Thermal decomposition study of HAuCl4·3H2O and AgNO3 as precursors for plasmonic metal nanoparticles

Thermal decomposition of HAuCl4·3H2O and AgNO3, as precursors for Au and Ag nanoparticles, respectively, was monitored by coupled TG–DTA with TG/EGA–FTIR and EGA–MS techniques in a flowing 80 %Ar + 20 %O2 and Ar atmospheres in the temperature range of 30–600 °C. The intermediate and final products of thermal decomposition were analysed by ex situ XRD and FTIR techniques. The thermal degradation of HAuCl4·3H2O starts immediately after melting at 75 °C and takes place in three steps in the temperature range of 75–320 °C with total mass loss of 49.4 and 49.7 % in artificial air and Ar atmospheres, respectively. EGA by MS and FTIR revealed a simultaneous release of H2O and HCl in the temperature range of 75–235 °C. EGA by MS revealed a release of Cl2 at around 225 °C and in the interval of 250–320 °C. According to the XRD analysis, the main solid product in the end of the first decomposition step at 190 °C is AuCl3; in the end of the second decomposition step at 240 °C is AuCl and the final product at 320 °C is Au. The thermal decomposition of AgNO3 takes place in a single step in the temperature range of 360–515 °C with a total mass loss of 39.0 and 37.8 % in flowing artificial air and Ar atmospheres, respectively. According to EGA–MS and EGA–FTIR the main evolved gases are NO2, NO and O2. The final product of the thermal decomposition at 600 °C is Ag irrespective of the atmosphere.