Preparation of macroporous SnO2 films using PMMA microspheres and their sensing properties to NOx and H2

Macroporous SnO2 (mp-SnO2(P-n); P means polymethylmethacrylate (PMMA) and n = diameter of PMMA microsphere) thick film gas sensors were fabricated by a modified sol-gel method by employing PMMA microspheres (n = 800, 400, 250 and 150 nm) as a template and SnCl2 as a tin source. Morphology of mp-SnO2 films was markedly dependent on the SnCl2 concentration and the diameter of PMMA microspheres. Especially, the ratio of the thickness of the SnO2 wall to the diameter of the hollow SnO2 microsphere seems to increase with decreasing the diameter of PMMA microspheres used. Among the films prepared, mp-SnO2(P-250) exhibited the largest response to NO and NO2 in air at 225 degrees C, whereas its response transients were relatively slow, indicating low adsorption and desorption speeds of negatively charged chemisorbed NOx species on the SnO2 surface. On the other hand, mp-SnO2(P-800) showed the largest H-2 response among the sensors at temperatures higher than 400 degrees C. It has been revealed that the thickness and porous structure of the SnO2 thick films are important factors to determine the sensing properties to NO2 and H-2. (c) 2004 Elsevier B.V. All rights reserved.