Fundamentals of selective ion transport through multilayer polyelectrolyte membranes
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Tipus de documentArticle
Data publicació2013-01-14
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Abstract
Membranes composed of multilayer poly(4-styrenesul-
fonate) (PSS)/protonated poly(allylamine) (PAH)
fi
lms on porous
alumina supports exhibit high monovalent/divalent cation selectivities.
Remarkably, the di
ff
usion dialysis K
+
/Mg
2+
selectivity is >350.
However, in nano
fi
ltration this selectivity is only 16, suggesting
some convective ion transport through
fi
lm imperfections. Under
MgCl
2
concentration gradients across either (PSS/PAH)
4
- or (PSS/
PAH)
4
PSS-coated alumina, transmembrane potentials indicate Mg
2+
transference numbers approaching 0. The low Mg
2+
transference
numbers with both polycation- and polyanion-terminated
fi
lms likely
stem from exclusion of Mg
2+
due to its large size or hydration energy.
However, these high anion/cation selectivities decrease as the solution
ionic strength increases. In nano
fi
ltration, the high asymmetry of
membrane permeabilities to Mg
2+
and Cl
−
creates transmembrane di
ff
usion potentials that lead to negative rejections (the ion
concentration in the permeate is larger than in the feed) as low as
−
200% for trace monovalent cations such as K
+
and Cs
+
.
Moreover, rejection becomes more negative as the mobility of the trace cation increases. Knowledge of single-ion permeabilities
is vital for predicting the performance of polyelectrolyte
fi
lms in the separation and puri
fi
cation of mixed salts.
CitacióCheng, C.; Yaroshchuk, A.; Bruening, M. Fundamentals of selective ion transport through multilayer polyelectrolyte membranes. "Langmuir", 14 Gener 2013, vol. 29, núm. 6, p. 1885-1892.
ISSN0743-7463
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