Sensor performance of nanostructured TiO₂ thin films derived from particulate sol-gel route and polymeric fugitive agents

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., 181 m²/g), a value that could be increased up to 304 m²/g, 274 m²/g and 200 m²/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 °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 NO₂ at a low operating temperature of 200 °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, HPC/TiO₂ 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 NO₂ > 2 ppm operated at 200 °C. The response of the sensors to both CO and NO₂ 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.