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  • Viet Nam National University Ho Chi Minh City  (38)
  • 1
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2016
    In:  Science and Technology Development Journal Vol. 19, No. 3 ( 2016-09-30), p. 129-137
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 19, No. 3 ( 2016-09-30), p. 129-137
    Abstract: This paper reports the production of fatty acid methyl esters (FAMEs) and fatty acid ethyl esters (FAEEs) by the transesterification reaction of rubber seed oil (RSO) in supercritical methanol and ethanol without using any catalyst. Experiment were carried out in a batch reactor, and reactions were studied at 260, 280, 300 and 320 oC at a pressure of 8.1-19 MPa with various mole ratios of ethanol – to - methanol from 0 to 100%. The extent of the reaction was explored using a convertibility parameter, which corresponds to the maximum ester content attainable from the feedstock. The highest FAME and FAEE contents achieved were 91.8 % and 86.4%, respectively. Results show that transesterification of RSO in methanol was more efficient than that in ethanol; the temperature had the strongest influence.
    Type of Medium: Online Resource
    ISSN: 1859-0128 , 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2016
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  • 2
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2015
    In:  Science and Technology Development Journal Vol. 18, No. 3 ( 2015-08-30), p. 153-161
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 18, No. 3 ( 2015-08-30), p. 153-161
    Abstract: The variation of lamellar structures of poly(styrenesulfonic acid)-grafted poly (ethylene-co-tetrafluoroethylene) proton exchange membranes dependence on preparation procedures and grafting degree (GD) was investigated by small angle X-ray scattering. The detail structures of lamellar including lamellar period L, thickness of lamellar crystal Lc, thickness of lamellar amorphous La, and linear crystallinity Lc/L were examined by a 1D correlation function. The lamellar structures were recognized at the grafting step and did not change under the sulfonation process. With GD  79 %, Lc significantly decreased (corresponding to the increase of La) and then retained in the GDs of 79-117 %. Note that the retained values of Lc, La, and linear crystallinity in the GDs of 79-117 % are the origin of high conductivity and mechanical strength of membranes under severe operation conditions for fuel cell applications.
    Type of Medium: Online Resource
    ISSN: 1859-0128 , 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2015
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  • 3
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2012
    In:  Science and Technology Development Journal Vol. 15, No. 2 ( 2012-06-30), p. 62-69
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 15, No. 2 ( 2012-06-30), p. 62-69
    Abstract: Gas sensors based on multi-walled carbon nanotube (MWCNT) for detecting gaseous molecules of ammoniac (NH3) were developed and investigated. MWCNT film was grown directly by chemical vapor deposition (CVD) method on Pt electrodes to fabricate sensor device. The CNT based – gas sensor is shown sensitively and selectively to NH3 gas at room temperature.
    Type of Medium: Online Resource
    ISSN: 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2012
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  • 4
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2022
    In:  Science and Technology Development Journal Vol. 25, No. 3 ( 2022)
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 25, No. 3 ( 2022)
    Abstract: Introduction: ZnO is a potential semiconductor material for thermoelectric (TE) applications at high temperature. In this study, doping Bi atoms aims to improve the power factor of ZnO ceramic. Based on the analyses of structural and TE properties, the enhancement in Seebeck coefficient proves the benefit of Bi doping. Methods: The ZnO and Bi-doped ZnO (BZO) ceramics were fabricated by solid-state reaction at 1400oC in air. The Seebeck LSR-3 system measured both samples’ TE properties, with a combined Hall effect at room temperature. The crystalline structure was analyzed through the X-ray diffraction (XRD) technique. Results: The XRD patterns show all samples having polycrystalline hexagonal wurtzite structure. Although the crystallinity is enhanced, Bi doping reduces significantly carrier concentration from 3.4×1019 to 1.1×1019 cm-3 at room temperature. As a result at 500oC, the electrical conductivity, Seebeck coefficient, and power factor are 126 Scm-1, -99 µVK-1, and 124 µWm-1K-2 for pure ZnO; and 76 Scm-1, -142 µVK-1, and 165 µWm-1K-2 for BZO ceramic, respectively. Conclusion: The power factor of Bi-doped ZnO is improved by 32% as compared to pure ZnO at 500oC. The raise of Seebeck coefficient is the main reason for the growth of power factor.
    Type of Medium: Online Resource
    ISSN: 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2022
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  • 5
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2020
    In:  Science and Technology Development Journal Vol. 23, No. 4 ( 2020-12-16), p. 788-794
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 23, No. 4 ( 2020-12-16), p. 788-794
    Abstract: Introduction: Zinc oxide (ZnO) is well-known as a promising thermoelectric material owing to its safety, inexpensiveness, and thermal stability. This research provides an overview of thermoelectric potentials, including structure, electrical conductivity, Seebeck coefficient, and power factor of pure ZnO semiconductor synthesized in bulk and thin-film forms. Methods: The ZnO bulk was synthesized by solid-state reaction at high temperature, while the thin film was prepared by d.c. magnetron sputtering technique. The temperature-dependent thermoelectric properties of all the samples were measured by the Seebeck LSR-3 system. The crystallographic and surface morphological information of the samples were obtained by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. Results: The XRD results confirm that both the bulk and thin-film have polycrystalline structure and characteristics of hexagonal-wurtzite ZnO. Through the FESEM observation, the bulk is well densified under high-temperature condition, while the thin-film achieve good orientation and close-packed grains. At 573 K, the obtained thermoelectric properties (electrical conductivity, Seebeck coefficient, and power factor) are respectively 352.4 S/cm, -89.5 µV/K and 282.5 µW/mK2 for the ZnO bulk; and 289 S/cm, -113.8 µV/K and 374.3 µW/mK2 for the ZnO film. Conclusion: The comparative study shows the good thermoelectric potential of ZnO material in both forms of bulk and thin film. Among them, the thin film has better results, especially in the Seebeck coefficient and power factor than one.
    Type of Medium: Online Resource
    ISSN: 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2020
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  • 6
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2015
    In:  Science and Technology Development Journal Vol. 18, No. 1 ( 2015-03-31), p. 40-47
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 18, No. 1 ( 2015-03-31), p. 40-47
    Abstract: π-Conjugated oligomeric and polymeric semiconductors have been the focus of intense research over the past few decades as alternatives to inorganic semiconductors for lowcost electronic applications such as organic thinfilm transistors (OTFTs), light-emitting diodes (OLEDs), and photovoltaics (OPVs). These materials enable vapor- or solution-phase fabrication of large-area, lightweight electronic devices and are compatible with plastic substrates for mechanically flexible, conformable, and wearable electronics. In this research, we aim at modification of the H/Br end groups of poly (3-hexylthiophene) to CHO/Br end groups via Vilsmeier-haack reaction using POCl3 and DMF as the catalytic system in toluene medium. The end groups of the obtained polymer were determined via FT-IR spectroscopy and were further confirmed by Maldi-ToF. The result showed that completion of the Vilsmeierhaack reaction was obtained after 24 h at 75 °C.
    Type of Medium: Online Resource
    ISSN: 1859-0128 , 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2015
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  • 7
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2021
    In:  Science and Technology Development Journal - Natural Sciences Vol. 5, No. 2 ( 2021-04-16), p. first-
    In: Science and Technology Development Journal - Natural Sciences, Viet Nam National University Ho Chi Minh City, Vol. 5, No. 2 ( 2021-04-16), p. first-
    Abstract: Climate change is promoting researches on materials which is capable of converting environmentally friendly energy, in which materials that convert heat into electricity are receiving significant attention, because their ability of converting heat to electricity not only generates the electricity but also contributes to slow down the consumption of fossil fuel. The existence of point defects in the semiconductors greatly effected properties of materials, especially thermoelectric properties. Therefore, the study of defects in materials is a popular research trend today. In this study, we focus on evaluating the existence of oxygen interstitial in CuCr1 􀀀 xMgxO2 [0.00 x 0.30] compounds, because oxygen int erstitial greatly affected the thermoelectric properties of this material. Based on X-ray photoelectron spectroscopy (XPS) analysis, at the large ratio of Mg impurity x = 0.15, the compound had the highest percentage of oxygen interstitial and was also a good thermoelectric material. In addition, it could be also seen that CuCrO2 material being doped a large Mg doping ratio (x = 0.15) was suitable for thermal-to-electrical applications rather than the ones with a small ratio (x 0.05).
    Type of Medium: Online Resource
    ISSN: 2588-106X , 2588-106X
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2021
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  • 8
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2018
    In:  Science and Technology Development Journal - Natural Sciences Vol. 1, No. 6 ( 2018-12-07), p. 163-176
    In: Science and Technology Development Journal - Natural Sciences, Viet Nam National University Ho Chi Minh City, Vol. 1, No. 6 ( 2018-12-07), p. 163-176
    Abstract: The synthesis of thiacalix[3]triazines and 1,3,5- tris(4-bromophenyl)benzene have been synthesized via simple steps and was characterized to determine the chemical structure. The structure of Thiacalix[3] triazines was characterized via 1H NMR and 13C NMR that conformed the expected structure of compound. In addition, the thiacalix[3]triazines exhibited the λmax at 560 nm and λonset at 720 nm which corresponding to the bandgap of 1.7 ev. Thiacalix[3] triazines, cyclotrimeric metacyclophanes with direct S linkages between the heteroaryl constituents, were shown to associate with anion that could be useful for chemsensor application.
    Type of Medium: Online Resource
    ISSN: 2588-106X , 2588-106X
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2018
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  • 9
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2021
    In:  Science and Technology Development Journal Vol. 24, No. 2 ( 2021-05-10), p. first-
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 24, No. 2 ( 2021-05-10), p. first-
    Abstract: Introduction: Harvesting the waste heat emitted from the activities of humanity based on thermoelectric devices is an appropriate way to reduce the overconsumption of fossil fuel nowadays. Methods: In this work, CuCr0:85Mg0:15O2 compounds prepared by conventional solid-state reaction method were investigated to find out that the short sintering time is enough for thermoelectric applications, directly low the cost of the devices. Results and Conclusion: We find out that there is a significant change in the crystal structure, the chemical state, and thermoelectric properties along with the increase of the sintering time, but eventually, the dimensionless figure of merit ZT is almost constant regardless of the long or short sintering time which means that the increase of electrical conductivity will compromise the increase of thermal conductivity. The highest ZT value is 0.03 measured at 500 oC for both samples prepared at the sintering time of 3 and 12 hours.
    Type of Medium: Online Resource
    ISSN: 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2021
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  • 10
    Online Resource
    Online Resource
    Viet Nam National University Ho Chi Minh City ; 2013
    In:  Science and Technology Development Journal Vol. 16, No. 1 ( 2013-03-31), p. 15-25
    In: Science and Technology Development Journal, Viet Nam National University Ho Chi Minh City, Vol. 16, No. 1 ( 2013-03-31), p. 15-25
    Abstract: The purpose of this study is to i) fabricate a biodegradable nanoparticle formulation of Ketoprofen, ii) evaluate its characteristics, iii) investigate its in vitro dissolution and in vivo pharmaceutical property. The nanoparticle formulation was prepared by spray drying method using Eudragit L100 as the matrix polymer. Size and morphology of drug-loaded nanoparticles were characterized with the electron microscopes (TEM, SEM). These successfully prepared nanoparticles by spray drying method are spherical in shape and quite homologous with diameter size of 100 – 200 nm. The in vitro dissolution studies were conducted at pH 1.2 and 7.4. The results indicated that there is a significant increase in Keto concentration at pH 7.4 compared to pH 1.2. For the in vivo assessment, our Keto-loaded nanoparticles and referential Profenid were administered by oral gavages to rabbits. The results implied that Keto-loadednanoparticles remarkably increased AUC compared to Profenid.
    Type of Medium: Online Resource
    ISSN: 1859-0128 , 1859-0128
    Language: Unknown
    Publisher: Viet Nam National University Ho Chi Minh City
    Publication Date: 2013
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