Duc Dung Nguyen

Superhydrophobic and superoleophilic properties of graphene-based sponges fabricated using a facile dip coating method

Superhydrophobic and superoleophilic graphene-based sponges are demonstrated as efficient absorbents for a broad range of oils and organic solvents with high selectivity, good recyclability, and excellent absorption capacities up to 165 times their own weight. The findings show promise for large-scale removal of organic contaminants, especially in the field of oil spillage cleanup.

Synthesis of ethanol-soluble few-layer graphene nanosheets for flexible and transparent conducting composite films

We report a facile method of preparing few-layer graphene nanosheets (FLGs), which can be soluble in ethanol. Atomic force microscopy and high-resolution transmission electron microscopy studies reveal that FLGs have average thicknesses in the range of 2.6-2.8 nm, corresponding to 8-9 layers. A graphene/nafion composite film has a sheet resistance of 9.70 kΩ/sq at the transmittance of 74.5% (at 550 nm) while the nafion film on polyethylene terephthalate has a sheet resistance of 128 kΩ/sq at transmittance of 90.0%. For the cycling/bending test, almost no change in resistance was exhibited when the film was bent at an angle up to 140°, and no obvious deviation in resistance could be found after 100 bending cycles was applied. In addition, an FLGs-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite layer was demonstrated as the effective hole transporting layer to improve the hole transporting ability in an organic photovoltaic device, with which the power conversion efficiency was enhanced from 3.10% to 3.70%. The results demonstrated the promising applications of FLGs on graphene-based electronics, such as transparent electrode and flexible conducting film.

Low Vacuum Annealing of Cellulose Acetate on Nickel Towards Transparent Conductive CNT–Graphene Hybrid Films

We report a versatile method based on low vacuum annealing of cellulose acetate on nickel (Ni) surface for rapid fabrication of graphene and carbon nanotube (CNT)-graphene hybrid films with tunable properties. Uniform films mainly composed of tri-layer graphene can be achieved via a surface precipitation of dissociated carbon at 800 °C for 30 seconds under vacuum conditions of ∼0.6 Pa. The surface precipitation process is further found to be efficient for joining the precipitated graphene with pre-coated CNTs on the Ni surface, consequently, generating the hybrid films. As expected, the hybrid films exhibit substantial opto-electrical and field electron emission properties superior to their individual counterparts. The finding suggests a promising route to hybridize the graphene with diverse nanomaterials for constructing novel hybrid materials with improved performances.

Macroscopic, freestanding, and tubular graphene architectures fabricated via thermal annealing.

Manipulation of individual graphene sheets/films into specific architectures at macroscopic scales is crucially important for practical uses of graphene. We present herein a versatile and robust method based on annealing of solid carbon precursors on nickel templates and thermo-assisted removal of poly(methyl methacrylate) under low vacuum of ∼0.6 Pa for fabrication of macroscopic, freestanding, and tubular graphene (TG) architectures. Specifically, the TG architectures can be obtained as individual and woven tubes with a diameter of ∼50 μm, a wall thickness in the range of 2.1-2.9 nm, a density of ∼1.53 mg·cm(-3), a thermal stability up to 600 °C in air, an electrical conductivity of ∼1.48 × 10(6) S·m(-1), and field emission current densities on the order of 10(4) A·cm(-2) at low applied electrical fields of 0.6-0.7 V·μm(-1). These properties show great promise for applications in flexible and lightweight electronics, electron guns, or X-ray tube sources.

Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel Wires

Corrosion protection of complex surface is an active area of research due to its importance to commercial applications such as electrochemical fabrication. However, conventional coatings exhibit limited conductivity, thermal stability, and durability and are thus not suitable. Recent work has shown the potential of graphene, a two-dimensional carbon allotrope, for corrosion protection. The studies, however, limited themselves to simple planar geometries that provide limited insight in the applicability to relevant morphologies such as mesh electrodes and roughened surfaces. We here study the corrosion protection ability of tubular graphene (TG) on Ni-wires as a model system for such complex geometries. TG-covered Ni wires of approximately 50 μm diameters were produced by the annealing of cellulose acetate (CA) on Ni. The high quality of the TG coating was confirmed by Raman spectroscopy, scanning electron microscopy, and electrical measurements. We show that the graphene layer number could be controlled by adjusting the CA membrane quantity. We found a direct relation between the degree of corrosion inhibition with the variation of graphene layer number. The increase of graphene layers on a Ni surface could enhance its corrosion inhibition in acidic, basic, and marine environments, which shows the potential of our approach for future applications.

Hollow Few-Layer Graphene-Based Structures from Parafilm Waste for Flexible Transparent Supercapacitors and Oil Spill Cleanup

We report a versatile strategy to exploit parafilm waste as a carbon precursor for fabrication of freestanding, hollow few-layer graphene fiber mesh (HFGM) structures without use of any gaseous carriers/promoters via an annealing route. The freestanding HFGMs possess good mechanical flexibility, tailorable transparency, and high electrical conductivity, consequently qualifying them as promising electrochemical electrodes. Because of the hollow spaces, electrolyte ions can easily access into and contact with interior surfaces of the graphene fibers, accordingly increasing electrode/electrolyte interfacial area. As expected, solid-state supercapacitors based on the HFGMs exhibit a considerable enhancement in specific capacitance (20-30 fold) as compared to those employing chemical vapor deposition compact graphene films. Moreover, the parafilm waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer graphene composite meshes with superior electrochemical performance, outstanding superhydrophobic property, good self-cleaning ability, and great promise for oil spill cleanup.

High-performance flexible electron field emitters fabricated from doped crystalline Si pillar films on polymer substrates

We report a new approach for the synthesis of various crystalline Si nanostructures on a polyimide (PI) substrate via microwave plasma enhanced chemical vapor deposition (MWPECVD) using SiCl4/H2 as precursors, and study the effects of conducting type (i.e., intrinsic, n-type, and p-type) on the electron field emission (EFE) properties of the Si nanostructures. H2 plasma treated B-doped crystalline Si pillars (H2: p-Si pillars) with a diameter of 50 nm and a sharp tip radius of 16 nm on a Mo-coated PI substrate reveals the best EFE performance with a low turn-on field of 5.85 V μm−1, high current density of 1.37 mA cm−2@10 V μm−1, and an extremely high field enhancement factor of 1281.13. This superior EFE performance is achieved because of its geometric features and high conductivity across the emitters. In addition, a flexible crystalline Si film-based field emission prototype device using the H2: p-Si pillar sample as the cathode is constructed. No obvious deterioration on EFE characteristics is observed when the device is subjected to bending at a radius of curvature (R) of 10 mm. According to the lifetime test, we achieve a half-life time over 10 h when a repeating FE-on/off test of 9 times at an R of 10 mm is performed, indicating high flexibility and good stability. These results thus demonstrate important steps toward a low-cost approach for creating high-performance and flexible field emission displays.

Tubular graphene architectures at the macroscopic scale: fabrication and properties

Abstract Specific graphene architectures at the macroscopic scale are paramount for exploring new functions and practical uses of graphene. In this study, macroscopic, freestanding, and tubular graphene (TG) architectures were successfully fabricated through a versatile and robust process based on the annealing of cellulose acetate (CA) on Ni templates. These TG architectures can be obtained as woven tubes with diameters of approximately 50 μm; they possess high graphitic crystallinity, strong electrical conductivity, and favorable corrosion resistance. The effects of processing parameters, such as annealing temperature, annealing time, and amount of CA, on the graphene properties of these architectures were investigated and are discussed in this paper. The graphene properties were characterized through field emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, four-point probe resistivity, and electrochemical measurements.

Correction to Layer Control of Tubular Graphene for Corrosion Inhibition of Nickel Wires

Inhibition of Nickel Wires An T. Nguyen, Wei-Cheng Lai, Bao Dong To, Duc Dung Nguyen, Ya-Ping Hsieh, Mario Hofmann, Hung-Chih Kan, and Chia-Chen Hsu* ACS Appl. Mater. Interfaces 2017, 9 (27), pp 22911−22917. DOI: 10.1021/acsami.7b04381 D to a production error, this paper originally published with a Supporting Information file belonging to another paper. The correct file is now present on the Web site. The ACS apologizes for the error. Addition/Correction