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A comparative study of TiO 2 powders prepared by precipitation and sol-gel methods was conducted. Titanium tetrachloride and titanium tetraisopropoxide were used as the starting materials for the precipitation and sol-gel processes, respectively. The effects of the two different drying methods, freeze drying and normal drying at 100°C, of the precipitates on the properties of the prepared TiO 2 powders were also investigated. The effects of the synthesis methods on phase, surface area, crystallite size, and photodegradation of methylene blue were studied by XRD, SEM, TEM, BET, and UV/ Vis techniques. It was found that the major phase of the synthesized TiO 2 was anatase, but small amounts of the brookite phase (Ͻ10 %) were found in some samples. The synthesized anatase TiO 2 with no pretreatment was found to be stable up to 600°C for the samples prepared by the precipitation

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Mesoporous silica (MPS) is a porous silica material with various pore structures. In this study, mesocellular foam silica (MCF) was synthesized and functionalized by hexamethyldisilazane (HMDS) to study effects of surface chemistry on benzene adsorption capability. Physical and chemical properties of pristine and functionalized MCFs were characterized and compared. Scanning and transmission electron microscopy showed that the complex pore structures of the MCFs were retained after the functionalization at relatively high temperature (573K). TGA and FTIR results showed that the functionalization led to a reduction of water adsorbed on the surfaces of the MCF. The functionalization improved adsorption of benzene compared to the pristine MCF and the optimum HMDS:SiO2 molar ratio was 1.5. The amount of benzene adsorbed has a linear relationship with the concentration of benzene in the environment. This relationship enables quantitative benzene detection by using the functionalized MCF as sensing materials in resistive-type or gravimetric-type benzene gas sensors.