The current gas sensors have a problem in selectivity of gas and using the dynamic response is one solution to identify the gas type. In the dynamic response, the information from the non-linear phenomena under the transient temperature conditions was used to recognize various gas types with a single sensor element. The mechanism was slightly revealed so far and this work aimed at determining the key factors of the dynamic response. Non-doped SnO2 films were prepared by a liquid phase deposition (LPD) method to control the morphology of the film and the components of the sensor. Nano-scale control in the thickness was demonstrated by the simple LPD process. The gas type was successfully identified even with the non-doped SnO2 films. The film thickness did not largely affect the profile of the signal and the dynamic response was considered to be due to basic phenomena between the gas and the sensor material itself such as adsorption and desorption.

Because of thermal stability, tunable porosity and modifiable surface, mesoporous silica is a promising material in catalysis, drag delivery and environmental applications. These industrial potentials could be enhanced by compounding mesoporous silica with Fe 3 O 4 nano-particles, since its para-magnetism brings about the spatial mobility controlled under magnetic field. For the present research work, tetraethylorthosilicate was hydrolyzed and poly-condensed over the self-assembled surfactant micelles in the presence of Fe 3 O 4 nano-particles in order to embed it in mesoporous silica SBA-15. Under the acidic condition caused by an aqueous solution of FeCl 3 , the poly-condensates were formed into the well-ordered hexagonal arrays of one-dimensional channels without dissolution of Fe 3 O 4 nano-particles. This was the first successful synthesis of SBA-15 in which Fe 3 O 4 nano-particles were embedded. On the other hands, another approach where SBA-15 was synthesized over Fe 3 O 4 coated with amorphous silica in HCl aqueous solution ended in failure because the coated silica could not prevent Fe 3 O 4 from dissolving in HCl aqueous solution. For the SBA-15/ Fe 3 O 4 composite prepared successfully, a quaternary alkyl-ammonium salt was grafted in order to prove the catalytic application.