Hydrothermal assisted magnetic nano-hydroxyapatite encapsulated alginate beads for efficient Cr(VI) uptake from water

Abstract

The biopolymer, alginate can be made into various usable forms like beads, membrane and candle for the development of water technology. In the present study, an attempt has been made to prepare the alginate in an usable bead form. Here, magnetic nano-hydroxyapatite encapsulated alginate beads (Fe3O4@n-HApAlg) were synthesized by hydrothermal method for selective chromium removal. The synthesized Fe3O4@n-HApAlg beads have enhanced chromium sorptive capacity (SC) of 29.14 mg/g than the individual components. The synthesized materials were characterized by various instrumental techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) isotherm studies. The Cr(VI) sorptive mechanism of Fe3O4@n-HApAlg beads were interpreted by electrostatic attraction. Sorption behavior of the magnetic beads was explained using Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. The thermodynamic studies indicate the spontaneous and endothermic nature of Cr(VI) sorption. In the kinetic data demonstration, pseudo-first-order, pseudo-second-order, intra particle diffusion and particle diffusion models were employed. The reusability of Fe3O4@n-HApAlg beads was carried out using NaOH eluent and they can be used upto five cycles. The magnetic alginate hybrid beads showed the promising results against the chromium contaminated groundwater by removing Cr(VI) ions below the tolerance limit.