9
54
Bull. Chem. Soc. Jpn. Vol. 84, No. 9 (2011)
Photocatalytic Synthesis of 2-Methylquinolines from Nitrobenzenes
reported in our previous paper.24 Pt(x)TiO samples, contain-
10¹6 einstein L¹1 s ) after purging with N for 30 min. N2
¹1
2
2
¹
1
ing different platinum loadings [x (wt %) = Pt/(TiO +
bubbling (flow rate = 6.1 mL s ) and magnetic stirring of the
suspension were continued throughout the reaction while the
temperature was maintained at 30 « 1 °C. Progress of the
reaction was monitored by TLC. Product analysis was
performed by GC analysis, Perkin-Elmer GC-9000 with a
capillary column of DB-5 and flame ionization detector was
used. GC/MS analysis was carried out using a Varian 2000
Thermo with the following features: capillary column VF5MS
(5% phenyl95% methylpolysiloxane), 30 m length, 0.25 mm
internal diameter, 0.25 ¯m film thickness, temperature of
2
Pt)100; x = 0.5, 1.0, 1.5, and 2.0%] were prepared.
Apparatus. X-ray diffraction (XRD) patterns of TiO and
2
PtTiO powder samples were obtained using a Model D/Max
2
2
550V with Cu anticathode radiation. The diffractograms were
recorded in 2ª range between 10 and 80° in steps of 0.02° with
count time of 20 s at each point. The crystalline phase can be
determined from integration intensities of anatase (101), rutile
(110), and brookite (120) peaks and the average crystallite sizes
were determined according to the DebyeScherrer equation
using the full width half maximum data of each phase.
¹
1
column range from 50 to 280 °C (10 °C min ), and injector
temperature 250 °C, attached to mass spectrometer model SSQ
000. The isolation was performed by column chromatography
D ¼ K=¢ cos ª
ð1Þ
7
Where D is the crystal size of the catalyst, is the X-ray
wavelength (0.154 nm), ¢ is the full width half maximum
on a silica gel column by eluting with a cosolvent of hexane
and ethyl acetate (volume ratio: 8:2).
(
FWHM) of the catalyst, K = 0.89, and ª is the diffraction
angle.
The phase formation, particle size, surface morphology, and
Results and Discussion
Catalyst Characterization. Pt-loaded TiO (1.5 wt % Pt)
2
crystallinity of pure and loaded catalysts were examined using
transmission electron microscopy (TEM) (Model JEOL TEM-
catalyst was characterized by X-ray diffraction (XRD), BET
surface area, atomic force microscopy (AFM), transmission
electron microscopy (TEM), and diffuse reflectance spec-
troscopy (DRS). The XRD pattern of prepared TiO2 is identical
with the standard pattern of anatase (JCPDS 01-078-2486 C),
and rutile lines (01-089-0553 C) are absent. The peaks at 25.43,
37.92, 48.03, 53.97, 55.05, 62.70, 68.80, 70.39, and 75.05° are
the diffractions of the (101), (004), (200), (105), (211), (204),
(116), (200), and (215) crystal planes of anatase TiO2,
respectively (Figure S1). These results confirm that photo-
deposition of the platinum does not modify the basic crystal
structure of the TiO2 used (tetragonal, a = 0.37845 nm,
c = 0.95143 nm, body centered). The diffraction patterns of
the PtTiO2 samples do not show XRD peaks of metallic
platinum at 39.76, (111); 67.71°, (220); etc. This may be
because of either homogeneous dispersion of discrete platinum
3
010) operated at 300 keV. The samples for TEM analysis
were prepared by dispersion of the catalysts in ethanol under
sonication and deposition on a copper grid. High-resolution
TEM (HR-TEM) measurements were carried out using a JEOL-
JEM-2010 UHR instrument operated at an acceleration voltage
of 200 kV with a lattice image resolution of 0.14 nm. X-ray
photoelectron spectra (XPS) of the catalysts were recorded with
an ESCA-3 Mark II spectrometer (VG Scientific Ltd., England)
using Al K¡ (1486.6 eV) radiation as the source. The spectra
were referenced to the binding energy of C(1s) (285 eV).
The DRS of all the catalysts were recorded on a Shimadzu
UV 2450 model UVvisible spectrophotometer in the range of
8
00190 nm equipped with an integrating sphere and using
powdered BaSO4 as a reference. Reflectance spectra were
converted to the absorbance spectra using the KubelkaMunk
equation
deposits in the nanoscale on the surface of the TiO or because
2
of very low platinum content.
2
In Figure S2 an AFM 3D image of a dense Pt-loaded TiO2
nanoparticle is shown. PtTiO2 particles are well dispersed
without any trace of coalescence. Consequently we can be
ð1 ꢀ R1Þ
FðR1ðÞÞ ¼
ð2Þ
2
R1
The specific surface areas of the catalysts were determined
using a Micromeritics ASAP 2020 sorption analyzer. The
samples were degassed at 423 K for 12 h and analysis was
assured that Pt particles in TiO layer are either overcoated or
sandwiched.
TEM images at two different regions permit easy differ-
2
performed at 77 K with N gas as the adsorbate. The Brunauer
entiation of Pt loading in TiO crystallites (Figures 1a and 1b).
2
2
EmmettTeller (BET) multipoint method least-squares fit
provided the specific surface area.
Pt nanocrystals are seen on the surface of the TiO particle as
2
dark dots. The particle size of PtTiO nanoparticles has been
2
To study the morphology of catalyst, an atomic force
microscope (AFM) JSPM-5200TM, JEOL model was used.
This AFM uses a silicon tip with a radius of 20 mm and a low-
resonance frequency cantilever that has a manufacturer’s spring
constant of 3565 N m . Scans of 1.8 © 1.8 ¯m were obtained
for each sample. The images were recorded in the noncontact
mode. All recordings were made in air under ambient
conditions to produce 2D and 3D images.
analyzed in HR-TEM and shown in Figure 1c. It can be seen
that the size of PtTiO particles are in the range from 5 to
2
25 nm with an average particle size of 14.8 nm. Pt metal
particles are randomly dispersed on the TiO surface. Further
2
¹
1
observations from high-resolution TEM micrograph show that
the Pt particles diameters are in the range of 312 nm and
randomly located on the crystal surface. Figures 1d and 1e
show the lattice fringes of Pt and TiO and SAED pattern of
2
Photocatalytic Synthesis of 2-Methylquinolines.
In a
PtTiO2. The distance between the fringes is measured with
analysis software included in the instrument. The statistical
d-value is 0.225 nm for the Pt particles and 0.351 nm for the
typical experimental run, 50 mg 1.5%PtTiO was suspended
2
in 25 mL of an absolute ethanolic solution containing 25 mM of
the nitrobenzene and irradiated by a 365 nm medium-pressure
mercury lamp (Sankyo Denki, Japan; intensity I = 1.381 ©
TiO crystals, indicating that the observed fringes are for the
2
Pt(111) plane and TiO (101) anatase facets, respectively.
2