NO2 Gas-sensing Properties Research Articles

Fabrication of Nanosized Island-Like CdO Crystallites-Decorated TiO₂ Rod Nanocomposites via a Combinational Methodology and Their Low-Concentration NO₂ Gas-Sensing Behavior.

TiO2–CdO composite rods were synthesized through a hydrothermal method and sputtering thin-film deposition. The hydrothermally derived TiO2 rods exhibited a rectangular cross-sectional crystal feature with a smooth surface, and the as-synthesized CdO thin film exhibited a rounded granular surface feature. Structural analyses revealed that the CdO thin film sputtered onto the surfaces of the TiO2 rods formed a discontinuous shell layer comprising many island-like CdO crystallites. The TiO2–CdO composite rods were highly crystalline, and their surfaces were rugged. A comparison of the NO2 gas-sensing properties of the CdO thin film, TiO2 rods, and TiO2–CdO composite rods revealed that the composite rods exhibited superior gas-sensing responses to NO2 gas than did the CdO thin film and TiO2 rods, which can be attributed to the microstructural differences and the formation of heterojunctions between the TiO2 core and CdO crystallites.

Preparation and Characterization of Indium Oxide Nanoparticles by Sol-Gel Method and its NO2 Gas Sensing Properties

In this work, In2O3 nanoparticles were prepared by sol-gel method and deposited on quartz substrate by dip coating technique and annealed in air at different temperatures of (450, ,550 and 650) ̊ C at constant time (60 min). X-ray analysis has confirmed the formation of polycrystalline cubic phase that increases in crystaline size with increasing annealing temperature. The optical properties of In2O3 nanostructure thin film were studied. The transmittance was measured in the wavelength range from(300nm to 1100 nm) for all the films.The sensitivity toward NO2 gas has been measured,where In2O3 annealed at different temperatures.

Effect of fluorine doping on the NO2-sensing properties of ZnO thin films

Fluorine-doped ZnO (FZO) thin films were fabricated on glass substrates using a chemical spray pyrolysis method for NO2 gas detection. The physical properties of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible (UV–Vis) spectrometry as a function of fluorine concentration (2 and 5at%). The films exhibited a hexagonal wurtzite structure, and the inclusion of fluorine did not significantly influence the morphology of the films. Optical measurements showed that the band gap energies of the films were affected by the fluorine concentration. Furthermore, the NO2 gas-sensing properties of pristine and FZO thin films were investigated in the concentration range of 100–1000ppb. Fluorine doping in ZnO was found to improve the NO2-sensing capability at the least. All gas sensor measurements showed an optimal sensor response at a temperature of 200°C. In addition, the 2% FZO was found to be more suitable candidate for detecting NO2 gas.

English

One-pot polyol process was combined with metal organic decomposition (MOD) method to fabricate a room-temperature NO2 gas sensor based on tin dioxide and reduced graphene oxide (SO2/RGO) nanocomposite films. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to analyze the structure and morphology of the fabricated films. The electrical and NO2 gas-sensing properties of SnO2 to which various amounts of RGO were added were measured in detail as a function of concentration of NO2 gas at room temperature, to elucidate the contribution of RGO to the NO2 gas-sensing capacity. The sensor that was based on a nanocomposite film of SnO2/RGO exhibited a strong response to low concentrations of NO2 gas at room temperature, satisfactory linearity and favorable long-term stability. Keyword: Tin dioxide (SnO2); reduced graphene oxide (RGO); nanocomposite film; room-temperature NO2 sensor.

NO2 Gas Sensing Properties of Multiple Networked ZnGa2O4 Nanorods Coated with TiO2.

The NO2 gas sensing properties of ZnGa2O4-TiO2 heterostructure nanorods was examined. ZnGa2O4-core/TiO2-shell nanorods were fabricated by the thermal evaporation of a mixture of Zn and GaN powders and the sputter deposition of TiO2. Multiple networked ZnGa2O4-core/TiO2-shell nanorod sensors showed the response of 876% at 10 ppm NO2 at 300 degrees C. This response value at 10 ppm NO2 is approximately 4 times larger than that of bare ZnGa2O4 nanorod sensors. The response values obtained by the ZnGa2O4-core/TiO2-shell nanorods in this study are more than 13 times higher than those obtained previously by the SnO2-core/ZnO-shell nanofibers at 5% NO2. The significant enhancement in the response of ZnGa2O4 nanorods to NO2 gas by coating them with TiO2 can be explained based on the space-charge model.

Fabrication and NO2 gas-sensing properties of reduced graphene oxide/WO3 nanocomposite films

One-pot polyol process was combined with the metal organic decomposition (MOD) method to fabricate a room-temperature NO2 gas sensor based on tungsten oxide and reduced graphene oxide (RGO/WO3) nanocomposite films. Fourier Transform infrared spectrometer (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the microstructure and morphology of the fabricated films. The electrical and NO2 gas-sensing properties of WO3 to which various amounts of RGO were added were measured in detail as a function of concentration of NO2 gas at room temperature, to elucidate the contribution of RGO to the NO2 gas-sensing capacity. The NO2 gas-sensing mechanism of the RGO/WO3 nanocomposite films were explained by considering their composition and microstructures. The sensor that was based on a nanocomposite film of RGO/WO3 exhibited a strong response to low concentrations of NO2 gas at room temperature, satisfactory linearity and favorable long-term stability.

Enhanced NO2 gas-sensing properties of SnO2 nanorods with a TiO2 capping

The influence of ZnO capping on the NO2 gas-sensing properties of SnO2 nanorods was examined. SnO2-core/TiO2-shell nanorods were fabricated by using a two-step process comprising the thermal evaporation of Sn powders and the metal-organic chemical-vapor deposition of TiO2. The diameters of the SnO2 nanorods ranged from a few tens to a few hundreds of nanometers, and the lengths were up to a few hundreds of micrometers. Transmission electron microscopy and X-ray diffraction showed that the cores and the shells of the nanorods were tetragonal-structured single crystal SnO2 and amorphous TiO2, respectively. Multiple networked SnO2-core/TiO2-shell nanorod sensors showed a response of 65.08% at NO2 concentration of 50 ppm at 100 °C. The response of the SnO2 nanorod sensors to 50-ppm NO2 was increased 29 times when TiO2 capping was used. This substantial improvement can be explained by using a space-charge model.

A morphological control of tungsten oxide nanowires by thermal evaporation method for sub-ppm NO2 gas sensor application

Controlling the proper geometrical morphology of metal oxide nanowires (NWs) with large surface areas is important for enhancement of gas-sensing performance through the improvement of sensing sites. In this study, we synthesized geometrically controllable tungsten oxide NWs for detection of NO2 at sub-ppm concentrations. Tungsten oxide NWs were grown through the thermal evaporation method using WO3 powders and W foils as precursor and substrates, respectively. Effects of growth conditions on the morphologies and gas-sensing properties of synthesized NWs were investigated. Results revealed that the as-obtained NWs possessed a cross-section of polygonal shapes, and their diameters increased as the growth temperature increased from 950 °C to 1000 °C. However, the NWs formed bundles and generated porous structures as the growth temperature increased up to 1050 °C. The comparative NO2 gas-sensing properties of tungsten oxide NWs synthesized at different growth temperatures indicated that the NWs synthesized at 1050 °C exhibited relatively good NO2 sensing performance at the sub-ppm level because of the formation of porous NW structures. This phenomenon suggested that porous tungsten oxide NWs are effective for highly sensitive NO2 gas sensor applications.

Electrical Properties of ITO Deposited on Various YSZ Substrates and Their NO2 Gas Sensing Properties

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Tellurium sputtered thin films as NO2 gas sensors

Abstract Tellurium thin films were deposited onto glass and alumina substrates by an rf sputtering system for NO2 gas sensor applications. The surface morphology and structure of the deposited films were investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. As the thickness of the film was increased from 100 to 300 nm the morphology of films changed from a smooth amorphous to polycrystalline nature. The NO2 gas-sensing properties were determined by measurement of the resistance variation of the films as a function of working temperature and gas concentration. Gas sensitivity was largely influenced by the surface morphology of the films. The films with a thickness of 300 nm deposited on a glass substrate showed the maximum response to NO2 at room temperature. Response and recovery times, reproducibility and long-term stability of these films were also investigated.

High aspect ratio In2O3 nanowires: Synthesis, mechanism and NO2 gas-sensing properties

Abstract Flexural In 2 O 3 nanowires with high aspect ratios were synthesized via a hydrothermal–annealing route. The as-synthesized In 2 O 3 nanowires had diameters of 30–50 nm and length up to several microns. Various reaction parameters, such as the kind of reagents, the time of hydrothermal treatment, annealing time and annealing temperature, were investigated by a series of control experiments. The as-synthesized In 2 O 3 nanowires showed excellent gas-sensing properties to NO 2 in terms of sensor response and selectivity.

The optical gas-sensing properties of an asymmetrically substituted porphyrin

In this paper we have investigated the NO2 gas-sensing properties of LB film assemblies of 5,15-bis(4-aminophenyl)-10,20-bis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (CAH4). The optical absorbance spectrum of these films is dramatically affected when exposed to low concentrations of NO2 gas. LB films of CAH4 were prepared by using ultra-fast deposition and characterized by imaging ellipsometry. The high deposition rates employed (500 mm min−1) led to an inhomogeneous structure with high porosity. The LB film exposed to 4.6 ppm NO2 showed a sensitivity of 60% relative absorbance change at 439 nm. The response was found to be faster than that measured in similar systems. The fast response can be explained in terms of the molecular structure of the porphyrin as well as the enhanced surface area of the porous film. The optical response of the CAH4 film gradually decreases as its temperature is increased, a result of a shift in the adsorption–desorption equilibrium towards desorption. An activation energy of 0.48 eV is obtained. Full recovery of the original spectrum after exposure to NO2 is obtained and can be dramatically accelerated with gentle heating (353 K). The concentration dependence of the optical response over the range 0.46–4.6 ppm NO2 obeyed a Langmuir adsorption model. Ageing experiments have shown that the basic response of the CAH4 assemblies is not affected over a time period of at least 1 year.