Magnetic domain orientation in magnetite Fe3O4 nanoparticles coated with natural extracts from Syzygium aromaticum, Illicium verum or Lippia graveolens

Abstract

This work contributes with the development of an alternative direct processing of magnetite nanoparticles (<20 nm) coated with polyphenols (Fe₃O₄NPs@polyphenols), which could be regarded as starting point from Fe–OH, and Fe–CH₃O to bind organic groups for the formulation or attaching of multifunctional systems. Fe₃O₄NPs@polyphenols have shown reproducible uniaxial Single Magnetic Domains (SMDs) and superparamagnetic performance, ideal directional core as single magnetic domains with agglomeration in low dimension and promising development as nano-stirring, nano-carriers or nano-trigger formulations. The synthesis and coating were performed using an improved Massat's co-precipitation route and adding polyphenol extracts from (1) Syzygium aromaticum, (2) Illicium verum, or (3) Lippia graveolens. The phenol chains allowed the synthesis of SPIONs with particle sizes ranging from 3.09 to 7.31 nm, coated with a polyphenol thin layer of thickness t ≈ 1–3 nm. pH values of 13–14 and temperatures within 70–80 °C were necessary to obtain Fe₃O₄NPs@polyphenols. Fe₃O₄NPs@polyphenols exhibited an inverse spinel structure and small lattice distortion related to γ-Fe₂O₃ formation over their surface as well as superparamagnetic response, phenol bonding Fe–OH on their interphase, and directional behavior with effective uniaxial magnetic response as SMDs compass.