Crystalline Ordered Mesoporous Tio <sub> 2 </ Sub> Synthesis And Photocatalytic Properties

In recent years, titania, as a photocatalysis is intensely investigated in the decomposition of organic pollutant. In the photocatalysis reaction, the high specific surface area of mesoporous TiO₂ is favorable to the adsorption of the organic pollutant. Meanwhile, the mesopores are favorable to the diffusion of the organic pollutant and can enhance the optical absorption by increasing the times of the incidence light's diffuse reflection. So far, most reported literatures in the synthesis of mesoporous titania were about anatase phase, ordered rutile mesoporous titania has not been reported. And some literatures reported that rutile or A/R mixed titania (such commercial P25) shows better photocatalysis activity to some organic pollutant. If we get ordered mesoporous rutile or A/R titania, they may have much better photocatalysis activity. In this thesis, efforts are thus made to prepare order mesoporous rutile or A/R titania. The synthesis methods include hydrothermal method and evaporation induced self-assembly method. One-step low-temperature hydrothermal procedure is adopted to try to obtain crystalline ordered mesoporous titania in order to avoid the mesostructural collapse during the crystallization by calcination. Efforts are also made to get A/R mixed or pure R order mesoporous titania using EISA method. We investigate the effects of the precursors, the mol ratio of the "acid-base pair ", temperature, humidity on the formation of the mesostructures, phase compositions and photocatalysis activity.This thesis divides three major parts. In chapter 2, we try to get crystalline mesoporous titania by one-step low-temperature hydrothermal method. We change experiment parameter such as : mol ratio of precursor to surfactant (1 to 12.5,1 to 75), temperature(30℃, 40℃, 50℃, 60℃), surfactants (P123, CTAB, SDS). Rutile titania nanorods (diameter, 5 run; length, 40 nm) are founded formed using TiCl₄ as precursor, P123 as template at 40℃. We get rutile nanorods and anatase disorder mesoporous mixed titania by using TiCl₄ as precursor, SDS as template at 60℃. We get smaller nano crystals(diameter,4nm) when using TiCl₃ as precursor whose hydrolyzation is slower than that of TiCl₄.In chapter 3, order mesoporous titania are prepared by the evaporation-induced self-assembly (EISA) process. The effect of the mol ratio of the "acid-base pair ", EISA temperature and humidity are investigated on the mesostructures and crystalline. The sample having the best order mesoporous structure is from precursors with the mol ratio of TiCl₄:TBOT =1: 1. At 35℃and 100% humidity, we get samples mixed with anatase meso-structure and rutile nano-particle, which show great photocatalysis activity. The mesoporous structure of as-prepared anatase titania is found collapsed after calcination at 500℃In chapter 4, in order to enhance the thermal stability of the mesostructured titania, as-made ordered mesoporous titania are post-treated by TEOS vapor at 90℃for 1 hour before removing the surfactants by calcination. The mesoporous structure of the as-treated sample is found maintained after calcination at 700℃. The phase transition of anatase to rutile is not observed. The EDX data show the ratio of Si:Ti is 1:9. The BET surface area is 178.9 m²/g after calcination at 500℃, and can be 89.6 m²/g after calcination at 700℃. The IR spectra shows the present of Si-O-Si bond and Si-O-Ti bond. Following the TEOS post-treatment, high crystallization of anatase phase can be obtained by further water vapor treatment without sacrifice the mesoporous structure.