Gas-sensing properties of ordered mesoporous SnO2 and effects of coatings thereof

Mesoporous structure and gas-sensing properties of SnO2 powders prepared by utilizing the self-assembly of a cationic surfactant under different conditions have been investigated. As-prepared SnO2 powders were characterized with ordered and hexagonal mesoporous structure (d1 0 0≈4.4 nm) having a small crystallite size of 1.6–2.0 nm, and the size of agglomerated secondary particles tended to decrease with decreasing the concentration of a Sn source and a surfactant in a precursor solution. Treatment of as-prepared powders with phosphoric acid (PA) was effective for depressing the growth of SnO2 crystallite during calcination at elevated temperatures and then maintaining the ordered mesoporous structure, while the volume of ordered mesopores decreased. However, mesoporous SnO2 (m-SnO2) powder with a specific surface area of 374 m2 g−1 could be prepared even after calcination at 600 °C for 5 h by optimizing the preparation conditions. The m-SnO2 powders exhibited excellent H2 sensitivity in proportion to surface area and high NO sensitivity comparable to NO2 sensitivity. However, their resistance levels in air were close to the limit for practical measurement. Surface modification of conventional SnO2 (c-SnO2) powder with m-SnO2 was found to be effective for improving gas-sensing properties of c-SnO2, while maintaining the sensor resistance in air to be close to that of c-SnO2. H2 sensitivity of the c-SnO2 modified with m-SnO2 was lower than that of m-SnO2, but NO2 sensitivity improved markedly by the surface modification with m-SnO2.