Development of Ion Sensors Based on Organic-Inorganic Composite as Membrane Materials

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In this study, ion sensors, which are based on organic-inorganic composite as membrane materials, were constructed. Two types of materials, sol-gel glass and mesoporous silica, were selected, and used for ion sensors as membrane materials.1.Sulfate ion sensors based on sol-gel derived membranesThe compound bearing a triethoxysilyl group and a thiourea group (1)was synthesized. Sol-gel derived membranes modified chemically with compounds 1 were prepared, by adding compound 1 into the mixture of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS), through their hydrolysis, dehydration, and condensation. The electrodes did not respond to sulfate ion activity changes. On the other hand, in the case that silicone rubber was used as a membrane material, the EMF responses were almost Nernstian.2.Calcium ion sensors based on sol-gel derived membranesThe compound bearing two ether-amide groups and long alkyl chains with double bonds (2)was synthesized, and then, two triethoxysilyl groups were introduced into compound 2 (3)Sol-gel derived membranes encapsulating compound 2 and modified chemically with compounds 3 were prepared. Both membrane electrodes showed Nernstian responses to calcium ion activity changes.3.Ion sensors based on mesoporous silicaTEOS, cetyltrimethylammonium bromide, and 16-crown-5 derivative bearing a triethoxysilyl group were used, in order to prepare mesoporous silica which was chemically modified with ionophores. The powdery product was added into the mixture of TEOS and DEDMS, and, therefore, mesoporous silica membranes were formed by sol-gel method. The membrane electrodes showed near-Nernstian responses at higher range of sodium ion activities.