Flexible core-shell/bead-like alginate@PEI with exceptional adsorption capacity, recycling performance toward batch and column sorption of Cr(VI)

•Core-shell/bead-like alginate@PEI with abundant amino groups was firstly fabricated for Cr(VI) removal.•Easy-to-handle fabrication process with large-scale production character.•A much higher adsorption capacity than most of reported similar sorbents.•Excellent stability, reusability and convenient separation.

A chemically modified alginate beads for heavy metal removal was prepared using polyethylenimine (PEI) as a modification reagent, which high density active sites were introduced favorably onto the surface by cross-linking reaction, leading to the designing of flexible core-shell/bead-like alginate@PEI sorbent and employed for the adsorption of Cr(VI) from aqueous solutions. This new sorbent was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) etc. The results demonstrated that the optimized pH value was observed at 2.0. The adsorption processes fitted well with the pseudo-second-order kinetic model and the Freundlich isotherm in a batch system. The experimental maximum adsorption capacity for Cr(VI) was 431.6 mg/g under an optimal testing condition, which was much higher than that of sodium alginate (SA) (24.2 mg/g). Thomas and Bohart-Adams models were successfully fitted with breakthrough curves obtained under different experimental conditions in a continuous column process. More importantly, the adsorption capacity of the alginate@PEI only showed a slight loss after ten cycles of adsorption-desorption studies. Compared to other reported adsorptive materials, this core-shell/bead-like composite promises advantages of ultra-high adsorption capacity, low-cost, environmental friendliness and excellent recycling performance.

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