A hydrothermal method was used to synthesize nanocrystalline SnO 2 particles with an average particle size of 3.0 ± 0.5 nm. Thermally treated SnO 2 with an average diameter of 3.3 ± 0.6 nm was obtained by the annealing of the as-synthesized SnO 2, which was treated at 300 °C for 1 h under 10% H 2 /Ar. An atomic ratio of 2.3/1 (O/Sn) was observed for the thermally treated SnO 2 compared to 1.2/1 for the as-synthesized one. However, a smaller surface area of 92 m 2 /g was measured for the thermally treated SnO 2 as compared with 130 m 2 /g for the as-synthesized SnO 2 . Due to the occupation of the chloride ions in the oxygen sites of the as-synthesized SnO 2, the thermally treated SnO 2 displayed better sensing performance for ethanol when compared with as-synthesized SnO 2 . The sensing performance of the as-synthesized SnO 2 sensor can be greatly improved by simply heating it at 350 °C for 5 min to partly remove Cl - from SnO 2 nanoparticles. The thermally treated SnO 2 exhibited good sensitivity to alcohol, i.e., methanol, ethanol, and propanol. The concentration detection limit can be as low as 1.7 ppm. Furthermore, the increased sensor signal was found to depend on the carbon chain number of the alcohol.
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Chiu et al. (2007) studied this question.