Ion separation of binary metallic aqueous solutions at acidic Langmuir monolayer surfaces
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Ion Separation of Binary Metallic Aqueous Solutions at Acidic Langmuir Monolayer Surfaces Tai Young Kim, Gil Sun Lee and Dong June Ahn +
Nano & lnterfacial Engineering Laboratory, Department of Chemical Engineering, Korea University, Seoul 136-701, Korea (Received 5 March 200l . accepled 16 ,hdy 2001)
Abstract-We fi~cused on analyzing the capabili~, of the acidic monolayer surfaces tbr separation of toxic metal ions out of house-prepared binary inorganic ionic ~lutions such as calcium-lead, calcium-chromium, calcium-copper, and calcium-zinc aqueous sy~ems. The alfinities of the fihns to toxic metal kms were analyzed b? using Fourier translbrm infrared spectroscopy. A model considering both the electrochemical and thermodynamic aspects was also applied m quantit} the surface ion affinities. It is noted that surface ion binding capability tbr bina~, ionic solutions can be much diflLvent li'om that lbr pure ionic solutions. As a result. SUl-thcebinding constants were lbund to be 4.5," 10", -" lbr lead ions, 1,5", 10" ~br chromium ions. 5.5 o~10~ lbr copper ions, and 6~ i0 ~lbr zinc ions, respectively, at pH=5,5, For the separation experiments done at pl t=5.5, lead, copper: zinc ions were separated more efficiently from the mixed ionic solutions by the ]5~to~ of ca. 30,000, I0X)00, 3,700, and 400, respectively, compared to calcium ions of which binding constant is 1.5"- 102. Interestingly. when compared to con'esponding pure ionic systems, copper and lead ions were separated as much, while chromium and zinc ions were less by the thctor of 500 and 50, respectively.
Key words: Langmuir Monolayer. B]naly. I(m Adsorption. Surface, FHR, Modelling
troy et al,, 1982; Alto et aL, 1991, 1994: tlyun et al., f997], Surface adsorpfivity of many metallic ions was found to deviate much from bulk adsorptivity [Kim, 2000.[. In this study, we present new results on ion separation out of aqueous solutions containing binary metallic ion species, which is more meanhgful for real processes involving multieomponents. Results show that ion adsorption in binary systems can be much different from that in pure systems previously studied, depending on the nature of metallic species,
INTRODUCTION
A Langmuir monolayer on an air/water interface is an interesting system out of many supramolecular assemblies in the sense that it enables one to conveniently investigate surface reactivity and molecular structure by varying packing density of constituent amphiphilic molecules [Kim et al., 1996]. Such properties are essential information in order to harvest useful functions from more complex suprarnolecular systems having molecular arrays in 3-dimensions. Functional and stable Langmuir monolayers can be directly deposited into mulfilayered Langmuir-Blodgclt (LB) films, which have been investigated extensively for potential applications to chemical and biological sensors, photon or electron devices, selective membranes, and reaction or immobilization substrates [Swalen, 1986; Vijendra, 1988]. Properties of Lanm~nuir monolayers are in general depend
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