NH3-Sensing Mechanism Using Surface Acoustic Wave Sensor with AlO(OH) Film.

Xiaofeng Xu,Jingxia Yu,Dongyi Ao,Sean Li,Xiaotao Zu,Wanfeng Xie,Yongliang Tang,Xia Xiang,Yongqing Fu

doi:10.3390/nano9121732

Abstract

In this study, AlO(OH) (boehmite) film was deposited onto a surface acoustic wave (SAW) resonator using a combined sol-gel and spin-coating technology, and prepared and used as a sensitive layer for a high-performance ammonia sensor. The prepared AlO(OH) film has a mesoporous structure and a good affinity to NH3 (ammonia gas) molecules, and thus can selectively adsorb and react with NH3. When exposed to ammonia gases, the SAW sensor shows an initial positive response of the frequency shift, and then a slight decrease of the frequency responses. The sensing mechanism of the NH3 sensor is based on the competition between mass-loading and elastic-loading effects. The sensor operated at room temperature shows a positive response of 1540 Hz to 10 ppm NH3, with excellent sensitivity, selectivity and stability.

Highlights

Various poisonous gases [1,2], produced daily by factories in industry and appliances used in our daily life, are hazardous toward environment and people’s health
Our results show that the film has a mesoporous structure, and abundant hydroxyl groups in the film
The sensor shows good sensitivity, selectivity and repeatability at room temperature when exposed to ammonia gas, and the sensing mechanism is identified to be influenced by the competitions between mass-loading and elastic-loading effects

Summary

Introduction

Various poisonous gases [1,2], produced daily by factories in industry and appliances used in our daily life, are hazardous toward environment and people’s health. Tang et al fabricated high-performance SAW NH3 sensors using the composite films of TiO2/SiO2, Co3O4/SiO2 and Fe2O3/SiO2 as the sensing layers, and reported that the addition of SiO2 could enhance the sensitivity of a SAW sensor because of its porous structures [20,21,22]. All these reported materials have porous structures and active sites for the adsorption of NH3. The sensor shows good sensitivity, selectivity and repeatability at room temperature when exposed to ammonia gas, and the sensing mechanism is identified to be influenced by the competitions between mass-loading and elastic-loading effects

Experimental Details

Structural Characterization

Gas-Sensing Properties

Sensing Mechanisms

Conclusions