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Nanostructured TiO2-CeO2 mixed oxides by an aqueous sol-gel process: Effect of Ce:Ti molar ratio on physical and sensing properties

Mohammadi, M. R ; Sharif University of Technology | 2010

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  1. Type of Document: Article
  2. DOI: 10.1016/j.snb.2010.08.029
  3. Publisher: 2010
  4. Abstract:
  5. Nanostructured TiO2-CeO2 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-TiO2, rutile-TiO2 and cubic-CeO2 phases, as well as Ti 8O15, Ti3O5 and Ce 11O20 depending on annealing temperature and Ce:Ti molar ratio. Furthermore, it was found that CeO2 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 TiO2-CeO2 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-CeO2 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
  6. Keywords:
  7. Ce:Ti molar ratio ; Nanostructure ; TiO2-CeO2 ; Anatase-to-rutile transformations ; Annealing temperatures ; Aqueous particulate sol-gel ; Average grain size ; Binary mixed oxides ; Calibration curves ; Cerium chloride ; Crystallisation ; Crystallite growth ; Field emission scanning electron microscopes ; Gas concentration ; Gas sensing applications ; Hydroxypropyl cellulose ; Iso-propoxide ; Low concentrations ; Low operating temperature ; Low temperatures ; Microstructural properties ; Mixed oxide ; Molar ratio ; Nanostructured morphology ; Nanostructured TiO ; Optimised conditions ; Power Consumption ; Power law ; Sensing films ; Sensing property ; Sensor response ; Sol-gel routes ; Thermal stability ; TiO ; Transmission electron microscope ; Activation energy ; Cerium ; Cerium compounds ; Chlorine compounds ; Crystallites ; Electron microscopes ; Field emission ; Fourier transform infrared spectroscopy ; Fourier transforms ; Gas sensing electrodes ; Gases ; Gels ; Nanostructures ; Oxide minerals ; Powders ; Scanning electron microscopy ; Sensors ; Sol-gels ; Sols ; Thermodynamic stability ; Thin films ; Titanium ; Titanium dioxide ; Transmission electron microscopy ; Vapor deposition ; X ray diffraction ; X ray powder diffraction ; Sol-gel process
  8. Source: Sensors and Actuators, B: Chemical ; Volume 150, Issue 2 , 2010 , Pages 631-640 ; 09254005 (ISSN)
  9. URL: http://www.sciencedirect.com/science/article/pii/S0925400510006908