Eric Siu-Wai Kong

Reduced graphene oxide–polyaniline hybrid: Preparation, characterization and its applications for ammonia gas sensing

Here we present a useful ammonia (NH3) gas sensor based on reduced graphene oxide (RGO)–polyaniline (PANI) hybrids. PANI nanoparticles were successfully anchored on the surface of RGO sheets by using RGO–MnO2 hybrids as both of the templates and oxidants for aniline monomer during the process of polymerization. The resultant RGO–PANI hybrids were characterized by transmittance electron microscopy, infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and scanning electron microscopy. The NH3 gas sensing performance of the hybrids was also investigated and compared with those of the sensors based on bare PANI nanofibers and bare RGO sheets. It was revealed that the synergetic behavior between both of the candidates allowed excellent sensitivity and selectivity to NH3 gas. The RGO–PANI hybrid device exhibited much better (3.4 and 10.4 times, respectively, with the concentration of NH3 gas at 50 ppm) response to NH3 gas than those of the bare PANI nanofiber sensor and bare graphene device. The combination of the RGO sheets and PANI nanoparticles facilitated the enhancement of the sensing properties of the final hybrids, and pave a new avenue for the application of RGO–PANI hybrids in the gas sensing field.

Ultrasonic nanowelding of carbon nanotubes to metal electrodes

As imple ultrasonic nanowelding technique has been developed to reliably bond single-wall carbon nanotubes (SWCNTs) onto metal electrodes, by pressing SWCNTs against electrodes under a vibrating force at ultrasonic frequency. The bonds formed have been demonstrated to be mechanically robust. Using this technique, a stable low-Ohmic contact between SWCNTs and metal electrodes was achieved, with resistances in the range of 8–24 k� for a 1 µ ml ong metallic SWCNT at room temperature. The performance of carbon nanotube field-effect transistors (FETs) fabricated using this ultrasonic nanowelding method has also been greatly improved. Transconductance as high as 3.6 µ Sa mong the solid-state back-gate individual nanotube FETs has been achieved. (Some figures in this article are in colour only in the electronic version)

Single-walled carbon nanotube/cobalt phthalocyanine derivative hybrid material: preparation, characterization and its gas sensing properties

A novel hybrid material composed of single-walled carbon nanotubes (SWNTs) and cobalt phthalocyanine (CoPc) derivatives have been obtained. The resultant hybrid has been confirmed by infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy and X-ray photoelectron spectrometry. The results revealed that the CoPc derivatives had been successfully anchored on the surface of nanotubes through π–π stacking. The quantitatively determination of the CoPc derivatives have also been carried out through characterization by thermogravimetric analysis. Furthermore, the morphology of the resultant SWNT-CoPc derivative hybrids has been observed by transmission electron microscopy and scanning electron microscopy. Finally, gas sensor tests were performed to check the potential of this hybrid material while the sensing devices have been fabricated. The synergetic behavior between both of the candidates allows an excellent sensitivity and selectivity to dimethyl methylphosphonate (DMMP) (stimulant of nerve agent sarin). Overall, we present the advantages of combining metallophthalocyanine (MPc) with SWNTs in enhancing the properties of the final product, and pave a new avenue for the application of SWNT-MPc hybrids in the gas sensing field.

Nanowelded Carbon‐Nanotube‐Based Solar Microcells

Photovoltaic (PV) cells are of immense interest due to their vast application potential in the fields of energy and communication. The adoption of ideal photoactive material and the design of optimum device structure are critical to achieving low-cost, high-efficiency PV cells. The semiconducting single-walled carbon nanotubes (SWNTs) are potentially an attractive material for PV applications due to their many unique structural and electrical properties. They are almost defect free to greatly decrease carrier recombination, bear a wide range of direct bandgaps matching the solar spectrum, and show strong photoabsorption and photoresponse from ultraviolet to infrared, and exhibit high carrier mobility [16] and reduced carrier transport scattering. Indeed, previous studies had attempted to fabricate SWNT films into photoelectrochemical solar cells. However, due to the inefficient separation and collection of photoexcited carriers and large intertube interaction, the maximum monochromatic incident photo-to-current conversion efficiency (IPCE) obtained for the cell is only 0.15%. Here, we report a novel approach that enables fabricating SWNT PV solar microcells with high power-conversion efficiency. In this cell, a directed array of monolayer SWNTs was nanowelded onto two asymmetrical metal electrodes with high and low work functions, respectively, resulting in a strong built-in electric field in SWNTs for efficient separation of photogenerated electron–hole pairs. Under solar illumination,

The Prospective Two-Dimensional Graphene Nanosheets: Preparation, Functionalization, and Applications

Graphene, as an intermediate phase between fullerene and carbon nanotube, has aroused much interests among the scientific community due to its outstanding electronic, mechanical, and thermal properties. With excellent electrical conductivity of 6000 S/cm, which is independent on chirality, graphene is a promising material for high-performance nanoelectronics, transparent conductor, as well as polymer composites. On account of its Young’s Modulus of 1 TPa and ultimate strength of 130 GPa, isolated graphene sheet is considered to be among the strongest materials ever measured. Comparable with the single-walled carbon nanotube bundle, graphene has a thermal conductivity of 5000 W/(m·K), which suggests a potential application of graphene in polymer matrix for improving thermal properties of the graphene/polymer composite. Furthermore, graphene exhibits a very high surface area, up to a value of 2630 m2/g. All of these outstanding properties suggest a wide application for this nanometer-thick, two-dimensional carbon material. This review article presents an overview of the significant advancement in graphene research: preparation, functionalization as well as the properties of graphene will be discussed. In addition, the feasibility and potential applications of graphene in areas, such as sensors, nanoelectronics and nanocomposites materials, will also be reviewed.

Preparation of high aspect ratio nickel oxide nanowires and their gas sensing devices with fast response and high sensitivity

NiO p-type semiconducting nanowires with high aspect ratios up to approximately 2000 have been prepared by chemical reduction under assistance of magnetic fields and subsequent heat treatment method. The diameter of NiO nanowires is about 150 nm and the length can be up to 300 μm. Ni nanowires have been prepared from a structure of Ni nanospheres at atmospheric pressure. Transformation from Ni nanowires to NiO semiconducting nanowires via in situ chemical oxidation process in open air have been conducted by undergoing a process of an amorphous oxidation. Heat treatment results in significant influence on the grain size in the NiO nanowire structure. NiO nanowires with crystalline grain size of about 12 nm is characteristic with a band gap energy of about 4.20 eV, which is larger than the bulk NiO material (3.65 eV). Meanwhile, we find that the optical band gap energy gradually increases with the decrease of the crystalline grain size. NiO nanowires with different grain sizes have been used to fabricate arrays for a gas sensor under an external magnetic field. NH3 gas sensing capability at room temperature by NiO nanowire arrays is characteristic for its high sensitivity, fast response, rapid recovery and good reproducibility.

A Facile Route for the Large Scale Fabrication of Graphene Oxide Papers and Their Mechanical Enhancement by Cross-linking with Glutaraldehyde

A facile route for the large scale production of graphene oxide (GO) papers and their mechanical enhancement has been presented in this work. The novel paper-like GO made from individual GO sheets in aqueous suspension can be achieved in large scale by a simple drop casting method on hydrophobic substrates. Significant enhancement in mechanical stiffness (341%) and fracture strength (234%) of GO paper have been achieved upon modification with a small amount (less than 10 wt%) of glutaraldehyde (GA). The cross-linking reaction takes place between hydroxyl groups on the surface of GO and aldehyde groups of GA, through forming hemiacetal structure, which can result in distinct mechanical enhancement of the GO papers.

Carbon nanotube photovoltaic device with asymmetrical contacts

A photovoltaic (PV) device based on “high-work-function metal/single-walled carbon nanotube/low-work-function metal” hybrid junction has been studied theoretically by the self-consistent nonequilibrium Green’s function approach. The PV effect and power conversion efficiency (η) of the device under light illumination are simulated, with a monochromatic η of higher than 40% for incident photon energies near the nanotube band-gap energy predicted. It is shown that the gate voltage and gate oxide thickness have an important influence on the device η.

Self-assembly of CdTe nanocrystals at the water/oil interface by amphiphilic hyperbranched polymers.

A general strategy for realizing the self-assembly of aqueous CdTe nanocrystals (NCs) at the water/oil interface by means of an amphiphilic core-shell hyperbranched polymer has been proposed. Aqueous CdTe NCs were firstly transferred into the chloroform phase in the presence of palmityl chloride functionalized hyperbranched poly(amidoamine) (HPAMAM-PC), and then self-assembled at the water/chloroform interface by decreasing the pH value of the aqueous phase or introducing α-CDs to the aqueous phase. The resulting CdTe/HPAMAM-PC self-assembly film was characterized by fluorescence microscopy, UV-vis, PL, TEM, EDS, FT-IR, DSC and TGA.

Preparation and growth mechanism of nickel nanowires under applied magnetic field

Nickel nanowires with large aspect ratio of up to 300 have been prepared by a hydrazine hydrate reduction method under applied magnetic field. The diameter of nickel nanowires is about 200 nm and length up to 60 μm. The role of magnetic field on the growth of magnetic nanowires is discussed and a magnetic nanowire growth mechanism has been proposed. Nickel ions are firstly reduced to nickel atoms by hydrazine hydrates in a strong alkaline solution and grow into tiny spherical nanoparticles. Then, these magnetic particles will align under a magnetic force and form linear chains. Furthermore, the as-formed chains can enhance the local magnetic field and attract other magnetic particles nearby, resulting finally as linear nanowires. The formation and the size of nanowires depend strongly on the magnitude of applied magnetic field.