Core-Shell Bimetallic Au-Pd Nanoparticles: Synthesis, Structure, Optical and Catalytic Properties

Colloidal dispersions of bimetallic nanoparticles composed of gold and palladium were prepared by wet chemical method, in which Au(III) and Pd(II) ions in an aqueous solution in the presence of a cationic surfactant, Cetyltrimethylammonium bromide (CTAB). The structure and composition of the metallic nanoparticles were characterized by UV-visible spectroscopy (UV-Vis), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy photographs showed spherical particles whose size had a fairly narrow distribution with a geometric mean diameter about 9.4 nm. Analyses with UV-Vis spectra indicated that Au(III) ions were first reduced and after their consumption reduction of Pd(II) ions set in. A core-shell structure of the particles, a core of gold and a shell of palladium was confirmed by high-resolution TEM and X-ray diffraction. The catalytic activities of nanoparticles are tested on the hydrogenation reaction between NaBH4 and 4-Nitrophenol reduction was studied spectrophotometrically. Bimetallic nanoparticles exhibited better catalysis that the mono metallic nanoparticles, which may be due to the electronic effects of the core to shell metal atoms.