la402633x_si_001.pdf (1.36 MB)
Download fileLayer-by-Layer Assembly of Thick, Cu2+-Chelating Films
journal contribution
posted on 2013-10-15, 00:00 authored by Salinda Wijeratne, Merlin L. Bruening, Gregory L. BakerLayer-by-layer adsorption of protonated
poly(allylamine) (PAH)
and deprotonated poly(N,N-dicarboxymethylallylamine)
(PDCMAA) yields thick films with a high density of iminodiacetic acid
(IDA) ligands that bind metal ions. When film deposition occurs at
pH 3.0, PAH/PDCMAA bilayer thicknesses reach 200 nm, and Cu2+ binding capacities are ∼2.5 mmol per cm3 of film.
(PAH/PDCMAA)10 films deposited at pH 3.0 are 4–8-fold
thicker than films formed at pH 5.0, 7.0, or 9.0, presumably because
of the low charge density on PDCMAA chains at pH 3.0. However, with
normalization to film thickness, all films bind similar amounts of
Cu2+ from pH 4.1 solutions of CuSO4. In micrometer-thick
films, equilibration of binding sites with Cu2+ requires
∼4 h due to a low Cu2+ diffusion coefficient (∼2.6
× 10–12 cm2/s). Sorption isotherms
determined at several temperatures show that Cu2+ binding
is endothermic with a positive entropy (binding constants increase
with increasing temperature), presumably because metal-ion complexation
involves displacement of both a proton from IDA and water molecules
from Cu2+. (PAH/PDCMAA)10 films retain their
binding capacity over four absorption/elution cycles and may prove
useful in metal-ion scavenging, catalysis, and protein binding.