Browsing by Author "Nhat Huy Nguyen"

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Effect of washing pH on the properties of titanate nanotubes and its activity for photocatalytic oxidation of NO and NO2
(2015-11-15)
Nhat Huy Nguyen
;
Bai, Hsunling
;
環境工程研究所
;
Institute of Environmental Engineering
This study reports for the first time on the role of contaminant sodium to neutralize the acidic reaction products during the NOx photocatalytic reaction and prevent surface deactivation of TNTs (titanate nanotubes and their derived materials). TNTs were synthesized by the hydrothermal method and washed under different pH values. The materials were then characterized by SEM, TEM, BET, ICP, TPD, and XRD analyses. The photocatalytic oxidations of NO and NO2 were tested under the ambient condition to evaluate the activity of the materials. The results showed that the value of washing pH was an effective control factor for achieving TNTs with desired microstructure and physical-chemical properties. In the photocatalytic removals of NO and NO2, it revealed that both of the Na content and the structure of TNTs materials play important roles on the NOx removal pathway, initial efficiency and decay rate. The highest efficiencies were achieved by TNTs washed at pH 3-5 (T-3-5), which may be due to their high amount of crystalline anatase for photocatalytic reaction and high sodium content for neutralization of acidic products. The mechanism based on the neutralization of the HNO3 resultant from the NOx photo-oxidation was also proposed. (C) 2015 Elsevier B.V. All rights reserved.
Photocatalytic reduction of CO2 using molybdenum-doped titanate nanotubes in a MEA solution
(2015-01-01)
Wu, Hung-Yu
;
Nhat Huy Nguyen
;
Bai, Hsunling
;
Chang, Sue-min
;
Wu, Jeffrey C. S.
In this study, the photocatalytic reduction of CO2 in a monoethanolamine solution to form valuable energy sources was investigated using Mo-doped TNTs photocatalysts for the first time. The results revealed that the structure of Mo-doped TNTs changed with the increase of calcination temperature. For Mo-doped TNTs calcined at 500 degrees C, the partial corruption of titanate nanotubes into anatase particles caused the reduction of Mo species from Mo6+ to Mo5+ and produced oxygen vacancies, which resulted in the highest CO2 reduction ability. The yield rates of CH4, CO and total combustible organic compounds were 0.52, 10.41 and 13.53 mu mol g(cat)(-1), respectively, under UVA (8 W, 63 mu W cm(-2)) irradiation. The photoreduction quantum efficiencies of CH4 and CO were achieved at 0.036% and 0.180%, respectively. It was found that the molybdenum structure and oxygen vacancies could be the key factors controlling the photocatalytic reduction efficiency of CO2. A possible structure transformation of Mo-doped TNTs at different calcination temperatures was inferred and the reaction mechanism for photocatalytic CO2 reduction with oxygen vacancy sites of Mo-doped TNTs was proposed.
Photocatalytic reduction of NO2 and CO2 using molybdenum-doped titania nanotubes
(2015-06-01)
Nhat Huy Nguyen
;
Wu, Hung-Yu
;
Bai, Hsunling
;
環境工程研究所
;
Institute of Environmental Engineering
The preparation of molybdenum-doped hydrothermal titania nanotubes (Mo-doped TNTs) and its special photocatalytic reduction activity on NO2 and CO2 gases are reported for the first time. The TNTs photocatalysts were synthesized by hydrothermal method while Mo metal species was doped at different process steps corresponding to three fabrication methods: hydrothermal, precipitation, and impregnation. The materials were then characterized by BET, SEM, TEM, ICP, TPD, XPS, UV-Vis adsorption, and XRD analyses. The results indicated that Mo doping was successful by precipitation and impregnation, but not by the conventional hydrothermal method. It also revealed that the doping of Mo did not considerably affect the morphology, microstructure, and crystalline structure. However, it moderately changed the electronic band structure as well as surface acidity and basicity of the TNTs materials. The NO2 photocatalytic reaction results showed that the doping of Mo sharply declined the oxidation ability of TNTs while surprisingly enhanced its reduction ability. The CO2 reduction results further confirmed this special reduction ability of Mo-doped TNTs, which produced much higher yields of methane and carbon monoxide. The photocatalytic reaction results of both NO2 and CO2 showed that Mo-doped TNTs prepared by the precipitation method provided the highest reduction ability, which may be due to its chemical oxidation states of Mo4+ and Mo5+. (C) 2015 Elsevier B.V. All rights reserved.
Photocatalytic removal of NO and NO2 using titania nanotubes synthesized by hydrothermal method
(2014-05-01)
Nhat Huy Nguyen
;
Bai, Hsunling
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, the photocatalysts of titania nanotubes (TNTs) were synthesized at different calcination temperatures using commercial Degussa TiO2 (P25) as a precursor. The materials were then characterized by BET, SEM, TEM, and XRD analyses. The photocatalytic reactions with NO and NO2 under UV-A irradiation were both performed. The results showed that the photocatalytic reaction rate of NO was much faster than that of NO2, and the conversion of NO2 to nitrate was the rate-limiting step for photocatalytic removal of NOx if the nitrate produced cannot be removed continuously from the photocatalyst surface. For TNTs calcined at different temperatures, a significant enhancement was observed on the total NOx removal efficiency by TNT calcined at 500 degrees C for both NO and NO2 photocatalytic reaction, which could be attributed to its high anatase crystallinity as well as high surface area. These two factors affect primarily on the NO2 conversion step in which the high anatase crystallinity could be responsible for the high efficiency at the beginning, while the high surface area could be accounted for retaining this high efficiency from nitric acid poisoning during the test period.