Au@Pd Core-Shell Nanoparticle Incorporated Alumina Sols and Coatings: Transformation of Au@Pd to Au-Pd Alloy Nanoparticles

Au@Pd nanoparticles (NPs) of size range 4.5-13 nm (< D > approximate to 7.2 nm) were generated inside the alumina matrix sol without using any additional reducing agent. Partially acetylacetonato (acac) complexed aluminum tri-sec-butoxide has been used to prepare the matrix alumina sol. First, An NPs of size range 3-9 nm (< D > approximate to 5.3 nm) were generated in the alumina sol following our reported method (J. Mater. Chem. 2008, 18, 2816). The addition of Pd-acetate in this An NPs containing sol resulted in formation of Pd shells onto the Au NPs. The previously formed An NPs were acting as seeds and the mild reducing environment of the reaction medium (due to Al-alkoxide) reduced the Pd ions to form Pd shells onto the Au NPs. The strong plasmon band observed at 520 nm in the case of An NPs containing sol has been significantly dampened due to the formation of Pd shells. Grazing incidence X-ray diffraction and transmission electron microscopy (including scanning TEM, EDS using nanoprobe, and HRTEM) analyses revealed the core-shell structure of the NPs. The above sol call be used to prepare Au@Pd core-shell NPs incorporated alumina coatings oil glass substrates. The Au@Pd NPs were transformed to Au-Pd alloy NPs inside the film matrix after heat treatment at 500 degrees C in air.