Cross-linked sodium alginate-carboxymethyl chitosan hydrogel beads for adsorption of Ni(II) ions

A cross-linked sodium alginate-carboxymethyl chitosan hydrogel beads (CHB) was synthesized using calcium chloride and epichlorohydrin as cross-linkers. The synthesized CHB adsorbent was characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Ni(II) removal by the CHB was investigated, several parameters influencing the adsorption of Ni(II) ions such as contact time, pH, initial Ni(II) concen-tration and regeneration performance were investigated. Results revealed that the adsorption equi-librium was reached within 6 h and the maximum capacity of CHB for Ni(II) was obtained to be 128.4 mg/g. The equilibrium adsorption data fitted well to the Freundlich model and the adsorp-tion kinetic data followed the pseudo-second-order model. Furthermore, the prepared CHB showed good adsorption performance after five cycles of regeneration. Finally, FTIR and X-ray photoelec-tron spectroscopy analysis showed that the hydroxyl, amino and carboxyl groups were involved in the adsorption of Ni(II).