High-performance NO2 Gas Sensor Research Articles

Synthesis and room temperature NO2 gas sensitivity of vanadium dioxide nanowire structures by chemical vapor deposition

Vanadium dioxide (VO2) nanowire structures were synthesized by chemical vapor deposition on unpolished quartz substrates. The effects of synthesis time, from 2 h to 6 h, on VO2 nanowires structure and room temperature NO2 gas sensing properties were studied. We used field emission scanning electron microscope and X-ray diffraction to characterize the morphology and crystal structure of the nanowires. The results show that networked VO2 nanowire structure was obtained at deposition time of 4 h. The structure evolution process was related to the strong interfacial interaction and continuing growth on the rough substrate surface. We explored the sensitivity of nanowires structure to 1–5 ppm NO2 gas at room temperature. The samples at deposition time of 4 h had the highest sensitivity for the networked structure. This study provides a reference for the fabrication of high performance NO2 gas sensor based on metal oxide semiconductor nanowire structures.

Facile Synthesis of Porous CuO Nanosheets as High-performance NO2 Gas Sensor

Present work reports on the synthesis of 2-dimensional (2D) CuO nanostructures with enhanced NO2 gas sensing properties by a facile solvothermal method. 2D CuO nanostructures were investigated using X-ray diffraction, Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). FESEM studies revealed as synthesized nanostructures possess a nanosheets like morphology. Gas sensing studies showed that sensor of as prepared 2D CuO nanostructures exhibit enhanced gas sensing properties with excellent selectivity towards NO2 as compared to other volatile gases such as ethanol, methanol and acetone.

Chemical bath deposition of ZnO films at low pH for high chemoresistivity towards NO2 gas

Zinc oxide (ZnO) films of nanograins were obtained on a glass substrate by simple and rapid chemical bath deposition method with zinc nitrate and urea as precursors at low pH condition (∼9) without adding any complexing agent. The structure, morphology and surface chemistry were confirmed from the XRD, EDX, Raman spectroscopy, x-ray photoelectron spectroscopy, BET, FE-SEM and TEM imaging measurements. Chemiresitive selectivity and sensitivity of ZnO film sensor toward NO2 gas was better than other target gases like methanol, ethanol, hydrogen sulphide and chlorine. Remarkable high sensitivities from 176% to 610% towards NO2 gas have been obtained under variation of concentration from 10 ppm to 200 ppm @200 °C operating temperature. Large response about 84.42% against first day measurement on 15th day supports chemical stability and mechanical robustness of ZnO film-based sensor. Hence, the present study signifies the potentiality of ZnO in fabricating low-cost and high-performance NO2 gas sensors.

Room-temperature synthesis of CuO/reduced graphene oxide nanohybrids for high-performance NO2 gas sensor

We report the room-temperature synthesis of CuO/reduced graphene oxide (CuO/rGO) nanohybrids via a one-pot solution process, in which the reduction of GO and the formation of CuO were completed simultaneously at room temperature. The as-prepared sheet-like CuO with hundreds nanometer in sizes are well-mixed together uniformly with rGO in the nanohybrids. The gas sensors based on the as-prepared CuO/rGO nanohybrids were fabricated and used to detect low-concentration NO2 gas (1–75 ppm) with excellent selectivity. Upon exposure to 1 ppm NO2 at room temperature, the as-prepared CuO/rGO nanohybrids display a sensitive response of about 14 and the reponse time and recovery time are about 66 and 34 s, respectively. The low detection limit is evaluated to be as low as 60 ppb at room temperature. The high sensing response can be attributed to the large surface area of CuO/rGO nanohybrids and enhanced carrier transfer between NO2 molecules and nanohybrids. We believe that this low-cost strategy provides a facile route to prepare other rGO-based nanohybrids for nanosensors.

Nitrogen doped high quality CVD grown graphene as a fast responding NO2gas sensor

Nitrogen doped high quality CVD grown graphene is demonstrated for application in a high performance NO2gas sensor.

Enhanced nitrogen oxide sensing performance based on tin-doped tungsten oxide nanoplates by a hydrothermal method

The great demand for gas sensors in practical applications has stimulated tremendous attention in this area due to its important significance in real life. A facile synthesis of WO3 nanoplates and their subsequent Sn doping strategy by using a hydrothermal method was investigated to enhance gas sensing performance for NO2 gas, one of the gases toxic to human beings and the environment. Various techniques were used to characterize all the products. The morphology characterizations demonstrated that all the samples exhibited a similar nanoplate structure with or without Sn doping. The gas sensing properties of the sensors based on different doping concentrations (0, 1, 2 and 5wt%) have been systematically investigated. The sensor based on the 2wt% Sn-doped WO3 nanoplates showed the maximum response to NO2 (55–100ppb NO2). Furthermore, the introduction of Sn ions into the sensing materials of WO3 resulted in shorter response and recovery times. This finding could be attributed to the increased number of oxygen vacancies on the surface of the sensing material and the resistance of the gas sensors. The results provide a new doping strategy to fabricate high performance NO2 gas sensors.

Scalable fabrication of high-performance NO2 gas sensors based on tungsten oxide nanowires by on-chip growth and RuO2-functionalization.

The on-chip growth and surface-functionalization have been recently regarded as promising techniques for large-scale fabrication of high performance nanowires gas sensors. Here we demonstrate a good NO2 gas-sensing performance of the tungsten oxide nanowires (TONWs) sensors realized by scalable on-chip fabrication and RuO2-functionalization. The gas response (Rg/Ra) of the RuO2-functionalized TONWs to 5 ppm of NO2 was 186.1 at 250 °C, which increased up to ∼18.6-fold compared with that of the bare TONWs. On the contrary, the responses of the bare and functionalized sensors to 10 ppm of NH3, 10 ppm of H2S and 10 ppm of CO gases were very low of about 1.5, indicating the good selectivity. In addition, the TONW sensors fabricated by the on-chip growth technique exhibited a good reversibility up to 7 cycles switching from air-to-gas with a response of 19.8 ± 0.033 (to 1 ppm of NO2), and this value was almost the same (about 19.5 ± 0.027) for 11 cycles after three months storage in laboratory condition. The response and selectivity enhancement of RuO2-functionalzied TONWs sensors was attributed to the variation of electron depletion layer due to the formation of RuO2/TONWs Schottky junctions and/or the promotion of more adsorption sites for NO2 gas molecule on the surface of TONWs, whereas the good reversibility was attributed to the formation of the stable monoclinic WO3 from the single crystal of monoclinic W18O49 after annealing at 600 °C.

Synthesis and NO2-Sensing Properties of One-Dimensional Tungsten Oxide Nanowire Bundles

Tungsten oxide nanowires were synthesized by solvothermal method with tungsten hexachloride (WCl6) as precursor. X-ray diffraction, field emission scanning electron microscope and transmission electron microscope characterizations indicated that the as-synthesized nanowires are single phase monoclinic W18O49. With WCl6 concentration increasing, the bundled nanowire became shorter and thicker. The gas-sensing properties of W18O49 nanowire towards NO2 gas were evaluated and the results showed that the optimal gas sensitivity is achieved at 150 degrees C and the thinner nanowire exhibits the higher sensitivity. The results indicate that tungsten oxide nanowire is a promising gas-sensing material for high performance and low power cost NO2 gas sensor.

High-performance NO2 gas sensor based on ZnO nanorod grown by ultrasonic irradiation

A facile and fast sonochemical route for the fabrication of a resistive-type ZnO gas sensor has been demonstrated. Vertically aligned ZnO nanorod arrays were grown on a Pt-electrode patterned alumina substrate under ambient conditions. The average diameter and length of the ZnO nanorods were 50 and 500nm, respectively. Sonochemically grown ZnO nanorod gas sensor was highly sensitive to NO2 gas with a very low detection limit of 10ppb at 250°C; further, its response and recovery time were short. Considering the advantageous properties of this sonochemical technique, we believe that it can be used to fabricate high-performance gas sensors.