Vu Ngoc Phan

Enhanced magnetic anisotropy and heating efficiency in multi-functional manganese ferrite/graphene oxide nanostructures.

A promising nanocomposite material composed of MnFe2O4 (MFO) nanoparticles of ∼17 nm diameter deposited onto graphene oxide (GO) nanosheets was successfully synthesized using a modified co-precipitation method. X-ray diffraction, transmission electron microscopy, and selected area electron diffraction confirmed the quality of the synthesized samples. Fourier transform infrared measurements and analysis evidenced that the MFO nanoparticles were attached to the GO surface. Magnetic measurements and analysis using the modified Langevin model evidenced the superparamagnetic characteristic of both the bare MFO nanoparticles and the MFO-GO nanocomposite at room temperature, and an appreciable increase of the effective anisotropy for the MFO-GO sample. Magnetic hyperthermia experiments performed by both calorimetric and ac magnetometry methods indicated that relative to the bare MFO nanoparticles, the heating efficiency of the MFO-GO nanocomposite was similar at low ac fields (0-300 Oe) but became progressively larger with increasing ac fields (>300 Oe). This has been related to the higher effective anisotropy of the MFO-GO nanocomposite. In comparison with the bare MFO nanoparticles, a smaller reduction in the heating efficiency was observed in the MFO-GO composites when embedded in agar or when their concentration was increased, indicating that the GO helped minimize the physical rotation and aggregation of the MFO nanoparticles. These findings can be of practical importance in exploiting this type of nanocomposite for advanced hyperthermia. Magnetoimpedance-based biodetection studies also indicated that the MFO-GO nanocomposite could be used as a promising magnetic biomarker in biosensing applications.

Enhancement of the electrical properties of silver nanowire transparent conductive electrodes by atomic layer deposition coating with zinc oxide.

Transparent conductive electrodes for applications in optoelectronic devices such as solar cells and light-emitting diodes are important components and require low sheet resistance and high transmittance. Herein, we report an enhancement of the electrical properties of silver (Ag) nanowire networks by coating with zinc oxide using the atomic layer deposition technique. A strong decrease in the sheet resistance of Ag nanowires, namely from 20-40 Ω/□ to 7-15 Ω/□, was observed after coating with ZnO. Ag nanowire electrodes coated with 200-cycle ZnO by atomic layer deposition show the best quality, with a sheet resistance of 11 Ω/□ and transmittance of 75%.

Functional manganese ferrite/graphene oxide nanocomposites: effects of graphene oxide on the adsorption mechanisms of organic MB dye and inorganic As(V) ions from aqueous solution

In this study, manganese ferrite-graphene oxide (MFO-GO) nanocomposites were prepared via a co-precipitation reaction of Fe3+ and Mn2+ ions in a GO suspension. The effects of graphene oxide on the physicochemical characteristics, magnetic properties and adsorption activities of the MFO-GO nanocomposites were studied. Methylene blue (MB) and arsenic(V) were used in this study as model water pollutants. With an increase in the GO content in the range of 10 wt% to 50 wt%, the removal efficiency for both MB dye and arsenic(V) ions was improved. Our adsorption data revealed that the adsorption behavior of MB dye showed good agreement with the Langmuir isotherm model and pseudo-second-order equation, whereas the Freundlich isotherm model was more suitable for simulating the adsorption process of arsenic(V) ions on the MFO-GO nanocomposites. In addition, an important role of the GO content in the adsorption mechanisms of both MB dye and arsenic(V) ions was found, in which GO nanosheets play a key role in the mechanisms of electrostatic/ionic interactions, oxygen-containing groups and π–π conjugation in the case of the adsorption of MB dye, whereas the role of the GO content is mainly related to the mechanism of electrostatic/ionic interactions in the case of the adsorption of arsenic(V). Graphene oxide has the functions of increasing the number of active binding sites comprising oxygen-containing functional groups, reducing the agglomeration of MFO nanoparticles, increasing the number of adsorption sites, and improving the electrostatic/ionic interactions between adsorbents and adsorbates in order to enhance the adsorption performance of cationic organic dyes and/or heavy metal anions from aqueous solutions.

Microstructure and Chemo-Physical Characterizations of Functional Graphene Oxide-Iron Oxide-Silver Ternary Nanocomposite Synthesized by One-Pot Hydrothermal Method

In this work, a functional graphene oxide-iron oxide-silver (GO-Fe3O4-Ag) ternary nanocomposite was synthesized by using one-pot hydrothermal treatments of mixture solutions of silver nitrate (AgNO3), ferrous chloride tetrahydrate (FeCl2 4H2O), polyvinylpyrrolidone (PVP), graphene oxide (GO), and ammonium hydroxide solution (NH4OH). The systematic effects of synthesis conditions on the microstructure and formation of binary and ternary composite systems were studied. Importantly, high-crystalline GO-Fe3O4-Ag ternary nanomaterials with average sizes of Fe3O4 particles ~16 nm and of Ag particles ~20 nm were obtained at optimized conditions (125 °C, 2.5 mM of AgNO3 and 5 mL of NH4OH). Magnetic analysis indicated that the saturated magnetization value of Fe3O4-Ag binary composite sample (~73.1 emu/g) was improved as compared with pure Fe3O4 nanoparticles (~60.6 emu/g), while this of GO-Fe3O4-Ag ternary composite sample was about 57.3 emu/g. With exhibited advantages of low-cost, high purity and short synthesis time, the hydrothermal-synthesized GO-Fe3O4-Ag ternary nanocomposite can be a promising candidate for advanced environmental catalyst and biomedical applications.

Photochemical Decoration of Silver Nanocrystals on Magnetic MnFe2O4 Nanoparticles and Their Applications in Antibacterial Agents and SERS-Based Detection

In this study, multifunctional nanocomposites consisting of silver nanoparticles and manganese ferrite nanoparticles (Ag–MnFe2O4) were successfully synthesized using a two-step chemical process. The formation of Ag–MnFe2O4 nanocomposites were analyzed by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy measurements. Noticeable antibacterial activity of the Ag–MnFe2O4 nanocomposites was demonstrated against two Gram-negative bacteria, Salmonella enteritidis and Klebsiella pneumoniae. A direct-drop diffusion method can be an effective way to investigate the antibacterial effects of nanocomposite samples. Interestingly, we also demonstrated the use of Ag–MnFe2O4 nanocomposites as a surface-enhanced Raman scattering (SERS) platform to detect and quantify trace amounts of organic dye in water solutions. The combination of Ag and MnFe2O4 nanoparticles opens opportunities for creating advantages such as targeted bactericidal delivery, recyclable capability, and sensitive SERS-based detection for advanced biomedicine and environmental monitoring applications.

Investigation of a stable Mo substrate for chalcopyrite solar cells: a green process for sustainable energy applications

Abstract Molybdenum (Mo) films (~1 μm) as back contacts for chalcopyrite solar cells are usually deposited onto the glass substrate by DC-sputtering because of their high deposition rate with a column structure. During selenization, selenium (Se) is infiltrated deeply into the column structure of Mo films. Although the difference in sheet resistance and resistivity values before and after selenization is negligible, the selenized Mo films are easily peeled off from the glass substrate even with the tape testing. The existence of Se in Mo films with a column structure was investigated by scanning electron microscopy cross-section, energy-dispersive X-ray spectroscopy, and X-ray diffraction measurement. To overcome this obstacle, a 200-nm-thick Mo compact layer was deposited by RF-sputtering on top of the Mo film to prevent Se infiltration. Finally, the bilayer of Mo was passed with tape testing for both films before and after selenization. The results may be helpful to further achieve highly stable fabrication processes of chalcopyrite solar cells.