Calorimetry studies for interaction in solid/liquid interface between the modified cellulose and divalent cation

Abstract

Cellulose (Cel) was initially modified with thionyl chloride in order to increase its reactivity. In another step, chlorinated cellulose (CelCl) was reacted with ethylenediamine (CelEn) molecule. The last reaction step was reacting CelEn with ethylene sulfide molecule, yielding the solid named CelEnEs. The two last steps occur in free solvent conditions. Elemental analysis showed the incorporation of an enormous amount of chlorine in the CelCl structure, the nitrogen entrance from the ethylenediamine molecule, as well as the huge amount of sulfur that was added due to entry of the ethylene sulfide molecule. Infrared spectroscopy, thermogravimetry, and 13C NMR in the solid state demonstrated the effectiveness of the reaction, in which the last one has shown signals at 30 and 32 ppm for CelEnEs due to the change in the methylene group environment. Divalent metal uptake by chemically modified biopolymer gave the order Ni2+ > Co2+ > Cu2+ > Zn2+, reflecting the corresponding acidity of these cations in bonding to the sulfur and the basic nitrogen atoms available on the pendant chains. The equilibrium data were fitted to Langmuir model. The maximum monolayer adsorption capacity for the cations was found to be 5.561 ± 0.017, 4.694 ± 0.013, 1.944 ± 0.062, and 1.733 ± 0.020 mmol g−1 for Ni2+, Co2+, Cu2+, and Zn2+, respectively. Through calorimetric titrations thermodynamic parameters could be obtained, and the results proved the favor of the interactions between cations and basic centers of modified cellulose. This new synthesized biopolymer can be used as a material for cation removal from aqueous solution.