Synthesis of gold nanoparticles within silica monoliths through irradiation techniques using Au(I) and Au(III) precursors

The formation of gold nanoparticles (GNPs) within mesoporous silica matrices by means of irradiation techniques is reported. The xerogels were impregnated with solutions of two different gold precursors: (Ph3P)AuCl for Au(I) and [(Bu4N)-Bu-n]AuCl4 for Au(III). The irradiations were performed with two continuous wave laser sources (266 and 532 nm), with a femtosecond pulsed laser (800 nm), and with a mercury vapour lamp emitting in the UV region. It has been shown that no reducing agent was ever required to obtain GNP formation. XRD data exhibited the typical patterns of fcc gold, except for two cases involving the Au(I)-doped matrices, where a preferential crystallographic orientation was observed. Excluding the case of the UV irradiations performed on Au(III)-doped samples, we always obtained the formation of roughly spherical and well dispersed GNPs of relatively small size (6-60 nm). The gold-reduction mechanisms proposed depend on the chosen irradiation technique. Moreover, when laser sources are employed, GNP formation can be selectively limited to the irradiated areas, thus making it possible to obtain reproducible patterns of GNPs.