Ultrathin films of metal hexacyanometalates were prepared upon multiple sequential adsorption of metal cations M m + (Fe3+, Fe2+, Co2+, and Ni2+) and hexacyanometalate anions [M(CN)6] n - (Fe(CN)6 3-, Fe(CN)6 4-, and Co(CN)6 3-) on solid supports. The layer-by-layer deposition led to the formation of films of the metal complex salts with monolayer precision. The films were characterized using UV and IR spectroscopic methods and cyclic voltammetry. The alternating adsorption of Fe3+ and Fe(CN)6 4- ions led to dense and defect-free films of Prussian Blue, which were useful as membranes for ion separation. The porous, zeolitic structure of Prussian Blue was permeable for ions with a small Stokes radius such as Cs+, K+, and Cl-, whereas large hydrated ions such as Na+, Li+, Mg2+, or SO4 2- were blocked. The effect of ion sieving increased with the thickness of the membrane. After a hundred dipping cycles, high separation factors α(CsCl/NaCl) and α(KCl/NaCl) of 6.5 and 6.2, respectively, were found. Corresponding membranes of cobalt and nickel hexacyanoferrate were also useful for ion separation, but the α-values were lower. Possible reasons for the differences in selectivity are discussed.

Structure, morphology, and elemental composition as well as the size-selectivity of the ion transport behavior of ultrathin membranes of iron(III) hexacyanoferrate(II) (FeIIIHCFII), iron(II) hexacyanoferrate(III) (FeIIHCFIII), cobalt(II) hexacyanoferrate(III) (CoIIHCFIII), and nickel(II) hexacyanoferrate(III) (NiIIHCFIII) are described. The membranes were prepared upon multiple sequential adsorption of metal cations and hexacyanometalate anions on porous polymer supports. Scanning electron and scanning force microscopy indicate that the membranes of the complex salts consist of a multitude of small, densely packed particles with diameter in the 10−100 nm range. Energy-dispersive X-ray analysis indicates that the iron hexacyanoferrate (Prussian blue) membranes consist of the potassium-rich, so-called “soluble” modification, KFe[Fe(CN)6], while the membranes of the analogous complex salts consist of a mixture of the potassium-rich and potassium-free modification. The porous, zeolitic structure of the inorganic complex salts was permeable for ions with a small Stokes radius such as Cs+, K+, and Cl-, whereas large hydrated ions such as Na+, Li+, Mg2+, or SO4 2- were blocked. Ion separation became progressively more effective, if the number of complex layers increased. The highest separation factors α(CsCl/NaCl) and α(KCl/NaCl) of 7.7 and 5.9, respectively, were found for the FeIIIHCFII membrane subjected to a hundred dipping cycles. Membranes of iron(II), cobalt(II), and nickel(II) hexacyanoferrate(III) were also useful for ion separation, but the α values were lower. Effects on the ion flux rates caused by the feed concentration and the polyelectrolyte precoating of the support are also discussed.

The first study of ion transport across self‐assembled multilayered films of p‐sulfonato‐calix[n]arenes and poly(vinyl amine) (PVA) is presented. The films are prepared by the alternate electrostatic layer‐by‐layer assembly of the anionic calixarenes and cationic PVA on porous polyacrylonitrile (PAN) supports. We use tetra‐p‐sulfonato‐calix[4]arene (calix4), hexa‐p‐sulfonato‐calix[6]arene (calix6), and octa‐p‐sulfonato‐calix[8]arene (calix8) as the calixarenes. Ultraviolet (UV) studies indicate that dipping solutions of pH 6.8, without a supporting electrolyte, are most suited for film preparation. Calix8 is adsorbed in higher concentrations per layer than calix6 or calix4, probably because desorption is less pronounced. The permeation rates, PRs, of monovalent alkali‐metal chlorides (Li, Na, K, Cs), magnesium chloride, divalent transition‐metal chlorides (Ni, Cu, Zn), trivalent lanthanide chlorides (La, Ce, Pr, Sm), and sodium sulfate across the calix4/PVA, calix6/PVA, and calix8/PVA membranes are studied and compared with the corresponding PR values across a poly(styrene sulfonate) (PSS)/PVA multilayer membrane prepared under the same conditions. The PR values of the alkali‐metal salts are between 4 and 17 × 10–6 cm s–1, those of magnesium chloride and the transition‐metal salts are 0.2–1.3 × 10–6 cm s–1, and those of the lanthanide salts are about 0.1 × 10–6 cm s–1. Possible origins for the large differences are discussed. Ion transport is first of all controlled by electrostatic effects such as Donnan rejection of di‐ and trivalent ions in the membrane, but metal‐ion complexation with the calixarene derivatives also plays a role. Complexation occurs especially between Li+ or Na+ and calix4, Mg2+, or Cu2+ and calix6, Cu2+, Zn2+, or the lanthanide ions and calix8. Divalent sulfate ions are found to replace the calixarene polyanions in the membrane. UV studies of the permeate solutions indicate that calix4 especially is displaced during sulfate permeation.

No abstract

Membranes. -Ultrathin films of metal hexacyanometalates are prepared with monolayer precision by multiple sequential adsorption of metal cations (Fe 3+ , Fe 2+ , Co 2+ , and Ni 2+ ) and hexacyanometalate anions ([Fe(CN) 6 ] 3-, [Fe(CN) 6 ] 4-, and [Co(CN) 6 ] 3-) on solid supports. The films are characterized by UV and IR spectroscopy, and cyclic voltammetry. The self-assembled films are colored and electroactive and can be switched between different oxidation states of the metal ions. The films might be useful as electrochromic displays or catalytic surfaces. They are also useful as membranes for separation of alkali-metal ions. The separation factors α(CsCl/NaCl) and α(KCl/NaCl) are 6.5 and 6.2, respectively. -(PYRASCH, M.; TOUTIANOUSH, A.; JIN, W.; SCHNEPF, J.; TIEKE*, B.; Chem. Mater. 15 (2003) 1, 245-254; Inst. Phys.