Madsen L, Grøn C, Lind I, Engell J
Department of Geology and Geotechnical Engineering
J Colloid Interface Sci. 1998 Sep 1;205(1):53-64. doi: 10.1006/jcis.1998.5592.
The adsorption of benzoic acid on synthetic calcite dispersed in cyclohexane has been studied between 296 and 346 K. The results can be successfully explained by a two-step model involving a Langmuir adsorption of first a layer of molecules oriented parallel to the surface and next, as the concentration of the adsorbate in the liquid phase increases, a gradual replacement of this layer with a monolayer of molecules oriented perpendicular to the surface. The maximum adsorption of benzoic acid in the perpendicular oriented monolayer has been determined to be 7.345 µmol/m2, independent of the temperature, and close to the theoretical value of 7.4 µmol/m2. The Langmuir constant for the second step, in which parallel adsorbed molecules are replaced by perpendicular adsorbed ones, varies from 2 x 10(3) L/mol at 296 K to 16 x 10(3) L/mol at 346 K, and the enthalpy and entropy changes associated with this part of the adsorption process are 37.9 kJ/mol and 0.191 kJ/mol K, respectively. In the same temperature interval the Langmuir constant for the first step of the adsorption process involving parallely adsorbed benzoic acid molecules is estimated to be fairly constant, and within a factor of 2 from the best fit value of 33 x 10(3) L/mol. Copyright 1998 Academic Press.
研究了296至346K温度范围内苯甲酸在分散于环己烷中的合成方解石上的吸附情况。研究结果可以通过一个两步模型成功解释，该模型包括首先是一层与表面平行排列的分子的朗缪尔吸附，接着，随着液相中吸附质浓度的增加，这一层逐渐被一层与表面垂直排列的分子单层所取代。已确定苯甲酸在垂直排列的单层中的最大吸附量为7.345µmol/m²，与温度无关，且接近7.4µmol/m²的理论值。第二步的朗缪尔常数，即平行吸附的分子被垂直吸附的分子所取代的过程，在296K时为2×10³L/mol，在346K时为16×10³L/mol，与该吸附过程这一部分相关的焓变和熵变分别为37.9kJ/mol和0.191kJ/mol·K。在相同温度区间内，涉及平行吸附苯甲酸分子的吸附过程第一步的朗缪尔常数估计相当恒定，且与最佳拟合值33×10³L/mol相差不超过2倍。版权所有1998年学术出版社。
