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Khoa, Nguyen Tri,Kim, Soon Wook,Yoo, Dae-Hwang,Cho, Shinuk,Kim, Eui Jung,Hahn, Sung Hong American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.6
<P>Heterostructures of gold-nanoparticle-decorated reduced-graphene-oxide (rGO)-wrapped ZnO hollow spheres (Au/rGO/ZnO) are synthesized using tetra-<I>n</I>-butylammonium bromide as a mediating agent. The structure of amorphous ZnO hollow spheres is found to be transformed from nanosheet- to nanoparticle-assembled hollow spheres (nPAHS) upon annealing at 500 °C. The ZnO nPAHS hybrids with Au/rGO are characterized using various techniques, including photoluminescence, steady-state absorbance, time-resolved photoluminescence, and photocatalysis. The charge-transfer time of ZnO nPAHS is found to be 87 ps, which is much shorter than that of a nanorod (128 ps), nanoparticle (150 ps), and nanowall (990 ps) due to its unique structure. The Au/rGO/ZnO hybrid shows a higher charge-transfer efficiency of 68.0% in comparison with rGO/ZnO (40.3%) and previously reported ZnO hybrids. The photocatalytic activities of the samples are evaluated by photodegrading methylene blue under black-light irradiation. The Au/rGO/ZnO exhibits excellent photocatalytic efficiency due to reduced electron–hole recombination, fast electron-transfer rate, and high charge-transfer efficiency.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-6/acsami.5b00152/production/images/medium/am-2015-00152a_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b00152'>ACS Electronic Supporting Info</A></P>
High Photoresponse in Conformally Grown Monolayer MoS<sub>2</sub> on a Rugged Substrate
Nguyen, Tri Khoa,Nguyen, Anh Duc,Le, Chinh Tam,Ullah, Farman,Tahir, Zeeshan,Koo, Kyo-in,Kim, Eunah,Kim, Dong-Wook,Jang, Joon I.,Kim, Yong Soo American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.47
<P>Conformal growth of atomic-thick semiconductor layers on patterned substrates can boost up the performance of electronic and optoelectronic devices remarkably. However, conformal growth is a very challenging technological task, since the control of the growth processes requires utmost precision. Herein, we report on conformal growth and characterization of monolayer MoS<SUB>2</SUB> on planar, microrugged, and nanorugged SiO<SUB>2</SUB>/Si substrates via metal-organic chemical vapor deposition. The continuous and conformal nature of monolayer MoS<SUB>2</SUB> on the rugged surface was verified by high-resolution transmission electron microscopy. Strain effects were examined by photoluminescence (PL) and Raman spectroscopy. Interestingly, the photoresponsivity (∼254.5 mA/W) of as-grown MoS<SUB>2</SUB> on the nanorugged substrate was 59 times larger than that of the planar sample (4.3 mA/W) under a small applied bias of 0.1 V. This value is record high when compared with all previous MoS<SUB>2</SUB>-based photocurrent generation under low or zero bias. Such enhancement in the photoresponsivity arises from a large active area for light-matter interaction and local strain for PL quenching, wherein the latter effect is the key factor and unique in the conformally grown monolayer on the nanorugged surface.</P> [FIG OMISSION]</BR>
High-temperature-treated multiwall carbon nanotubes for hydrogen evolution reaction
Nguyen, Tri Khoa,Bannov, Alexander G.,Popov, Maxim V.,Yun, Jong-Won,Nguyen, Anh Duc,Kim, Yong Soo Elsevier 2018 International journal of hydrogen energy Vol.43 No.13
<P><B>Abstract</B></P> <P>We investigated the hydrogen evolution reaction (HER) properties of multi-wall carbon nanotubes (MWCNTs) treated at extremely high temperature (2600 °C). The heat treatment not only improves the crystallinity of the MWCNTs, but also reduces the carbon-oxygen (CO) bonding as it is replaced by the defect-carbon (<I>sp</I> <SUP>3</SUP> and CH) bonding. These modifications in the heat treated MWCNT structure lead to the increase of electrochemical charge transfer. The heat treatment of MWCNTs in the composite with Pt (MWCNT-Pt composite) further facilitates electrocatalysis. The MWCNTs-Pt composite shows strong enhancement in the HER performance with an onset of overpotential of −0.04 V vs reversible hydrogen electrode and a Tafel slope of 10.9 mV/decade. This performance is indeed better than that of Pt, which is the best working material for HER.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heat treatment effects to reorder nanotube structures by connecting the broken crystals. </LI> <LI> CO bonding density is reduced and porosity properties are increased after heat treatment. </LI> <LI> Hydrogen evolution reaction (HER) performance is enhanced after heat treatment. </LI> <LI> Charge transfer resistance in HER is strongly decreased after heat treatment. </LI> <LI> Heat-treated MWCNT-Pt composite yields the excellent HER properties. </LI> </UL> </P>
Nguyen Tri Khoa,Su Min CHOI,윤종원,Soon Wook KIM,박수정,Shinuk Cho,Sung Hong HAHN,Yong Soo KIM,Eui Jung Kim 한국물리학회 2016 새물리 Vol.66 No.10
We investigate the negative effect on the performance of t dye-sensitized solar cell (DSSC) due to increased annealing time of a ZnO nanoparticle-assembled microsphere-based photoanode. Annealing at 600 $^\circ$C for 30 to 300 min causes an increase in the oxygen interstitial (O$_i$) density to occur in the ZnO crystals. The ZnO crystals prepared with different annealing times are applied as photoanode layers in DSSCs to study the effect of annealing time on the efficiency of the DSSC. The efficiency of DSSCs decreases with increasing annealing time because (1) the O$_i$ defects generated in the ZnO crystal reduce the photocurrent density of the device by trapping the photo-excited electrons that diffuse from the dye to the photoanode layer, and (2) the improvement in the necking between ZnO nanoparticles with increasing annealing time causes the adsorption of dye on the ZnO surface to diminish.
Yun Jong-Won,Nguyen Tri Khoa,Lee Sunghan,Kim Sungdo,Kim Yong Soo,Nguyen Tri Khoa,Nguyen Cao Khang,Ha Yang 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.10
The transport of charge carriers across the heterojunction of an optoelectronic device plays a crucial role in the performance of the device. This issue is particularly important in the area of heterogeneous metal-semiconducting photocatalysis in terms of harvesting the hot carriers generated under plasmonic resonance. This paper presents the results of a case study on the impact of electrochemical surface reduction on the transport properties of plasmonic electrons, which are generated on gold nanoparticles (Au NPs) under visible light irradiation to TiO2 nanorods (TiO2 NRs). Based on microscopic and spectroscopic characterizations, this study examined the subtle changes in the structural and the optical properties of the Au NPs/TiO2 NRs upon surface reduction of the oxygen layer which is ubiquitous on TiO2 NRs. These results suggest that the oxygen layer works as a blocking layer that limits the charge transfer efficiency of plasmonic electrons from Au to TiO2 and, consequently, reduces the device performance. The main thesis was verified directly by comparing the photocatalytic activities of pristine Au NPs/TiO2 NRs and Au NPs/reduced TiO2 NRs with methylene blue as a reference. The photocatalytic performance of the Au NPs/reduced TiO2 NRs was two times higher than that of the pristine one owing to the efficient charge transfer across the Au/TiO2 interface. This simple surface treatment can be employed widely to enhance the charge transport efficiency of various optoelectronic materials and devices derived from metal-semiconducting heterostructures.
김순욱,Nguyen Tri Khoa,Doan Van Thuan,Dinh Khoi Dang,허승현,김의정,한성홍 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.2
ZnO nanoparticle-assembled hollow spheres (raspberry-like) and elliptical nanorods (rice-like) were synthesized via a facile polyol process. Employing ethylene glycol as a polyol led to a ZnO nanoparticle-assembled hollow sphere structure, while diethylene glycol resulted in an elliptical nanorod structure. The ZnO hollow spheres had a higher Brunauer-Emmett-Teller (BET) surface area, better dye adsorption, more incident light trapping, and lower defect density than the ZnO elliptical nanorods. The ZnO hollow sphere-based dye-sensitized solar cells (DSSCs) exhibited a three-times higher current density than the ZnO elliptical nanorod-based DSSCs.
Van Thuan, Doan,Nguyen, Tri Khoa,Kim, Soon-Wook,Chung, Jin Suk,Hur, Seung Hyun,Kim, Eui Jung,Hahn, Sung Hong,Wang, Mingsong Elsevier 2017 CATALYSIS COMMUNICATIONS - Vol.101 No.-
<P><B>Abstract</B></P> <P>Oval-shaped graphene/ZnO quantum hybrid (GZQH) is synthesized via chemical-hydrothermal method and tested for the photoenhanced selective reduction of nitroarenes. A facile molecular fusion process is employed to produce graphene quantum dots (GQDs) from pyrene, which is followed by hydrothermal treatment with embryonic ZnO quantum dots (5nm in size) to yield the GZQHs. Zn<SUP>2+</SUP> ions on ZnO embryo react with a functional group of graphene, which forms Zn-O-C bonding leading to highly crystalline quantum hybrids with uniform interface. The GZQHs have a quenched photoluminescence intensity as compared to the GQDs (2nm in size) due to electron transfer at the graphene-ZnO interface. Hydrogen molecules dissociate into hydrogen atoms by photogenerated electrons which transfer and perturb at the interface under UV irradiation. The GZQHs exhibit an excellent UV-induced catalytic performance for the selective reduction of nitroarenes. The effect of ZnO:graphene ratio on reduction reaction rate constant is also investigated.</P> <P><B>Highlight</B></P> <P> <UL> <LI> Excellent hydrogenation reduction of noble-metal-absent catalyst: Graphene and ZnO. </LI> <LI> Graphene and zinc oxide composite at the quantum scale particle synthesis. </LI> <LI> Hydrogen dissociation at G/ZnO interface and spillover to graphene. </LI> <LI> UV stimulated electron transfer and perturbation within Gr/ZnO. </LI> <LI> Catalytic dependence of NaBH<SUB>4</SUB> and Gr/ZnO ratio and reduction of different nitroarenes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Mental Health Among Healthcare Workers During the COVID-19 Pandemic in Vietnam
Nhan Phuc Thanh Nguyen,Ha Phan Ai Nguyen,Cao Khoa Dang,Minh Tri Phan,Huynh Ho Ngoc Quynh,Van Tuan Le,Chinh Van Dang,Tinh Huu Ho,Van Trong Phan,Van Trong Phan,Thang Phan,Dang Thi Anh Thu 대한예방의학회 2024 예방의학회지 Vol.57 No.1
Objectives: The objective of this study was to characterize mental health issues among Vietnamese healthcare workers (HCWs) and to identify related factors.Methods: A cross-sectional study was conducted with 990 HCWs in 2021. Their mental health status was measured using the Depression, Anxiety, and Stress Scale.Results: In total, 49.9%, 52.3%, and 29.8% of respondents were found to have depression, anxiety, and stress, respectively. The multivariable linear regression model revealed that factors associated with increased anxiety scores included depression scores (β, 0.45; 95% confidence interval [CI], 0.39 to 0.51) and stress scores (β, 0.46; 95% CI, 0.41 to 0.52). Factors associated with increased depression scores included being frontline HCWs (β, 0.57; 95% CI, 0.10 to 1.10), stress scores (β, 0.50; 95% CI, 0.45 to 0.56), and anxiety scores (β, 0.41; 95% CI, 0.36 to 0.47), while working experience was associated with reduced depression scores (β, -0.08; 95% CI, -0.16 to -0.01). Factors associated with increased stress scores included working experience (β, 0.08; 95% CI, 0.00 to 0.16), personal protective equipment interference with daily activities (β, 0.55; 95% CI, 0.07 to 1.00), depression scores (β, 0.54; 95% CI, 0.48 to 0.59), and anxiety scores (β, 0.45; 95% CI, 0.39 to 0.50), while age was associated with reduced stress scores (β, -0.12; 95% CI, -0.20 to -0.05).Conclusions: Specific interventions are necessary to enhance and promote the mental health of HCWs so they can successfully cope with the circumstances of the pandemic.