Limits...
Metal oxide nanostructures and their gas sensing properties: a review.

Sun YF, Liu SB, Meng FL, Liu JY, Jin Z, Kong LT, Liu JH - Sensors (Basel) (2012)

Bottom Line: 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.Besides, doping is also an effective method to decrease particle size and improve gas sensing properties.The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China. sunyufeng118@126.com

ABSTRACT
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.

Show MeSH

Related in: MedlinePlus

(a) FESEM images of the as-synthesized precursor, (b) porous ZnO nanosheets, (c) their high-magnification observation, (d) low-magnification image with the corresponding SAED pattern as an inset. Reprinted with permission from [92]. Copyright (2009) IOP Publishing Ltd.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3376589&req=5

f9-sensors-12-02610: (a) FESEM images of the as-synthesized precursor, (b) porous ZnO nanosheets, (c) their high-magnification observation, (d) low-magnification image with the corresponding SAED pattern as an inset. Reprinted with permission from [92]. Copyright (2009) IOP Publishing Ltd.

Mentions: Previous work has indicated that polycrystalline structural sensing materials have high response and poor stability. In contrast, single-crystalline materials exhibit low response and good stability. For sensor developers, the difficulty is to maintain the balance of high response and good stability. Porous metal oxide nanosheets have the characteristic of remaining a single-crystalline structure and providing a relatively high surface area [89,90]. Therefore, porous single-crystalline nanostructures are the ideal material which maintains a balance between high response and good stability. Sysoev et al. have investigated the gas sensing properties of single-crystalline SnO2 nanowires which revealed high sensitivity and long-term stability [91]. However, it is difficult to synthesize a large amount of porous single-crystalline nanowires. For nanosheets, it is relatively easy to simultaneously possess single-crystalline structure and lots of pores. Liu et al. have prepared novel single-crystalline ZnO nanosheets with porous structure via annealing ZnS(en)0.5 (en = ethylenediamine) complex precursor as shown in Figure 9 [92]. There are numerous mesopores with a diameter of about 26.1 nm all through each nanosheet in a high density. Besides, ZnO nanosheets gas sensor not only exhibits good response and short response and recovery time, but also have stability in a long term. The research results confirm that it is feasible to fabricate highly sensitive and stable gas sensors based on porous single-crystalline nanomaterials. Besides, similar two dimensional porous nanostructures also exhibited excellent gas sensing properties [93–96].


Metal oxide nanostructures and their gas sensing properties: a review.

Sun YF, Liu SB, Meng FL, Liu JY, Jin Z, Kong LT, Liu JH - Sensors (Basel) (2012)

(a) FESEM images of the as-synthesized precursor, (b) porous ZnO nanosheets, (c) their high-magnification observation, (d) low-magnification image with the corresponding SAED pattern as an inset. Reprinted with permission from [92]. Copyright (2009) IOP Publishing Ltd.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376589&req=5

f9-sensors-12-02610: (a) FESEM images of the as-synthesized precursor, (b) porous ZnO nanosheets, (c) their high-magnification observation, (d) low-magnification image with the corresponding SAED pattern as an inset. Reprinted with permission from [92]. Copyright (2009) IOP Publishing Ltd.
Mentions: Previous work has indicated that polycrystalline structural sensing materials have high response and poor stability. In contrast, single-crystalline materials exhibit low response and good stability. For sensor developers, the difficulty is to maintain the balance of high response and good stability. Porous metal oxide nanosheets have the characteristic of remaining a single-crystalline structure and providing a relatively high surface area [89,90]. Therefore, porous single-crystalline nanostructures are the ideal material which maintains a balance between high response and good stability. Sysoev et al. have investigated the gas sensing properties of single-crystalline SnO2 nanowires which revealed high sensitivity and long-term stability [91]. However, it is difficult to synthesize a large amount of porous single-crystalline nanowires. For nanosheets, it is relatively easy to simultaneously possess single-crystalline structure and lots of pores. Liu et al. have prepared novel single-crystalline ZnO nanosheets with porous structure via annealing ZnS(en)0.5 (en = ethylenediamine) complex precursor as shown in Figure 9 [92]. There are numerous mesopores with a diameter of about 26.1 nm all through each nanosheet in a high density. Besides, ZnO nanosheets gas sensor not only exhibits good response and short response and recovery time, but also have stability in a long term. The research results confirm that it is feasible to fabricate highly sensitive and stable gas sensors based on porous single-crystalline nanomaterials. Besides, similar two dimensional porous nanostructures also exhibited excellent gas sensing properties [93–96].

Bottom Line: 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.Besides, doping is also an effective method to decrease particle size and improve gas sensing properties.The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Automotive Engineering, Anhui Polytechnic University, Wuhu 241000, China. sunyufeng118@126.com

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus