| In recent years, graphene, hexagonal boron nitride sheets (h-BN),layered transition metal dichalcogenides (such as MoS2, WS2) have been widely studied with the development of the new type of two-dimensional material. Graphene has huge potential in many fields due to its excellent physical and chemical properties, however, its band gap is zero and the application in optoelectronic devices is strictly limited. MoS2 is a semiconductor with layered structure, and it has been confirmed a transition from an indirect band gap (Eg = 1.29 eV) to a direct band gap(Eg=1.90 eV) as the thickness of the MoS2 decreased to monolayer.Compared with the bulk MoS2, the single-layer or few-layer MoS2 exhibit unique photoelectric properties and become the focus of current research.MoS2 is easy to agglomerate under the action of molecular force, the composite material prepared by introducing graphene as growth substrate of MoS2 can effectively reduce the stacking of MoS2 and adjust its band gap, and it can also improve the conductivity and structural stability of MoS2. The composite has great application prospect in the fields of lithium ion batteries, optical (electric) catalytic hydrogen evolution,optoelectronic devices, super capacitor and other fields. This research is devoted to the study of MoS2/r-GO composites and their synergistic effects, the main contents and results are as follows:(1)The ultrathin MoS2 /r-GO heterogeneous nanostructure of high quality was prepared by exploring a hydrothermal method with graphene oxide, ammonium molybdate and thiourea as raw materials. The samples were characterized by test methods such as XRD, SEM, TEM, etc. We found that there are two ways to combine MoS2 with r-GO: One is that the ultrathin MoS2 nanosheets grows on the surface of r-GO; the other is the formation of r-GO-MoS2-r-GO sandwich structure of a few layers of MoS2 in the r-GO folds.(2)The nonlinear optical properties of MoS2/r-GO were studied by Z-scan technique, and it was found that the composites shows a strong saturated absorption (SA) response, the possible reason is that the heterogeneous nanostructured materials become a good electron donor /acceptor system with the help of the heterojunction between MoS2 and graphene.(3)The degradation ability of MoS2/r-GO under UV irradiation to the organic dye was studied. The composite has higher photocatalytic efficiency than pure MoS2. On the one hand the introduction of r-GO reduces the number of MoS2 layers and increases the number of active sites in edges; On the other hand, it can also effectively transfer the carriers generated from MoS2 with the irradiation of UV light and inhibit the recombination of electron hole pairs, thus improving the photocatalytic efficiency. The material was then annealed at different temperatures and the photocatalytic degradation of the materials were studied, the results show that the photocatalytic ability became weaker with the increase of annealing temperature, a large number of defects will be introduced in MoS2/r-GO at high temperature and the conjugated ?bonds in the surface of graphene was destroyed, which leading to a decrease in conductivity and thus weakening the photocatalytic capacity. |
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