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Reduction of hexavalent chromium by Pannonibacter phragmitetus LSSE-09 coated with polyethylenimine-functionalized magnetic nanoparticles under alkaline conditions

Xu, Lin, Yang, Liangrong, Luo, Mingfang, Liang, Xiangfeng, Wei, Xuetuan, Zhao, Junmei, Liu, Huizhou
Journal of hazardous materials 2011 v.189 no.3 pp. 787-793
chromium, coprecipitation, electrostatic interactions, immobilized cells, iron oxides, isoelectric point, magnetic fields, nanoparticles, pH, particle size, sodium citrate, temperature, wastewater, zeta potential
A novel cell separation and immobilization method for Cr (VI)-reduction under alkaline conditions was developed by using superparamagnetic Fe₃O₄ nanoparticles (NPs). The Fe₃O₄ NPs were synthesized by coprecipitation followed by modification with sodium citrate and polyethyleneimine (PEI). The surface-modified NPs were monodispersed and the particle size was about 15nm with a saturation magnetization of 62.3emu/g and an isoelectric point (pI) of 11.5 at room temperature. PEI-modified Fe₃O₄ NPs possess positive zeta potential at pH below 11.5, presumable because of the high density of amine groups in the long chains of PEI molecules on the surface. At initial pH 9.0, Pannonibacter phragmitetus LSSE-09 cells were immobilized by PEI-modified NPs via electrostatic attraction and then separated with an external magnetic field. Compared to free cells, the coated cells not only had the same Cr (VI)-reduction activity but could also be easily separated from reaction mixtures by magnetic force. In addition, the magnetically immobilized cells retained high specific Cr (VI)-reduction activity over six batch cycles. The results suggest that the magnetic cell separation technology has potential application for Cr (VI) detoxification in alkaline wastewater.