Gold nanoparticles enclosed in silica xerogels by high-pressure processing

The dispersion of gold nanoparticles (AuNPs) in solid matrices, maintaining their optical properties as in liquid medium, has been explored, enlarging the possibilities of handling and applications of these nanoparticles. In this study, AuNPs were successfully enclosed in silica using the sol–gel method and high-pressure processing at 7.7 GPa, at room temperature, obtaining compacts with densities as high as 85% of silica glass and Vickers microhardness of 50% of quartz. This densification was confirmed by the reduced values of specific surface area and closed pores. UV–Vis spectra showed that the AuNPs maintain their optical properties, in the monoliths and in the compacts, presenting an absorption band in the characteristic region of AuNPs smaller than 20 nm. The slight red-shifts of the absorption peaks cannot be explained in the same way as for AuNPs in solution, where it is associated to an increase in particle diameter. In solid samples, additional factors as matrix properties should be considered. Transmission electron microscopy (TEM) images showed that the AuNPs have spherical shape both in solution and in the monolith, with an average diameter not exceeding 10 nm. It was also observed that the high-pressure processing did not destroy or misshape the AuNPs.