All reagents are of analytical grade and used without further
purification.
Synthesis of Nearly Monodisperse PbWO4 and CaWO4 Microspheres. In a typical experiment, 2 mmol of acetate MAc2 (M ) Pb,
Ca) and 2 mmol of trisodium citrate were placed in separate beakers,
distilled water (20 mL) was added, and the contents were magnetically
stirred to form homogeneous solutions. The MAc2 solution was added
slowly to the trisodium citrate solution under strong magnetic stirring
to form a mixture containing amorphous particulates. Two millimoles
of sodium dodecyl benzenesulfonate (SDS) or cetyltrimethyl ammonium
bromide (CTAB) was added to the above mother solution. Then, a 4
mmol Na2WO4 solution was added to the former solution. The pH was
adjusted to a suitable value using NaOH or acetic acid solution (1 mol
L-1). The resulting precursor suspension was transferred to a Teflonlined stainless-steel autoclave or glass jar. The container was sealed
and maintained at a certain temperature for the desired reaction time
and then allowed to cool slowly to room temperature. The products
were collected by filtration, washed several times with distilled water
and absolute ethanol, and finally dried in a vacuum oven at 60 °C for
4 h. The yields for the products obtained using SDS and CTAB can
reach as high as 95 and 92%, respectively.
Characterization. The products were characterized by X-ray
diffraction (XRD), recorded on a MAC Science Co. Ltd. MXP 18 AHF
X-ray diffractometer with monochromatized Cu KR radiation (λ )
1.54056 Å). The microscopy was performed with a Hitachi (Tokyo,
Japan) H-800 transmission electron microscope (TEM) at an accelerating voltage of 200 kV, and a JEOL-2010 high-resolution TEM, also at
200 kV. SEM images were taken on a JEOL JSM-6700F scanning
electron microscope; the infrared spectrum was obtained on a Fourier
transform infrared spectrometer (FRIR, Magna-IR-750); thermogravimetric analysis (TGA) was carried out on a TGA-50 thermal analyzer
(Shimadzu Corporation) with a heating rate of 10 °C min-1 in flowing
air. The experiments to measure the optical properties of the samples
at low temperature were performed at the Time-Resolved Spectroscopy
Station of the National Synchrotron Radiation Laboratory (NSRL, Hefei,
China).
All reagents are of analytical grade and used without furtherpurification.Synthesis of Nearly Monodisperse PbWO4 and CaWO4 Microspheres. In a typical experiment, 2 mmol of acetate MAc2 (M ) Pb,Ca) and 2 mmol of trisodium citrate were placed in separate beakers,distilled water (20 mL) was added, and the contents were magneticallystirred to form homogeneous solutions. The MAc2 solution was addedslowly to the trisodium citrate solution under strong magnetic stirringto form a mixture containing amorphous particulates. Two millimolesof sodium dodecyl benzenesulfonate (SDS) or cetyltrimethyl ammoniumbromide (CTAB) was added to the above mother solution. Then, a 4mmol Na2WO4 solution was added to the former solution. The pH wasadjusted to a suitable value using NaOH or acetic acid solution (1 molL-1). The resulting precursor suspension was transferred to a Teflonlined stainless-steel autoclave or glass jar. The container was sealedand maintained at a certain temperature for the desired reaction timeand then allowed to cool slowly to room temperature. The productswere collected by filtration, washed several times with distilled waterand absolute ethanol, and finally dried in a vacuum oven at 60 °C for4 h. The yields for the products obtained using SDS and CTAB canreach as high as 95 and 92%, respectively.Characterization. The products were characterized by X-raydiffraction (XRD), recorded on a MAC Science Co. Ltd. MXP 18 AHFX-ray diffractometer with monochromatized Cu KR radiation (λ )1.54056 Å). The microscopy was performed with a Hitachi (Tokyo,Japan) H-800 transmission electron microscope (TEM) at an accelerating voltage of 200 kV, and a JEOL-2010 high-resolution TEM, also at200 kV. SEM images were taken on a JEOL JSM-6700F scanningelectron microscope; the infrared spectrum was obtained on a Fouriertransform infrared spectrometer (FRIR, Magna-IR-750); thermogravimetric analysis (TGA) was carried out on a TGA-50 thermal analyzer(Shimadzu Corporation) with a heating rate of 10 °C min-1 in flowingair. The experiments to measure the optical properties of the samplesat low temperature were performed at the Time-Resolved SpectroscopyStation of the National Synchrotron Radiation Laboratory (NSRL, Hefei,China).
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