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Structural and photocatalytic properties and X-ray absorption spectroscopic study of BiVO4 nanoparticles incorporated with Fe synthesized by sonochemical method
(2022-11-01)
Wechprasit, Tirapat
;
Bootchanont, Atipong
;
Sailuam, Wutthigrai
;
Wattanawikkam, Chakkaphan
;
Kansaard, Thanaphon
In this work, Fe-incorporated BiVO<inf>4</inf> nanoparticles with different Fe-loading contents (0–4%) were synthesized via one-step sonochemical process. Crystal structure of all samples was investigated by X-ray diffraction technique (XRD). XRD patterns obviously show the main structure of monoclinic BiVO<inf>4</inf> structure. The secondary phase is found in the form of Fe-based oxide as a hematite Fe<inf>2</inf>O<inf>3</inf> phase at for Fe-loading contents ≥ 2%. Relevant chemical bonding of as-synthesized samples was carried out by Raman spectroscopy indicating the fundamental vibration with various vibration modes of VO<inf>4</inf>3− tetrahedron and V–O band, respectively. Morphological structure of pure BiVO<inf>4</inf> shows rod-like structure while 1–4%Fe-incorporated BiVO<inf>4</inf> display different morphologies. The chemical compositions and oxidation numbers of all elements of the samples were carried out via X-ray photoelectron spectroscopy (XPS). XPS spectra indicate the existence of all elements on their surface and the oxidation states of all elements are clearly scrutinized. Local structure of all samples was investigated to interrogate the local atomic site of Fe atoms by X-ray absorption spectroscopy (XAS). The normalized Fe K-edge XANES spectra of all samples indicate that the local atomic site of Fe atoms would not replace in local sites of either Bi or V sites in BiVO<inf>4</inf> crystal verified by simulated XANES spectra. However, the specific features of measured XANES spectra of all samples corresponds to the Fe K-edge XANES spectra of Fe<inf>2</inf>O<inf>3</inf> and BiFeO<inf>3</inf> structure suggesting that local structure of all samples are formed to Fe-based oxide between Fe<inf>2</inf>O<inf>3</inf> and BiFeO<inf>3</inf> structure. Fitting EXAFS spectra of 1–4%Fe-incorporated were practically conducted by artemis program with Fe<inf>2</inf>O<inf>3</inf> and BiFeO<inf>3</inf> used as structural models to identify local atomic environment of Fe atoms. Results show agreeable fitting with their structural models and reveal pertinent information of localization of Fe atoms. Optical properties of the samples were analyzed by UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). DRS results exhibit the absorption edge in visible range of all samples. Meanwhile, influence of Fe loading contents into pure BiVO<inf>4</inf> displays to confirm the red-shift on the absorption edge in visible range to higher wavelength, which suggests the lower optical band gap of pure BiVO<inf>4</inf>. The optimized photocatalytic degradation of RhB was performed by 4%Fe–BiVO<inf>4</inf> with 82% decolorization under visible-light irradiation within 10 min and exhibited rate constant at 0.150 min−1.
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Phase evolution in annealed Ni-doped WO3 nanorod films prepared via a glancing angle deposition technique for enhanced photoelectrochemical performance
(2022-05-15)
Wattanawikkam, Chakkaphan
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Bootchanont, Atipong
;
Porjai, Porramain
;
Jetjamnong, Chanthawut
;
Kowong, Rattanachai
Ni-doped WO<inf>3</inf> nanorod films were fabricated via a reactive magnetron cosputtering with a glancing angle deposition technique. The crystal structure and surface morphology were observed using grazing incident X-ray diffraction and field emission Scanning Electron Microscopy, respectively. The chemical compositions and oxidation state of each element were investigated by X-ray photoemission spectroscopy. The local structure and phase evolution were investigated via X-ray absorption spectroscopy. The local structure of Ni atoms in WO<inf>3</inf> nanorod films is characterized as a NiWO<inf>4</inf> nanocluster in the WO<inf>3</inf> matrix, which is supported by calculated spectra. The phase information obtained after annealing demonstrates that short-length order in amorphous transitions to crystallinity. The phase information of the local structures were acquired and discussed as well as the effect on the annealing process. The coupling of amorphous WO<inf>3</inf>, crystalline WO<inf>3</inf>, and amorphous NiWO<inf>4</inf> exhibits high photoelectrochemical activity of the sample annealed at 400 °C, which was observed with a large current density (2.35 μA/cm2) at 1.20 V vs. Ag/AgCl under visible light irradiation, which is greater than that of the unmodified WO<inf>3</inf> photoelectrode (1.38 μA/cm2).
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Effect of thermal annealing on the structure of LiCoO2 powders prepared by co-precipitation method
(2021-12-01)
Khejonrak, Awadol
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Chanlek, Narong
;
Sukkha, Usa
;
Triamnak, Narit
;
Chirawatkul, Prae
Lithium cobalt oxide (LiCoO<inf>2</inf>) powder was prepared by co-precipitation method and annealed at different temperatures of between 300 and 700 °C. The effect of annealing temperature and effect washing process with deionized water on the crystal structures of the prepared LiCoO<inf>2</inf> powders were thoroughly studied by Synchrotron powder X-Ray Diffraction (Syn-XRD), X-ray Absorption Spectroscopy (XAS), Dispersive Raman Microscopy (Raman) techniques. The change in chemical composition as a function of annealing temperature was also investigated by X-ray Photoelectron Spectroscopy (XPS) technique. The crystal structural results identified the phase evolution of the prepared LiCoO<inf>2</inf> powders upon heat treatment. The formation of HT-LiCoO<inf>2</inf> phase was observed at annealing temperature as low as 300 °C.
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Simultaneous O2 plasma and thermal treatment for improved surface conductivity of Cu-Doped SnO2 films
(2019-08-01)
Somjaijaroen, Natthawirot
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Sakdanuphab, Rachsak
;
Chanlek, Narong
;
Chirawatkul, Prae
;
Sakulkalavek, Aparporn
Cu-doped SnO<inf>2</inf> thin films were deposited on a glass substrate using radio frequency magnetron sputtering. The effects of varying the O<inf>2</inf> partial pressure during the deposition process and post-O<inf>2</inf> plasma treatment at 420 °C were investigated. Bulk and surface oxidation states were measured by X-ray absorption near-edge structure spectroscopy and X-ray photoelectron spectroscopy. The as-deposited films exhibited oxygen deficient compositions and Cu+ or Cu2+ ions, which depend on the deposited O<inf>2</inf> partial pressure. After the post-plasma treatment, the films changed from an amorphous structure into a low crystalline film. X-ray diffraction results indicated substitutional doping, wherein some Sn4+ ions were replaced with Cu+ or Cu2+ ions. The O<inf>2</inf> plasma treatment can remove Cu2+ and O2− from the film surface. The oxygen deficiency defects and Cu+- or Cu2+- doped present at the surface are the key factors in controlling the sheet resistance of the Cu-doped SnO<inf>2</inf> film. The minimum sheet resistance was obtained after the plasma treatment of the films deposited at a 2% O<inf>2</inf> partial pressure.

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