Adsorption of Organic Dyes on Magnetic Iron Oxide Nanoparticles. Part II: Field-Induced Nanoparticle Agglomeration and Magnetic Separation

This paper (part II) is devoted to the effect of molecular adsorption on the surface of magnetic iron oxide nanoparticles (IONP) on the enhancement of their (secondary) field-induced agglomeration and magnetic separation. Experimentally, we use Methylene Blue (MB) cationic dye adsorption on citrate-coated maghemite nanoparticles to provoke primary agglomeration of IONP in the absence of the field. The secondary agglomeration is manifested through the appearance of needlelike micron-sized agglomerates in the presence of an applied magnetic field. With the increasing amount of adsorbed MB molecules, the size of the field-induced agglomerates increases and the magnetic separation on a magnetized micropillar becomes more efficient. These effects are mainly governed by the ratio of magnetic-to-thermal energy alpha, suspension supersaturation Delta(0), and Brownian diffusivity D-eff of primary agglomerates. The three parameters (alpha, Delta(0), and D-eff) are implicitly related to the surface coverage theta of IONP by MB molecules through the hydrodynamic size of primary agglomerates exponentially increasing with theta. Experiments and developed theoretical models allow quantitative evaluation of the theta effect on the efficiency of the secondary agglomeration and magnetic separation.

Automated summary

This study investigates the impact of molecular adsorption on the surface of magnetic iron oxide nanoparticles on the enhancement of field-induced agglomeration and magnetic separation. Experimental results demonstrate that with an increasing amount of adsorbed molecules, the size of the agglomerates and efficiency of magnetic separation also increase.