Highly-Controllable Molecular Imprinting at Superparamagnetic Iron Oxide Nanoparticles for Ultrafast Enrichment and Separation

Here, we report a general protocol for coating molecularly imprinted polymers (MIPs) at the superparamagnetic iron oxide nanoparticles (Fe3O4 NPs) to make highly controllable core-shell Fe3O4@MIP NPs for rapid enrichment and separation of herbicides in water. Acrylic acid monomers were first anchored at the surface of Fe3O4 by the simple complexing reaction with unsaturated iron ions at the nanoparticle surface, which forms a polymerizable molecule monolayer. It was found that the monolayer highly directed the selective occurrence of molecular imprinting polymerization at the surface of Fe3O4 NPs, and the homogeneous copolymerization in solution phase was completely prohibited by the optimized reaction conditions. As a result, one can easily produce the uniformly spherical Fe3O4@MIP NPs with tunable MIP shell thickness from several to tens of nanometers that can simply be achieved by changing the amounts of precursors. The Fe3O4@MIP NPs with saturation magnetization of 38 emu/g exhibit the capability of ultrafast enriching and separating herbicide 2,4-dichlorophenoxyacetic acid (similar to 2% in weight) and are renewable and cyclically exploited due to their monodispersive and superparamagnetic features. The method of molecular imprinting at superparamagnetic particles can be extended to a wide range of applications for pollutant water treatment, biological molecule purification, and drug separation.