Noble metal immersion spectroscopy of silica alcogels and aerogels

We have fabricated aerogels containing gold and silver nanoparticles for ga s catalysis applications. The technique of immersion spectroscopy is extend ed to porous or heterogeneous media allowing the surface area of metal avai lable for catalytic gas reaction to be determined. Specifically, we apply t he predominant effective medium theories to the heterogeneous interlayer su rrounding each particle to determine the average fractional composition of each component in this inhomogeneous layer. The technique is satisfactory f or statistically random metal particle distributions but needs further modi fication for aggregated or surfactant modified systems. Additionally, the k inetics suggest that collective particle interactions in coagulated cluster s are perturbed during silica gelation resulting in a change in the aggrega te geometry.