Preparation and gas-sensing properties of thermally stable mesoporous SnO2

Ordered mesoporous SnO2 was prepared from sodium stannate by utilizing the self-assembly of a cationic surfactant (n-cetylpyridinium chloride (C16PyCl)) and its thermal stability was improved by the treatment with phosphoric acid (PA) prior to calcination. Under the most suitable preparation conditions, an ordered mesoporous structure (d(100) = ca. 3.2 nm) with a large specific surface area (ca. 305 m(2) g(-1)) was obtained after calcination of the resultant solid product (having ordered mesopores of d(100) = ca. 4.1 nm) at 600 degreesC for 5 h. The sensitivity of a thick film-type sensor (ca. 85 mum thick) fabricated with the mesoporous SnO2 to 500 ppm H-2 (maximum sensitivity k(M,H2) = 22.9 at 350 degreesC) was much higher than that to 500 ppm CO (k(M,CO) = 3.72 at 450 degreesC). The H-2 sensitivity of the mesoporous SnO2 sensor was superior to that of a conventional SnO2 sensor fabricated from tin oxalate, whereas the enhancement in H-2 sensitivity due to the development of mesopores was not so remarkable in spite of the large specific surface area (ca. 305 m(2) g(-1)) and small crystallite size (ca. 2 nm). The main reason for the unexpected low H-2 sensitivity may arise from agglomeration of mesoporous SnO2 particles, i.e. the potential barrier height at the boundaries between agglomerated particles may be less-sensitive to H-2, while that at grain boundaries Of SnO2 crystallites is highly sensitive. (C) 2002 Elsevier Science B.V. All rights reserved.