Using poly(ethyleneimine) (PEI) polymer substrates, spherical FePt nanoparticles (NPs) with diameter <10 nm have been synthesized by photoreduction and chemical reduction in aqueous media at room temperature. In the photoreduction approach, PEvI acts as both the template into which the metal ions are coordinated and as a reductant when irradiated by ultraviolet light. In the chemical reduction method, PEI acts as only a template, with NaBH 4 as the reductant. The asprepared NPs were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Starting from the same precursor state and relative concentrations, the as-prepared NPs from both methods are spherical, crystalline solid solutions with a chemically disordered face-centered cubic (fcc) structure. The as-prepared NPs from both methods are superparamagnetic with some contribution from a ferromagnetic phase. The photoreduced NPs have broad size distribution of (5 ± 1.0 nm), an expanded lattice (3.913 Å), and relatively lower magnetic moment (0.02 emu/g) compared to the narrower size distribution (4 ± 0.7 nm), shortened lattice (3.890 Å), and a dominant moment (15 emu/g) of the chemically reduced NPs. The difference in the rate of particle formation apparently leads to a low efficiency of FePt NP formation via photoreduction compared to chemical reduction.

Thermodynamically stable (ordered) platinum-based bimetallic nanoparticle (NP) catalysts are auspicious candidates for catalyzing the oxygen reduction reaction (ORR) in fuel cells. Although the cubic (L1 2 ) and tetragonal (L1 0 ) ordered phases have been extensively studied, very little is known about the cubic (D 7 ) thermally stable/ordered CuPt 7 with regard to its synthesis at room temperature and ORR activity. The typical synthetic approach to the ordered phase (L1 2 and L1 0 ) has been by thermal annealing of the disordered phase in an inert atmosphere. We demonstrate that by coordinating Cu 2+ and Pt 4+ ions to amino groups in aqueous polyethyleneimine (PEI) (precursor solution), slow crystal growth by a UV-light assisted photoreduction can be used to achieve ordered CuPt 7 NPs at room temperature. Slow crystal growth produces a relatively expanded lattice (7.766 Å) of CuPt 7 and a lesser ORR activity via a four-electron transfer pathway. Conversely, fast crystal growth through a NaBH 4 assisted chemical reduction produces a disordered CuPt phase at room temperature and a contracted lattice (3.809 Å) that enhances the ORR activity of CuPt via a two-electron transfer pathway. Our comparative observations of CuPt and CuPt 7 support the observation that lattice contraction is critical in the ORR activity of Cu−Pt nanoalloys.