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 d(100) value of 3:2 nm a crystallite size of 2.0 mn and a large specific surface area of 305 m(2) g(-1) even after calcination at 600 degreesC 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. (C) 2003 Elsevier Ltd. All rights reserved.