An in situ X-ray absorption spectroscopy study of copper nanoparticles in microemulsion

The present study investigated the formation of Cu0 metal nanoparticle clusters in reverse micelles of pseudo-ternary systems of cetyltrimethylammonium bromide (CTAB) surfactant, butanol (cosurfactant), heptane as the oil phase and aqueous solutions of CuSO4·5H2O and NaBH4 using in situ X-ray absorption spectroscopy (XAS). Microemulsions were prepared with a fixed percentage (60%) of the oil phase and a variable proportion of water and surfactant/cosurfactant. The reduction of Cu2+ and the formation of Cu0 metal nanoparticle clusters were monitored using sodium borohydride as a reducing agent. X-ray absorption spectroscopy in the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions allows the reduction of Cu2+ and the formation of Cu0 clusters to be analysed. A decrease in the water concentration from 15% to 13% resulted in an increase in Cu0 production.