0
0.2 0.4 0.6 0.8 1
Relative pressure
Figure 7. Benzene adsorption/desorption isotherms of organosilyl groups containing nanoporous titania spherical particles after
removing ODA. : adsorption, ©: desorption.
titania
titania-C3NH2
titania-C3SH
titania-C18H37
titania-C6H5
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
500 nm
Figure 8. SEM images of organosilyl groups containing nanoporous titania spherical particles after heat treatment at 25, 80, and
150 °C (hydrothermal).
(Figure 7) depending on the kind of silane-coupling reagents.
The type of incorporated organosilyl groups probably affects
the difference. The relative BET surface area (benzene/water)
indicates that titania-C3NH2 is relatively hydrophobic among
all the products, however, hysteresis in its benzene adsorption/
desorption isotherms was the smallest. In order to discuss the
modified surface properties from incorporation of organosilyl
groups, samples with different amounts of organosilyl groups
should be prepared and the properties should be examined.
We preliminarily prepared titania-C18H37 with molar TMODS/
TTIP ratio of 0.1 and confirmed that monodispersed spherical
particles with larger particle size (ca. 700 nm) formed.
The silane-coupling reagent containing particles were
dispersed into water and heat treated under various conditions:
25 and 80 °C under air pressure, and 150 °C hydrothermal
condition. Titania-C3NH2, titania-C18H37, and titania-C6H5
maintained the spherical shape after treating with 25 °C water
(Figure 8). Spherical shape of titania-C3NH2 collapsed after
the treatment at 80 °C, while titania-C18H37 and titania-C6H5
maintained the spherical shape even after the hydrothermal
treatment at 150 °C. No difference was found in the CV values
of titania, titania-C18H37, and titania-C6H5 after ODA removal
and water treatment. Titania-C3NH2 and titania-C3SH, how-
ever, showed larger CV values and irregular shape after water
treatment, indicating water penetrated into the particles due
to hydrophilicity and spherical particles were etched to form
fragmented particles.30
The XRD patterns revealed that the silane-coupling reagent
containing particles showed diffractions attributed to anatase
(Figure 9) after they were heat treated at 80 °C and hydro-
thermally treated at 150 °C. The size of anatase crystallites
calculated from the XRD diffraction (101 reflection) based on
the Scherrer’s equation were ca. 5 and 7 nm, respectively.
The amount of organosilyl groups after the hydrothermal
treatment was determined based on the weight loss in the TG
curves in the temperature range from 200 to 600 °C (Figure 10)
where the organosilyl groups thermally decomposed. The
amount of organosilyl groups were not changed significantly

1046 Bull. Chem. Soc. Jpn. Vol. 85, No. 9 (2012)
25 °C
Organosilylated Monodispersed Titania
80 °C
150 °C hydrothermal
: anatase
titania-C6H5
titania-C18H37
titania-C3SH
titania-C3NH2
titania
10 20 30 40 50 60 70 10 20 30 40 50 60 70 10 20 30 40 50 60 70
2θ / ° (Cu Kα)
Figure 9. XRD patterns of organosilyl groups containing nanoporous titania spherical particles after heat treatment at 25, 80, and
150 °C (hydrothermal).
titania-C3NH2 titania-C3SH titania-C18H37 titania-C6H5
0
2
30
20
10
0
4
6
8
-10
-20
10
12
100 300 500 700 100 300 500 700 100 300 500 700 100 300 500 700
Temperature / °C
Figure 10. TG-DTA curves of organosilyl groups containing nanoporous titania spherical particles after hydrothermal treatment at
150 °C. The weight loss in the temperature range from 200 to 600 °C (pointed with a blue curved line) was used to calculate the
residual amount of organosilyl groups.
by the hydrothermal treatment. When the organosilyl groups
were distributed heterogeneously within each particle, the
residual amount of organosilyl groups varied after the hydro-
thermal treatment due to the dissolution of ca. 30% (Table 1).
As a result, it is possible to say that the organosilyl groups were
incorporated into titania particles and the organosilyl groups
could be distributed similarly in each particle.
In our preliminary experiments where the titania-ODA
particles were silylated by the postsynthetic route, products
were not obtained in a reproducible fashion. On the other hand,
the present coprecipitation is reproducible so that it is a possi-
ble way to obtain homogeneous products (both in the chemical
composition and particle size distribution).
containing nanoporous titania particles showed smaller BET
surface area (240 to 400 m2 g¹1) than that (500 m2 g¹1) of
nanoporous titania prepared without using silane-coupling
reagents. Postsynthetic hot water (80 °C) or hydrothermal
(150 °C) treatment resulted in the crystal phase transition into
anatase with retaining the particle morphology.
Supporting Information
FT-IR spectra of organosilyl groups containing nanoporous
titania spherical particles after removing ODA, and particle
size distributions of nanoporous titania and organosilyl groups
containing nanoporous titania spherical particles before and
after water treatment (at 25 and 80 °C). This material is availa-
ble free of charge on the Web at: http://www.csj.jp/journals/
bcsj/.
Conclusion
Titania-octadecylamine (titania-ODA) hybrid spherical par-
ticles with uniform particle size and containing organosilyl
groups such as aminopropyl, sulfanylpropyl, octadecyl, and
phenyl groups were prepared by the sol-gel reaction of titanium
tetraisopropoxide and silane-coupling reagents in the presence
of ODA and with the aid of a flow reactor. After washing with
acidic ethanol to remove ODA, these particles were transformed
into nanoporous particles and they showed adsorption of water
and benzene equal to or larger than that of nanoporous titania
without organosilyl groups, although the organosilyl groups
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