H. Matsui et al. / Journal of Alloys and Compounds 513 (2012) 184–188
185
25 ~ 28ºC
Table 1
HfOCl2 8H2O
+
starch
HfOCl2 / starch
I
Elemental analysis of precursor I and calcined materials Ics.
stirring for 1 hr
Materials
Found (%)
Hf
C
H
Cl
Ce(acac)3
Microwave treatment
I
9.86
30.86
30.01
33.36
32.59
55.27
55.41
57.99
5.34
2.10
1.62
0.32
3.07
HfO2 / carbon clustersStirring at 25 ~ 28 ºC for 24 hr
Ic
Ic-3
Ic-6
Ic-9
0
0
0
HfO2 / carbon clusters / Ce(acac)3
Ic Ce(acac)3
Calcination at 300 ºC for 10 min
HfO2 / carbon clusters / CeO2
CeO2
Ic
Scheme 1. Synthesis of materials.
LG Company MJ-60HL5 (2450 MHz, 500 W) for 3, 6 and 9 min to obtain calcined
materials Ic-3, Ic-6 and Ic-9, respectively.
2.4. CeO2-loading on the surface of Ic-6
A mixture of 300 mg of Ic-6 and 52.61 mg (0.375 mmol) of Ce(acac)3 in 60 mL
of THF was stirred at room temperature for 24 h. The precipitate was collected and
dried at 60 ◦C under a vacuum to obtain Ce(acac)3-loaded material Ic-6·Ce(acac)3.
Then the complex was heated at 300 ◦C for 10 min under an air atmosphere using
Barnstead Thermolyne electric furnace FB1300 to obtain CeO2-loaded HfO2/carbon
cluster composite material Ic-6·CeO2.
Fig. 1. XRD pattern of calcined material Ic-9.
2.5. Surface modification of Ic-6·CeO2 and Ic-6 with Pt particles
3. Results and discussion
A mixture of 30 mg of Ic-6·CeO2 and 0.8 mL of methanol was added into 0.8 mL
of an aqueous 0.05 mmol/L hydrogen hexachloroplatinate(IV) solution, and then the
mixture was stirred at room temperature under the irradiation of light above 460 nm
for 30 min using Hoya–Schott Megalight halogen lamp (100 W). The precipitate was
collected, washed with distilled water and dried at 60 ◦C under a reduced pressure
for overnight to obtain Pt-modified material Ic-6·CeO2·Pt. Similar treatment of Ic-6
produced the corresponding Pt-modified material Ic-6·Pt.
The elemental analysis of precursor I (Table 1) shows the pres-
ence of Hf and Cl atoms. The SEM–EDX spectra of precursor I
The above results clearly indicate the formation of precursor I.
materials Ics. The results of the elemental analysis of Ics are also
shown in Table 1. The content of H decreases with the increase of
irradiation time, indicating that the carbonization of the material
was successfully carried out. The XRD patterns of Ic-9 (Fig. 1) show
main peaks at 2ꢁ = 28.4◦, 35.2◦, 50.2◦and 60.1◦ due to HfO2. The
XPS analysis of Ics show binding energies at 214.0–214.1 eV due
to the Hf4d orbital of HfO2. The TEM observations of samples Ic-3,
Ic-6 and Ic-9 showed particles with the diameters of ca. 10, 20 and
50 nm, possibly HfO2, in the carbon phases. These results indicated
that the calcined materials are composed of nano-sized HfO2 and
carbon cluster.
ined. The ESR spectra of Ics (Fig. 2) show a peak at 337 mT (g = 2.003).
The radical spin quantity (rsq) of the calcined materials was deter-
mined by the double integrating calculation of the differential
absorption line with the use of DPPH (Table 2), and the highest rsq
value was obtained for Ic-6. It is assumed that an electron trans-
fer between the HfO2 particle and the carbon cluster takes place to
form a free electron on the carbon cluster and therefore the high-
est charge separation occurred for Ic-6. The largest rsq value of Ic-6,
indicates that the most effective charge separation can takes place
2.6. Characterization
Elemental analysis was performed for C and H using Yanaco MT-6, for Cl using
Yanaco YS-10, and for Hf, Ce and Pt by inductively coupled plasma atomic emission
spectrometry (ICP-AES) using Shimadzu ICP-7500. Raman spectrum was measured
on a single-grating spectrometer (Jobin Yvon HR-800) equipped with an Ar ion
laser at 514.5 nm for the excitation. Scanning electron microscope coupled with
energy dispersive X-ray spectroscopy (SEM–EDX) measurement was carried out
using Hitachi High technologies S-4800 FE-SEM and Horiba Emax Energy EX-450.
X-ray diffraction (XRD) spectra were taken using Rigaku Mini Flex. X-ray photospec-
trometry (XPS) spectra were measured using Shimadzu ESCA-850. Transmission
electron microscopy (TEM) observations were done using Jeol JEM-3010. Electron
spin resonance (ESR) spectra were measured using Jeol JES-TE200. UV–vis spectra
were taken using Hitachi U-4000 spectrometer. Visible light was generated using
Hoya–Schott Megalight 100 halogen lamp. TCD gas chromatogram was taken using
Shimadzu GC-8A gas chromatography.
The reduction reaction of methylene blue in the presence of calcined material
Ics was carried out as follows. A mixture of 3 mg of Ics and 10 mL of 0.03 mmol
methylene blue and 0.12 mmol citric acid aqueous solution was stirred at room
temperature in the dark for overnight. The citric acid was used as electron donor
reagent. The mixture was irradiated by visible light (light intensity = 2 mW/cm2)
above the wavelength of 460 nm under an argon atmosphere and the concentration
of methylene blue was estimated by UV–vis spectral analysis.
The oxidation–reduction reaction of an aqueous silver nitrate solution in the
presence of Ic-6·CeO2 was performed in the following way. 10 mg of Ic-6·CeO2 was
added to 1 mL of an aqueous 0.05 mol/L silver nitrate solution and then it was deaer-
ated by argon bubbling for 1 h and finally the mixture was irradiated by visible light
above 460 nm. The evolved O2 gas was estimated by gas chromatography and the
obtained Ag was analyzed by ICP.
Table 2
Radical spin quantity (rsq) and reduction activity (ra) of calcined materials Ics.
Water photo-decomposition experiment in the presence of Ic-6·CeO2·Pt, Ic-
6·CeO2, Ic-6·Pt and Ic-6 was performed and details are given below. 10 mg of the
material was added into 0.2 mL of distilled water and then deaerated by argon bub-
bling for 1 h in the dark. Visible light (ꢀ > 460 nm) was irradiated to the mixture for
3 h, and the evolved H2 and O2 gases were estimated by gas chromatography.
Materials
rsq (spins/g)
ra (mol/g h)
Ic-3
Ic-6
Ic-9
2.97 × 1019
1.55 × 1020
5.76 × 1019
2.18
2.58
0.63