The Effect of Zeolite Composition and Grain Size on Gas Sensing Properties of SnO2/Zeolite Sensor

Abstract

In order to improve the sensing properties of tin dioxide gas sensor, four kinds of different SiO2/Al2O3 ratio, different particle size of MFI type zeolites (ZSM-5) were coated on the SnO2 to prepared zeolite modified gas sensors, and the gas sensing properties were tested. The measurement results showed that the response values of ZSM-5 zeolite (SiO2/Al2O3 = 70, grain size 300 nm) coated SnO2 gas sensors to formaldehyde vapor were increased, and the response to acetone decreased compared with that of SnO2 gas sensor, indicating an improved selectivity property. The other three ZSM-5 zeolites with SiO2/Al2O3 70, 150 and 470, respectively, and grain sizes all around 1 μm coated SnO2 sensors did not show much difference with SnO2 sensor for the response properties to both formaldehyde and acetone. The sensing mechanism of ZSM-5 modified sensors was briefly analyzed.

Enhancing Formaldehyde Selectivity of SnO2 Gas Sensors with the ZSM-5 Modified Layers

“…Zeolites show movable frame and sieve pore structure, which is widely utilized in catalytic and plasma exchange applications [16,17]. Considering zeolite can act as a molecular sieve due to its structure with tiny pores, the selectivity of the sensors are greatly improved when zeolite is coated on the sensitive material as a modified layer [18][19][20][21][22]. Vilaseca et al coat the Pd/SnO 2 surface with a non-continuous zeolite A (LTA) layer by microdropping from a zeolite suspension.…”

“…The hydrocarbon (methane and propane)/ethanol mixtures were measured and the sensors presented remarkable filtering capacity [18]. ZSM-5 and silicalite-1 are the most commonly applied zeolites to improve the selectivity of gas sensors [19][20][21][22]. The [010] highly preferred-orientation silicalite-1 layer coated on SnO 2 thin film sensor was proved to be able to resist the influence of H 2 O when detecting C 2 H 4 [19].…”

“…In particular, the selectivity of metal oxide semiconductor (MOS) gas sensors is very poor [19]. zeolites are very effective for improving the selectivity of MOS gas sensors to formaldehyde, whether they are used as external [20] or in-situ membranes [21,22]. When an external 3 µm zeolite MFI film is placed in front of the gas sensor, it is difficult for VOCs, such as acetone, ethanol, and isoprene, to pass through the film and react with the sensitive material except formaldehyde [20].…”

“…Sun et al modified the SnO 2 sensors with different SiO 2 /Al 2 O 3 ratios and different particle sizes of ZSM-5 to explore the influence on the gas sensitivity of the SnO 2 sensor. They found that the response value of the SnO 2 gas sensor coated with ZSM-5 molecular sieve (SiO 2 /Al 2 O 3 = 70, particle size 300 nm) to formaldehyde gas increased, meanwhile the response value to acetone decreased, therefore improved the selectivity [21]. Sun et al also proved that the SnO 2 /ZSM-5 composite nanofibers could resist the interference of ethanol and acetone when formaldehyde was measured [22].…”

Nanocomposites SnO2/SiO2 for CO Gas Sensors: Microstructure and Reactivity in the Interaction with the Gas Phase

“…This requirement is met by amorphous SiO 2 , which is also characterized by high thermal stability (Tamman temperature is 714 °C) [13]. In a number of studies on the synthesis of SnO 2 /SiO 2 composites of various morphologies, a decrease in the growth rate and stabilization of SnO 2 microstructure parameters, as well as an increase in the sensor signal to acetone, ethanol, and CO in dry and moist air were observed [14,15,16,17,18,19,20,21]. The decisive factor in the synthesis of such composites is the selection of the optimal Si:Sn ratio.…”