Gas Sensing Properties Of Sensors Research Articles

Ppb-Level NO2 Sensor with High Selectivity Fabricated by Flower-like Au-Loaded In2O3

With increasingly serious environmental problems caused by the improvement in people’s living standards, the number of cars has increased sharply in recent years, which directly leads to the continuous increase in the concentration of NO2 in the air. NO2 is a common toxic and irritant gas, which is harmful to both the human body and the environment. Therefore, this research focuses on NO2 detection and is committed to developing high-performance, low detection limit NO2 sensors. In this study, flower-like Au-loaded In2O3 was successfully fabricated using the hydrothermal method and the wet impregnation method. The morphological features and chemical compositions of the as-prepared samples were characterized using SEM, TEM, XRD and XPS. A variety of sensors were fabricated and the gas-sensing properties of sensors were investigated. The results indicate that the sensor based on 0.5 mol% Au/In2O3 shows a response value of 1624 to 1 ppm NO2 at 100 °C, which is 14 times that based on pure In2O3. Meanwhile, the detection limit of the sensor based on 0.5 mol% Au/In2O3 for NO2 is 10 ppb, and the response value is 10.4. In addition, the sensor based on 0.5 mol% Au/In2O3 also has high selectivity to NO2 among CO, CO2, H2, CH4, NH3, SO2 and H2S. Finally, the sensitization mechanism of Au/In2O3 was discussed, and the reasons for improving the performance of the sensor were analyzed. The above results and analysis demonstrate that the gas-sensing attributes of the sensor based on 0.5 mol% Au/In2O3 to NO2 improved remarkably; at the same time, it has been proved that the composite material has extensive potential in practical applications.

Adsorption of Hydrogen Sulfide on Reduced Graphene Oxide-Wrapped Titanium Dioxide Nanofibers

This work presents a fabrication of room-temperature gas sensor for hydrogen sulfide (H2S) adsorption. Pristine titanium dioxide (TiO2) nanofibers, reduced graphene oxide (rGO) sheets, and reduced graphene oxide-wrapped titanium dioxide (rGO-wrapped TiO2) nanofibers were presented in the form of integrated suspension used for a gas-sensing layer. The TiO2 nanofibers were firstly synthesized by using an electrospinning method with a polyvinylpyrrolidone (PVP) polymer. The rGO sheets were then wrapped around TiO2 nanofibers by a hydrothermal method. Scanning electron microscope, transmission electron microscope, X-ray diffractometer, and Raman spectrometer confirmed the presence of rGO sheets onto the surface of TiO2 nanofibers. Ultraviolet-visible spectrophotometer was also considered and displayed to calculate the band gap of TiO2 and rGO-wrapped TiO2 nanofibers. After preparing the gas-sensing suspensions, they were dropped onto the polyethylene terephthalate substrates with silver-interdigitated electrodes. The gas-sensing properties of sensors were evaluated for H2S adsorption at room temperature. Based on the results, the rGO-wrapped TiO2 nanofiber gas sensor exhibited higher H2S sensitivity and selectivity than pristine TiO2 nanofiber and pure rGO gas sensors. The H2S-sensing mechanism of rGO-wrapped TiO2 nanofiber gas sensor was discussed based on a formation of p-n heterojunctions between p-type rGO sheets and n-type TiO2 nanofibers. Furthermore, a direct charge-transfer process by physisorption was also highlighted as a second H2S-sensing mechanism.

Role of molybdenum substitutional dopants on H2S-sensing enhancement of flame-spray-made SnO2 nanoparticulate thick films

In this work, Mo-doped SnO2 nanoparticulate sensing films were fabricated by flame spray pyrolysis (FSP) and spin-coating processes with varying Mo-doping concentrations (0–2wt%) and numbers of spin-coating cycles (1–5). Structural characterizations by electron microscopy and X-ray analysis suggested that Mo atoms were substitutionally doped in polycrystalline SnO2 nanoparticles at low Mo concentrations (<1wt%) but then segregated as secondary MoO3 crystallites at high Mo levels (1–2wt%). In addition, the incorporation of Mo resulted in the reduction of size and the increase of surface area of SnO2 nanoparticles. The gas-sensing properties of sensors were investigated towards H2S, NO2, NH3, H2 and CO at the working temperature ranging from 150°C to 350°C. The results showed that the moderate Mo-doping level of 0.5wt% and the high number of spin-coating cycles of 4 led to the optimal enhancement of H2S response. The optimal Mo concentration could be correlated to the highest doping level that did not induce secondary MoO3 crystallites. In particular, the 0.5wt% Mo-doped SnO2 sensor prepared with 4 spin-coating cycles exhibited a high response of ∼105 and a short response time of ∼5s–10ppm H2S at an optimal working temperature of 250°C. Furthermore, the optimal sensor displayed good H2S selectivity against NO2, NH3, H2 and CO. Therefore, the flame-spray-made Mo-doped SnO2 thick film sensor is a promising candidate for sensitive and selective detection of H2S at a threshold limit value (TLV) of lower than 10ppm and may be useful for general industrial applications.

Synergistic Effects of a Combination of Cr2O3-Functionalization and UV-Irradiation Techniques on the Ethanol Gas Sensing Performance of ZnO Nanorod Gas Sensors.

There have been very few studies on the effects of combining two or more techniques on the sensing performance of nanostructured sensors. Cr2O3-functionalized ZnO nanorods were synthesized using carbothermal synthesis involving the thermal evaporation of a mixture of ZnO and graphite powders followed by a solvothermal process for Cr2O3-functionalization. The ethanol gas-sensing properties of multinetworked pristine and Cr2O3-functionalized ZnO nanorod sensors under UV illumination were examined to determine the effects of combining Cr2O3-ZnO heterostructure formation and UV irradiation on the gas-sensing properties of ZnO nanorods. The responses of the pristine and Cr2O3-functionalized ZnO nanorod sensors to 200 ppm of ethanol at room temperature by UV illumination at 2.2 mW/cm(2) were increased by 3.8 and 7.7 times, respectively. The Cr2O3-functionalized ZnO nanorod sensor also showed faster response/recovery and better selectivity than those of the pristine ZnO nanorod sensor at the same ethanol concentration. This result suggests that a combination heterostructure formation and UV irradiation had a synergistic effect on the gas-sensing properties of the sensor. The synergistic effect might be attributed to the catalytic activity of Cr2O3 for ethanol oxidation as well as to the increased change in conduction channel width accompanying adsorption and desorption of ethanol under UV illumination due to the presence of Cr2O3 nanoparticles in the Cr2O3-functionalized ZnO nanorod sensor.

A room temperature ammonia sensor based on nanosized copper hexacyanoferrate(II)

Abstract In the ultrasonic wave from 20–70 kHz, nanosized copper hexacyanoferrate(II) materials were synthesized by the reaction of copper sulfate and potassium ferrocyanide(II) and at room temperature, respectively, and 323 K. The sensors based on nanosized copper hexacyanoferrate(II) were fabricated in spray technology. The gas-sensing properties of sensors were tested at different temperature and operating voltage. The sensors exhibited an excellent selection for ammonia at room temperature and had a linear response at 5, 10 and 15 V operating voltage. The optimum operating voltage of the sensor was 5 V. The influence of temperature on the sensor response to NH 3 was significant. Response of the sensor for ammonia is mainly based on a weak chemisorption.

Gas sensors with porous three-dimensional framework using TiO 2/polymer double-shell hollow microsphere

The correlations between the structures and gas-sensing properties of porous thin-film gas sensors made of packed hollow spheres are investigated. For this purpose, hollow polymeric spheres were used as templates. Double-shell hollow spheres were prepared by encapsulating the polymeric hollow spheres with TiO 2 shells. Solid polymeric spheres were used as templates for comparison. Porous thin-film gas sensor with interconnected three-dimensional pores was prepared by using the TiO 2 encapsulated hollow spheres. The double-shell hollow spheres and porous titania films were characterized by XRD, BET, TEM and SEM. The gas-sensing properties of the sensors toward NO 2 depend on the type of template and the three-dimensional porous structure of the films. Using the hollow sphere template and adding precursors during the film formation procedure help to prevent the collapse of hollow sphere and form the mesopores in films after removing the template. These films show enhanced gas sensitivity when compared to TiO 2 polycrystalline films. Such improvement in sensitivity results from the porous architecture of the hollow microsphere films which not only increase the active surface area but also promotes the gas diffusion.