(285d) Self-Assembly and Sedimentation of Superparamagnetic Iron Oxide Nanoparticles Using Enhanced Quadrupole Magnetic Sorters

Superparamagnetic iron oxide nanoparticles (SPIONs) are cutting-edge materials with rapid development and great application value, especially in biomedical and chemical engineering fields, particularly in wastewater management, targeted drug delivery, biosensing, etc. Nevertheless, magnetically driven isolation methods are required to separate the desired entity from the media. However, due to the nanometric size of SPIONs, their magnetic motion is disturbed by Brownian motion and viscous drag, making their separation a very difficult engineering task. Nowadays, the two most common methods of magnetic separation are high gradient separation (HGMS) and low gradient magnetic separation (LGMS). Nevertheless, the effect of horizontal (perpendicular to gravity), high fields and gradients (higher than LGMS) on the horizontal magnetophoresis and vertical sedimentation of SPIONs has not been studied thoroughly and could potentially achieve the separation of these small materials.

In this work, we report, the magnetic aggregation and sedimentation of 5, 15 and 30 nm particles by applying fields and gradients perpendicular to gravity. The particles suspensions were filled in glass channels and then placed in the separators, where the magnetic field was generated by permanent magnets arranged in quadrupolar configurations (QMS). Different conditions were studied and multiple variables were evaluated, including the particle size, the initial SPIONs concentration, the temperature, the magnetic field gradient and operation time.

Our experimental data suggest that particles agglomerated in chains due to dipole-dipole interactions, while the magnetic force promoted their movement to the glass channel wall where has the highest magnetic flux density. They also settled down as a result of the higher gravitational force exerted on the particle clusters. Furthermore, the particle separation was enhanced by decreasing the temperature and increasing the particle concentration. Finally, the separation process was observed to happen in less than 5 min, which is encouraging considering the long operation times (up to days) necessary to separate particle of similar sizes in LGMS columns.