Grafting polymerization of acrylic acid onto chitosan-cellulose hybrid and application of the graft as highly efficient ligand for elimination of water hardness: Adsorption isotherms, kinetic modeling and regeneration

Abstract

Grafting copolymerization of acrylic acid from chitosan-cellulose hybrid ((CTS/Cell)-g-PAA) was conducted and the grafting efficiency and crosslinking level were optimized at 86.5% and 2.5%, respectively. Investigation using scanning electron microscopy (SEM) indicated a mechanically robust material with a porous surface which allows diffusion. This property along with the high water absorption under wide range of pH values qualified the material for application as adsorbent/ligand to metal ions from aqueous solutions. This was additionally signified using fourier transform infrared (FTIR) spectra collected for the graft before and after chelation to metal ions that cause water hardness, which confirmed that the oxygenated and nitrogenated groups are the main sites for binding metal ions in high capacity with removal efficiency above 90% in most cases. Application of Langmuir and Freundlich adsorption isotherm models for the metal ions on the graft copolymer indicated that the adsorption data are better fitted by Freundlich model for all metal ions while a chemisorption nature of adsorption was deduced by a kinetic modeling study. Further, the adsorption was highly favoured in case of Ca(II) and Mg(II) while to a much lesser extent in case of Na(I). The polymeric ligand showed also outstanding performance during competitive removal of a mixture of metal ions from aqueous solution with a selectivity order Ca(II) > Mg(II) >> Na(I), such selective removal activity of the ligand was almost not influenced after induced desorption and reuse for additional four succeeding cycles.