Browsing by Author "Le Trung Hieu"

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Enhanced Photocatalytic Performance of Nitrogen-Doped TiO2 Nanotube Arrays Using a Simple Annealing Process
(2018-12-01)
Phuoc Huu Le
;
Le Trung Hieu
;
Tu-Ngoc Lam
;
Nguyen Thi Nhat Hang
;
Nguyen Van Truong
Nitrogen-doped TiO2 nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N-2 gas at 450 degrees C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH4F/ethylene glycol solution. The N-doping concentration (0-9.47 at %) can be varied by controlling N-2 gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light ( 400 nm) illumination at 120 mWcm(-2). N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h(-1), which was a 125% improvement over that of TNAs (0.115 h(-1)). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electronhole recombination rate.
The antioxidant activity of natural diterpenes: theoretical insights
(2020-04-15)
Vo, Quan V.
;
Nguyen Minh Tam
;
Le Trung Hieu
;
Mai Van Bay
;
Nguyen Minh Thong
Diterpenes that were isolated from Crossopetalum gaumeri (Loes.) Lundell (Celastraceae) plants are reported to exhibit a range of biological activities, in particular as radical scavengers. Thus further insight into the antioxidant activity of diterpenes in physiological environments is much needed but not studied yet. In this study, the antioxidant activity of nine natural diterpenes was evaluated using kinetic and thermodynamic calculations. It was found that the sequential proton loss electron transfer (SPLET) mechanism is favored in polar environments, whereas formal hydrogen transfer (FHT) is the main pathway for the radical scavenging of these diterpenes in the gas phase as well as in lipid media. The rate constants for the HOO & x2d9; radical scavenging of these compounds in the gas phase, polar and nonpolar solvents are in the range of 2.29 x 10(-2) to 4.58 x 10(7), 9.74 x 10(-3) to 1.67 x 10(8) and 3.54 x 10(-5) to 1.31 x 10(5) M-1 s(-1), respectively. 7-Deoxynimbidiol (6), exhibits the highest HOO & x2d9; radical scavenging with k(overall) = 1.69 x 10(8) M-1 s(-1) and 9.10 x 10(4) M-1 s(-1) in water and pentyl ethanoate solvents, respectively, that is about 1300 times higher than that of Trolox in polar environments. It is thus a promising natural antioxidant in physiological environments.