Abstract

High specific surface area (SSA) nanocrystalline powders and dip-coated TiO2 thin films have been prepared by a particulate sol-gel route with added polymeric fugitive agents (PFAs), namely trehalose dihydrate (THD), polyethylene glycol (PEG6000) and hydroxypropyl cellulose (HPC). One of the highest SSA reported in the literature, obtained without PFA, was achieved (i.e., 1 g I m(2)/g), a value that could be increased up to 304 m2/g, 274 m(2)/g and 200 m(2)/g for PEG/TiO2, HPC/TiO2 and THD/TiO2 powders, respectively. Furthermore, the crystallite size varied from 1 nm for as-produced powders up to 4 nm for powders heat-treated at 600 degrees C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a stable and reproducible response towards CO and NO, at a low operating temperature of 200 degrees C. Calibration curves revealed that all sensors followed the power law (S = A[gas](B)) (where S is sensor response, and coefficients A and B are constants) for the two kinds of gases and they have good capability for the detection of low gas concentrations (25 ppm CO and 0.5 ppm NO2). Amongst all sensors, HPCMO2 sensor showed the highest response towards CO <= 100 ppm and NO2 <= 2 ppm, whereas PEG/TiO2 sensor had the highest response towards CO > 100 ppm and NO, > 2 ppm operated at 200 degrees C. The response of the sensors to both CO and NO, changed with operating temperature reaching a maximum at a specific temperature. Moreover, the sensor response decreased by increasing the film annealing temperature. The response magnitude and response time of the sensors obtained in this work are superior to those reported in previous studies. Furthermore, their low power consumption as a result of their low operating temperature manifests their good potential for industrial application. (c) 2006 Elsevier B.V. All rights reserved.