Silica gels doped with gold nanoparticles and gold thiolate complexes: The effect of heating and preparation conditions

• A sol-gel “in situ” preparation scheme for the production of polydisperse AuNPs containing silica nanocomposites, based on the presence of DDT and l-AsAc is demonstrated. • Different silica gels containing AuNPs, Au-SC12 or both species can be obtained by variation of the preparation conditions. • Thermal treatment of the composites improves the color brightness, leading to ceramic pigments close to purple of Cassius. • An UV/Vis spectra-structure analysis, based on Mie's theory reveals the presence of AuNPs with a different surrounding in agreement with XRD and TEM/EDAX observations. • The thermal conductivities of the nanocomposites are in the order of 0.05–0.07 W/m·K with a decreasing trend (about 10 %) at heating at 700 °C. A novel sol-gel strategy for the preparation of silica nanocomposites, containing gold nanoparticles (AuNPs), Au(I)-thiolate complexes (Au-SC12) or both disperse phases is demonstrated. The color of the species depends on the size and surrounding of the AuNPs. The nanocomposites obtained are characterized with UV/Vis reflectance spectroscopy, X-Ray diffraction, TEM / EDAX and thermal conductivity measurements. An analysis of the UV/VIS spectra, based on Mie's theory, suggests the presence of 5 - 30 nm AuNPs with different chemical surroundings. Heating of the nanocomposites at 700 °C leads to red or violet colored SiO 2 :AuNPs powders. The thermal conductivity of the nanocomposites is about 0.05–0.07 W/m.K, depending on sintering and chemical composition. A discussion about the microstructure of the composites is also presented.