Sullivan EJ, Carey JW, Bowman RS
Department of Earth and Environmental Science and Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, New Mexico, 87801
J Colloid Interface Sci. 1998 Oct 15;206(2):369-380. doi: 10.1006/jcis.1998.5764.
Sorption enthalpies of hexadecyltrimethylammonium bromide (HDTMA) as monomers and micelles and tetraethylammonium bromide (TEA) were used with surfactant, counterion, and co-ion sorption isotherms to infer the conformation, sorption mechanism, and relative stability of the sorbed surfactants on natural clinoptilolite. The average value of the sorption enthalpy was -10.38 kJ/mol for monomers, -11.98 kJ/mol for micelles, and +3.03 kJ/mol for TEA. Sorption of monomers produced a lower sorption plateau than equivalent micelle sorption (maxima 145 mmol/kg, 225 mmol/kg). Analysis of the sorption data demonstrated a change in the sorption mechanism at the external cation exchange capacity (ECEC) of clinoptilolite. Sorption data from below and above the ECEC were fit to a simple polynomial model and the Gibbs free energy of sorption (DeltaG0m) and sorption entropies were calculated. Resultant values of DeltaG0m were -9.27 and -14.38 kJ/mol for HDTMA monomers and micelles, respectively, for sorption below the ECEC, and -16.11 and -23.10 kJ/mol, respectively, for sorption above the ECEC. The value for TEA was -1.04 kJ/mol, indicating weaker sorption than for HDTMA. Monomer sorption to clinoptilolite exceeded the ECEC, even when the solution concentration was below the critical micelle concentration. Hydrophobic (tail-tail) components of DeltaG0m were the driving force for sorption of HDTMA, both below and above the ECEC. A significant kinetic effect was observed in the sorption isotherms with a period of rapid sorption followed by slow equilibration requiring 7 days to achieve steady state for HDTMA; TEA equilibration occurred within 24 h. Copyright 1998 Academic Press.
十六烷基三甲基溴化铵（HDTMA）作为单体和胶束以及四乙基溴化铵（TEA）的吸附焓，与表面活性剂、抗衡离子和共离子吸附等温线一起用于推断天然斜发沸石上吸附的表面活性剂的构象、吸附机制和相对稳定性。单体的吸附焓平均值为-10.38 kJ/mol，胶束为-11.98 kJ/mol，TEA为+3.03 kJ/mol。单体的吸附产生的吸附平台低于等效胶束吸附（最大值分别为145 mmol/kg、225 mmol/kg）。吸附数据分析表明，在斜发沸石的外部阳离子交换容量（ECEC）处吸附机制发生了变化。ECEC以下和以上的吸附数据拟合到一个简单的多项式模型，并计算了吸附的吉布斯自由能（ΔG0m）和吸附熵。对于HDTMA单体和胶束，在ECEC以下吸附时，ΔG0m的结果值分别为-9.27和-14.38 kJ/mol，在ECEC以上吸附时分别为-16.11和-23.10 kJ/mol。TEA的值为-1.04 kJ/mol，表明其吸附比HDTMA弱。即使溶液浓度低于临界胶束浓度，单体对斜发沸石的吸附也超过了ECEC。在ECEC以下和以上，ΔG0m的疏水（尾-尾）成分都是HDTMA吸附的驱动力。在吸附等温线中观察到显著的动力学效应，HDTMA在快速吸附一段时间后接着是缓慢平衡，需要7天才能达到稳态；TEA在24小时内达到平衡。版权所有1998年学术出版社。
