Gas detection with SnO2 sensors modified by zeolite films

Zeolite films have been grown on top of SnO2 sensors to modify their response to gas phase molecules with the aim of improving their selectivity. To this end SnO2 sensors were first prepared using conventional procedures, and then zeolite layers (silicalite and zeolite A) were grown on the outer SnO2 surface, using different synthesis procedures. The zeolite-modified sensors were tested in the analysis of single gases (H2O, H2, CO, CH4, C3H8, and C2H5OH, at concentrations from 20 to 10,000 ppm) and mixtures, and their response was compared with that of uncoated SnO2 sensors. The zeolite-coated sensors were able to suppress the response towards certain analytes, while maintaining or even improving the sensitivity towards others. The differences in sensor behaviour and the improvement of sensor selectivity increased with the quality of the zeolite layer. The best zeolite films were obtained on SnO2 layers pretreated at 450 °C, in which the external surface had a lower roughness.