Decoration of Au Nanoparticles on MoS2 Nanospheres: From Janus to Core/Shell Structure

A flexible route is presented for the controlled decoration of the Au nanoparticles (NPs) on the spherical MoS2 particles, just by dropping the HAuCl4 aqueous solution into the hydrothermal reaction-induced MoS2 colloidal solution at room temperature. In the absence of surfactants in the colloidal solution, it has been found that the obtained products are mostly the MoS2/Au Janus particles, in which the hemispherical Au particles are separately attached on the single MoS2 spheres about 100 nm in size. The hemispherical Au particles are built of the ultrafine NPs (<10 nm) and comparable to the MoS2 spheres in size. Further experiments have revealed that the existence of surfactants in the colloidal solution could significantly influence the distribution and decoration of Au NPs on the MoS2 nanospheres. When the MoS2 colloidal solution contains the nonionic or anionic surfactant, such as poly(vinylpyrrolidone) and sodium dodecyl benzene sulfonate, in appropriate content, the addition of HAuCl4 induces the Au ultrafine NPs highly uniformly attached or decorated on the MoS2 spheres. The distribution of the Au ultrafine NPs on the MoS2 spheres evolves from a dispersed decoration to the intact core/shell structure with the rising HAuCl4 addition amount. However, the cationic surfactant could prevent Au NPs from decoration on the MoS2 spheres and induce the self-agglomeration of Au NPs. The formation of MoS2/Au Janus particles is attributed to the aggregation growth of Au ultrafine NPs on the MoS2 spheres, whereas the dispersed decoration of Au ultrafine NPs on the MoS2 spheres is ascribed to the surfactant-induced uniform distribution of Au NPs. Interestingly, such decorated spherical MoS2 NPs have exhibited a much higher surface-enhanced Raman scattering effect than the decorated MoS2 nanoplates. This work presents a simple approach to the controllable decoration of Au NPs on the spherical MoS2 particles.