Thermodynamic studies of the interaction at the solid/liquid interface between metal ions and cellulose modified with ethylenediamine

The chelate molecule, ethylenediamine, has been incorporated onto the surface of cellulose by sequential reaction of cellulose fibres with phosphorous oxychloride followed by the chelating agent. The modified material (CelNN) retained its fibrous nature and was shown to be efficient at adsorbing divalent metal cations from water by complexation. Adsorption isotherms were determined for suspensions of CelNN in metal ion solutions of different concentrations, and the data were adjusted to fit the modified Langmuir equation. The maximum numbers of moles of Cu2+, Ni2+ and Zn2+ adsorbed per gram of modified cellulose were 1.64 × 10−3, 5.25 × 10−4 and 1.06 × 10−3, respectively. The thermodynamic effects related to the adsorption of metal ion onto the cellulose surface were determined by calorimetric titration. Gibbs free energy was spontaneous for all interactions. The adsorption processes all exhibited endothermic enthalpy values and were accompanied by increases in entropy.