A Mechanism Study on the Synthesis of Cu/Pd Nanoparticles with Citric Complexing Agent

We have previously synthesized Cu/Pd nanoparticles with a citric complexing agent, demonstrating well the suspension and high catalytic ability of electroless copper deposition. Herein, we report the in situ investigation of the synthesis of Cu/Pd nanoparticles with a citric complexing agent by X-ray absorption near-edge structure (XANES). By characterizing the XANES spectra of Cu and Pd upon the stepwise addition of an alkaline solution, the reaction mechanism of Cu as well as Pd complexing ions was elucidated. Slow reduction of Pd ions and fast reduction of Cu ions induced by zerovalent Pd are found in XANES spectra. A three-stage formation mechanism of Cu/Pd nanoparticles was proposed in which a Pd reduction initial stage, a Cu-dominated reduction middle stage, and a Pd-dominated reduction final stage were indicated. As a result, a Pd-rich outer shell formed on the surface of synthesized Cu/Pd particles in the final stage. In summary, the formation mechanism and the Pd-rich outer shell structure of synthesized Cu/Pd nanoparticles were found in this citric complexing agent synthesis method.