Noble Metal Immersion Spectroscopy of Silica Alcogels and Aerogels

We have fabricated aerogels containing gold and silver nanoparticles for gas catalysis applications. The technique of immersion spectroscopy is extended to porous or heterogeneous media allowing the surface area of metal available for catalytic gas reaction to be determined. Specifically, we apply the predominant effective medium theories to the heterogeneous interlayer surrounding each particle to determine the average fractional composition of each component in this inhomogeneous layer. The technique is satisfactory for statistically random metal particle distributions but needs further modification for aggregated or surfactant modified systems. Additionally, the kinetics suggest that collective particle interactions in coagulated clusters are perturbed during silica gelation resulting in a change in the aggregate geometry.