HRTEM / EELS Analysis, Structural Characterization and Sensor Performances of Hydrothermal Nano-TiO 2
- PDF / 703,791 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 36 Downloads / 193 Views
A4.10.1
HRTEM / EELS Analysis, Structural Characterization and Sensor Performances of Hydrothermal Nano-TiO2 Ana M. Ruiz1, J. Arbiol2, A. Cornet2, K. Shimanoe3, Joan R. Morante2, and N. Yamazoe3 1
Centro Nacional de Microelectrónica (IMB-CSIC), Campus UAB, 08193 Bellaterra, Spain EME, Department of Electronics, University of Barcelona, C/ Marti i Franques 1, Barcelona 08028, Spain 3 Department of Materials Science, Kyushu University, Kasuga-shi, Fukuoka 816-8580, Japan 2
ABSTRACT Pure nanophased TiO2 with controlled microstructure and resistant to thermal induced grain growth has been prepared by hydrothermal treatments. The synthesized nano-TiO2 presents small size and well defined and faceted surface, as shown by Raman spectroscopy, XRD, EELS and HRTEM. Such performances are slightly changed with the posterior temperature treatments up to 700 ºC, maintaining anatase phase structure and grain size about 20nm. The extent of stabilization depended on the pH of the treatment, being pH 2 more convenient for stabilizing the size, and pH 3 for the phase. HRTEM and EELS measurements showed the coexistence of rutile big particles (~100 nm) with anatase small particles (~40 nm) at pH 3 and calcination at 900oC. Thick-films of precipitated TiO2 and hydrothermally treated TiO2 were tested for the CO and the ethanol response. The hydrothermal treatment allowed obtaining stable sensitive films which exhibited enlarged sensor response and improved transients, specially in the case of the materials treated at pH 3.
INTRODUCTION Gas sensing requirements have claimed for sensing materials with very high active surface. Thus, different methods have been used during the last years to prepare them [1-4]. Among others, methods based on modified sol-gel routes, laser pyrolysis or spray pyrolysis, have satisfied the size requirements, but not the material stability and, as a straightforward consequence, the gas sensor presents drifts, short lifetime and lack of stability. Thermal treatments under different ambient conditions are usually applied in order to increase the sensor performances related to the material stability. Such treatments punish significantly properties like active surface area and sensitivity characteristics. In the case of TiO2, it is commonly accepted that the difference in structure can exert influences on the catalytic or gas-sensing properties [5-10]. Nevertheless, there is still discussion about which of the three natural polymorphs (brookite, anatase and rutile) is the most convenient for gas sensing purposes. Up to now, it seems there is more supporting evidence in favor of anatase as the most promising surface for gas detection due to its higher surface reactivity to gases [11,12]. For practical applications as gas sensors the materials have to be thermally stabilized at temperatures over the operating temperature (typically 300 oC ~ 600 oC). Therefore, it is important to prepare stable anatase TiO2 with endurance to phase transformation. Anatase irreversibly converts to rutile phase at temperatures around
Data Loading...
