Filtration of Nanoparticle Agglomerates in Aqueous Colloidal Suspensions Exposed to an External Radio-Frequency Magnetic Field

Abstract

The study investigated the phenomenon of the fast aggregation of single-domain magnetic iron oxide nanoparticles in stable aqueous colloidal suspensions due to the presence of a radio-frequency (RF) magnetic field. Single-domain nanoparticles have specific magnetic properties, especially the unique property of absorbing the energy of such a field and releasing it in the form of heat. The localized heating causes the colloid to become unstable, leading to faster agglomeration of nanoparticles and, consequently, to rapid sedimentation. It has been shown that the destabilization of a stable magnetic nanoparticle colloid by the RF magnetic field can be used for the controlled filtration of larger agglomerates of the colloid solution. Two particular cases of stable colloidal suspensions were considered: a suspension of the bare nanoparticles in an alkaline solution and the silica-stabilized nanoparticles in a neutral solution. The obtained results are important primarily for biomedical applications and wastewater treatment.

Effect of Magnetic Heating on Stability of Magnetic Colloids

“…When analyzing the shape of the curves for unsonicated and sonicated samples, it can be noticed that for the former, there was a jump after some time of exposure to the RFMF, as described in our previous article [ 17 ]. For our samples, as the plots in Figure 4 demonstrate, such a jump can be observed after about 5 min.…”

“…To evaluate the stability of the MNP suspension, its behavior was observed for different storage times and different values of pH ranging from 7 to 13 [ 17 ]. Based on these studies, we found that colloidal suspensions of bare nanoparticles appeared to be the most stable at pH = 11.5.…”

“…Figure 5 presents the intensity-based size distributions, before and after magnetic heating, for a few exemplary sonications. The case of untreated suspension, the starting point for this study, was discussed in our previous article [ 17 ]. We were then interested in the efficiency of filtering large agglomerates from the suspension, so our analysis focused on the particles remaining in the supernatant.…”

“…Recently, it has been shown that a magnetic colloidal suspension can be destabilized by exposure to the RFMF [ 17 ]. The resulting agglomeration process of magnetic nanoparticles may lead to undesirable phenomena, such as weakening the effect of hyperthermia on colloidal suspensions of magnetic nanoparticles.…”

“…In our previous publication [ 17 ], we reported that the radio frequency magnetic field (RFMF) destabilizes a colloidal suspension of magnetic nanoparticle clusters. The reason was the aggregation of nanoparticles as a result of localized thermal fluctuations induced by the magnetic nanoparticles heated by the AC magnetic field and magnetic dipole-dipole interactions.…”