Facilitated ion transport through polyelectrolyte multilayer films containing metal-binding ligands

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• 作者：Chunjuan Sheng ; Salinda Wijeratne ; Chao Cheng ; Gregory L. Baker¹ ; Merlin L. Bruening ; ^{bruening@chemistry.msu.edu" class="auth_mail}
• 关键词：Facilitated ion transport ; Polyelectrolytes ; Layer-by-layer adsorption ; Diffusion dialysis
• 刊名：Journal of Membrane Science
• 出版年：1 June, 2014
• 年：2014
• 卷：459
• 期：Complete
• 页码：169-176
• 全文大小：1093 K

文摘

Alternating layer-by-layer adsorption of poly[(N,N'-dicarboxymethyl) allylamine] (PDCMAA) and protonated poly(allylamine) (PAH) at low pH yields thin films with abundant Cu²⁺-binding sites. When deposited on porous alumina substrates, (PDCMAA/PAH)₃PDCMAA or (PDCMAA/PAH)₄ films show average Cu²⁺/Mg²⁺ diffusion dialysis selectivities around 50. PDCMAA/PAH membranes also exhibit Cu²⁺/Ni²⁺ and Cu²⁺/Ca²⁺ selectivities >10. The high Cu²⁺/Mg²⁺ selectivity despite similar aqueous diffusion coefficients and equal charges for the two ions suggests a facilitated transport mechanism. For comparison, poly(styrene sulfonate)/PAH films with 7 bilayers show Cu²⁺/Mg²⁺ selectivities around 10, perhaps also due to facilitated transport via PAH. With PDCMAA/PAH membranes, Cu²⁺ flux increases nonlinearly with increasing CuCl₂ concentrations in the feed. Sorption isotherms show that PDCMAA/PAH films contain both strong and weak binding sites, and the nonlinear increase in flux with increasing CuCl₂ feed concentration likely represents hopping between weak binding sites, probably the amine groups of PAH. Strong binding of Cu²⁺ to PDCMAA may displace ionic cross-links in the film and create free amine groups for facilitated transport. Additionally, Cu²⁺ binding to the film suppresses Mg²⁺ transport, either through electrostatic exclusion or occupation of hopping sites.