Improved selectivity, response time and recovery time by [0 1 0] highly preferred-orientation silicalite-1 layer coated on SnO 2 thin film sensor for selective ethylene gas detection

Abstract

In this work, sensing response, response time and recovery time for selective ethylene gas detection were improved by coating a layer of [0 1 0] highly preferred-orientation silicalite-1 polycrystals on SnO 2 thin film sensors. The sensors were prepared by primarily depositing SnO 2 on borosilicate glass substrates using ultrasonic spray pyrolysis technique. Conventional and [0 1 0] preferred orientations of silicalite-1 layers were then directly coated on the SnO 2 thin film sensors by hydrothermal crystallization technique with different gel compositions. The silicalite-1/SnO 2 thin film sensors were calcined at 550 °C in dry air. The crystal structure and surface morphology of SnO 2 and silicalite-1 layers were characterized by XRD and SEM techniques. XANES and TPR were used to verify oxidation state and reduction temperature of the SnO 2 thin film sensors, respectively. The interaction of C 2H 4 and H 2O with silicalite-1 was determined by TPD. The sensing performances, such as selectivity, dynamic range, response time and recovery time were evaluated for the C 2H 4 and H 2O. The results showed that the incorporated silicalite-1 layers readily improve the C 2H 4 selectivity and dynamic range by preferential adsorption of C 2H 4 molecules on the silicalite-1 filtering layers. The response time and recovery time for the [0 1 0] highly preferred-orientation silicalite-1/SnO 2 thin film sensor ( t 90%, 14 and 144 s) were shorter than those of the conventional one ( t 90%, 25 and 208 s). It is suggested that the [0 1 0] preferred-orientation silicalite-1, with a pore direction perpendicular to SnO 2 thin film surface, can accelerate the molecular diffusion and reduce the diffusion pathway of ethylene to the sensing film.