Van Hoang Luan

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.

Preparation of a reduced graphene oxide hydrogel by Ni ions and its use in a supercapacitor electrode

A three-dimensional (3D) reduced graphene oxide hydrogel (rGOH) was prepared by hydrothermal synthesis based on the electrostatic force and chemical reaction between graphene oxide (GO) and Ni ions in a nickel acetate solution. The Ni–rGOH fabricated in this study exhibited a highly increased surface area compared to NiO nanoparticles owing to the formation of 3D networks. After the reduction of functional groups in Ni–GOH, Ni–rGOH showed highly enhanced capacitance (351 F g−1) at a charge/discharge current density of 0.625 A g−1 and 90% capacitance retention after 1000 cycles. The energy density of Ni–rGOH was 175.5 W h kg−1 at a power density of 1.125 kW kg−1, while maintaining a high-energy density of 118 W h kg−1 at a power density of 4.5 kW kg−1.

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.