Study of Photophysical Process and Photocatalytic Activity of Anchored Catalyst Prepared by thev Sol-Gel Method

随着SI-AI和Si-Ti混合醇氧化物溶胶-凝胶反应的进行，观察了一些芳香光探针分子（l-萘酚、苯并喹啉、罗丹明VB、荧光素和芘）的吸收光谱、荧光光谱和荧光激发光谱。溶胶-凝胶过程中的光谱变化反映了反应样品光探针周围的极性、微粘度等化学物理性质的变化。在AI含量较低的情况下，凝胶化过程相对较慢，光探针分子周围的极性和微粘度增加较快。另一方面，在AI含量较大的情况下，观察到相反的化学和物理现象。在酸催化剂的情况下，水解进行得很快，决定速率的反应是缩合反应。另一方面，在碱性催化剂的情况下，缩合进行得很快，速率决定步骤是水解。观察芳香分子的荧光光谱是在分子水平上研究金属烷氧化物溶胶-凝胶-干凝胶转变的一种有用的光物理和光化学探针。溶胶-凝胶法制备的包封在干凝胶态的芳香分子的热稳定性和光稳定性类似，是功能材料实用的重要方面之一。我们发现包封的罗丹明B和荧光素分子比在空气环境中具有更高的热稳定性。这种增强可归因于防止氧气渗透到所制备的硅胶的孔隙中。在溶胶-凝胶反应过程中，芘的准分子样荧光在凝胶化前消失，但在Si-Ti和SI-AI的孔内包封状态下荧光强度变强。这一惊人的现象可以归因于两个分子在Ti位点的吸附以及芳香分子与AI之间形成1:1的配合物。

The absortion, fluorescence, and fluorescence-excitation spectra of some aromatic photoprobe molecules(l-naphthol, benzoqunolines, rhodamine VB, fluorescein, and pyrene)have been observed along with the progress of the sol-gel reaction of SI-AI and Si-Ti mixed alkoxides. The spectral changes during the sol-gel process reflected the changes of the polarity, microviscosity, and other chemical and physical properties around the photoprobes of the reaction specimes. In a case of small fraction of AI, gelation occurred relatively slow and polarity and microviscosity around the photoprobe molecules increased relatively fast. On the other hand, the reverse chemical and physical phenomena are observed in a case of large fraction of AI. In a case of acid catalyst, hydrolysis proceeded fast and the rate determing reaction is condensation step. On the other hand, in a case of basic catalyst, the condensation proceeds fast and the rate determining step is hydrolysis. Observation of the fluorescence spectra of aromatic molecules is a useful photophysical and photochemical probe for studying the sol-gel-xerogel transition of metal alkoxides on a molecular level.The thermal stability, similar to the photostability, of aromatic molecules encapsulated in xerogel state prepared by the sol-gel method is one of the important point for the utility of functional materials. We found that the encapsulated rhodamine B and fluorescein molecules have increased thermal stability than in air circumstance. This enhancement can be sttributed to the prevention of the permeation of oxygen into the pores of the prepared silica gel.Excimer-like fluorescence of pyrene during the sol-gel reaction disappeared before gelation, but the fluorescence intensity became strong in encapsulated state into pores of the Si-Ti and SI-AI. This striking phenomenon can be attributable to the adsorption of two molecules at Ti site and 1 : 1 complex formation between aromatic molecules and AI.