Surfactant bilayer on chitosan bead surface for enhanced Ni(II) adsorption

Abstract

Surfactant bilayer formation on charged solid surfaces under suitably chosen conditions and their utilization for adsolubilizing the inorganic ions with improved efficiency is an established phenomenon. Such bilayer formation on solid substrates such as alumina, silica, carbon etc., although is more common, however, organic biomaterials for such purpose is not explored. Chitosan modifications through derivatization or composite formation (with bentonite, alumina, silica, and even with surfactant) are known already for pollutant removal with higher efficiency. This is the first time we explore here the formed bilayer on chitosan bead for the removal of Ni(II) from water. Chitosan bead surface was modified with sodium dodecyl sulfate (SDS) at different concentrations (1500 and 6000 mg L−1) to prepare different kinds of adsorbents, which were used to remove Ni(II) from the water environment. This is a new kind of approach which involves the ‘adsolubilization’ phenomenon. Detailed studies on adsorption kinetics, effect of pH, variation of adsorbent dose, evaluation of thermodynamic parameters, interference of common ions and desorption phenomenon were performed on the removal of Ni(II) from aqueous media. The adsorption followed pseudo-second order kinetics and Langmuir isotherm model. It was also found that intra-particle diffusion subsisted in the Ni(II) adsorption process, but that it was not the only rate-limiting step. Thermodynamic studies indicated that the adsorption was endothermic and spontaneous in nature. Based on the kinetic and thermodynamic studies, it could be concluded that, the adsorption is governed by both physisorption and chemisorption mechanisms. On treatment with dilute HNO3 or H2SO4, 100% desorption of Ni(II) was accomplished. The recovered Ni(II) either can be reused, or after the Ni(II) adsorption onto the surfactant-modified chitosan beads the material can be converted to a suitable catalyst. This leads to a sustainable sludge management procedure.