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.