Self-Assembled Fernlike Microstructures of Polyhedral Oligomeric Silsesquioxane/Gold Nanoparticle Hybrids

We have used a thiol-functionalized polyhedral oligomeric silsesquioxane (SH-POSS) as a protective group for the preparation of POSS-protected gold nanoparticles (POSS-Au NPs). The organic/inorganic hybrid SH-POSS NPs exhibited an interesting platelike morphology arising from steric hindrance between the isobutyl groups of SH-POSS. An XRD study of the SH-POSS crystal revealed the relatively large interstice (1.64 nm lattice constant a > 1.3 nm diameter SH-POSS) on the basal plane of the unit cell, which resulted in a platelike morphology having lateral dimensions on the order of a few micrometers and thicknesses of a few hundred nanometers. In addition to behaving as a stabilizer for the preparation of Au NPs, an excess of SH-POSS colloids led to the formation of a crystalline template that incorporated the POSS-Au hybrid NPs on its surface, providing a unique fernlike microstructure. After removal of the POSS template (through sublimation and decomposition to a silica char) at 350 degrees C in air for I h, nanosized Au islands having diameters of 50-100 nm and thicknesses of 2-20 nm were sintered onto the substrate. As a result, SH-POSS is an excellent protective group for the preparation of Au NPs of high stability in the powder state. In addition, we suspect that SH-POSS crystals could be used to disperse Au NPs onto substrates for a wide range of applications (e.g., Au catalysts).