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

摘要

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.