Room Temperature Synthesis of Noble Metal Clusters in the Mesopores of Mechanically Strong Silica-Polymer Aerogel Composites

Abstract

Clusters of Ag and Au have been formed in the bulk of mechanically strong silica-polymer aerogel composite monoliths. For that purpose, base-catalyzed silica hydrogels were washed with a 50% w/w acetone/diisocyanate (di-ISO) solution, and cured at 55°C for 3 days. Unreacted di-ISO solution was washed off with acetone, and the gels were washed with a acetone solutions of Ag+ or AuCl−4 (3 × 10−4 mol · L−1), containing also 0.2 mol · L−1 of 2-propanol as radical scavenger. Metal clusters were formed upon radiolytic reduction (γ rays, 48–72 h, 7–7.5 kGy) of the precursor ions. After irradiation, the hydrogels were washed with acetone, and dried in supercritical CO2. The resulting aerogel monoliths had a density of 0.56 g·cm−3, a surface area of about 160 m2 · g−1, and an average pore diameter of about 200 nm. Transmission electron microscopy showed that the metal clusters are free of contamination, with a cubic face centered structure, and a narrow size distribution, centered around 10 nm. The elastic module, measured with a three-point flexural bending method, was in the 60–70 MPa range, and the load at rupture between 16 and 19 kg. Thermogravimetric analysis showed that the composites were stable up to about 300°C. These results are in excellent agreement with results obtained previously for as-grown, di-ISO cross-linked silica aerogels, and show that addition of metal clusters and gamma irradiation to a dose corresponding to a permanence of several years in low earth orbit at high inclination did not affect the chemical identity, the mechanical strength, the porosity and the bulk density of the composite aerogel monoliths.