Yingyot Poo-arporn

Synthesis, characterization, and magnetic properties of monodisperse CeO2 nanospheres prepared by PVP-assisted hydrothermal method

Ferromagnetism was observed at room temperature in monodisperse CeO2 nanospheres synthesized by hydrothermal treatment of Ce(NO3)3·6H2O using polyvinylpyrrolidone as a surfactant. The structure and morphology of the products were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and field-emission scanning electron microscopy (FE-SEM). The optical properties of the nanospheres were determined using UV and visible spectroscopy and photoluminescence (PL). The valence states of Ce ions were also determined using X-ray absorption near edge spectroscopy. The XRD results indicated that the synthesized samples had a cubic structure with a crystallite size in the range of approximately 9 to 19 nm. FE-SEM micrographs showed that the samples had a spherical morphology with a particle size in the range of approximately 100 to 250 nm. The samples also showed a strong UV absorption and room temperature PL. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide. The magnetic properties of the samples were studied using a vibrating sample magnetometer. The samples exhibited room temperature ferromagnetism with a small magnetization of approximately 0.0026 to 0.016 emu/g at 10 kOe. Our results indicate that oxygen vacancies could be involved in the ferromagnetic exchange, and the possible mechanism of formation was discussed based on the experimental results.

Time-resolved XAS (Bonn-SUT-SLRI) beamline at SLRI.

An energy-dispersive X-ray absorption spectroscopy beamline has been constructed at the Synchrotron Light Research Institute, Thailand. The beamline was designed to utilize the synchrotron radiation with photon energies between 2400 and 8000 eV. The horizontal focusing of the bent crystal in the energy-dispersive monochromator offers a small polychromatic focal spot of 1 mm at the sample position. By employing an energy-dispersive scheme, the whole X-ray absorption near-edge structure (XANES) can be obtained simultaneously using a position-sensitive detector with a fastest readout speed of 25 ms. The short data collection time opens a new opportunity for time-resolved X-ray absorption spectroscopy (XAS) experiments such as studies of changes of the electronic structures or the local coordination environments of an atom during a change in thermodynamic conditions. For this purpose, an in situ cell was designed and fabricated for the beamline. Thermal oxidation of TiO(2) was chosen as an in situ experiment example. The structural change of TiO(2) as a function of temperatures was monitored from the change in the measured XAS spectra. The obtained Ti K-edge XANES spectra clearly show the formation of an anatase phase when the temperature was raised to 673 K.

Investigation of damaged interior walls using synchrotron-based XPS and XANES

Evidence of internal sulfate attack in field exposure was demonstrated by the damaged interior wall of a three-year-old house situated in Nakhon Ratchasima Province, Thailand. Partial distension of the mortar was clearly observed together with an expansion of a black substance. Removal of the black substance revealed a dense black layer. This layer was only found in the vicinity of the damaged area, suggesting that this black material is possibly involved in the wall cracking. By employing synchrotron-based X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) techniques, the unknown sample was chemically identified. The S 2p and O 1s XPS results mutually indicated the existence of sulfate species in the materials collected from the damaged area. The XANES results indicated the presence of ferrous (II) sulfate, confirming sulfate-induced expansion and cracking. The sulfate attack in the present case appeared to physically affect the structure whereas the chemical integrity at the molecular level of the calcium silicate hydrate phase was retained since there was a lack of spectroscopic evidence for calcium sulfate. It was speculated that internal sulfate probably originated from the contaminated aggregates used during the construction. The current findings would be beneficial for understanding the sulfate-attack mechanism as well as for future prevention against sulfate attack during construction.

Promotional Effects of Zn Doping on Cu/Core–Shell Al-MCM-41 for Selective Catalytic Reduction of NO with NH3

A Cu-Zn/core-shell Al-MCM-41 catalyst with various Cu and Zn species was investigated for selective catalytic reduction of NO with NH₃. The roles of Zn in the NOx adsorption properties and the acidity of the catalysts were studied by temperature-programmed desorption of NOx and in situ Fourier transform infrared spectroscopy of NO+O₂ adsorption and NH₃ adsorption. The presence of Zn can promote the number of acid sites and improve the NOx adsorption capacity by providing the additional sites for NOx adsorption and subsequent nitrite and nitrate formation. Based on the experimental results, a possible reaction pathway was suggested. Cu-Zn/Al-MCM-41 exhibited higher activity compared with that of Cu/Al-MCM-41, having an average NO conversion of 73%. However, the average NO conversion was increased to 77% when Zn was loaded as ZnO form instead of various Zn species. in situ X-ray adsorption near edge structure during reduction by H₂ revealed that there is a higher number of Cu+ in Cu-ZnO/Al-MCM-41 than that in Cu-Zn/Al-MCM-41. Under wet condition, the average NO conversion of Cu-ZnO/core-shell Al-MCM-41 was dropped to 68%. However, activity of Cu-ZnO/core-shell Al-MCM-41 was more stable than that of Cu-Zn/core-shell Al-MCM-41.

In Situ X-ray Absorption Near Edge Structure Study of Amorphous-TiO2 Phase Transformation.

The in situ X-ray absorption near edge structure (XANES) measurement and linear combination fitting were applied to monitor phase transformation of titanium dioxide. In this study, TiO2 (TiSG) was prepared by a sol-gel method.using titanium isopropoxide as a precursor. At low preparation temperature, the results revealed the formation of an amorphous structure. To obtain the anatase phase, the calcination at 843 K was necessary. Using phase fraction plot, TiO2 phase-transition can be observed at temperatures between 748 and 778 K and remain unchanged at 873 K.

Nanobiocomposite-Based Bienzyme Screen-Printed Electrode for Glucose Monitoring

Multi-walled carbon nanotubes (MWNTs) were coated first with methylene blue (MB) by noncovalent adsorption and then by horseradish peroxidase (HRP) and glucose oxidase (GOD) by covalent-linking. The MB-MWNTs/GOD/HRP composites formed stable films on screen-printed electrodes (SPE). The electrochemical and electrocatalytic behaviors of the bienzyme modified SPE were studied using cyclic voltammetry (CV) and amperometry. Using the MB-MWNT/GOD/HRP composites, glucose could be calibrated by amperometry at −0.35 V vs. SCE. The optimized response (at pH 7.0) had a sensitivity of 2.4 mA.M−1 and a limit of detection (3×S/N) of 35 µM. Tests of the portable bienzyme sensor demonstrate its imperviousness to the effects of ascorbic acid, uric acid and p-acetaminophen, as well as its ability to measure glucose concentrations ranging from 0.25 to 2 mM.