ZnO-Al2O3 nanocomposite as a sensitive layer for high performance surface acoustic wave H2S gas sensor with enhanced elastic loading effect

Abstract

ZnO-Al2O3 nanocomposite was synthesized and developed as a high performance sensitive and selective layer for surface acoustic wave (SAW) sensor, aiming for in-situ detection of H2S gas in ppb level operated at room temperature. ZnO-Al2O3 nanocomposite, synthesized though a sol-gel method, was spin-coated onto a quartz based SAW resonator. This composite layer inherits the mesoporous structure of the Al2O3 layer and good affinity to H2S gas molecules of the ZnO layer, and thus can selectively adsorb and react with H2S gas molecules to form ZnS compounds on its surface. This reaction leads to significant decreases of both pore sizes and total pore volume of the layer, an increase of layer's elastic modulus, thus causing a large positive shift of the frequency responses of the SAW sensor. The sensor operated at room temperature shows a frequency response of ~500 Hz to 10 ppb H2S, with an excellent selectivity and good recovery property.

Advances in Doped ZnO Nanostructures for Gas Sensor

“…For example, the detection limit of Al 2 O 3 doped ZnO for H 2 S is as low as 10ppb. [110] Noble metal doped ZnO showed excellent gas sensitivity to NO 2 . Au, Pt, Pa and other modified ZnO can detect NO 2 with a concentration of 1 ppm at low temperature.…”

ZnO Metal Oxide Semiconductor in Surface Acoustic Wave Sensors: A Review

“…The most important features of a SAW sensor, sensitivity and selectivity, are affected and improved by means of the sensitive thin film. The development is, therefore, very important in research aimed at obtaining an outstanding performance in the detection of various gases [ 22 , 80 , 82 , 83 ]. Although a wide range of materials has been studied related to the field of sensors, this is still an active domain of research, so that a review bringing together recent results in the domain, including the considerable disadvantages still present, is an important starting point for future research.…”

“…The best results were obtained for the ZnO: SiO 2 ratio of 1:2, with a frequency shift of 1.132 kHz for 10 ppm NH 3 , a result much higher than that recorded for the ZnO only sensor. For SAW sensors, the ZnO sensitivity for H 2 S was greatly improved by Tang et al [ 82 ] through using a mesoporous ZnO-Al 2 O 3 composite. The mesoporous structure of Al 2 O 3 was inherited by the composite material, which favored the adhesion of H 2 S molecules to the layer.…”

“…Among the gases most targeted for detection using ZnO- and ZnO-based materials in SAW sensors, as shown in Table 2 , are hydrogen [ 45 , 112 ], acetone [ 100 , 165 ], hydrogen sulfide [ 82 , 166 ], ethanol [ 44 , 100 ], and ammonia [ 80 , 150 ]. Of these, most RT SAW sensors were made for hydrogen, ammonia and ethanol, for which sensitivities between 11 and 0.005 Hz/ppm were obtained ( Table 2 ) [ 1 ].…”

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

“…It has been established in literature that three effects can contribute to the SAW sensor's responses, i.e., the changes of mass (mass loading effect), elastic modulus (elastic loading effect) and electrical conductivity (electric loading effect) [39][40][41]. Taking into account that the AlO(OH) has the characteristic of electrical insulation, the electric conductivity has little effect on the response of the SAW sensor with the AlO(OH) film [18,19].…”