Facile Synthesis of Monodispersed PdO Nanoparticles within Mesoporous Silica with Sonication

Abstract

The synthesis and characterization of nanosized materials is an important issue in basic science research as well as in technological applications, as they have their own characteristic optical, electronic, magnetic, and catalytic properties greatly different from the bulk materials. Therefore, considerable effort has focused on the size and shape selective nanocrystal growth using a variety of synthetic methods including templating, electrochemistry, photochemistry, and seeding. Since powders and films of mesoporous silica have uniform pore diameters in the range of 4-30 nm and large surface area, these materials have been a promising template for the growth of various materials including polymers, semiconductors, metals, and metal oxides. Extensive efforts have been directed to the formation of metal nanoparticles inside the mesoporous structures via a solution-based infiltration process. Stucky and coworkers reported the preparation of isolated freestanding metal (Au, Ag, Pt) nanowires using SBA-15, followed by removal of the silica frame-work. Chemical vapor infiltration of volatile metal precursors and their subsequent decomposition in the channels of mesoporous silica have been also reported. Recently, a sonochemical method has been utilized for the preparation of SBA-15supported Ru nanoparticles by irradiating the Ru(III) mixture with intense ultrasound. Generally, the confined nanoparticles within the pores of mesoporous silica have shown an improved stability. However, the processes using mesoporous silica have sometimes resulted in poor morphology control and undesired particle formation outside silica surface. In this note, we describe a simple sonication-assisted synthetic route for the production of highly dispersed and uniform PdO nanoparticles within the pore channels of SBA-15 without any surface modification outside SBA-15. Most of PdO nanoparticles were imbedded inside the pores of SBA-15, which was confirmed by the analysis of a series of through-focused transmission electron microscope (TEM) images. In this study, PdO nanoparticles were prepared within the pore channels of mesoporous silica since it has been shown that these have catalytic applications in many reactions as well as sensor applications. It has been also reported that PdO nanostructures are easily converted to Pd, which has extensive catalytic applications, by H2 reduction process at an elevated temperature.