Thermal and radiolysis assisted formation of Au–Pd heteroaggregates

In the presence of pre-synthesized Au nanoparticles both pulse radiolysis and 2-propanol assisted reduction of Pd (II) chloride to palladium have been investigated with the intention to check the possible formation of Au–Pd heteroaggregates. Pulse radiolysis of Pd2+ (50 Gy dose/pulse at 298 K in 270 mM 2-propanol to scavange OH radicals) produced Pd nanoparticles of 3.9–2.5 nm depending on the citrate concentration (2.8–12 × 10−4 M). UV–vis measurements and TEM investigations confirmed that part of the Pd particles were attached to the Au particles of 28 ± 6 nm forming Au–Pd heteroaggregates. Hydrothermal treatment of Pd hydrosol at 363–395 K in the presence of Au nanoparticles was observed to facilitate formation of Pd tendrils on Au and 2D Pd structures by aggregation process. Reduction of Pd2+ with 2-propanol (1.55–2.2 M) in Au hydrosol and sodium citrate as capping agent was also tested at 348–353 K. At pH 3.5–4.5 reduction of Pd2+ resulted in an effective decoration of the gold particles with small crystals of Pd. The observed structures definitely differ from the usual Au/Pd core/shell nanoparticles. The Pd–Au samples were characterized by UV–vis, transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS). Hydrogenation of 1,3-cyclooctadiene in the liquid phase was applied for the additional characterization of the structurally different samples.