Preparation of ethylenediamine-anchored cellulose and determination of thermochemical data for the interaction between cations and basic centers at the solid/liquid interface

Cellulose was first modified with thionyl chloride, giving 99% substitution at C6, and then reacted with ethylene-1,2-diamine to produce 6-(2′-aminoethylamino)-6-deoxy-cellulose. From the 8.5% of nitrogen incorporated in the polysaccharide backbone, the amount of ethylene-1,2-diamine anchored per gram of modified cellulose was determined to be 3.03 ± 0.01 mmol. This chemically immobilized surface was characterized by FTIR, TG, 13C NMR, and SEM techniques. The available basic nitrogen centers covalently bonded to the biopolymer skeleton were studied for copper, cobalt, nickel, and zinc adsorption from aqueous solutions and the respective thermal adsorption effects were determined by calorimetric titration. The ability to adsorb cations gave a capacity order of Co2+ > Cu2+ > Zn2+ > Ni2+ with affinities of 1.91 ± 0.07, 1.32 ± 0.07, 1.31 ± 0.02, and 1.08 ± 0.04 mmol/g, respectively. The net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation and the enthalpy of the interaction was calculated to give the following exothermic values: −20.8 ± 0.05, −11.72 ± 0.03, −7.32 ± 0.01, and −6.27 ± 0.02 kJ/mol for Co2+, Cu2+, Zn2+, and Ni2+, respectively. With the exception of the entropic value for copper, the other thermodynamic data for these systems are favorable for cation adsorption from aqueous solutions at the solid/liquid interface, suggesting the use of this anchored biopolymer for cation removal from the environment.