Polyamine-modified magnetic graphene oxide nanocomposite for enhanced selenium removal.

A poly (allylamine)-modified magnetic graphene oxide (PAA-MGO) with a high adsorption capacity for selenium oxyanions was prepared by a simple and facile method at room temperature. Poly (allylamine) (PAA) and magnetic iron oxide particles were synthesized on graphene oxide (GO) by an EDC (N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide)/NHS (N-hydroxysuccinimde) reaction and co-precipitation, respectively. The chemical structure and physical properties of PAA-MGO were characterized by Fourier transform infrared spectroscopy, thermo gravimetric analysis, zeta potential measurement, X-ray photoelectron spectroscopy, transmission electron microscopy, and magnetic hysteresis tests. Under external magnetic field, PAA-MGO was separated from solution within 5 min. The adsorption capacity of PAA-MGO nanocomposite at pH 5.8 is 120.1 mg/g for Se (IV) and 83.7 mg/g for Se (VI), respectively, which is not only much higher than GO and MGO, but also higher than most adsorbents reported in literature. The adsorption isotherms fit well with Freundlich model for Se (IV) and Se (VI) indicating multilayer adsorption on the rough surface of PAA-MGO. The high adsorption efficiency of PAA-MGO could be attributed to high surface area of GO matrix, active sites of iron oxide and positively charged amine groups. At 30 min, the selenium adsorption on PAA-MGO reaches 90% of the equilibrium for Se (IV) and 93% of the equilibrium for Se (VI). The pH effect on Se adsorption indicates that acidic pH benefits selenium adsorption on PAA-MGO, and the maximum adsorption capacities of PAA-MGO nanocomposite for Se (IV) and Se (VI) were both achieved at pH 3.1. The adsorbed selenium was stripped off at alkaline pH. The mechanism study illustrates that the enhanced selenium removal by PAA-MGO is attributed to dual interactions including ligand exchange between surface hydroxyl group of iron oxide and Se oxyanions, and electrostatic interaction between amine and Se oxyanions. Since PAA-MGO composite show near complete (over 99.3% for Se (IV) and 99.7% for Se (VI)) removal within 2 ppb for both Se oxyanions, it is practically usable for Se separation from wastewater. [ABSTRACT FROM AUTHOR]