Nowack B, Stone AT
Department of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, Maryland, 21218
J Colloid Interface Sci. 1999 Jun 1;214(1):20-30. doi: 10.1006/jcis.1999.6111.
The adsorption of one phosphonate, two hydroxyphosphonates, and five aminophosphonates onto the iron (hydr)oxide goethite (alpha-FeOOH) has been studied as a function of pH. At phosphonate concentrations significantly lower than the total number of available surface sites, nearly 100% adsorption is observed below pH 8.0. Adsorption decreases to negligible levels as the pH is increased to 12.0. Under the conditions just described, adsorption of nitrilotris(methylenephosphonic acid) as a function of pH is nearly independent of the ionic strength (from 1 mM to 1 M). At phosphonate concentrations close to the total number of available surface sites, adsorption decreases over a broader range in pH and reflects the number of phosphonate groups. At pH 7.2, the maximum extent of adsorption decreases as the number of phosphonate groups increases from one to five. Adsorption is modeled using a 2-pK constant capacitance model that postulates formation of a 1:1 surface complex involving one surface site and one phosphonate functional group. Denoting the fully deprotonated phosphonate ligand as La-, different protonation levels for adsorbed phosphonate species are represented by a series of equilibrium constants of the form For a phosphonate of charge a-, there are (a - 1) possible surface protonation levels. For a surface protonation level n, log betan,surf values derived from this modeling approach are related to the surface complex charge Z through the following linear relationship: Using this approach, adsorption as a function of phosphonate concentration and pH can be fully accounted for. Copyright 1999 Academic Press.
研究了一种膦酸酯、两种羟基膦酸酯和五种氨基膦酸酯在铁（氢）氧化物针铁矿（α-FeOOH）上的吸附情况与pH值的关系。在膦酸酯浓度显著低于可用表面位点总数时，在pH值低于8.0时观察到近乎100%的吸附。随着pH值升高至12.0，吸附量降至可忽略不计的水平。在上述条件下，次氮基三（亚甲基膦酸）的吸附量与pH值的关系几乎与离子强度（从1 mM至1 M）无关。在膦酸酯浓度接近可用表面位点总数时，吸附在更宽的pH范围内降低，并反映了膦酸酯基团的数量。在pH 7.2时，随着膦酸酯基团数量从一个增加到五个，最大吸附程度降低。吸附作用采用双pK恒电容模型进行模拟，该模型假定形成涉及一个表面位点和一个膦酸酯官能团的1:1表面络合物。将完全去质子化的膦酸酯配体表示为La-，吸附的膦酸酯物种的不同质子化水平由一系列形式的平衡常数表示。对于电荷为a-的膦酸酯，存在（a - 1）种可能的表面质子化水平。对于表面质子化水平n，通过这种建模方法得出的log betan,surf值与表面络合物电荷Z通过以下线性关系相关：使用这种方法，可以完全解释吸附量与膦酸酯浓度和pH值的关系。版权所有1999年，学术出版社。
