Reduction mechanism of Au metal ions into Au nanoparticles on molybdenum disulfide

Abstract

MoS₂ has attracted tremendous attention as a substrate for supporting noble metal nanoparticles profiting from its ability to spontaneously reduce noble metal ions into nanoparticles. However, little is known of the mechanism and behavior of such spontaneous reduction. In this work, observation of Au³⁺ reduction on MoS₂ is performed using atomic force microscopy (AFM) to obtain a better understanding of the reduction mechanism and behavior. AFM, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) confirm that Au³⁺ could be well reduced into Au nanoparticles when MoS₂ serves as a substrate. No oxidation of MoS₂ is observed during the reduction of Au³⁺, suggesting that the oxidation of MoS₂ is not the driving force for the reduction. AFM and XPS demonstrate that the reduction is a light-induced reaction. MoS₂ would release free photogenerated electrons under light irradiation, which are the electrons involved in the reduction reaction and lead to the reduction of Au³⁺ into Au nanoparticles. AFM further reveals that light intensity, near-ultraviolet light, and temperature promote the reduction of Au³⁺. In addition, Au nanoparticles prefer to assemble along the edges of MoS₂. The findings in this work could give insights into the control and growth of noble metal nanoparticles on the MoS₂ substrate for producing better composites for photocatalysis and surface enhanced Raman scattering sensing.