Preparatoin and Function of Molecular Sieving Silica Overlayr

苯甲醛被吸附在像氧化锡这样的碱性金属氧化物上，形成稳定的苯甲酸阴离子。另一方面，硅烷的化学气相沉积形成了单层二氧化硅，完全覆盖了表面。将这两种现象结合起来，探索了一种获得具有分子筛分性能的二氧化硅覆盖层的新技术：在苯甲酸阴离子被吸附后，在氧化锡上进行化学气相沉积硅醇盐，预吸附物种起到模板的作用并最终被去除。苯甲醛的吸附行为为化学吸附行为，且受温度控制。硅醇盐的沉积量是由固定在表面的醇盐的水解度控制的，首先考察了不同分子尺寸的吸附剂的吸附性能。观察了其分子筛分特性：大于模板分子的分子很难被吸附，并考察了其在气敏传感器中的应用。为此，大约一半的模板覆盖和另一半的二氧化硅聚合是合适的。在这样的样品上，各种醛、醇、烷烃和芳香烃的分子尺寸控制了传感器的传感性能，并且以萘醛代替苯甲醛作为模板。考察了模板分子大小对分子筛性能的影响，并以氧化铝为载体进行了表征。结果表明，二氧化硅在氧化铝表面的化学气相沉积产生了固体酸，其酸度受微观结构控制。预吸附模板剂的密度对二氧化硅的酸性有很强的影响，说明模板剂分子对二氧化硅的微观结构有控制作用。

Benzaldehyde is adsorbed on such a basic metal oxide as tin oxide to form a stable benzoate anion. On the other hand, the chemical vapor deposition of silicon alkoxide forms a monolayr of silica to cover the surface completely. By combining these two phenomena, a novel technique was investigated to obtain a silica overlayr possessing a molecular sieving property : the chemical vapor deposition of silicon alkoxide was done on tin oxide after the benzoate anion had been adsorbed, and the pre-adsorbed species playd a role of template and was finally removed.The conditions of preparation was determined based on the preliminary experiments. The adsorption behavior of benzaldehyde was that of the chemisorption and controlled by the temperature. The deposition amount of silicon alkoxide was controlled by the hydrolysis of alkoxide anchored on the surface.The adsorption property of thus prepared sample was first examined for the adsorbates with various molecular sizes. The molecular sieving property was observed : the molecule larger than the template molecule became hard to be adsorbed.The application to the gas sensor was then examined. For this purpose, about a half of the coverage by the template and another half of the converge by silica were suitable. On such a sample, the sensing property was controlled by the molecular size for various aldehydes, alcohols, alkanes and aromatic hydrocarbons.Furthermore, naphtaldehyde was used as the template in place of the benzaldehyde. The molecular sieving property was also obtained, and clarified to be controlled by the template molecular size.Alumina was also used as the support. It has been clarified that the chemical vapor deposition of silica on alumina generated the solid acidity, and the acidity was controlled by the microstructure. The density of pre-adsorbed template strongly affected the acidity, showing the microstructure of silica was controlled by the template molecule.