5 years ago

Absorption of Cu(II) in layered diaminoalkyl- and monoaminoalkyl-polysilsesquioxane

Absorption of Cu(II) in layered diaminoalkyl- and monoaminoalkyl-polysilsesquioxane
Lamellar polysilsesquioxane containing two kinds of aminoalkyl groups were synthesized using alkanoic acids. Our intension with this synthesis was to increase the exposure to the absorbate of the absorption sites in the polymer solid without sacrificing its high density of sites. That is, this method is designed to weaken the interactions around the amine sites that inhibit diffusion of the aqueous cation pollutants. The mixing ratio, x: y, of 3-aminopropyltrimethoxysilane (AP silane) and N-(aminoethyl)-3-aminopropyltrimethoxysilane (AeAP silane) in the liquid precursor agrees well with that of the AP and AeAP groups in the solid, [(C13H27COOH) x (C12H23CH(COOH)CH2COOH) y (NH2C3H6) x (NH2C2H4NHC3H6) y Si10O15]n or [(MAS) x (C12SA) y (AP) x (AeAP) y Si10O1.5]n (x + y = 10). A good lamellar structure was obtained with x: y ratio higher than 2: 8. FT-IR spectroscopy reveals that increasing the x: y ratio enhances the bands due to hydrogen-bonded –COOH and dissociated –COO-, suggesting an increase in water molecule insertion around the carboxyl and amine groups with x: y. In 13C CP-MAS NMR, unresolved peaks due to carboxylate carbons disappear at x: y = 4: 6 and 2: 8, suggesting that carboxylate is isolated at these mixing ratios probably due to hydration. In addition, continuous growth of the peak due to ionized carboxylate is observed. The amount of absorbed aqueous Cu(II) is particularly large when x: y = 4: 6, which is revealed by analysis with the Langmuir equation. In contrast, the ESR spectrum of Cu(II) is independent on the x: y ratio, suggesting the accessibility of the absorption sites is simply improved when x: y = 4: 6. It is likely that this mixing ratio provides a particularly effective structure for exposing the absorption sites of aqueous Cu(II).

Publisher URL: www.sciencedirect.com/science

DOI: S0032386117310686

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