Browsing by Author "Chaudhary, Manchal"

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Electrical and Dielectric Properties of Exfoliated Thermally Reduced Graphene Based Polyurethane Nanocomposites
(2017-12-01)
Bansala, Taruna
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Joshi, Mangala
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Mukhopadhyay, Samrat
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Doong, Ruey-An
;
Chaudhary, Manchal
Thermally reduced graphene nanosheets (TRG) were prepared by using thermal exfoliation followed by annealing and then were served as fillers to well disperse in thermoplastic polyurethane (TPU) in a concentration range of 0.5-5.5 vol.%. The electrical conductivity, dielectric and mechanical properties of as-prepared TPU/TRG nanocomposite thin films were examined. The DC electrical conductivity was improved up to 3 x 1x10(-2) S m(-1) for the 5.5 vol.% TPU/TRG nanocomposite in comparison to 2 x 81x10(-11) S m(-1) for neat TPU matrix. Addition of TRG nanosheets enhanced the Young's modulus but reduced the strain-at-break and tensile strength of the nanocomposite films. The dielectric behavior including dielectric constant (epsilon) and tangent loss varied with the TRG loading in the nanocomposites. Results showed the increase in dielectric constant from 1 to 550 as well as the increase in tangent loss from 0.03 to 350 upon increasing concentration of TRG in the frequency range of 20-106 Hz. The high dielectric constant values in the low frequency region is mainly attributed to the Maxwell-Wagner polarization effect, while high values of tangent loss is contributed from the current leakage through the electrically conducting network of TRG sheets formed within the TPU matrix at high filler loadings.
Electrically conducting graphene-based polyurethane nanocomposites for microwave shielding applications in the Ku band
(2017-02)
Bansala, Taruna
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Joshi, Mangala
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Mukhopadhyay, Samrat
;
Doong, Ruey-an
;
Chaudhary, Manchal
Electrically conducting, thermally reduced graphene nanosheets (TRG) were synthesized through thermal exfoliation and subsequent annealing of graphene oxide at 800 A degrees C. Thermoplastic polyurethane (TPU)-based nanocomposites with different concentrations (ranging between 0 and 5.5 vol%) of TRG nanosheets were prepared by the solution blending method. Morphology, phase purity, and conducting properties of TPU and TPU/TRG nanocomposites were investigated through scanning electron microscopy, X-ray diffraction, conductive atomic force microscopy (C-AFM) and Raman spectroscopy. C-AFM images show the presence of electrically conducting TRG nanosheets embedded in the TPU matrix. Electromagnetic interference (EMI) shielding measurements were also undertaken on 2-mm-thick rectangular pellets. Shielding parameters such as shielding effectiveness, DC electrical conductivity, and dielectric properties, i.e., real and imaginary parts of permittivity were investigated. Our results show that the TPU/TRG nanocomposite at 5.5 vol% loading exhibits an enhanced electrical conductivity of the order of 3.1 x 10(-2) S/m and shows a superior EMI SE of similar to-26 to -32 dB in the Ku band frequency region. EMI shielding values were found to be dominated by the material\'s absorption behavior. The dielectric properties of TPU/TRG nanocomposites were also analyzed, and they demonstrate a good correlation with EMI shielding.
Formation of Cu2O/Titanate/Titania Heterojunctions from Hydrothermally Induced Dual Phase Transitions
(2016-09-29)
Chaudhary, Manchal
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Chang, Sue-min
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Doong, Ruey-an
;
Tsai, Hsin-mu
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環境工程研究所
A microwave-assisted hydrothermal method has been developed as an efficient approach to readily induce phase transition of titanate assemblies in conjunction with decoration of Cu2O dusters on the surface. The influence of Cu2+ ions on the hydrothermally induced structural evolution was examined, and the roles of heterojunctions in the resulting composites in charge separation for improved photocatalytic activity were clarified. Hierarchical titanate assemblies with high adsorption capacity for Cu2+-ions (95.7 meg) were prepared from a low alkaline condition, Microwave-assisted hydrothermal treatment was then used to transform the adsorbents into Cu2O/titanate/titania photocatalysts in 20 min via inducing titanate-to-titania and Cu2+-to-Cu2O dual transitions. While tubular architecture was maintained in, the composites, the Cu2O dusters highly dispersed on the surface. Adsorbed Cu2+ ions have been found to retard the titanate-to-titania transformation locally, thus leading to Cu2O/titanate/titania heterojanctions. The multiheterojunctions enabled the composites to exhibit 1.7-5.1 times higher activity than the commercial product P25 (k(obs), 0.06 min(-1)) for decomposition of bisphenol A due to charge separation. EPR results dearly reveal that the type II band alignment effectively drove electrons and holes to migrate toward the titania and the Cu2O moieties, respectively, and the titanate moiety positioning in between prevented back recombination. The optimal C(u)2O loading to the highest activity (k(obs),0.306 min(-1)) Was -3.7 wt %. Over the optimal amount, the rower reduction potential in the valence band of the Cu2O dusters compensated for the positive effect from charge separation, thus causing the activity to decline in turn.
Synthesis and shielding properties of PVP-stabilized-AgNPs-based graphene nanohybrid in the Ku band
(2016-11)
Bansala, Taruna
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Mukhopadhyay, Samrat
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Joshi, Mangala
;
Doong, Ruey-an
;
Chaudhary, Manchal
PVP-stabilized silver nanoparticles (AgNP)-based graphene nanohybrid (Ag-PVP-CRG) have been synthesized and high performance shields for electromagnetic interference (EMI) in the microwave region have been developed. Morphological characterization of Ag-PVP-CRG nanohybrid by scanning electron microscopy, X-ray diffraction and high resolution transmission electron microscopy revealed PVP-stabilized AgNPs (diameter: 15-30 nm) decorated graphene sheets. The Ag-PVP-CRG nanohybrid showed excellent shielding response in the Ku band frequency region, which is majorly governed by absorption losses. The results show that the total EMI shielding effectiveness (SE) value is 58 dB for Ag-PVP-CRG at 2.0 mm thickness in the Ku-band region, dominated by absorption mechanism, which overpowered the 10 dB value of graphene oxide. The presence of AgNPs on graphene sheets enhances space charge polarization, multiple scattering and effective anisotropy energies of the nanohybrid, resulting in high electromagnetic shielding effectiveness. The dielectric behavior was evaluated to correlate with the EMI shielding mechanism. (C) 2016 Elsevier B.V. All rights reserved.
Ternary Au/ZnO/rGO nanocomposites electrodes for high performance electrochemical storage devices
(2017-10-31)
Chaudhary, Manchal
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Doong, Ruey-an
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Kumar, Nagesh
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Tseng, Tseung Yuen
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環境工程研究所
The combination of metal and metal oxide nanoparticles with reduced graphene oxides (rGO) is an active electrode material for electrochemical storage devices. Herein, we have, for the first time, reported the fabrication of ternary Au/ZnO/rGO nanocomposites by using a rapid and environmentally friendly microwave-assisted hydrothermal method for high performance supercapacitor applications. The ZnO/rGO provides excellent electrical conductivity and good macro/mesopore structures, which can facilitate the rapid electrons and ions transport. The Au nanoparticles with particle sizes of 7-12 nm are homogeneously distributed onto the ZnO/rGO surface to enhance the electrochemical performance by retaining the capacitance at high current density. The Au/ZnO/rGO nanocomposites, prepared with the optimized rGO amount of 100 mg exhibit a high specific capacitance of 875 and 424 F g(-1) at current densities of 1 and 20 A g-1, respectively, in 2 M KOH. In addition, the energy and power densities of ternary Au/ZnO/rGO can be up to 17.6-36.5 Wh kg(-1) and 0.27-5.42 kW kg(-1), respectively. Results obtained in this study clearly demonstrate the excellence of ternary Au/ZnO/rGO nanocomposites as the active electrode materials for electrochemical pseudocapacitor performance and can open an avenue to fabricate metal/metal oxide/rGO nanocomposites for electrochemical storage devices with both high energy and power densities. (C) 2017 Elsevier B.V. All rights reserved.
The roles of phosphate and tungstate species in surface acidities of TiO2-ZrO2 binary oxides - A comparison study
(2018-05-15)
Chaudhary, Manchal
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Shen, Po-fan
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Chang, Sue-min
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環境工程研究所
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Institute of Environmental Engineering
Porous tungstated and phosphated TiO2-ZrO2 (TZ) binary oxides with high and strong acidity were successfully prepared by means of sol-gel or impregnation approaches. In addition, the influences of the two types of modifiers on the microstructures and acidity were systematically examined, compared, and clarified. The TZ oxide derived from a surfactant-templating method exhibited a high surface area of 195 m(2)/g with a pore size of 6.3 nm. Moreover, it had a high acidity of 859 mu mol/g with a density of 4.4 mu mol/nm(2) because of defective surface. Phosphation significantly increased the acidity to 1547 mmol/g and showed the highest acid density of 6.7 mu mol/nm(2) at a surface P density of 22.7P/nm(2). On the other hand, tungstated compounds just showed the highest acidity of 972 mmol/g and the highest acid density of 4.8 mu mol/nm(2) at 4.7 W/nm(2). Compared to tungstate species, phosphate anions are more capable of promoting the acidity because they are able to distort the host network and inhibit elemental rearrangement. While Lewis acidity prevailed in the tungstated compounds, Bronsted acidity was dominant in the phosphated oxides. The W=O and P-OH groups were responsible for strong acidity in the modified compounds. Phosphated compounds formed strong Bronsted acid sites on the P-OH groups with a particular strength, and tungstation produced Lewis acid sites with a continuous strength on the metal ions adjacent to the tungstate moieties. Cyclic NH3 adsorption-desorption processes revealed that the active sites for NH3 adsorption were stable in both the tungstate and phosphate modified compounds, revealing that these solid acids are promising as the adsorbents for removal of base gases. (C) 2018 Elsevier B.V. All rights reserved.