Huynh Ngoc Tien

Synthesis of a highly conductive and large surface area graphene oxide hydrogel and its use in a supercapacitor

In this report, we describe the structure of a robust and highly conductive 3D graphene oxide hydrogel. The reduced graphene oxide hydrogel or rGH is fabricated by a crosslinking reaction with ethylene diamine followed by a hydrazine reduction. The material showed a high electrical conductivity of 1351 S m−1 and a specific surface area of 745 m2 g−1 with 10.3 MPa break strength. When used as electrodes for a supercapacitor, it showed a high specific capacitance of 232 F g−1.

Novel conductive epoxy composites composed of 2-D chemically reduced graphene and 1-D silver nanowire hybrid fillers

In this study, 1-D Ag nanowires (NWs), 2-D chemically reduced graphene (CRG), and hybrid CRG–Ag NW fillers were investigated for use as conductive epoxy composites. By combining the 2-D CRG with 1-D Ag NWs, the percolation limit of the Ag NWs decreased from 30 wt% to 10 wt% and the electrical conductivity was dramatically enhanced because of the decreased tunneling resistance between the Ag NWs due to the thin 2-D conductive CRGs. Their thermal and mechanical properties were also improved due to the chemical crosslinking effects between CRGs and the hardener in the epoxy matrix as well as the physical crosslinking effects between nano-structures and polymer chains. The break strength of the CRG/Ag-NW/epoxy composite was 50% higher than that of the pure epoxy resin.

Fabrication of 3D structured ZnO nanorod/reduced graphene oxide hydrogels and their use for photo-enhanced organic dye removal

Hybrid 3-dimensional (3D) structures composed of zinc oxide (ZnO) nanorods and reduced graphene oxide hydrogel (rGOH) were fabricated by chemical reaction between Zn ions and GO followed by in-situ lateral growth of ZnO nanorods using Zn ions as seed points. The 3D networked ZnO nanorod-rGOH (ZNR-rGOH) fabricated in this study exhibited excellent methylene blue (MB) removal efficiency due to efficient physical adsorption of dye molecules because of electrostatic attractive forces and enhanced photocatalytic activity by the laterally grown ZnO nanorods. The Langmuir-Hinshelwood rate constant of ZNR-rGOH was 4-fold higher than that of pristine rGO due to the enhanced photocatalytic effects obtained by incorporating laterally grown ZnO nanorods inside the rGOH network.

Fast and effective electron transport in a Au–graphene–ZnO hybrid for enhanced photocurrent and photocatalysis

A novel ZnO nanosheet aggregated hollow sphere (nSAHS) has been hydrothermally synthesized. Wrapping Au/reduced graphene oxide (Au/rGO) onto the ZnO nSAHS facilitates electron transfer at the ZnO interface. The photoinduced charge transfer of the Au/rGO/ZnO hybrid has been characterized using photoluminescence (PL) and a time-resolved PL decay profile. The quenched PL emission of Au/rGO/ZnO indicates decreased electron–hole pair recombination and facilitated electron transport, which results from the large surface area of the ZnO nSAHS structure, good physical adsorption of Au/rGO onto ZnO, and the excellent chemical interaction at the Au/rGO–ZnO interface. The Au/rGO/ZnO hybrid exhibits fast (4.46 ps) and effective (80.49%) charge transfer at the hybrid interface, indicating that Au/rGO/ZnO has better photocurrent responses and photocatalytic activities than rGO/ZnO and ZnO.

Enhancement of recombination process using silver and graphene quantum dot embedded intermediate layer for efficient organic tandem cells

High performance of organic tandem solar cell is largely dependent on transparent and conductive intermediate layer (IML). The current work reports the design and fabrication of an IML using a simple solution process. The efficiency of a homo-tandem device with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester as an active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly(ethylenimine) as an IML was initially found to be 3.40%. Further enhancement of the cell efficiency was achieved using silver nanoparticles (Ag-NPs) of different sizes and graphene quantum dot embedded IML. A maximum efficiency of 4.03% was achieved using 7 nm Ag-NPs that contribute to a better recombination process. Also, the performance of the tandem cell was solely based on the electrical improvements indicated by the current - voltage measurements, external quantum efficiency and impedance analysis. The use of Ag-NPs in the IML has been shown to lengthen the life time of electron-hole pairs in the device. This study thus paves way to develop such efficient IMLs for more efficient tandem solar cells.

Fabrication of novel 2D nio nanosheet branched on 1D-ZnO nanorod arrays for gas sensor application

Fabrication of 3D structures composed of 1D n-type ZnO nanorods (NRs) and 2D p-type NiO nanosheets (NSs) by a low-cost, low-temperature, and large-area scalable hydrothermal process and its use in highly sensitive NO2 gas sensors were studied. The p-n heterojunctions formed by NiO-ZnO interfaces as well as large area two-dimensional NiO NSs themselves increased the adsorption of NO2. Moreover, the charge transfer between NiO and ZnO enhanced the responsivity and sensitivity of NO2 sensing even at a concentration of 1 ppm. The 30-min NiO NS growth on ZnO NRs in the hybrid sensor showed the highest sensitivity due to the formation of optimum p-n heterojunctions between ZnO NRs and NiO NSs for gas adsorption and carrier transport. Low responsivity toward reducing gases was also observed.

Three-Dimensional Porous Nitrogen-Doped NiO Nanostructures as Highly Sensitive NO2 Sensors

Nickel oxide has been widely used in chemical sensing applications, because it has an excellent p-type semiconducting property with high chemical stability. Here, we present a novel technique of fabricating three-dimensional porous nitrogen-doped nickel oxide nanosheets as a highly sensitive NO2 sensor. The elaborate nanostructure was prepared by a simple and effective hydrothermal synthesis method. Subsequently, nitrogen doping was achieved by thermal treatment with ammonia gas. When the p-type dopant, i.e., nitrogen atoms, was introduced in the three-dimensional nanostructures, the nickel-oxide-nanosheet-based sensor showed considerable NO2 sensing ability with two-fold higher responsivity and sensitivity compared to non-doped nickel-oxide-based sensors.