Role of ortho-functional groups in stabilizing catechol surface complexes on ferrite nanoparticles

Résumé fourni par la source

Molecular-level interactions of naturally occurring catechol derivatives with ferrite surfaces were investigated using permanently magnetic barium hexaferrite nanoplatelets and superparamagnetic iron oxide nanoparticles. Catechol (1,2-benzenediol) and guaiacol (2-methoxyphenol) were selected as representative aromatic ligands relevant to catechol- and guaiacyl-containing natural compounds. First-principles calculations indicated facile proton transfer from the ligands to surface oxygen or hydroxyl sites and predicted strong H-bonding between the resulting surface-bound species and neighbouring surface groups. Consistent with these predictions, spectroscopic and thermal analyses together with zeta-potential measurements support a surface-complexation mechanism in which the complexes are stabilized by hydrogen bonds, also involving the ortho-phenol or methoxy group and an adjacent surface hydroxyl group. Ligand adsorption did not significantly affect the magnetic behaviour of either ferrite. Both nanoparticle systems remained chemically stable after the catechol adsorption at pH 10, while barium hexaferrite nanoplatelets were also stable under near-neutral conditions. In contrast, catechol derivatives accelerated the decomposition of barium hexaferrite nanoplatelets at pH 3. Moreover, barium hexaferrite nanoplatelets catalyzed the oxidation of catechols by molecular oxygen in aqueous dispersions. These results link proton transfer and hydrogen-bond-assisted surface complexation with the stability of ferrite nanoparticles and reactivity toward catechol ligands in aqueous environments.

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