Formation of Bimetallic Copper–Gold Alloy Nanoparticles Probed by in Situ X‐ray Absorption Fine Structure Spectroscopy

Advanced studies of the formation and growth processes of metal alloy nanoparticles are of great importance and provide a better understanding for the fine tuning of their properties for the desired applications. In this work, we followed the synthesis of Au 1– x Cu x colloidal nanoparticles by in situ time‐resolved X‐ray absorption fine structure (XAFS) spectroscopy. The particles were synthesized by a one‐pot approach with a homemade reactor adapted to the XAFS measurements. The colloidal nanoparticles were also characterized by complementary ex situ techniques. Analyses at the Cu‐ K edge and Au‐ L 3 edge confirmed that the initial reduction of the Au species occurs at low temperatures (<100 °C) to form Au seeds that are subsequently enriched with Cu to form Au 0.75 Cu 0.25 alloy nanoparticles at 225 °C. An important finding was the temporary formation of a Cu 2 O‐type phase during the colloidal synthesis. This phase was consumed with the concomitant formation of the Au 1– x Cu x alloy nanoparticles. These results directly confirm the previous proposal that the alloy formation occurs through a digestive‐ripening‐like process of an amorphous Cu‐enriched phase.