Gas-sensing properties of ordered mesoporous SnO 2 and effects of coatings thereof

Abstract

Mesoporous structure and gas-sensing properties of SnO 2 powders prepared by utilizing the self-assembly of a cationic surfactant under different conditions have been investigated. As-prepared SnO 2 powders were characterized with ordered and hexagonal mesoporous structure ( d 1 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 SnO 2 crystallite during calcination at elevated temperatures and then maintaining the ordered mesoporous structure, while the volume of ordered mesopores decreased. However, mesoporous SnO 2 (m-SnO 2) powder with a specific surface area of 374 m 2 g −1 could be prepared even after calcination at 600 °C for 5 h by optimizing the preparation conditions. The m-SnO 2 powders exhibited excellent H 2 sensitivity in proportion to surface area and high NO sensitivity comparable to NO 2 sensitivity. However, their resistance levels in air were close to the limit for practical measurement. Surface modification of conventional SnO 2 (c-SnO 2) powder with m-SnO 2 was found to be effective for improving gas-sensing properties of c-SnO 2, while maintaining the sensor resistance in air to be close to that of c-SnO 2. H 2 sensitivity of the c-SnO 2 modified with m-SnO 2 was lower than that of m-SnO 2, but NO 2 sensitivity improved markedly by the surface modification with m-SnO 2.