Mesoporous semiconducting oxides for gas sensor application

A fabrication procedure of thermally stable mesoporous SnO₂ and TiO₂ powders has been overviewed along with their gas-sensing properties. Treatment of an as-prepared composite material of a supramolecule surfactant and SnO₂, i.e. a self-assembly of the surfactant fringed with a SnO₂ thin wall, with phosphoric acid enabled us to fabricate thermally stable ordered mesoporous SnO₂ powder having a d₁₀₀ value of 3.2 nm, a crystallite size of 2.0 nm and a large specific surface area of 305 m² g⁻¹ even after calcination at 600 °C for 5 h. A thick film sensor fabricated with the ordered mesoporous SnO₂ powder exhibited higher sensing performance than that fabricated with SnO₂ powder prepared by a conventional method and therefore having a lower specific surface area. Surface modification of the conventional SnO₂ powder with a mesoporous SnO₂ layer was also found to be effective for improving the sensing properties. Mesoporous TiO₂ powder could be prepared by employing a modified sol-gel method with Ti(NO₃)₄ and polyethylene glycol having different molecular weights. Higher sensitivity was achieved with a disc-type sensor fabricated with mesoporous TiO₂ powder, in comparison with one fabricated with commercially available TiO₂ powder in the same form, but its sensing properties needed to be further modified.