The effectiveness of the protected amino group on crosslinked chitosans for copper removal and the thermodynamics of interaction at the solid/liquid interface

Acidic glutaraldehyde (Gh) crosslinked chitosan (ChGhH) when deprotonated the biopolymer (ChGh) presents high content of free amino groups. These modified biopolymers are comparable to epichlorohydrin (Ep) crosslinked (ChEp). CIN molar ratio of 6.1 for chitosan increases to 7.3, 7.5 and 7.1 for ChGhH, ChGh and ChEp. The effectiveness of the carbon-6 hydroxyl group in interconnecting chitosan units was supported by IR and (CNMR)-C-13, where Ep promotes increase in crystallinity. Copper uptake gave the order Ch > ChGh > ChGhH > ChEp, as: 1.35 +/- 0.06, 1.30 +/- 0.05, 1.05 +/- 0.07 and 0.96 +/- 0.22 mmol g(-1), reflecting the availability of nitrogen basic centers in adsorbing. The favorable thermodynamic data of adsorption through calorimetric titration gave exothermic enthalpic values: -28.98 +/- 0.05, -6.68 +/- 0.04, -6.13 +/- 0.07 and -0.65 +/- 0.23 kJ mol(-1) for Ch, ChGh, ChGhH and ChEp. Free Gibbs energy reflected spontaneity of interactions and, with the exception of chitosan, the entropic values are positive. (C) 2009 Elsevier Ltd. All rights reserved.