Transport of Iron-Based Nanoparticles: Role of Magnetic Properties

The transport of magnetic nanoparticles in aquatic environments was studied using maghemite (gamma-Fe2O3) and gamma-Fe2O3 based (FexNi1-x)(y)O-z nanoparticles as a function of pH and particle iron content that induced a different magnetic property. Transport studies were conducted in packed bed columns (1 mM KCl, pH 6 and 9) and stability studies were done by dynamic light scattering and sedimentation measurements. Results showed that the stability and transport of these magnetic nanoparticles were influenced by a combination of electrostatic and magnetic interactions. Transport results showed that the less magnetic nanoparticles (possessing higher nickel content) eluted to a greater extent than the more magnetic particles at both pH 6 and 9. The stability in water at both pH 6 and 9 also increased, as nickel content in particles increased suggesting that magnetic interactions enhance aggregation. The nanoparticles eluted to a greater extent at pH 9, at which they were more negatively charged, than at pH 6. Complementary experiments were conducted with alpha-Fe2O3, a nonmagnetic, highly negatively charged nanoparticle which was transported more than the other magnetic particles. The majority of particles were retained at the column inlet (1-2 cm) for all transport experiments, with the greatest amount of retention being that of the magnetic nanoparticles (gamma-Fe2O3), indicating that magnetically induced aggregation and subsequent straining resulted in greater retention.