Instant synthesis of porous SnO2 nanosheets for ultrahigh sensitive NO2 gas sensors

Selective, sensitive, and stable NO2 gas sensor based on porous ZnO nanosheets

Semiconducting metal oxides can detect low concentrations of NO2 and other toxic gases, which have been widely investigated in the field of gas sensors. However, most studies on the gas sensing properties of these materials are carried out at high temperatures. In this work, Hollow SnO2 nanofibers were successfully synthesized by electrospinning and calcination, followed by surface modification using ZnO to improve the sensitivity of the SnO2 nanofibers sensor to NO2 gas. The gas sensing behavior of SnO2/ZnO sensors was then investigated at room temperature (~20 °C). The results showed that SnO2/ZnO nanocomposites exhibited high sensitivity and selectivity to 0.5 ppm of NO2 gas with a response value of 336%, which was much higher than that of pure SnO2 (13%). In addition to the increase in the specific surface area of SnO2/ZnO-3 compared with pure SnO2, it also had a positive impact on the detection sensitivity. This increase was attributed to the heterojunction effect and the selective NO2 physisorption sensing mechanism of SnO2/ZnO nanocomposites. In addition, patterned electrodes of silver paste were printed on different flexible substrates, such as paper, polyethylene terephthalate and polydimethylsiloxane using a facile screen-printing process. Silver electrodes were integrated with SnO2/ZnO into a flexible wearable sensor array, which could detect 0.1 ppm NO2 gas after 10,000 bending cycles. The findings of this study therefore open a general approach for the fabrication of flexible devices for gas detection applications.

In view of facile, cost-effective, and environmentally friendly synthetic methods, palladium-doped copper oxide (Pd-CuO) nanoparticles have been synthesized from Ocimum sanctum (commonly known as "Tulsi") phytoextract for gas-sensing applications. The structural, morphological, and compositional properties of Pd-doped CuO nanoparticles were studied using various techniques such as XRD, FESEM, XPS, and EDX. The characterization results confirmed the doping of Pd on CuO nanoparticles, and Pd-CuO nanostructures appear as nanoflakes in FESEM analysis. The gas-sensing response of Pd (1.12 wt %)-CuO nanoflake-based sensor was measured at 5-100 ppm concentration of different gases, NO2, H2S, NH3, and H2, at 125 °C. Gas-sensing tests reveal that the sensitivity of the sensor were 81.7 and 38.9% for 100 and 5 ppm concentrations of NO2, respectively, which was significantly greater than that of pure CuO. The response and recovery times of the sensor were 72 and 98 s for 100 ppm of NO2 gas, while they were 90 and 50 s for 5 ppm NO2. The calculated limit of detection (LOD) value of the sensor is 0.8235. This appealing LOD is suitable for real-time gas detection. The gas sensor was found to exhibit excellent selectivity toward NO2 gas and repeatability and stability in humid (80%) conditions. The Pd doping in CuO nanostructures plays a significant role in escalating the sensitivity and selectivity of CuO-based NO2 gas sensor suitable to work at low operating temperatures.

High sensitive room temperature NO2 gas sensor based on the avalanche breakdown induced by Schottky junction in TiO2-Sn3O4 nanoheterojunctions

Highly sensitive and low detection limit NO2 gas sensor based on In2O3 nanoparticles modified peach kernel-like GaN composites

The air pollution caused by the emission of NO2 from vehicles in large cities is threatening human health. Thus, a highly sensitive gas sensor is required to monitor this gas. Here, we introduced the arc-discharge deposition of single-walled carbon nanotubes (SWCNTs) over SnO2 nanowires for highly sensitive NO2 gas sensors. The high-quality SnO2 nanowires were grown on-chip on interdigital Pt electrodes, whereas the SWCNTs were deposited by in situ arc-discharge method. To form the heterojunction between SnO2 nanowires and SWCNTs film, we controlled the length of the SnO2 nanowires to avoid bridging of the two electrode fingers while covering the entire surface of Pt electrodes. The SWCNTs were deposited through a shadow mask to ensure the contact between the SWCNTs and SnO2 nanowires but not the Pt electrodes. Electrical measurements confirmed the formation of non-linear contact between SnO2 nanowires and SWCNTs because of the n-p heterojunction. An increment in resistance (decrease in resistance) of the sensor was observed when measured in NO2 gas, indicating the good response characteristics of the device based on heterojunction between SnO2 nanowires and SWCNTs. In addition, gas-sensing measurement at different temperatures indicated that the fabricated sensor could detect low concentrations of NO2 gas in the range of 1–10 ppm, with response values of 20–80. The results demonstrated that the arc-discharge deposition of SWCNTs over SnO2 nanowires is effective for the fabrication of highly sensitive NO2 gas sensors.

Fig. 1. Schematic illustration of SILAR fabrication process [1].The use of semiconducting metal oxides to develop highly sensitive NO gas sensors remains an important approach in the field of gas sensing applications [2]. In this research, we describe the synthesis, characterization, and application of a very promissing NO gas sensing material ZnO doped with different atomic percentages of Ti and prepared by a simple SILAR [3] method. Synthesized specimens were structurally and morphologically characterized. The NO sensing characteristics of pristine ZnO and Ti-doped ZnO were compared using a gas sensing measurement system. The sensitivity, operating temperature, and response/recovery time were systematically investigated based on the change in electrical resistance of the materials in the presence of NO. Experimental results confirmed that 50 at% Ti-doped ZnO showed a maximum response to NO gas at an operating temperature. The sensing mechanism of the pristine and Ti-doped ZnO nanostructures is discussed in detail. We believe that the Ti-doped, flower-like ZnO nanostructure is a potential material for semiconductor-oxide-based NO gas sensors. Key words: NO gas sensor, SILAR method, flower-like, Ti-doped ZnO. Acknowledgement This research was supported by the research grant 021220FD2201 “Development of highly sensitive MOS based nano-film gas sensors” from Nazarbayev University. Reference [1] B. Soltabayev, M.A. Yıldırım, A. Ateş, S. Acar, The effect of indium doping concentration on structural, morphological and gas sensing properties of IZO thin films deposited SILAR method, Mater. Sci. Semicond. Process. 101 (2019) 28–36. https://doi.org/10.1016/j.mssp.2019.05.026.[2] V.S. Bhati, M. Hojamberdiev, M. Kumar, Enhanced sensing performance of ZnO nanostructures-based gas sensors: A review, Energy Reports. 6 (2020) 46–62. https://doi.org/10.1016/j.egyr.2019.08.070.[3] T. Çorlu, I. Karaduman, M.A. Yildirim, A. Ateş, S. Acar, Effect of Doping Materials on the Low-Level NO Gas Sensing Properties of ZnO Thin Films, J. Electron. Mater. 46 (2017) 3995–4002. https://doi.org/10.1007/s11664-017-5503-z. Figure 1

Ultrasensitive NO2 gas sensing performance of two dimensional ZnO nanomaterials: Nanosheets and nanoplates

Hydrothermally grown α-MnO2 interlocked mesoporous micro-cubes of several nanocrystals as selective and sensitive nitrogen dioxide chemoresistive gas sensors

Application of a cubic-like mesoporous silica film to a surface photovoltage gas sensing system

Hydrogen sulfide even with low concentration in environment is very pernicious to the health, Therefore, the design of gas sensors for detecting H2S is highly desirable. In this work, porous spinel ZnCo2O4 nanosheets (NSs) were synthesized via a hydrothermal method and followed by the thermal treatment. Structural characterizations indicate that the porous NSs are composed of ~ 14 nm interconnected ZnCo2O4 nanoparticles. The porous spinel ZnCo2O4 NSs exhibit enhanced H2S sensing performance in comparison to Co3O4 NSs. The detection limit of the porous ZnCo2O4 NSs is down to 100 ppb H2S with a sensor response value of 1.32 even at relatively low operating temperature of 120 °C. Furthermore, the porous ZnCo2O4 NSs have fascinating selectivity and good long-term stability and relatively rapid response time. The gas sensing mechanism of the ZnCo2O4 NSs gas sensor is also discussed in terms of the effects of oxygen vacancies. In view of the exciting gas-sensing properties and facile preparation method, the porous ZnCo2O4 NSs are ideal candidates for the H2S sensors.

Synthesis of novel BiVO4/Cu2O heterojunctions for improving BiVO4 towards NO2 sensing properties

Effect of mixing ratio on NO2 gas sensor response with SnO2-decorated carbon nanotube channels fabricated by one-step dielectrophoretic assembly

We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200 and a low NO gas detection limit of 0.2 ppm in dry air.

The highly sensitive and rapid NO gas sensor was prepared with polyaniline/TiO2/carbon nanotube composites. Aniline was polymerized on the surface of carbon nanotube (p‐type semiconductor) with embedding TiO2. The gas sensing property was measured by the changes of electrical resistance without or with UV irradiation to investigate the photodegradation of NO by TiO2. The photo‐degraded products such as HNO2, NO2, and HNO3, which were adsorbed on the PANi‐coated carbon nanotubes, resulted in the decreased electrical resistance in the p‐type semiconductors of carbon nanotube and polyaniline. The advantages of TiO2 photocatalyst in gas sensing were apparent in the improvement in both sensitivity and response rate.