1977 年 26 巻 288 号 p. 833-837
The adsorbed amounts of organic vapors, i.e. CH3OH, (CH3)2CO and (C2H5)2O, on NaBr particles preadsorbed by water Vapor have been determined at -78, -63.5, -45 and 0°C. Three different amounts of the preadsorbed water, Va, Vb and Vc, are used in this study, where Vb=2Va and Vc=3Va. The value Va was approximately equal to the value necessary for covering the unit surface area of NaBr particles with localized monolayer of water.
The monolayer capacity of methyl alcohol estimated from its adsorption isotherm for NaBr surface Va-preadsorbed was found to agree closely with the amount of preadsorbed water.
This result is explained by the following two assumptions that water molecules are adsorbed on (100) planes of NaBr crystals in the ratio of one watar molecule to two adjacent anions at Va-adsorption and that methyl alcohol molecules are adsorbed on such localized water molecules in a ratio of 1:1. Moreover, the adsorptive activity of Vb-preadsorbed NaBr surface for ethyl ether was slightly larger than that of the Va-preadsorbed surface. Therefore, in the Vb-preadsorbed surface, water molecules in the upper layer, i.e. second layer, are expected to adsorb on the localized monolayer so as to interact strongly with ethyl ether molecules. By using the three organic vapors in such“double adsorption”system, some significant informations were obtained about the adsorptive structure of water molecules attached on NaBr surface, and the interactions between preadsorbed water molecules and the organic molecules. From these results, the double adsorption method is considered to be an effective tool for studying the mechanism of a solid-gas adsorption.