Properties and mechanism study of SnO2 nanocrystals for H2S thick-film sensors

Two different laboratory-synthesized SnO2 nanocrystals using gel combustion method and hydrothermal method were used for the fabrication of nanocrystalline thick-film sensor samples through screen-printing technique. Their sensitive properties toward low concentrations of H2S gas in air (0.7-100 ppm) at 25-250 degrees C and microstructure features were examined for comparison. Interestingly, both of the two different samples showed maximum response at about 150 degrees C, and the response (S) as a function of H2S concentration (P-H2S) was approximately fit to S proportional to P-H2S(0.6). Theoretical calculation based on the surface chemistry suggests that at 150 degrees C, oxygen might be ionosorbed on SnO2 surfaces predominantly as O-2(-) and O- with the proportion ratio of 1:2. It was found that the sensor sample based on SnO2 nanocrystals produced by gel combustion method had higher response and shorter response time, which might be attributed to the more porous nanocrystalline (about 50 nm in size) microstructure than the one prepared from hydrothermal-synthesized SnO2 nanocrystals, where smaller SnO2 nanocrystals (about 12-13 nm) are densely packed and agglomerate into large entities of about 2-3 mu m in size. (C) 2009 Elsevier B.V. All rights reserved.