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 (d1 0 0=ca. 3.2 nm) with a large specific surface area (ca. 305 m2 g−1) was obtained after calcination of the resultant solid product (having ordered mesopores of d1 0 0=ca. 4.1 nm) at 600 °C for 5 h. The sensitivity of a thick film-type sensor (ca. 85 μm thick) fabricated with the mesoporous SnO2 to 500 ppm H2 (maximum sensitivity kM,H2=22.9 at 350 °C) was much higher than that to 500 ppm CO (kM,CO=3.72 at 450 °C). The H2 sensitivity of the mesoporous SnO2 sensor was superior to that of a conventional SnO2 sensor fabricated from tin oxalate, whereas the enhancement in H2 sensitivity due to the development of mesopores was not so remarkable in spite of the large specific surface area (ca. 305 m2 g−1) and small crystallite size (ca. 2 nm). The main reason for the unexpected low H2 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 H2, while that at grain boundaries of SnO2 crystallites is highly sensitive.