Synthesis of FePt Nanoparticles by Photoreduction\nand Chemical Reduction in Poly(ethyleneimine)

Abstract

Using\npoly­(ethyleneimine) (PEI) polymer substrates, spherical FePt\nnanoparticles (NPs) with diameter <10 nm have been synthesized\nby photoreduction and chemical reduction in aqueous media at room\ntemperature. In the photoreduction approach, PEvI acts as both the\ntemplate into which the metal ions are coordinated and as a reductant\nwhen irradiated by ultraviolet light. In the chemical reduction method,\nPEI acts as only a template, with NaBH₄ as the reductant.\nThe as-prepared NPs were characterized using X-ray diffraction (XRD),\ntransmission electron microscopy (TEM), and vibrating sample magnetometry\n(VSM). Starting from the same precursor state and relative concentrations,\nthe as-prepared NPs from both methods are spherical, crystalline solid\nsolutions with a chemically disordered face-centered cubic (fcc) structure.\nThe as-prepared NPs from both methods are superparamagnetic with some\ncontribution from a ferromagnetic phase. The photoreduced NPs have\nbroad size distribution of (5 ± 1.0 nm), an expanded lattice\n(3.913 Å), and relatively lower magnetic moment (0.02 emu/g)\ncompared to the narrower size distribution (4 ± 0.7 nm), shortened\nlattice (3.890 Å), and a dominant moment (15 emu/g) of the chemically\nreduced NPs. The difference in the rate of particle formation apparently\nleads to a low efficiency of FePt NP formation via photoreduction\ncompared to chemical reduction.