Browsing by Author "Nguyen Dang Phu"

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Control of crystal phase of BiVO4 nanoparticles synthesized by microwave assisted method
(2016-06)
Nguyen Dang Phu
;
Luc Huy Hoang
;
Pham Khac Vu
;
Kong, Meng-Hong
;
Chen, Xiang-Bai
Different crystalline phases BiVO4 nanoparticles (tetragonal-zircon, monoclinic-scheelite, and tetragonal-zircon/monoclinic-scheelite heterophase) have been prepared by fast microwave assisted method and annealing treatment. For the heterophase, the ratio of tetragonal-zircon and monoclinic-scheelite phases can be well controlled by controlling the annealing temperature. Furthermore, a tight interface junction has been formed between tetragonal-zircon BiVO4 and monoclinic-scheelite BiVO4 in a nanosize level. This tight interface junction can modify the electronic structure of BiVO4 nanoparticles, which would be very helpful for achieving high photocatalytic activity.
Growth and optical properties of ZnTe quantum dots on ZnMgSe by molecular beam epitaxy
(2015-09-01)
Fan, W. C.
;
Huang, S. H.
;
Chou, W. C.
;
Tsou, M. H.
;
Yang, C. S.
Self-assembled type-II ZnTe quantum dots (QDs) were grown on GaAs (0 0 1) substrates with Zn1-xMgxSe (x=0.24 and 0.52) buffer layers by molecular beam epitaxy. The optical properties of ZnTe QDs were investigated by low-temperature photoluminescence (PL) and time-resolved PL. An abrupt variation of the PL peak energy with coverage implies the existence of wetting layer of 3.2 MLs and 40 MLs for the Mg concentration x=0.24 and 0.52, respectively. The thickness of wetting layer is larger than that of Zaire QDs grown on ZnSe buffer layers because the strain between ZaTe and Zn1-xMgxSe is smaller. The non-mono-exponential decay profiles reflect the processes of carrier transfer and recapture. The Kohlrausch\'s stretching exponential well fits the decay profiles of ZaTe/Zn1-xMgxSe QDs. (C) 2015 Elsevier B.V. All rights reserved.
Photocatalytic activity enhancement of Bi2WO6 nanoparticles by Ag doping and Ag nanoparticles modification
(2020-05-25)
Nguyen Dang Phu
;
Luc Huy Hoang
;
Pham Van Hai
;
Tran Quang Huy
;
Chen, Xiang-Bai
Bi2WO6 nanoparticles doped with Ag, and modified with Ag nanoparticles, were successfully prepared using a two-step microwave assisted and hydrothermal synthesis. With Ag doping, the Bi ions were substituted by the dopant Ag ions in the host lattice structure of Bi2WO6. With Ag nanoparticles modification, the Ag nanoparticles grew on the surface of the Bi2WO6 nanoparticles without changing the host lattice structure. The photocatalytic activities of the samples were studied by visible light irradiation of rhodamine B. Both the Ag doping and the Ag nanoparticles modification enhanced the photocatalytic activity of the Bi2WO6 nanoparticles. Moreover, Ag nanoparticles modification produced a more than two times higher enhancement of the photocatalytic activity than the Ag doping method. Furthermore, a mechanism of the significant photocatalytic activity enhancement by Ag nanoparticles modification is proposed. (C) 2020 Elsevier B.V. All rights reserved.
Photocatalytic activity enhancement of Bi2WO6 nanoparticles by Gd-doping via microwave assisted method
(2017-08-01)
Luc Huy Hoang
;
Nguyen Dang Phu
;
Pham Do Chung
;
Guo, Peng-Cheng
;
Chen, Xiang-Bai
Gd-doped Bi2WO6 nanoparticles were successfully prepared through microwave assisted synthesis. The incorporation of Gd3+ ions into Bi2WO6 crystallite was analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The optical properties of the nanoparticles were characterized by UV-Vis absorption and photoluminescence spectroscopy. The photocatalytic activity of the nanoparticleswas investigated by degradation of Rhodamine B under visible-light irradiation. Our results showed that Gd-doping plays an important role for enhancing the visible light photocatalytic activity, and the enhanced photocatalytic activity of Gd-doped Bi2WO6 nanoparticles would be mainly correlated with the effective decrease of recombination rate of photogenerated electron-hole pairs.
Study of extending carrier lifetime in ZnTe quantum dots coupled with ZnCdSe quantum well
(2018-03-01)
Fan, W. C.
;
Chou, W. C.
;
Lee, J. D.
;
Lee, Ling
;
Nguyen Dang Phu
We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupled with a type-I Zn0.88Cd0.12Se/ZnSe quantum well (QW) on the (001) GaAs substrate by molecular beam epitaxy (MBE). As the spacer thickness is less than 2 nm, the carrier lifetime increasing from 20 ns to nearly 200 ns was successfully achieved. By utilizing the time-resolved photoluminescence (TRPL) and PL with different excitation power, we identify the PL emission from the coupled QDs consisting of two recombination mechanisms. One is the recombination between electrons in ZnSe barrier and holes confined within ZnTe QDs, and the other is between electrons confined in Zn0.88Cd0.12Se QW and holes confined within ZnTe QDs. According to the band diagram and power-dependent PL, both of the two recombinations reveal the type-II transition. In addition, the second recombination mechanism dominates the whole carrier recombination as the spacer thickness is less than 2 nm. A significant extension of carrier lifetime by increasing the electron and hole separation is illustrated in a type-II ZnTe/ZnSe QD structure coupling with a type-I ZnCdSe/ZnSe QW. Current sample structure could be used to increase the quantum efficient of solar cell based on the II-VI compound semiconductors.
Study of photocatalytic activities of Bi2WO6 nanoparticles synthesized by fast microwave-assisted method
(2015-10-25)
Nguyen Dang Phu
;
Hoang, Luc Huy
;
Chen, Xiang-Bai
;
Kong, Meng-Hong
;
Wen, Hua-Chiang
We present a study of photocatalytic activities of Bi2WO6 nanoparticles synthesized by fast microwave-assisted method. The photocatalytic activities of the nanoparticles were evaluated by the decolorization of methylene-blue under visible-light-irradiation. Our results show that the surface area of Bi2WO6 nanoparticles plays a major role for improving photocatalytic activity, while visible-light absorption has only a weak effect on photocatalytic activity. This suggests efficient transportation of photo-generated electrons and holes to the oxidation active sites on the surface of nanoparticles, indicating Bi2WO6 nanoparticles synthesized by fast microwave-assisted method are promising for achieving high photocatalytic activity under visible-light-irradiation. (C) 2015 Elsevier B.V. All rights reserved.
Study of photocatalytic activities of Bi2WO6/BiVO4 nanocomposites
(2017-09-01)
Nguyen Dang Phu
;
Luc Huy Hoang
;
Guo, Peng-Cheng
;
Chen, Xiang-Bai
;
Chou, Wu Ching
The Bi2WO6/BiVO4 nanocomposites were successfully synthesized using fast microwave assisted method. The photocatalytic activities of Bi2WO6/BiVO4 nanocomposites were evaluated by the degradation of Rhodamine B under visible irradiation. The optimal BiVO4 content of 30% was observed for improving the photocatalytic activity of Bi2WO6/BiVO4 nanocomposites, and the mechanism of photocatalytic activity enhancement was investigated. Our results suggest that for the Bi2WO6/BiVO4 nanocomposites, particle surface area plays the most important role for improving photocatalytic activity, and electron-hole recombination rate plays more important role than amount of light absorbed by nanocomposites for improving photocatalytic activity. [GRAPHICS]
Synthesis and characterization of MnWO4 nanoparticles encapsulated in mesoporous silica SBA-15 by fast microwave-assisted method
(2015-02-01)
Luc Huy Hoang
;
Pham Van Hanh
;
Nguyen Dang Phu
;
Chen, Xiang-Bai
;
Chou, Wu Ching
The MnWO4 nanoparticles encapsulated in mesoporous silica (MnWO4/SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO4/SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO4 nanoparticles were successfully distributed into the channels of SBA-15. The size of MnW04 nanoparticles in SBA-15 is significantly smaller than the size of MnWO4 nanoparticles prepared without SBA-15, indicating that the MnWO4/SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO4 nanoparticles. (C) 2014 Elsevier Ltd. All rights reserved.