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Abstract
Nanostructured TiO 2–CeO 2 thin films and powders were prepared by a straightforward aqueous particulate sol–gel route. Titanium (IV) isopropoxide and cerium chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. The effect of Ce:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders crystallised at the low temperature of 500 °C, containing anatase–TiO 2, rutile–TiO 2 and cubic-CeO 2 phases, as well as Ti 8O 15, Ti 3O 5 and Ce 11O 20 depending on annealing temperature and Ce:Ti molar ratio. Furthermore, it was found that CeO 2 retarded the anatase to rutile transformation up to 700 °C. The activation energy of crystallite growth was calculated in the range 1.92–8.79 kJ/mol. Transmission electron microscope (TEM) image showed that one of the smallest crystallite sizes was obtained for TiO 2–CeO 2 binary mixed oxide, being 3 nm at 500 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 17–28 nm at 500 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, calibration curves revealed that TiO 2–CeO 2 sensors follow the power law, S = A[gas] B (where S is sensor response, coefficients A and B are constants and [gas] is the gas concentration) for the two types of gases, and they have excellent capability for the detection of low gas concentrations.
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