Low temperature nanocrystalline TiO2–Fe2O3 mixed oxide by a particulate sol–gel route: Physical and sensing characteristics

Nanocrystalline TiO2–Fe2O3 thin films and powders were prepared by a straightforward aqueous particulate sol–gel route at the low temperature of 300 °C. Titanium(IV) isopropoxide and iron(III) chloride were used as precursors, and hydroxypropyl cellulose was used as a polymeric fugitive agent in order to increase the specific surface area. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powder crystallised at the low temperature of 300 °C, containing anatase-TiO2 and hematite-Fe2O3 phases. Furthermore, it was found that Fe2O3 retarded the anatase-to-rutile transformation up to 500 °C. The activation energies for crystallite growth of TiO2 and Fe2O3 components in the binary system were calculated 10.62 and 0.67 kJ/mol, respectively. Moreover, one of the smallest crystallite sizes was obtained for TiO2–Fe2O3 binary mixed oxide, being 6 nm at 300 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanostructured morphology. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas (i.e., 25 ppm) at low operating temperature of 150 °C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption. Furthermore, TiO2–Fe2O3 sensors follow the power law for the detection of CO gas.