A facile thermal evaporation route for large-area synthesis of tin oxide nanowires: Characterizations and their use for liquid petroleum gas sensor

Nguyen Van Hieu,Le Thi Ngoc Loan,Nguyen Duc Khoang,Nguyen Tuan Minh,Do Thanh Viet,Do Cong Minh,Tran Trung,Nguyen Duc Chien 한국물리학회 2010 Current Applied Physics Vol.10 No.2

In this paper, a very simple procedure was presented for the reproducible synthesis of large-area SnO2nanowires (NWs) on a silicon substrate by evaporating Sn powders at temperatures of 700, 750, and 800 ℃. As-obtained SnO2 NWs were characterized by field emission scanning electron microscopy (FESEM),transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. They revealed that the morphology of the NWs is affected by growth temperature and the SnO2 NWs are single-crystalline tetragonal. The band gap of the NWs is in the range of 4.2–4.3 eV as determined from UV/visible absorption. The NWs show stable photoluminescence with an emission peak centered at around 620 nm at room-temperature. The sensors fabricated from the SnO2 NWs synthesized at 700 ℃ exhibited good response to LPG (liquefied petroleum gas) at an operating temperature of 400 ℃.

Optimization of the eco-friendly synthesis of graphene oxide from graphite using Plackett–Burman and Box–Behnken models for industrial production orientation

Phuc Nguyen Thien,Giang Nguyen Thi Huong,An Vu Nguyen Thien Truong,Nam Nguyen Thanh Hoai,Anh Ly Duc,Nguyen Huynh Cam,An Hoang,Phong Mai Thanh,Hieu Nguyen Huu 한국탄소학회 2023 Carbon Letters Vol.33 No.2

In this study, graphene oxide (GO) was synthesized by the improved Hummers’ method. The degree of oxidation from graphite (Gi) to GO was determined through interlayer spacing calculated from X–ray diffraction. Besides, the effect of KMnO4:Gi ratios (X1), H2SO4 volume (X2), oxidation temperature (X3), oxidation time of stage 1 (X4), and oxidation time of stage 2 (X5) was screened by the Plackett–Burman model. The simultaneous impact of three factors that influenced the degree of oxidation (X1, X2, and X3) was studied by the Box–Behnken experimental model of response surface methodology to achieve suitable conditions for the GO synthesis process. The characterization of GO product was investigated via the modern analytical methods: X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. In addition, the study was also carried out on a pilot scale for orientation in industrial application with the yield of 14 g/batch.

Gas sensor based on nanoporous hematite nanoparticles: Effect of synthesis pathways on morphology and gas sensing properties

Nguyen Duc Cuong,Tran Thai Hoa,Dinh Quang Khieu,Nguyen Duc Hoa,Nguyen Van Hieu 한국물리학회 2012 Current Applied Physics Vol.12 No.5

The development of a low cost and scalable gas sensor for the detection of toxic and flammable gases with fast response and high sensitivity is extremely important for monitoring environmental pollution. In this work, we introduce two different synthesis pathways for the preparation of scalable Fe2O3nanoparticles for gas sensor applications. One is co-precipitation and the other is hydrothermal method. The gas sensing properties of the a-Fe2O3 nanoparticles (NPs) fabricated by different synthesis pathways were studied and compared. The performance of the NPs in the detection of toxic and flammable gases such as carbon dioxide, ammonia, liquefied petroleum gas, ethanol, and hydrogen was evaluated. The Fe2O3 NP-based gas sensors exhibited high sensitivity and a response time of less than a minute to analytic gases. However, the NPs fabricated by the one-step direct method exhibited higher sensitivities than those generated by the a-Fe2O3 NPs obtained by co-precipitation synthesis possibly because of their nanoporous structure. This performance is attributed to the large specific surface area of the NPs, which results in higher sensitivity. The development of a low cost and scalable gas sensor for the detection of toxic and flammable gases with fast response and high sensitivity is extremely important for monitoring environmental pollution. In this work, we introduce two different synthesis pathways for the preparation of scalable Fe2O3nanoparticles for gas sensor applications. One is co-precipitation and the other is hydrothermal method. The gas sensing properties of the a-Fe2O3 nanoparticles (NPs) fabricated by different synthesis pathways were studied and compared. The performance of the NPs in the detection of toxic and flammable gases such as carbon dioxide, ammonia, liquefied petroleum gas, ethanol, and hydrogen was evaluated. The Fe2O3 NP-based gas sensors exhibited high sensitivity and a response time of less than a minute to analytic gases. However, the NPs fabricated by the one-step direct method exhibited higher sensitivities than those generated by the a-Fe2O3 NPs obtained by co-precipitation synthesis possibly because of their nanoporous structure. This performance is attributed to the large specific surface area of the NPs, which results in higher sensitivity.

The complete mitochondrial genome sequence of the indigenous I pig (Sus scrofa) in Vietnam

Hieu Duc Nguyen,Tuan Anh Bui,Phuong Thanh Nguyen,Oanh Thi Phuong Kim,Thuy Thi Bich Vo 아세아·태평양축산학회 2017 Animal Bioscience Vol.30 No.7

Objective: The I pig is a long nurtured longstanding breed in Vietnam, and contains excellent indigenous genetic resources. However, after 1970s, I pig breeds have become a small population because of decreasing farming areas and increasing pressure from foreign breeds with a high growth rate. Thus, there is now the risk of the disappearance of the I pigs breed. The aim of this study was to focus on classifying and identifying the I pig genetic origin and supplying molecular makers for conservation activities. Methods: This study sequenced the complete mitochondrial genome and used the sequencing result to analyze the phylogenetic relationship of I pig with Asian and European domestic pigs and wild boars. The full sequence was annotated and predicted the secondary tRNA. Results: The total length of I pig mitochondrial genome (accession number KX094894) was 16,731 base pairs, comprised two rRNA (12S and 16S), 22 tRNA and 13 mRNA genes. The annotation structures were not different from other pig breeds. Some component indexes as AT content, GC, and AT skew were counted, in which AT content (60.09%) was smaller than other pigs. We built the phylogenetic trees from full sequence and D loop sequence using Bayesian method. The result showed that I pig, Banna mini, wild boar (WB) Vietnam and WB Hainan or WB Korea, WB Japan were a cluster. They were a group within the Asian clade distinct from Chinese pigs and other Asian breeds in both phylogenetic trees (0.0004 and 0.0057, respectively). Conclusion: These results were similar to previous phylogenic study in Vietnamese pig and showed the genetic distinctness of I pig with other Asian domestic pigs.

Detection of pathogenic microorganisms using biosensor based on multi-walled carbon nanotubes dispersed in DNA solution

Nguyen Thi Thuy,Phuong Dinh Tam,Mai Anh Tuan,Anh-Tuan Le,Le Thi Tam,Vu Van Thu,Nguyen Van Hieu,Nguyen Duc Chien 한국물리학회 2012 Current Applied Physics Vol.12 No.6

The present paper introduces a facile and cost-effective route for the direct dispersion of multi-walled carbon nanotubes (MWCNTs) in DNA solution. Their application in detecting Escherichia coli O157:H7using DNA biosensorwas demonstrated. The dispersion state of theMWCNTswas characterized via UVeVis spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. The interaction between DNA sequence and the MWCNTs was investigated using Raman spectroscopy and Fourier transform infrared spectroscopy. As-obtainedMWCNT solutionwas used in the preparation of DNA sensor. Results revealed that the developed DNA sensor can detect a DNA target as low as 1 nM in a buffer solution. The sensitivity of the DNA sensor reached approximately 0.19 nM/mV. The effect of dispersion parameters, including pH values, DNA concentration, ion strength, and sonication time, on sensor response was also studied. TheDNA sensor can respondwell to 120 min of sonication time, a pH value of 9, and 20 mM of DNA sequence concentration. The results of the present study showed a potential application of the DNA sensor in the detection of Escherichia coli O157:H7.

Determinants of Human Resource Accounting Disclosures: Empirical Evidence from Vietnamese Listed Companies

Duc Hieu PHAM,Thi Huyen CHU,Thi Minh Giang NGUYEN,Thi Hong Lam NGUYEN,Thi Nhinh NGUYEN 한국유통과학회 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.7

This paper aims to analyze whether company characteristics are potential determinants of human resource accounting (HRA) disclosure practices by Vietnamese listed companies. It examines the human resource disclosure level of 204 companies by content analysis of these companies’ annual reports. The study has relied on a multiple linear regression to test the association between a number of corporate attributes and the extent of human resource disclosure in companies’ annual reports. The extent of human resource disclosure was measured using unweighted human resource disclosure index. The explanatory variables considered in this study were firm size, firm age, profitability, leverage, industry profile, and auditor type. The results revealed that the most influential variable for explaining firms’ variation in human resource disclosure is firm size followed by firm age and profitability. Thus, it can be concluded that firm size, firm age and profitability are major predictors that may affect the variety of HRA disclosure practices on firms listed in the Vietnam Stock Exchange. However, neither industry profile nor auditor type seems to explain differences in human resource disclosure practices between Vietnamese listed firms, indicating that company’s industry profile and auditor type are not a matter for the company to disclose HRA information.

Preparing large-scale WO_3 nanowire-like structure for high sensitivity NH_3 gas sensor through a simple route

Nguyen Van Hieu,Vu Van Quang,Nguyen Duc Hoa,김도진 한국물리학회 2011 Current Applied Physics Vol.11 No.3

The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by the deposition of tungsten metal on the substrate of porous single-wall carbon nanotubes (SWCNTs) film, followed by thermal oxidation process. The morphology and crystallinity of the synthesized materials are analyzed by SEM, TEM, XRD, and Raman spectroscopy. Results showed that tungsten oxide NWs deposited on SWCNTs have a porous structure with an average diameter of about 70 nm and a length of up to micrometers. The NH3 gas-sensing properties of tungsten NWs were measured at different temperatures. A maximum response of 9.7―1500 ppm at 250 ℃ with rapid response and recovery times of 7 and 8 s are found,respectively. In addition, the gas sensing mechanism of fabricated NWs is also discussed in term of surface resistivity and barrier height model.

Pressure effects on EXAFS Debye-Waller factor and melting curve of solid krypton

Khac Hieu Ho,Viet Tuyen Nguyen,Nguyen Van Nghia,Nguyen Ba Duc,Vu Quang Tho,Tran Thi Hai,Doan Quoc Khoa 한국물리학회 2019 Current Applied Physics Vol.19 No.1

The pressure effects on atomic mean-square displacement, extended X-ray absorption fine structure (EXAFS) Debye-Waller factor and melting temperature of solid krypton have been investigated in within the statistical moment method scheme in quantum statistical mechanics. By assuming the interaction between atoms can be described by Buckingham potential, we performed the numerical calculations for krypton up to pressure 120 GPa. Our calculations show that the atomic mean-square displacement and EXAFS Debye-Waller factor of krypton crystal depend strongly on pressure. They make the robust reduction of the EXAFS peak height. Our results are in good and reasonable agreements with available experimental data. This approach gives us a relatively simple method for qualitatively calculating high-pressure thermo-physical properties of materials. Moreover, it can be used to verify future high-pressure experimental and theoretical works.

Adsorption/desorption kinetics of nitric oxide on zinc oxide nano film sensor enhanced by light irradiation and gold-nanoparticles decoration

Chinh, Nguyen Duc,Hien, Truong Thi,Do Van, Lam,Hieu, Nguyen Minh,Quang, Nguyen Duc,Lee, Seung-Mo,Kim, Chunjoong,Kim, Dojin Elsevier 2019 Sensors and actuators. B, Chemical Vol.281 No.-

<P><B>Abstract</B></P> <P>ZnO thin-films with precisely controlled thicknesses were fabricated by the atomic layer deposition and their <I>NO</I> gas sensing properties were investigated at different temperatures, and in particular, under light irradiation of various energy and intensity at room temperature with and without Au catalyst. The molecular dynamics of <I>NO</I> and <I>O</I> <SUB>2</SUB> during the response and recovery cycles in relation with the <I>NO</I> sensing performance in air environment was elaborated using the energy diagram modelled for adsorption and desorption kinetics of the gas molecules. The blue light irradiation combined with Au catalytic effect greatly enhanced the <I>NO</I> response rate, but delayed the recovery rate in the air environment via molecular dynamic interference from the environmental oxygen. The optimum condition for <I>NO</I> sensing was obtained for the film thickness, light energy and intensity. Critical issues for the stable sensor operation such as concentration dependence, gas selectivity, and humidity effect were also reported.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Gas sensing response/recovery kinetics of NO sensing by ZnO with light irradiation and Au catalytic effect at room temperature. </LI> <LI> Molecular dynamics consideration for adsorption and desorption to explain the detection of ppm level gas concentrations. </LI> <LI> The nano-effect in varying thicknesses of ZnO. </LI> </UL> </P>

Excellent detection of H₂S gas at ppb concentrations using ZnFe₂O₄ nanofibers loaded with reduced graphene oxide

Van Hoang, Nguyen,Hung, Chu Manh,Hoa, Nguyen Duc,Van Duy, Nguyen,Park, Inkyu,Van Hieu, Nguyen Elsevier Sequoia 2019 Sensors and actuators. B Chemical Vol.282 No.-

<P><B>Abstract</B></P> <P>Cost-effective fabrication of sensors and detection of ultralow concentrations of toxic gases are important concerns for environmental monitoring. In this study, the reduced graphene oxide (RGO)-loaded ZnFe<SUB>2</SUB>O<SUB>4</SUB> nanofibers (ZFO-NFs) were fabricated by facile on-chip electrospinning method and subsequent heat treatment. The multi-porous NFs with single-phase cubic spinel structure and typical spider-net morphology were directly assembled on Pt-interdigitated electrodes. The diameters of the RGO-loaded ZFO-NFs were approximately 50–100 nm with many nanograins. The responses to H<SUB>2</SUB>S gas showed a bell-shaped behaviour with respect to RGO contents and annealing temperatures. The optimal values of the RGO contents and the annealing temperatures were found to be about 1.0 wt% and 600 °C, respectively. The response of the RGO-loaded ZnFe<SUB>2</SUB>O<SUB>4</SUB> NFs to 1 ppm H<SUB>2</SUB>S gas was as high as 147 at 350°C while their cross-gas responses to SO<SUB>2</SUB> (10 ppm), NH<SUB>3</SUB> (100 ppm), H<SUB>2</SUB> (250 ppm), C<SUB>3</SUB>H<SUB>6</SUB>O (1000 ppm), and C<SUB>2</SUB>H<SUB>5</SUB>OH (1000 ppm) were rather low (1.8−5.6). The high sensor response was attributed to formation of a heterojunction between RGO and ZnFe<SUB>2</SUB>O<SUB>4</SUB> and due to the fact that NFs consisted of many nanograins which resulted in multi-porous structure and formation of potential barriers at grain boundaries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> rGO-loaded ZnFe<SUB>2</SUB>O<SUB>4</SUB> nanofibers have simply prepared by electrospinning. </LI> <LI> rGO-loaded ZnFe<SUB>2</SUB>O<SUB>4</SUB> nanofiber sensors can detect H<SUB>2</SUB>S gas down to ppb level. </LI> <LI> The loading rGO can result in an enhancement of H<SUB>2</SUB>S gas ensing performance. </LI> </UL> </P>