The challenge to produce magnetic nanoparticles from waste containing heavy metals aiming at biomedical application: New horizons of chemical recycling

Abstract

Silica-coated magnetite nanoparticles (SMNPs) were prepared by a green approach based on waste pickling acid. A set of techniques (PXRD, ATR, VSM, SEM, TEM, DLS and XPS) was used for their characterization, and for monitoring the levels of heavy metal impurities. The SMNPs presented an expected profile, similar to that reported for nanoparticles produced from fresh chemicals. The crystallinity and magnetic saturation confirmed the formation of the Fe3O4 phase, silanol and siloxane absorption bands, as well as TEM images confirmed the coating SiO2. The SMNPs chosen for the biomedical tests did not present a significant level of contaminants, and the non-toxic silica coat produced by the sol-gel method ensured a preliminary study on its biocompatibility with reproductive cells in vitro. SMNPs presented a high ability to immobilize spermatozoon cells, suggesting that a fine control of their surface charge must be carried out for specific biomedical purposes. The agglomeration of the solid NPs was evidenced by SEM and by DLS measurements. Its aggregation was tuned by sonication, and a 5-min long ultrasound treatment was capable of halving the agglomerate size, allowing a one-to-one interaction (one SMNPs agglomerate to each cell). The CASA system used to monitor the semen quality showed that vigor, motility and velocity parameters were kept at levels very close to the control group. Finally, a waste-based input submitted to a meticulous purification process could be used as a source for magnetic materials synthesis and evaluated in the biomedical field as long as all precautions are taken into account.