Browsing by Author "Thanh Binh Nguyen"

Now showing 1 - 4 of 4

Enhanced catalytic reduction of nitrophenols by sodium borohydride over highly recyclable Au@graphitic carbon nitride nanocomposites
(2019-01-01)
Thanh Binh Nguyen
;
Huang, C. P.
;
Doong, Ruey-an
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a photochemical green synthesis using thermal exfoliation process is developed to fabricate Au@graphitic carbon nitride (g-C3N4) nanocomposite, highly recyclable and reusable, for the catalytic reduction of nitrophenols by NaBH4. Au nanoparticles (Au NPs) in the diameter of 5-15 nm are deposited onto the surface of g-C3N4 in 3-6 layers of structure. The synthesized Au@g-C3N4 nanocomposites exhibit excellent catalytic activity and stability in the reduction of nitrophenols including 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-nitrophenol, and 2,4,6-nitriophenol. The catalytic performance of Au@g-C3N4 is highly dependent on the initial nitrophenol concentration, Au loading, inorganic anions, and pH. The rate constant of 4-nitrophenol reduction over Au@g-C3N4 (2 wt%) is 26.4 times that of pure Au NP in the presence of 7 mM of NaBH4 at pH 5. Moreover, Au@g-C3N4 can be reused for at least 10 consecutive cycles without considerable loss of catalytic activity. The presence of anions (0.1 M) such as H2PO4-, SO42-, HCO3-, and NO3- decreases the rate of 4-nitrophenol reduction by a factor of 1.2-8.8; whereas there is a 1.2-time increase in rate constant upon the addition of Cl- ion. The detection of H-center dot radical adducts indicates that Au NPs adsorbs BH4- ions and forms Au-H species. The porous and conductive g-C3N4 provides large surface area for nitroarene adsorption and subsequent electron transfer from the Au-H species to 4-nitrophenol, which results in accelerating the reduction of 4-nitrophenol. Results clearly demonstrate that Au@g-C3N4 is a promising green catalyst of enormous potential for nitroaromatic reduction, which provides a new venue for tailoring Au-based nanomaterials in elucidation of a wide variety of heterogeneous catalytic reactions.
Fabrication of highly visible-light-responsive ZnFe2O4/TiO2 heterostructures for the enhanced photocatalytic degradation of organic dyes
(2016-01-01)
Thanh Binh Nguyen
;
Doong, Ruey-an
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, a novel visible-light-sensitive ZnFe2O4-TiO2 photocatalyst has been fabricated by coupling 0.2-2 wt% p-type ZnFe2O4 narrow bandgap material with n-type anatase TiO2 for the enhanced photocatalytic degradation of organic dyes under 465 nm visible light irradiation. Transmission electron microscopy (TEM) and high resolution TEM confirm that ZnFe2O4 and TiO2 are strongly linked with an average particle size of 8-9 nm, leading to a decrease in hole-electron recombination rate as well as the enhanced photocatalytic activity of the ZnFe2O4-TiO2 heterostructures under visible light irradiation. The optimized 1 wt% ZnFe2O4 not only significantly extends the absorption edge of TiO2-based heterostructures to the visible light region but can also retain a stable photodegradation efficiency of >99% for at least 5 cycles. In addition, the photocatalytic activity of ZnFe2O4-TiO2 toward dye decomposition follows the order cationic rhodamine B > neutral methyl red > anionic methyl orange. Our results clearly demonstrate that the coupling of a low loading mass of ZnFe2O4 with anatase TiO2 is a reliable green technology approach to prepare visible-light-responsive heterostructure photocatalysts with great potential for application in the decomposition of organic dyes and other emerging pollutants in the treatment of water and wastewater.
Heterostructured ZnFe2O4/TiO2 nanocomposites with a highly recyclable visible-light-response for bisphenol A degradation
(2017-01-01)
Thanh Binh Nguyen
;
Doong, Ruey-an
;
環境工程研究所
;
Institute of Environmental Engineering
Novel visible-light-sensitive ZnFe2O4-TiO2 heterojunction photocatalysts are successfully fabricated by a facile solvothermal method for the enhanced photocatalytic degradation of bisphenol A (BPA) under different light sources. The photocatalytic degradation efficiency and rate of BPA by ZnFe2O4-TiO2 under the irradiation of different light sources follow the order 465 nm visible light > solar simulator > 365 nm UV light. The reaction rate of BPA by ZnFe(2)O(4-)TiO2 in the presence of 465 nm visible light is 42 times higher than that under 365 nm UV light irradiation. In addition, the ZnFe2O4-TiO2 nanocomposites exhibit excellent recycling and reusability and can retain their stable photocatalytic activity toward BPA photodegradation for at least 10 cycles of reaction with rate constants of 0.191-0.218 min(-1) under visible light irradiation. The photogenerated holes as well as oxygen-containing radicals are identified to be the predominant reactive species responsible for the photodegradation of BPA in the ZnFe2O4-TiO2 system. The possible reaction mechanisms for BPA photodegradation by p-n heterojunction ZnFe2O4-TiO2 are also proposed. Results obtained in this study clearly demonstrate the superior visible-light-driven photoactivity of ZnFe2O4-TiO2 toward BPA photodegradation and can open an avenue to fabrication of p-n heterojunctions of photocatalysts with a wide variety of potential applications in the fields of photocatalysis, water splitting and energy conversion.
Photocatalytic degradation of bisphenol A over a ZnFe2O4/TiO2 nanocomposite under visible light
(2019-01-01)
Thanh Binh Nguyen
;
Huang, C. P.
;
Doong, Ruey-an
;
環境工程研究所
;
Institute of Environmental Engineering
A ZnFe2O4-TiO2 nanocomposite combining p-type ZnFe2O4 and n-type TiO2 was successfully fabricated. The ZnFe2O4-TiO2 nanocomposite greatly enhanced the bisphenol A (BPA) photodegradation under visible light irradiation at 465 +/- 40 nm. Loading TiO2 with 1 wt% of ZnFe2O4 produced high photocurrent and low charge transfer resistance. The photodegradation rate of BPA by ZnFe2O4-TiO2, which was highly dependent on the water chemistry including pH, anions, and humic acid, was 20.8-21.4 times higher than that of commercial TiO2 photocatalysts. Chloride and sulfate ions enhanced BPA photodegradation mostly due to the production of more radical species; whereas nitrate, dihydrogen phosphate, and bicarbonate ions decreased the photodegradation rate of BPA due to the scavenge of hydroxyl radicals. The photoactivity and recyclability of ZnFe2O4-TiO2 in lake water was also assessed. A near complete BPA removal from lake water was observed under visible light irradiation. Furthermore, >90% of photocatalytic activity toward BPA degradation was achieved in 5 cycles of continuous addition of BPA to the lake water. The BPA degradation intermediates were identified by HPLC/MS/MS and possible reaction pathways were proposed. Results clearly demonstrate the excellent visible-light-sensitive photocatalytic degradation of BPA over ZnFe2O4-TiO2 composite which has a great application potential for the decomposition of emerging contaminants in impaired waters. (c) 2018 Published by Elsevier B.V.