Synthesis and Optical Properties of MoS2/Graphene Nanocomposite

In this work, we report a hybrid architecture of layered MoS2/graphene synthesized by an ultrasonic-assisted hydrothermal method at 230 degrees C with a reaction time of 2 h. The microstructure, morphology, chemical composition and optical properties of MoS2/graphene were analyzed by x-ray diffraction, field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), Raman spectroscopy, hard x-ray photoelectron spectroscopy (HAXPES), energy dispersive x-ray (EDX) spectroscopy and photoluminescence measurements. The FESEM results show that the ultrathin MoS2 nanosheets directly deposited on the surfaces of graphene sheets with high density and uniform shape. The TEM and HRTEM images indicate that MoS2 nanosheets with average thickness of similar to 3-6 nm (6-8 layers) grow vertically on the graphene surface, forming three-dimensional MoS2/graphene hybrid structures. Both XRD and Raman analyses elucidate that the as-grown MoS2 phase of MoS2/graphene composite crystalized in a hexagonal phase (2H-MoS2) with low impurity, which was later confirmed by the HAXPES and EDX. Interestingly, the D-band in the Raman spectrum of MoS2/graphene hybrid samples almost disappears as the 2D-band arises, revealing that defects in the graphene oxide are well repaired under the hydrothermal process. Furthermore, the as-synthesized MoS2/graphene exhibits strong photoluminescence with separately resolved emission peaks in the visible range (similar to 1.75-1.78 eV, similar to 1.89-1.93 eV and similar to 1.99-2.05 ,eV) which is a signature of mid-gap states in their optical bandgap compare to that of as-synthesized MoS2. Our synthesis approach is favorable for easy and low-cost preparation of MoS2/graphene composite, rendering the material attractive for various optoelectronic and catalysis applications.