Study On Preparation And Properties Of Molybdenum Disulfide/ Polyvinyl Alcohol And Molybdenum Disulfide/Pristine Graphene Composites

Due to its unique two-dimensional layered structure, molybdenum disulfide（MoS₂） showed excellent mechanical, chemical, thermal and catalytic properties. Therefore, it has broad potential applications in the peoperty enhancement ih the fileds of polymer composites and catalytic hydrogen evolution reaction. In this thesis, we explored the preparation of MoS₂ nanosheets, MoS₂-reinforced polymer composites and grapheme-based MoS₂ nanocomposites for catalytic hydrogen evolution reaction. The contents of this thesis mainly include the following aspects:1, MoS₂ nanosheets prepared by intercalatation of sodium naphthalenide. The commercial MoS₂ was exfoliated into single or few layered nanosheets by ultrasonic and intercalatation with sodium naphthalenide. The XRD result showed that the d-spacing of MoS₂ treated by sodium naphthalenide was increased. AFM、SEM and TEM indicated that single or few layered MoS₂ nanosheets were successfully obtained by intercalatation with sodium naphthalenide. After prolonged settlement, obvious precipitation does not appear in aqueous dispersion of the resulting MoS₂, showing that molybdenum disulfide nanosheets can be well dispersed in aqueous solution.2, MoS₂ nanosheets-reinforced polyvinyl alcohol（PVA）. In this section, the MoS₂ nanosheets were used as a filler. MoS₂/PVA nanocomposites were prepared by solvent blending method. XRD and TEM showed that MoS₂ nanosheets were uniformly dispersed in the PVA matrix. Severe agglomeration was not observed. SEM and FTIR results displayed a strong interaction between the MoS₂ and PVA. DSC and TGA curves indicated that thermal stability of MoS₂/PVA nanocomposites was significantly increased compared to blank PVA. The glass transition temperature（Tg） and maximum degradation temperature increased by 9 ℃ and 29 ℃, respectively. As compared to neat PVA, the mechanical strength of MoS₂/PVA composite was greatly improved. Tensile test showed an 85 % increase in tensile strength and a 49 % improvement in Young’s modulus upon incorporation of only 1 wt% of MoS₂ nanosheets. The improvements in the thermal and mechanical properties of MoS₂/PVA nanocomposites were attributed to the good dispersion of MoS₂ nanosheets and strong interactions between PVA and MoS₂.3, Graphene-supported MoS₂ nanoparticles for hydrogen evolution reaction（HER）. In this section, pristine graphene（PG）and ammonium tetrathiomolybdate（（NH₄）₂MoS₄） were used as the conductive carrier and precursor, respectively. A series of MoS₂/PG nanocomposites was prepared at different reaction temperature with the assistance of supercritical carbon dioxide（scCO₂）. TEM observation indicates that MoS₂ nanosheets with few layers and more exposed edges were uniformly dispersed on graphene surface. Furthermore, the lattice of MoS₂ nanosheets can be clearly observed in high resolution TEM images. The XPS results indicated that the content of Mo and S in the nanocomposite were 5.62 % and 11.43 %. The ratio is close to 1:2, in accordance with the atomic composition of MoS₂. The S and Mo element in the nanocomposite is mainly in the form of S^2- and Mo⁴⁺. The electrochemical test results showed that high temperature treatment and the addition of graphene have a great effect on the efficiency of catalytic hydrogen evolution of MoS₂.