Polyethyleneimine stabilized nanoscale zero-valent iron-magnetite (Fe3O4@nZVI-PEI) for the enhanced removal of arsenic from acidic aqueous solution: Performance and mechanisms

Nanoscale zero-valent iron (nZVI) particles have a high removal affinity toward arsenic. However, particle agglomeration and surface passivation hinder their practical application in wastewater treatment. Herein, we report the design and synthesis of an economically viable polyethyleneimine stabilized nZVI-magnetite (Fe3O4@nZVI-PEI) that exhibits a fast and efficient removal of arsenic (As(III/V)) from wastewater. Microstructure analyses by SEM and TEM indicated that PEI efficiently minimized particle agglomeration. The higher the point of zero charge (pHpzc) value of Fe3O4@nZVI-PEI (-9.4) over bare Fe3O4@nZVI (-8.2) is indicative of the role of PEI in the sorption of the arsenic species. The experimental results showed a removal efficiency of 95.8% for As(III) and 90.5% for As(V) at an optimum pH of 3.0. The adsorption kinetics followed the pseudosecond-order and the equilibrium isotherm data fitted to the Sips model with the superior maximum adsorption capacities of 572.40 mg/g for As(III) and 548.80 mg/g for As(V). FTIR, XRD, and XPS analyses provided insight into the possible adsorption mechanism that arsenic is taken up by generating monodentate and bidentate inner-sphere complexes with -OH, electrostatic interactions with primary amines, and partial oxidation of As(III) to As(V). In contrast to Cl-, NO3- , and SO42-, PO4 3- showed a significant competitive effect on the sorption of both As (III/V) species. Overall, this work provides a practical and highly efficient approach for arsenic remediation in wastewater and contaminated soils, and simultaneously resolves the stabilization problems of nZVI nanoparticles.