Porous Single-walled Carbon Nanotube Research Articles

Effect of bias voltage and carrier gas on the hydrogen gas-sensing properties of tungsten oxide nanobeads

We investigated the effect of bias voltage and carrier gas on the hydrogen sensing performance of tungsten oxide nanobeads. The tungsten oxide nanobeads were prepared by a template-assisted method followed by calcination. The porous single walled carbon nanotube thin film was used as sacrificed template for the deposition of tungsten, followed by thermal calcination at high temperature to oxidize W into WO3 and to burn out the template. The crystal structures and morphology of the synthesized materials were characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectra. Hydrogen gas sensing properties were tested in air and in N2 as refence for comparison. Our results indicated that Schottky junction was formed at the interface of WO3 and Pt electrodes. The sensor operated under revered bias voltage processed excellent hydrogen sensing performance. In addition, the H2 sensing performance of the WO3 nanobeads is higher when measured in N2 gas as reference.

Facile synthesis of porous single-walled carbon nanotube for sensitive detection of 8-Hydroxy-2′-deoxyguanosine

In this work, a facile strategy was proposed to prepare porous single-walled carbon nanotubes (PSWNT) via a green carbon thermal reduction for the first time. The morphology, structure and electrochemical properties of PSWNT were investigated by transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy. Transmission electron microscopy and nitrogen adsorption-desorption investigations indicated the average pore size of PSWNT is about 3nm. The electrochemical experiments demonstrated that PSWNT possess a relatively large surface area, strong adsorptive ability and excellent electrical conductivity. With the help of the unique porous structure in combination with inherent properties of carbon nanotubes, the PSWNT/GCE-based sensor showed outstanding electrochemical performance for 8-Hydroxy-2′-deoxyguanosine (8-OHdG) with a detection limit of 1.0nM. Therefore, it is believed that PSWNT is a promising candidate for applications in sensors. Moreover, the influence factors of DNA damage are also studied in detail, and some kinetics parameters are obtained.

Porous Au-embedded WO3 Nanowire Structure for Efficient Detection of CH4 and H2S.

We developed a facile method to fabricate highly porous Au-embedded WO3 nanowire structures for efficient sensing of CH4 and H2S gases. Highly porous single-wall carbon nanotubes were used as template to fabricate WO3 nanowire structures with high porosity. Gold nanoparticles were decorated on the tungsten nanowires by dipping in HAuCl4 solution, followed by oxidation. The surface morphology, structure, and electrical properties of the fabricated WO3 and Au-embedded WO3 nanowire structures were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and current–voltage measurements. Formation of a nanowire structure resulted in significant enhancement in sensing response to H2S and CH4 gases. Furthermore, Au embedment into the WO3 nanowire structures remarkably improved the performance of the sensors. The increase in response performance of sensors and adsorption–desorption kinetic processes on the sensing layers were discussed in relation with the role of Au embedment.

Electrochromic properties of porous WO3–TiO2 core–shell nanowires

A highly porous TiO2–WO3 core–shell nanowire structure for an electrochromic (EC) coating was fabricated by sputter deposition of titanium and tungsten on a porous single-walled carbon nanotube template. This process was followed by thermal oxidation. The morphology and crystalline quality of composite materials were investigated by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical and EC properties were also examined and compared with thin TiO2–WO3 composite films as well as individual WO3 and TiO2 nanowire structures. The highly porous composite nanowire structure showed a highly enhanced proton intercalation capacity with good reversible electrochemical cycling of intercalation–deintercalation. The nanostructure also showed significantly improved EC contrast and coloration efficiency. This enhancement was observed with high chemical stability of the material. We proposed an atomic model of proton insertion into oxygen vacancies to explain the EC property and gas sensing simultaneously.

General and scalable route to synthesize nanowire-structured semiconducting metal oxides for gas-sensor applications

The development of a general, low-cost, and scalable method for synthesizing nanowire (NW) structures made of different materials for use in the fast and accurate detection of toxic and flammable gases is extremely important for monitoring environmental pollution and gas leakage. This study reports on a scalable and general route for synthesizing nanowire-structured semiconducting metal oxides for gas nanosensors. Different metal oxide nanowires made of titanium oxide, tin oxide, zinc oxide, copper oxide, and tungsten oxide, were synthesized via sputter deposition of correlative metals over porous single-walled carbon nanotubes (SWNTs) templates followed by oxidation. The microstructures and morphologies of the metal oxide nanowires were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results showed that the synthesized materials could be nanowires or bead-like nanowires, depending on the adhesion between the deposited metals and the SWNTs substrates. Different metal oxide nanowires with lengths of up to several micrometers and controllable diameters could be easily synthesized and were found to be suitable for gas sensor applications. This synthetic method is expected to introduce new strategies and promised potential applications for NWs in other fields, such as in photocatalysts, electrochemicals, and biosensors.

Effective hydrogen gas nanosensor based on bead-like nanowires of platinum-decorated tin oxide

Abstract Development of low-cost and effective gas nanosensors for early detection and warning of hydrogen leakage is of crucial importance to prevent disastrous hydrogen explosion. Herein, we introduce the synthesis of Pt-decorated bead-like tin oxide nanowires for the effective detection of hydrogen, in which the Sn and Pt were sputter deposited in sequence over the porous single-wall carbon nanotubes film templates, followed by the oxidation process. The gas-sensing properties of undecorated and Pt-decorated nanosensors to H 2 , NH 3 , and NO x are investigated to determine the effect of the Pt decoration on sensor performance. Results show that the Pt decoration enhances the responsivity to the reducing gases (H 2 and NH 3 ) and decreases to the oxidizing gas (NO x ). The response to hydrogen of the Pt-decorated nanosensor is approximately 5.7 times higher than that of its undecorated counterpart and is thus effective for the detection of hydrogen concentrations at the lower explosive limit with a fast response time of less than a minute.

Preparing large-scale WO 3 nanowire-like structure for high sensitivity NH 3 gas sensor through a simple route

The large-scale nanowire-like (NW) structure of tungsten oxide is synthesized by the deposition of tungsten metal on the substrate of porous single-wall carbon nanotubes (SWCNTs) film, followed by thermal oxidation process. The morphology and crystallinity of the synthesized materials are analyzed by SEM, TEM, XRD, and Raman spectroscopy. Results showed that tungsten oxide NWs deposited on SWCNTs have a porous structure with an average diameter of about 70 nm and a length of up to micrometers. The NH 3 gas-sensing properties of tungsten NWs were measured at different temperatures. A maximum response of 9.7–1500 ppm at 250 °C with rapid response and recovery times of 7 and 8 s are found, respectively. In addition, the gas sensing mechanism of fabricated NWs is also discussed in term of surface resistivity and barrier height model.

Structural and Field Emission Properties of GaN–SWCNT Nanocomposites

GaN is deposited on the surface of single wall carbon nanotubes (SWCNTs) by molecular beam epitaxy using a single source molecular precursor at low temperatures. Porous SWCNTs are synthesized on substrates by modified arc discharge method. These porous template samples are used for growing GaN. The crystal quality and microstructure of the GaN–CNT composites are analyzed using grazing incident XRD, SEM equipped with energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and transmission electron microscopy. The field emission properties of the as-synthesized products are investigated. A turn-on field of and a high current density of at a field of are observed. The results could be related to the micro- and shell-core structures of GaN/CNT nanocomposites.

GaAs-Carbon Nanotubes Nanocomposite: Synthesis and Field-emission Property

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at under an atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from to . The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under , while nanowire structures begin to form on the beads above . The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

Synthesis of porous CuO nanowires and its application to hydrogen detection

Porous nanowire-structured cupric oxide (CuO) film is synthesized by deposition of Cu on porous single-walled carbon nanotube (SWNT) substrate followed by a thermal oxidation process. Oxidation is done in air at a temperature range of 300–800 °C to oxidize the Cu while removing the SWNT template. The oxidation temperature determines the stoichiometry of the CuO formed, and thus the electrical property. The structures and electrical properties of the synthesized materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and current–voltage measurements. Sensing property is examined using hydrogen gas. Gas sensing mechanism and the advantages of nanowire structure as a sensor are also discussed. The best response and recovery results are observed with the CuO nanowires oxidized at 400 °C at a working temperature of 250 °C.

Tin-Oxide Nanotubes for Gas Sensor Application Fabricated Using SWNTs as a Template

We develop a simple method to synthesize nano tube or wire structure of tin-oxide for gas sensor application. It is realized by the rheotaxial growth and thermal oxidation (RGTO) of tin on porous single-wall carbon nanotubes (SWNTs) as a template. The morphology and chemical property of thus formed nanostructures are examined. The electrical and NO(x) gas sensing properties are also investigated. The sensor exhibits a fast response time of less than 100 seconds and a good recovery. A sensing response of 23,400% to 10 ppm concentration at 200 degrees C is observed.

Fabrication of Ordered Porous SWNT‐Polymer Nanocomposites by Emulsion Templating

AbstractPorous polymer films were produced from water‐in‐oil emulsion. Aqueous droplets were dispersed in PMMA/benzene solution without any emulsifier. Simple dip‐coating of the emulsion on a substrate and air‐drying led to hexagonally ordered porous thin films. Porous single walled carbon nanotubes (SWNT)‐polymer composite films were prepared through the similar procedures also. The electrical conductivity of porous SWNT‐polymer composites increased with the content of SWNT.