Nguyen Duc Chien

The synthesis and characterization of platinum nanoparticles: a method of controlling the size and morphology

In this paper, Pt nanoparticles with good shapes of nanocubes and nano-octahedra and well-controlled sizes in the range 5-7 and 8-12 nm, respectively, have been successfully synthesized. The modified polyol method by adding silver nitrate and varying the molar ratio of the solutions of silver nitrate and H(2)PtCl(6) has been used to produce Pt nanoparticles of the size and shape to be controlled. The size and morphology of Pt nanoparticles have been studied by transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The results have shown that their very sharp and good shapes exist in the main forms of cubic, cuboctahedral, octahedral and tetrahedral shapes directly related to the crystal nucleation along various directions of the [100] cubic, [111] octahedral and [111] tetrahedral facets during synthesis. In particular, various irregular and new shapes of Pt nanoparticles have been found. Here, it is concluded that the role of silver ions has to be considered as an important factor for promoting and controlling the development of Pt nanoparticles of [100] cubic, [111] octahedral and [111] tetrahedral facets, and also directly orienting the growth and formation of Pt nanoparticles.

DNA sensor development based on multi-wall carbon nanotubes for label-free influenza virus (type A) detection

This paper describes the DNA immobilization using carbon multi-walled nanotubes (MWCNTs) for direct and label-free detection of influenza virus (type A). The DNA probe was attached on the sensor surface by means of covalent bonding between the amine and phosphate groups of the DNA sequence. The interaction between the DNA probe and the MWCNTs were characterized by Fourier Transform Infrared (FTIR) spectrometry, Raman spectra. The hybridization of the DNA probe and the target DNA were detected by changes in the conductance on the surface of sensors leading to the change in the output signal of the system. The results show that the DNA sensor can detect as low as 0.5 nM of the target DNA samples; the response time of DNA sensor is approximately 4 min.

Synthesis and characterization of polyhedral Pt nanoparticles: Their catalytic property, surface attachment, self-aggregation and assembly

In this paper, we presented the preparation procedure of Pt nanoparticles with the well-controlled polyhedral morphology and size by a modified polyol method using AgNO(3) in accordance with the reduction of H(2)PtCl(6) in EG at high temperature around 160°C. The methods of UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution (HR) TEM measurements were used to characterize their surface morphology, size, and crystal structure. We have observed that the polyhedral Pt nanoparticles of sharp edges and corners were produced in the preferential homogenous growth as well as the formation of porous and large Pt particles by self-aggregation and assembly originating from as-prepared polyhedral Pt nanoparticles. It is most impressive to find that the arrangement of Pt nanoparticles was observed in their surface attachments, self-aggregation, random and directed surface self-assembly by the bottom-up approach. Their high electrocatalytic activity for methanol oxidation was predicted. The findings and results showed that the polyhedral Pt nanoparticle-based catalysts exhibited the high electrocatalytic activity for their potential applications in developing the efficient Pt-based catalysts for direct methanol fuel cells.

First-principles study of the structural and electronic properties of graphene/MoS2 interfaces

In this paper, we study the structural and electronic properties of graphene adsorbed on MoS2 monolayer (G/MoS2) with different stacking configurations using dispersion-corrected density functional theory. Our calculations show that the interaction between graphene and MoS2 monolayer is a weak van der Waals interaction in all four stacking configurations with the binding energy per carbon atom of −30 meV. In the presence of MoS2 monolayer, the linear bands on the Dirac cone of graphene at the interfaces are slightly split. A band gap about 3 meV opens in G/MoS2 interfaces due to the breaking of sublattice symmetry by the intrinsic interface dipole, and it could be effectively modulated by the stacking configurations. Furthermore, we found that an n-type Schottky contact is formed at the G/MoS2 interface in all four stacking configurations with a small Schottky barrier about 0.49 eV. The appearance of the non-zero band gap in graphene has opened up new possibilities for its application in electronic device...

Controlled synthesis and properties of palladium nanoparticles

In our research, the preparation processes of Pd nanoparticles (Pd NPs) with different methods by adding a certain amount of silver nitrate, iron chloride or sodium iodide are presented in order to control their size and morphology. Various sizes and shapes of Pd NPs are observed by alcohol reduction. The results show the size and morphology control of Pd NPs with chemical reductions of Pd salts by ethanol and ethylene glycol (EG) that have very different reduction processes. The modified polyol method with the gradual addition of Pd and polyvinylpyrollidone precursors in EG at 160°C has led to control their size and morphology in the 10 nm range using 0.02 M AgNO3. It is observed that the Pd nanorod is also formed. The main factors that will control the shapes of Pd NPs have been presented to explain their growth and formation mechanisms in a control process.

Synthesis and LPG-sensing properties of TiO2 nanowires

TiO2 nanowires were synthesized by a hydrothermal process in KOH solution at 190?C using TiO2 powder as a source material. Characterizations indicate the high degree of crystallinity with diameter of ca. 10?20 nm and length in micrometer scale of the obtained TiO2 nanowires. Multiple nanowires gas sensors were fabricated by dispersing the TiO2 nanowires on an interdigit Pt-electrode. The TiO2 nanowires sensors show a high sensitivity to Liquefied Petroleum Gas (LPG) at working temperature of 400?C. The results demonstrate the possibility of using TiO2 nanowires for gas-sensing application.

Sharp cubic and octahedral morphologies of poly(vinylpyrrolidone)-stabilised platinum nanoparticles by polyol method in ethylene glycol: their nucleation, growth and formation mechanisms

Pt nanoparticles (NPs) were synthesised by a modified polyol method with the addition of silver nitrate. The results showed that the specific shapes of Pt NPs were influenced by the relevant factors, which are the contents of silver nitrate, synthetic time and temperature. A small content of silver nitrate has played an important role in determining their final shapes of platinum NPs. We observed that Pt NPs in the forms of very sharp shapes such as Pt cubes, octahedrons, cuboctahedrons and tetrahedrons have been obtained. In addition, the shape growth mechanisms and formation of Pt NPs have been studied. They exist in both cubic and octahedral shapes. Importantly, Pt nanocrystals can grow into main cubic and octahedral shapes for a short time less than 15 min. Moreover, Pt nanocrystals can also grow into different shapes from cubic and octahedral into spherical ones for several hours. Especially, they exhibited interesting shapes of multiple-branched Pt nanostructures because of their overgrowth and aggregations. Clearly, large cubic and octahedral Pt NPs of 160 nm diameter were observed. The growth and formation of large cubic and octahedral Pt NPs were due to the aggregation of Pt clusters or initial Pt seeds, even small Pt nanocrystals.

Hydrothermal Synthesis and Ammonia Sensing Properties of WO3/Fe2O3 Nanorod Composites

WO3 nanorods (NRs) and α-Fe2O3 NRs were fabricated by hydrothermal treatment. Composites of these materials were created by mixing with ratios of 1:2, 1:1 and 2:1 in weight. Morphology, structure and composition characteristics of the WO3/Fe2O3 NRs composites were characterized by scanning electron microscopy, x-ray diffraction and energy dispersive x-ray spectroscopy analyses. The results of sensing measurements indicated that the sensor based on WO3:Fe2O3 with the ratio of 2:1 exhibited fairly good sensitivity toward NH3 at 300°C and the sensor based on WO3:Fe2O3 with the ratio of 1:1 can be used as a NH3 sensor with an operating temperature of 350°C. Selectivity and response–recovery times are suitable for practical applications. Finally, the mechanism for the improvement in the gas-sensing property was discussed.

Low resistivity molybdenum thin film towards the back contact of dye-sensitized solar cell

This paper reports the optimization of the molybdenum thin film electrode as the back contact of dye-sensitized solar cell (DSSC). The molybdenum thin film was grown on the glass substrate by direct current sputtering techniques of which the sputtering power was 150 W at 18 sccm flow rate of Ar. At such sputtering parameters, the Mo film can reach the lowest resistivity of 1.28E −6 Ω cm at 400 nm thick. And the reflection of Mo membrane was 82%. This value is considered as a very good result for preparation of the back contact of DSSC.

Impact parameters investigation of DNA immobilisation process on DNA sensor response

This paper studies impact parameters of DNA sequence immobilisation on DNA sensor response. The parameters were examined including immobilisation time, carbon nanotubes concentration, DNA probe concentration and pH value. The DNA probe sequences were immobilised on surface of microelectrodes by using multi–walled carbon nanotubes (MWCNTs) as mediator. The hybridisation between DNA probe and DNA target was detected by changes in the conductance on the surface of sensors leading to the change in the output signal of the system. The experimental results showed that DNA sensor can well detect E. coli O157:H7 bacteria at optimal parameters including immobilisation time of 120 minute, MWCNTs of 1 mg, 20 µM DNA probe and pH7. Additionally, influence of BSA agent blocking was also studied. The result showed that DNA sensor response was decrease about 15% compared to that obtained in the absence of BSA blocking.