Synthesis of mesoporous TiO2-based powders and their gas-sensing properties

Ordered mesoporous TiO2 powders have been prepared by employing a modified sol-gel method with Ti(NO3)(4) and polyethylene glycol (PEG) having different molecular weights (MWs). Gel powder heat treated at 100 degreesC was crystallized in a mixture of anatase and rutile phase with a crystallite size of 12 nm and showed clear ordered mesoporous structure with a do 0 2 value of 4.2 nm in the case of PEG with a mean MW of 600 (PEG600). Beyond MW of 600, the crystal phase was transformed to a single anatase phase, and pore volume and surface area increased with increasing MW of PEG. The ordered mesoporous TiO2 gel powder with the largest surface area was obtained in the case of PEG6000 with a crystallite size of about 3.8 nm. Although the mesoporous structure of the TiO2 powder synthesized with PEG6000 was not thermally stable enough, and both the pore volume and the surface area decreased after calcination at elevated temperatures, some fractions of ordered mesoporous structure still remained even after calcination at 600 degreesC along with a large surface area of 66.3 m(2) g(-1). The loading of 0.5 mol% Nb2O5 to the TiO2 powder synthesized with PEG6000 was not effective to maintain the ordered mesoporous structure, but almost doubled surface area was kept even after the calcination at 600 degreesC. The TiO2 sensor prepared in the present study exhibited higher H-2 and CO sensitivities than the sensor fabricated with commercial TiO2 powder with a surface area of 9.7 m(2) g(-1). The TiO2 loaded with 0.5 mol% Nb2O5 sensor exhibited the highest H-2, and CO sensitivity among the sensors tested. Thus, it was confirmed that the ability of TiO2 powder as a sensor material could be improved by controlling the mesoporous structure. (C) 2002 Elsevier Science B.V. All rights reserved.