The effects of the SnO 2 pore size and metal oxide promoters on the sensing properties of SnO 2-based thick film gas sensors were investigated to improve the detection of very low H 2S concentrations (<1 ppm). SnO 2 sensors and SnO 2-based thick-film gas sensors promoted with NiO, ZnO, MoO 3, CuO or Fe 2O 3 were prepared, and their sensing properties were examined in a flow system. The SnO 2 materials were prepared by calcining SnO 2 at 600, 800, 1,000 and 1,200 °C to give materials identified as SnO 2(600), SnO 2(800), SnO 2(1000), and SnO 2(1200), respectively. The Sn(12)Mo5Ni3 sensor, which was prepared by physically mixing 5 wt% MoO 3 (Mo5), 3 wt% NiO (Ni3) and SnO 2(1200) with a large pore size of 312 nm, exhibited a high sensor response of approximately 75% for the detection of 1 ppm H 2S at 350 °C with excellent recovery properties. Unlike the SnO 2 sensors, its response was maintained during multiple cycles without deactivation. This was attributed to the promoter effect of MoO 3. In particular, the Sn(12)Mo5Ni3 sensor developed in this study showed twice the response of the Sn(6)Mo5Ni3 sensor, which was prepared by SnO 2(600) with the smaller pore size than SnO 2(1200). The excellent sensor response and recovery properties of Sn(12)Mo5Ni3 are believed to be due to the combined promoter effects of MoO 3 and NiO and the diffusion effect of H 2S as a result of the large pore size of SnO 2.
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