Rapid and selective magnetic separation of uranium in seawater and groundwater using novel phosphoramidate functionalized citrate-Fe3O4@Ag nanoparticles.

One-pot magnetic separation of uranium (U) in seawater and groundwater samples has been made possible by synthesizing phosphoramidate functionalized Ag coated citrate-Fe3O4 nanoparticles (NPs). The magnetic saturation value of these functionalized NPs is 27.1 emu g-1. The synergistic extraction mechanism of U(VI) ion by the surface-modified phosphoramidate and citrate molecules make these NPs highly selective towards U(VI). The adsorption kinetics follows a pseudo-second-order model and the adsorption isotherm fits successfully to the Langmuir adsorption model. The functionalized NPs show quantitative extraction efficiency in the pH range of 6.5-8 with a maximum loading capacity (Qm) of 108.7 mg g-1. The equilibration time required by these functionalized NPs to attain the Qm value is 120 s. The recycling of these NPs can be done up to 5-6 times with 1.0 mol L-1 of Na2CO3 or NH4OH for quantitative extraction of U(VI). These functionalized NPs show high resilience towards large number of naturally abundant metal ions.