Polyethylenimine functionalized halloysite nanotubes for efficient removal and fixation of Cr (VI)

Abstract

A typical nanoporous-geomaterial (halloysite nanotubes, HNTs) was functionalized by polyethyleneimine (PEI) grafting and the functionalized halloysite (PEI-HNTs) exhibited excellent performance for Cr (VI) removal from aqueous solution and immobilization by reduction. After PEI modification, the Cr (VI) uptake capacity of PEI-HNTs was about 64 times higher than that of the original HNTs and the maximum equilibrium removal capacity was found to be 102.5 mg g−1 at 328 K. Part of Cr (VI) was reduced to Cr (III) and then precipitated on the surface of adsorbent during the sorption process as determined by X-ray photoelectron spectroscopic analysis, suggesting that the PEI-HNTs are not only useful for Cr (VI) immobilization but also good for its reduction. The adsorption of Cr (VI) by the PEI-HNTs was fitted to Langmuir model and the kinetics of uptake could be described by a pseudo-second-order rate model very well. The results also demonstrated that PEI-HNTs could detoxify Cr (VI) at low pH value. The mechanism of uptake of Cr (VI) was postulated to be electrostatic interaction followed by its immobilization through reduction. The functionalized nano-geomaterial synthesized here could be a promising candidate of low cost for highly efficient Cr (VI) removal followed by its immobilization.