Abstract
The reaction of Fe(CO)5 and Pt2(dba)3 in 1-n-butyl-methylimidazolium tetrafluoroborate (BMIm.BF4), hexafluorophosphate (BMIm.PF6), and bis(trifluoromethanesulfonyl)imide (BMIm.NTf2) under hydrogen affords stable magnetic colloidal core–shell nanoparticles (NPs). The thickness of the Pt shell layer has a direct correlation with the water stability of the anion and increases in the order of PF6 > BF4 > NTf2, yielding the metal compositions Pt4Fe1, Pt3Fe2, and Pt1Fe1, respectively. Magnetic measurements give evidence of a strongly enhanced Pauli paramagnetism of the Pt shell and a partially disordered iron-oxide core with diminished saturation magnetization. The obtained Pauli paramagnetism of the Pt shell is 2 orders of magnitude higher than that of bulk Pt, owing to symmetry breaking at the surface and interface, resulting in a strong increase in the density of states at the Fermi level, and thus to enhanced Pauli susceptibility. Moreover, these ultrasmall NPs showed efficient catalytic activity for the di...
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