Acid-base and monomer-dimer equilibria of methylene blue in dip-coated thin films
Acid-base and monomer-dimer equilibria of methylene blue in dip-coated thin films
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DOI：
10.1246/bcsj.72.915
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发表时间：
1999-05-01
影响因子：
4
通讯作者：
Fujii, T
中科院分区：
文献类型：
--
作者：
Nishikiori, H;Nagaya, S;Fujii, T
制备了含亚甲基蓝（MB）的薄膜。它们使用正硅酸乙酯（TEOS）的溶胶-凝胶反应进行浸涂。在制备薄膜后，观察到各个薄膜的吸收光谱随时间的变化。得到了单体（MB+）、二聚体（（MB+）（2））和质子化物质（MBH 2+）对薄膜总吸收光谱的相对贡献。根据MBH 2+的相对丰度估计每个膜中的酸度。在包括大量HCl作为催化剂的体系的情况下，在刚制备膜之后，除了MB+和（MB+）（2）之外，MB还形成MBH 2+。而MBH ~（2+）在制备后5-10 min即消失。MBH 2+的形成表明MB分子周围的酸性非常高。在刚制备后的每个膜中，水解速率变慢，并且释放的质子的浓度显著增加，因为缩聚反应随着体积收缩而迅速进行。虽然生长的-SiOSi-网络阻止了酸与水和乙醇一起蒸发，但MBH 2+的减少表明由于蒸发而降低了膜中的酸度。
Thin films including Methylene Blue (MB) have been prepared. They were dip-coated using the sol-gel reaction of tetraethyl orthosilicate (TEOS). The absorption spectra of the individual thin films have been observed as a function of time after preparation of the films. The relative contributions of the monomer (MB+), dimer ((MB+)(2)), and protonated species (MBH2+) existing in the individual thin films to the total absorption spectra were obtained. The acidity in each film was estimated from the relative abundance of the MBH2+. In the case of the system including a large amount of HCl as a catalyst, MB formed MBH2+ in addition to MB+ and (MB+)(2) just after preparation of the films. However, MBH2+ in every film disappeared 5-10 min after the preparation. The formation of MBH2+ indicates the very high acidity around MB molecules. In each film just after the preparation, the rate of the hydrolysis became slower and the concentration of the released proton remarkably increased because the polycondensation rapidly proceeded with the contraction in volume. Although growing -SiOSi- networks prevent the evaporation of the acid together with water and ethanol, the decrease of MBH2+ indicates the lowering of acidity in the films due to the evaporation.