The nanoscale description of acid penetration to the gold colloids encapsulated in silica sol-gel matrix

Various sizes of gold nano colloidal particles ranging from 5 nm to 100 nm of size were encapsulated in a silica based sol-gel, and these surfaces were exposed to a pH 1 acid solution. This enabled us to observe the process of solvent intrusion and interaction with gold colloids by the absorption spectrum as a function of time. The rate was analyzed by a single exponential analytical function, and the maximum rate was found for gold colloid of 15 nm size. The least acid interaction and colour change was observed for the size of 60 nm. It was speculated that the surface of these gold colloids were homogeneously covered by the sodium tetra-borate buffer which insulated silica gel layer, thus avoiding direct contact of the acid with the surface of the gold colloid. This study confirmed that the nano scale dopant size affects the rate of solvent penetration into a sol-gel cavity.