Gold–Manganese Oxide Core–Shell Nanoparticles Produced by Pulsed Laser Ablation in Water

Abstract

A single-step procedure for the preparation of Au–MnOx NPs was achieved through pulsed laser ablation of a gold–manganese metal target made of a pressed metal powder mixture. First, a 248 nm nanosecond laser at 66.7 J cm–2 was used to synthesize Au–MnOx NPs from a gold–manganese metal target immersed in an aqueous solution at pH 11 (NaOH). It is demonstrated that the Au–MnOx NPs are made of a small Au core (around 5 nm in diameter) surrounded by a very thin manganese oxide layer (0.3–1.3 nm) as characterized by TEM, HAADF HR-STEM, and EELS. The superficial MnOx layer has a local structure that bears a close resemblance to that of Mn2O3 and MnO2 as revealed by EXAFS and XANES measurements. Comparative studies were also performed with a 1064 nm nanosecond laser at 1.4 J cm–2. In that case, the resulting colloids are mainly made of a mixture of Au NPs and MnOx NPs, with few Au–MnOx NPs, thereby suggesting the impact of the laser wavelength and fluence on the synthesis process. The mechanisms responsible for the production of Au–MnOx core–shell NPs are discussed.