Presence Of NO2 Gas Research Articles

Cr2O3:TiO2 Nanostructure Thin Film Prepared by Pulsed Laser Deposition Technique as NO2 Gas Sensor

Pulsed laser deposition (PLD) technique was applied to prepared Chromium oxide (Cr2O3) nanostructure doped with Titanium oxide (TiO2) thin films at different concentration ratios 3,5,7 and 9 wt % of TiO2. The effect of TiO2 dopant on the average size of crystallite of the synthesized nanostructures was examined by X-ray diffraction. The morphological properties were discussed using atomic force microscopy(AFM). Observed optical band gap value ranged from 2.68 eV to 2.55 eV by ultraviolet visible(UV-Vis.) absorption spectroscopy with longer wave length shifted in comparison with that of the bulk Cr2O3 ~3eV. This indicated that the synthesized samples are attributed to the enhancement of the quantum confinement effect. Gas response sensitivity, and recovery times of the sensor in the presence of NO2 gas were studied and discussed. In this work it is found that, the sensitivity increases when doping ratio increases from 3wt% to 5wt% of TiO2 and return to decrease over that. The optimum concentrations ratio for NO2 gas sensitivity is 5wt% of TiO2 and sensitivity is 168.75% at 200oC.

Poly vinyl alcohol-CeO2 nanocomposite films: a promising material for NO2 sensors at high temperatures

Nanoparticles of CeO2 were dispersed in Poly vinyl Alcohol to form nanocomposite films of various concentrations. Thick films of thickness around 100 μm were prepared by solution casting and pure PVA, PVA-2.5 wt% CeO2 and PVA-25 wt% CeO2 films were tested for their response as sensors to various gases. It was found that the PVA-2.5 wt% CeO2 film showed the best response of nearly 40% increase in resistance to 100 ppm of NO2 gas at 423 K. This indicated that it could be useful as a high temperature sensor for NO2 gas. Three of the above samples were also prepared by spin coating technique as thin films of thickness 1 μm, 5 μm and 50 μm, on a glass substrate and tested for sensing action of the same gases at 3 ppm concentration. It was seen that 2.5 wt% CeO2 film of 1 μm thickness gave the best response of 16% increase for NO2 gas, amongst all the films. The increase in resistance of the films in the presence of NO2 gas is due to chemisorption on the CeO2 nano fillers and the mechanism seems to be effective even at low concentration of the filler. The results of sensing in these films are better than that of other similar materials and suggest that they can be used as high temperature sensors.

Processing temperature dependent chemiresistive performance of spin-coated cerium oxide films

Abstract An influence of processing temperature on structural, morphological, and chemiresistive properties of cerium oxide (CeO2) films, deposited on glass substrate by a spin-coating method and composed of nanocrystallites (NCs), has been systematically investigated and reported. As-deposited CeO2 films demonstrate the cubic polycrystalline crystal structure and mixed-agglomerated type of surface morphology with several crevices, elevating easy and deep percolation to gas molecules for enhanced adsorption-desorption process. Chemiresistive gas sensing performance of CeO2 films studied to various target gases and operating temperatures; demonstrates excellent selectivity, rapid response/recovery time signatures, and consistent operation repeatability to nitrogen dioxide (NO2) gas @200 °C, over other target gases, along with superior response repeatability. The response signature of sensor increases from 6% to 45% when NO2 gas ppm level is increased from 5 to 100. Chemiresistive change in the CeO2 film sensor in presence of NO2 gas has been studied thoroughly and explored using band model and impedance spectroscopy analysis.

Preparation of nanostructured PbS thin films as sensing element for NO2 gas

Abstract In this work, we demonstrate that semiconducting films of AIVBVI compounds, in particular, of nanostructured lead sulfide (PbS) which prepared by chemical bath deposition (CBD), can be used as a sensing element for nitrogen dioxide (NO2) gas. The CBD method is versatile, simple in implementation and gives homogeneous semiconductor structures. We have prepared PbS nanocrystalline thin film at different reaction baths and temperatures. In the course of deposition, variable amounts of additives, such as organic substances among them, were introduced into the baths. The energy dispersive analysis (EDX) confirms the chemical composition of PbS films. A current–voltage (I–V) characterization of Pd/nc-PbS/a-SiC:H pSi(100)/Al Schottky diode structures were studied in the presence of NO2 gas. The gas sensing behavior showed that the synthesized PbS nanocrystalline thin films were influenced by NO2 gas at room temperature. The results can be used for developing an experimental sensing element based on chemically deposited nanostructured PbS films which can be applicable in gas sensors.

Bilayer Graphene Application on NO2 Sensor Modelling

Graphene is one of the carbon allotropes which is a single atom thin layer with sp2 hybridized and two‐dimensional (2D) honeycomb structure of carbon. As an outstanding material exhibiting unique mechanical, electrical, and chemical characteristics including high strength, high conductivity, and high surface area, graphene has earned a remarkable position in today’s experimental and theoretical studies as well as industrial applications. One such application incorporates the idea of using graphene to achieve accuracy and higher speed in detection devices utilized in cases where gas sensing is required. Although there are plenty of experimental studies in this field, the lack of analytical models is felt deeply. To start with modelling, the field effect transistor‐ (FET‐) based structure has been chosen to serve as the platform and bilayer graphene density of state variation effect by NO2 injection has been discussed. The chemical reaction between graphene and gas creates new carriers in graphene which cause density changes and eventually cause changes in the carrier velocity. In the presence of NO2 gas, electrons are donated to the FET channel which is employed as a sensing mechanism. In order to evaluate the accuracy of the proposed models, the results obtained are compared with the existing experimental data and acceptable agreement is reported.

The electrical properties of NOx-storing carbonates during NOx exposure

In order to gain a deeper understanding of the different components in multi-component automotive catalyst systems and integrating type NOx-sensors, in-situ electrical methods are examined. The conductivity of BaCO3 and K2CO3, key components in automotive NOx storage catalysts, was examined as a function of gas composition and temperature. Impedance measurements performed on BaCO3, K2CO3, and equimolar mixtures of both, demonstrated that, in all cases, the resistance decreases in the presence of NO2 gas with progressive NOx sorption on the carbonate surface. Mixing the hygroscopic but low resistivity K2CO3 with the very highly resistive but stable BaCO3 resulted in greater stability than K2CO3 alone, as well as improved ability to measure resistivity changes. The resistance of the mixture recovered about 50% of its value after removing NO2 from the gas stream, believed to result from migration of sorbed NOx from K to Ba, instead of desorption alone. These results on NOx trap materials show that in-situ impedance spectroscopy measurements offer real-time characterization of NOx loading levels in lean NOx trap catalyst components.

Chemsensor of NO2 gas based on porphyrin of 5, 10, 15, 20-tetraphenylporphyrin LB films and LS films

The sensitivity of 5, 10, 15, 20-tetraphenylporphyrin (H2TPP) to the presence of NO2 gas in diluted solutions and in Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) films was investigated by UV-visible spectroscopy. The shift of Soret and Q bands were analyzed and the energies involved were calculated. The exposure of LB porphyrin films deposited onto glass slides to NO2 has performed as an active chemsensor with 7000 ppm gas concentration. Furthermore, the UV-vis dichroism absorption results associated with the Soret bands have given evidence of the tilt angle of the macrocycle related to the substrate. H2TPP in LB film was tilted by an angle of 51 ± 5° and in the LS film was tilted by an angle of 36° ± 5° indicating the formation of a preferential organization of the molecular films depending on the deposition method.

Zirconia‐Based Electrochemical NOx Sensors with Semiconducting Oxide Electrodes

Electrochemical devices based on coupling an oxygen ionic conductor (Y2O3‐stabilized ZrO2: YSZ) with semiconducting oxides as sensing electrodes were investigated. LaFeO3, a p‐type semiconductor, and WO3, an n‐type semiconductor, were chosen because of their known good NO2‐sensing properties as resistive‐type sensors. The entire sensors were wholly exposed to the same atmosphere. The electromotive force (EMF) was measured for different NO2 concentrations and at fixed temperature. The EMF values of both sensors increased in NO2 atmosphere with a fast response time. The best performance was observed around 450°C for LaFeO3‐based and 650°C for WO3‐based sensors. Moreover, the response of the LaFeO3‐based sensors was found to be strongly affected by the grain size of the powder used for the preparation of the sensing electrode. The polarization curves of all sensors showed a nonlinearity; nevertheless an opposite behavior in the presence of NO2 gas was observed for the p‐ and n‐ type‐based oxide sensors. The nonlinearity was attributed to the potential drop for LaFeO3 or increase for WO3 at the electrode interface. Amperometric measurements, performed at a fixed potential of 1 V, were found in accordance with polarization curves. The electrochemical impedance spectroscopy (EIS) analysis showed that the resistance and reactance at the electrolyte/electrode interface decreased (for LaFeO3)/increased (for WO3) on introduction of NO2 gas, because of the lowering/increasing of the electrode overvoltage.

NO2 Gas Sensing with Au/Phthalocyanine/Si Heterostructures

The current-voltage characteristics of the heterostructure cell of Au / vanadylphthalocyanine (VOPc) layers/ Si were investigated in NO2 atmosphere. The cells showed a rectification behavior and an increase in current at the presence of NO2 gas. The NO2 gas was detected even for the Au/Si cell without VOPc layers and the sensitivity was found to be enhanced significantly by insertion of VOPc layers. The cell with 10 nm-thick VOPc layers exhibited an increase in current density by a factor of 15 in 6 ppm NO2 atmospher It was thus suggested that the interface between Au/Si and VOPc/Si play a key role to determine the gas sensing properties. The adsorbed NO2 gas molecules are thought to modify the interface potential.

Characterization and Electrical Properties of WO3 Sensing Thin Films

ABSTRACTThe microstructure and the electrical properties of thermallyevaporated WO3 thin films have been investigated by glancing angle XRD, atomic force microscopy AFM, X-ray photoelectron spectroscopy XPS and dc techniques. Thin films of 1500 Å thickness have been obtained by evaporating high purity WO3 powders by an electricallyheated crucible at 5 × 10−4 Pa on sapphire substrates. Theas-deposited films have resulted to be amorphous. After annealing at 500°C in dry air for 6, 12 and 24 hours the films have shown well crystallized structures with preferential orientations of WO3 in the (200)direction. The increase of the annealing time has shown marked influence onthe microstructural features of the films surface, as highlighted by AFM investigations. The binding energies of W 4f7/2 have been close to that of WO3, the 24 h annealed yielded an O/W ratio close to 2.9 which is in good agreement with the theoretical one. The gas sensitivity, selectivity and stability of the annealed films in presence of NO2 gas (between 0.7 and 5 ppm) have been evaluated by measuring the electrical change of the film resistance in dry air and in gasatmosphere conditions. The influence of NO and Humidity interfering gases to the NO2 electrical response has been also evaluated. The 500 °C annealed at 24 h has shown better electrical properties in terms of NO2 sensitivity, stability and cross sensitivity effects.