The Influence of Catechols on the Magnetization of Iron Oxide Nanoparticles

In this study, MNPs were functionalized with pyrocatechol (CAT), pyrogallol (GAL), caffeic acid (CAF), and nitrodopamine (NDA) at pH 8 and pH 11. The functionalization of the MNPs was successful, except in the case of NDA at pH 11. The thermogravimetric analyses indicated that the surface concentration of the catechols was between 1.5 and 3.6 molecules/nm(2). The saturation magnetizations (M-s) of the functionalized MNPs were higher than the starting material. XPS analyses showed only the presence of Fe(III) ions on the surface, thus refuting the idea of the Fe being reduced and magnetite being formed on the surfaces of the MNPs. Density functional theory (DFT) calculations were performed for two modes of adsorption of CAT onto two model surfaces: plain and adsorption via condensation. The total magnetization of both adsorption modes remained the same, indicating that the adsorption of the catechols does not affect the M-s. The analyses of the size and the size distribution showed an increase in the average size of the MNPs during the functionalization process. This increase in the average size of the MNPs and the reduction in the fraction of the smallest (i.e., <10 nm) MNPs explained the increase in the M-s values.

Automated summary

In this study, MNPs were successfully functionalized with CAT, GAL, CAF, and NDA at different pH values. The functionalized MNPs showed higher saturation magnetizations (M-s) compared to the starting material. XPS analyses confirmed the presence of Fe(III) ions on the surface, ruling out the formation of magnetite. DFT calculations demonstrated that the adsorption of catechols did not affect the M-s. The increase in the average size of the MNPs and the decrease in the fraction of the smallest MNPs explained the observed increase in M-s values.