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.

Decentralized Dynamic Sub-Carrier Assignment for OFDMA-Based Adhoc and Cellular Networks

NGUYEN, Van-Duc,HAAS, Harald,KYAMAKYA, Kyandoghere,CHEDJOU, Jean-Chamerlain,NGUYEN, Tien-Hoa,YOON, Seokho,CHOO, Hyunseung The Institute of Electronics, Information and Comm 2009 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.92 No.12

<P>In this paper, a novel decentralised dynamic sub-carrier assignment (DSA) algorithm for orthogonal frequency division multiple access (OFDMA)-based adhoc and cellular networks operating in time division duplexing (TDD) mode is proposed to solve the hidden and exposed node problem in media access control (MAC). This method reduces the co-channel interference (CCI), and thus increases the overall throughput of the network. Reduced CCI and increased throughput can be achieved, if time and frequency selectivity of the multi-path fading channel and the channel reciprocity offered by the TDD are fully exploited. The time and frequency selectivity of the channel are usually the main problem in mobile communication. However, in the context of channel assignment for OFDMA-based networks in TDD mode, the time and frequency selectivity of the channel are the key to reduce the interference. In the proposed channel assignment mechanism, several clusters of sub-carriers are assigned for data transmission between a transmitter and a receiver only if the corresponding channels of those sub-carriers linking this transmitter to potential victim receivers are deeply faded. In addition, the proposed algorithm works in a fully decentralised fashion and, therefore, it is able to effectively support ad hoc and multihop communication as well as network self-organisation. Numerical results show that the throughput obtained by the proposed approach for a given quality of service is higher than those of the conventional methods in any precondition of adhoc geographic scenario.</P>

Tin-oxide nanotubes for gas sensor application fabricated using SWNTs as a template.

Hoa, Nguyen Duc,Quy, Nguyen Van,An, Myungchan,Song, Hyejin,Kang, Youngjin,Cho, Yousuk,Kim, Dojin American Scientific Publishers 2008 Journal of nanoscience and nanotechnology Vol.8 No.10

<P>We develop a simple method to synthesize nano tube or wire structure of tin-oxide for gas sensor application. It is realized by the rheotaxial growth and thermal oxidation (RGTO) of tin on porous single-wall carbon nanotubes (SWNTs) as a template. The morphology and chemical property of thus formed nanostructures are examined. The electrical and NO(x) gas sensing properties are also investigated. The sensor exhibits a fast response time of less than 100 seconds and a good recovery. A sensing response of 23,400% to 10 ppm concentration at 200 degrees C is observed.</P>

One-Dimensional Tin-Oxide-Coated Single-Wall Carbon Nanotubes for Gas Sensor Applications

Nguyen Duc Hoa,Nguyen Van Quy,Li Wei,Myungchan An,송혜진,Youngjin Kang,Yousuk Cho,김도진 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.5

We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon nanotubes (SWNTs) for gas sensor applications The SWNTs are synthesized directly on a SiO2/Si substrate with comb-type electrodes via the arc-discharge method. Metallic Sn thin layers with various thicknesses are deposited over the grown SWNTs. After that, a rheotaxial and thermal oxidation is performed to spread and convert the tin metal on the surfaces of the SWNTs into tin oxide. The electrical and the NOx gas sensing properties of the sensor devices are then investigated. The as-grown SWNTs sensor exhibited a p-type semiconducting property whereas the tin-oxide- coated SWNTs exhibited an n-type semiconducting property. Moreover, the one-dimensional tin- oxidecoated SWNTs sensor exhibited a higher sensitivity than the pure SWNTs sensor. We introduce a simple method to synthesize one-dimensional tin-oxide-coated single-wall carbon nanotubes (SWNTs) for gas sensor applications The SWNTs are synthesized directly on a SiO2/Si substrate with comb-type electrodes via the arc-discharge method. Metallic Sn thin layers with various thicknesses are deposited over the grown SWNTs. After that, a rheotaxial and thermal oxidation is performed to spread and convert the tin metal on the surfaces of the SWNTs into tin oxide. The electrical and the NOx gas sensing properties of the sensor devices are then investigated. The as-grown SWNTs sensor exhibited a p-type semiconducting property whereas the tin-oxide- coated SWNTs exhibited an n-type semiconducting property. Moreover, the one-dimensional tin- oxidecoated SWNTs sensor exhibited a higher sensitivity than the pure SWNTs sensor.

Nanocomposite of SWNTs and SnO₂ fabricated by soldering process for ammonia gas sensor application

Duc Hoa, Nguyen,Van Quy, Nguyen,Suk Cho, You,Kim, Dojin WILEY-VCH Verlag 2007 Physica status solidi. PSS. A, Applications and ma Vol.204 No.6

<P>We introduce a simple method to fabricate an ammonia gas sensor with a nanocomposite of single-walled carbon nanotubes (SWNTs) and SnO<SUB>2</SUB>. The nanocomposite showed a semiconducting property. With exposure to ammonia gas, the electrical resistance of the nanocomposite sensor increases rapidly. It was found that the sensor can detect the concentration of NH<SUB>3</SUB> down to the 10 ppm level at room temperature. The sensor exhibited a fast response time of less than 100 s and good sensing response and recovery. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Second Order Suboptimal Power Allocation for MIMO-OFDM Based Cognitive Radio Systems

( Tien Hoa Nguyen ),( Thanh Hieu Nguyen ),( Van Duc Nguyen ),( Duyen Trung Ha ),( Guilllaume Gelle ),( Hyunseung Choo ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.8

This paper proposes an efficient and low complexity power-loading algorithm for MIMO-OFDM downlink based cognitive radio system that maximizes the sum rate of single secondary user (SU) under constraints on the tolerable interference thresholds between secondary user and primary user`s frequency bands and the total transmission power. Our suboptimal algorithm is based on the 2<sup>nd</sup> order interference tracking and nulling mechanism to allocate transmission power of the subcarriers among SU`s scheme. The performance of our proposed suboptimal scheme is compared with the performance of the classical power loading algorithms, e.g., water filling, 1^st order interference tracking, nulling, and other suboptimal schemes. Numerical results show that our algorithm has low complexity but obtains a higher channel capacity than that of some previous suboptimal algorithms in some scenarios. We dedicate also that for a given interference threshold, the 2^nd order interference tracking mechanism has dynamic number of nulling position instead fixed number of nulling position.

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>

Facile synthesis of multifunctional Ag/Fe3O4-CS nanocomposites for antibacterial and hyperthermic applications

Ngoan Thi Nguyen,Dai Lam Tran,Duc Cuong Nguyen,Thai Loc Nguyen,Thi Cham Ba,Binh Hai Nguyen,Thi Duong Ba,Nam Hong Pham,Dzung Tuan Nguyen,Thai Hoa Tran,Gia Dien Pham 한국물리학회 2015 Current Applied Physics Vol.15 No.11

Nanocomposites containing two or more functional constituents are attractive candidates for advanced nanomaterials. In this study, multifunctional Ag/Fe3O4-CS nanocomposites were successfully prepared, using chitosan as a stabilizing and cross-linking agent. The as-synthesized nanocomposites were characterized by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), UVevisible spectrophotometer (UVeVis) and vibrating sample magnetometer (VSM). The results demonstrated that Ag/Fe3O4-CS composite nanoparticles (NPs) were composed of parent components, Fe3O4 and Ag NPs, which were uniformly dispersed in the chitosan matrix. The hybrid NPs exhibited strong antibacterial property against Pseudomonas aeruginosa. With high magnetization value (67 emu/g), the synthesized Ag/Fe3O4-CS composite can be easily separated or recycled in potential biomedical applications. Furthermore, the results showed that the multicomponent hybrid nanostructures appeared to be the promising material for local hyperthermia, which can be used as thermoseeds for localized hyperthermia treatment of cancers.

A scintillation detector confi guration for pulse shape analysis

Phan Van Chuan,Nguyen Duc Hoa,Nguyen Xuan Hai,Nguyen Ngoc Anh,Nguyen Nhi Dien,Pham Dinh Khang 한국원자력학회 2018 Nuclear Engineering and Technology Vol.50 No.8

This paper presents a neutron detector configuration using EJ-301 scintillation liquid, a R9420 photomultiplierand a homemade preamplifier. The detector qualities which include the energy linearity, efficiencyresponse and neutron/gamma discrimination are guaranteed for neutron detection in the energyrange from 0 to 3000 keVee. Regarding the neutron/gamma discrimination capability, four pulse shapediscrimination (PSD) methods which are the threshold crossing time (TCT), pulse gradient analysis (PGA),charge comparison (CC) and correlation pattern recognition (CPR), were evaluated and discussed; amongof these, the CPR method provides the best neutron/gamma discrimination

Effect of Annealing Temperature on the Permeability and Magneto-Impedance Behaviors of Fe<SUB>68.5</SUB>Mn<SUB>5</SUB>Si<SUB>13.5</SUB>B<SUB>9</SUB>Nb₃Cu₁ Amorphous Alloy

Anh-Tuan Le,Nguyen Duy Ha,Chong-Oh Kim,Jang-Roh Rhee,Nguyen Chau,Nguyen Quang Hoa,Nguyen Duc Tho,Heebok Lee 한국자기학회 2006 Journal of Magnetics Vol.11 No.1

The effect of annealing temperature on the permeability and giant magneto-impedance (GMI) behaviors of Fe68.5Mn5Si13.5B9Nb₃Cu₁ amorphous alloy has been systematically investigated. The nan℃rystalline Fe68.5Mn5- Si13.5B9Nb3Cu1 alloys consisting of ultra-fine (Fe,Mn)₃Si grains embedded in an amorphous matrix were obtained by annealing their precursor alloy at the temperature range from 500℃ to 600℃ for 1 hour in vacuum. The permeability and GMI profiles were measured as a function of external magnetic field. It was found that the increase of both the permeability and the GMI effect with increasing annealing temperature up to 535℃ was observed and ascribed to the ultrasoft magnetic properties in the sample, whereas an opposite tendency was found when annealed at 600℃ which is due to the microstructural changes caused by high-temperature annealing. The study of temperature dependence on the permeability and GMI effect showed some insights into the nature of the magnetic exchange coupling between nan℃rystallized grains through the amorphous boundaries in nan℃rystalline magnetic materials.