Metal Oxide Nanostructures and Their Gas Sensing Properties: A Review

Department of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China.
Sensors (Impact Factor: 2.25). 12/2012; 12(3):2610-31. DOI: 10.3390/s120302610
Source: PubMed


Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called "small size effect", yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them. In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion. Besides, doping is also an effective method to decrease particle size and improve gas sensing properties. Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article. The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

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    • "Over the past decades, the design and development of gas sensors with high sensing performance has been a research hotspot due to its profound influence on human health and environmental protection [1]. Thanks to the advances in nanotechnologies and synthetic methods, various kind of sensing materials, such as metal-oxide semiconductors, polymers, carbon nanotubes, and moisture absorbing materials, have been developed and applied in gas sensors [2] [3] [4] [5]. Among them, the sensors based on metaloxide semiconductors have triggered great interest owing to their attractive characteristics such as low cost, high sensitivity, and controllable preparation [6] [7] [8]. "
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    ABSTRACT: In2O3 nanorod bundles with well-designed morphology, hierarchical nanostructure and large specific surface area were quickly prepared via microwave hydrothermal method in the presence of vitamin C. The observations of field emission electron microscopy and transmission electron microscopy revealed that the as-prepared In2O3 samples were constructed from lots of well-aligned nanorods with average diameter of about 50 nm. To demonstrate their potential application in detecting harmful gases, these bundle-like In2O3 samples were applied to fabricate gas sensor and their sensing properties were examined. It was found that the sensors based on such novel In2O3 nanorod bundles exhibited high response and excellent selectivity during detecting NO2 gas at the operating temperature of 100 °C.
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    • "However, the morphology and structure of the sensing materials significantly influence their sensing performances, therefore various nanostructured metal oxides have been prepared to improve gas sensing properties [8] [9] [10] [11] [12]. In particular, ZnO based nanostructures such as nanowires [13] [14], nanorods [15] [16] [17], nanosheets [18] and nanospheres [19] have been used as gas sensing materials because of the excellent electronic and photonic properties of ZnO [20] [21] [22] [23] [24]. "
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    • "Researchers are aiming to develop gas sensors to detect low gas concentrations in atmosphere at substantially lower operating temperatures [5]. Metal oxide semiconductors (MOS) are principal solid state gas detecting materials used widely for detection of toxic and polluting gases [6]. MOS based sensors have many advantages such as low cost, easy synthesis, compact size, durable, easy tenability and small drift in signal over long knowledge, the present study is designed to study effect of Ni doping on NO 2 sensing properties of ZnO thin films towards various gas concentrations and operating temperatures. "
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    ABSTRACT: The use of metal oxide semiconductor (MOS) gas sensors is limited due to lack of selectivity and high operating temperature. The aim of present investigation is to enhance gas response and sensitivity of the zinc oxide (ZnO) based thin film sensor towards nitrogen dioxide (NO2) by Ni doping. The achieved sensitivity is around 4.2%/ppm at moderate operating temperature of 200°C. The gas response of 108% and 482% is observed at 200°C operating temperature, towards 5ppm and 100ppm NO2, respectively. Ni doping increased the NO2 response and reduced the lower detection limit of NO2 to 5ppm which is much lower than the emergency exposure limit (20ppm). The hybrid structure of nanograined rods and hexagonal flakes are observed which enhanced gas response. The gas response dependence on various physical properties and chemical composition of the sensor is also studied. The response and recovery time of 1.5 atomic percentage (at%) Ni doped ZnO thin film sensor is 11 and 123s, respectively. The response of the sensor is reproducible and it has negligible cross sensitivity for other interfering gases such as CO2, SO2, H2S, NH3, LPG, methanol, ethanol, and acetone.
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