Effect of the catechol structure on the functionalization and magnetic properties of barium hexaferrite nanoplatelets

In this study, barium hexaferrite nanoplatelets (BHF NPLs) were functionalized with different catechols, pyrocatechol (CAT), dopamine (DA), and caffeic acid (CAFA). Possible adsorption mechanisms, structural effects, and their potential impact on the functionalization and decomposition of the NPLs were investigated. We synthesized the BHF NPLs hydrothermally and functionalized them with catechols in an aqueous suspension (pH = 3) using ultrasonication or heating at 80 °C. We characterized the morphologies and size distributions of the core and functionalized BHF NPLs using transmission electron microscopy (TEM). The functionalization of the BHF NPLs was followed by electrokinetic measurements and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Mass fractions of ligands in the functionalized samples were determined by thermogravimetric analysis (TGA), and the room-temperature magnetic properties of the core and functionalized BHF NPLs were measured with a vibrating-sample magnetometer (VSM). The analyses showed that CAT and CAFA attached stably under the studied conditions, whereas the attachment of DA with an electron-donating group was labile. Chemical analysis of the dissolved iron ions performed with inductively coupled plasma-optical emission spectroscopy (ICP-OES) revealed that catechols enhanced the decomposition of the BHF NPLs at acidic pH.