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

随着硅铝和硅钛混合醇盐的溶胶-凝胶反应的进行，观察到了一些芳香族光探针分子(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、微粘度等物理化学性质的变化。在AI含量较小的情况下，胶凝发生得相对较慢，而光探针分子周围的极性和微粘度增加得相对较快。另一方面，在AI比例较大的情况下，观察到相反的化学和物理现象。在酸性催化剂作用下，反应速度较快，决定反应速率的反应为缩合反应。另一方面，在碱性催化剂的情况下，缩合进行得很快，决定反应速度的步骤是水解。观察芳香族分子的荧光光谱是在分子水平上研究金属醇盐的溶胶-凝胶-干凝胶转变的有用的光物理和光化学探针，而溶胶-凝胶法制备的干凝胶状态下的芳香族分子的热稳定性与光稳定性类似，是功能材料应用的重要方面之一。我们发现，包裹的罗丹明B和荧光素分子比在空气环境中具有更高的热稳定性。这种增强可以归因于阻止了氧气向所制备的硅凝胶的孔内渗透。在溶胶-凝胶反应中，芘的类准分子荧光在凝胶化之前消失了，但在包埋状态下，荧光强度增强到了Si-Ti和SI-Al的孔中。这一现象可以归因于两个分子在钛中心的吸附和芳香分子与AI形成1：1的络合物。

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.