Controllable Preparation And Characterization Of Micro/nanometer Hexagonal Phase Molybdenum Disulfide

The molecular structure of molybdenum disulfide (MoS2) is constructed layers by layers, and the combination between two layers depends on Van der Waals intermolecular force. The intermolecular bond energy is very weak, which easily leads to slipping between two layers. So MoS2 materials possess excellent and unique chemical, mechanical and physical properties, have been being widely used in lubricating field and are known as the"king of solid lubricants". Especially, micro/nano-scale MoS2 materials that have higher specific surface area, stronger adsorbability, higher catalytic activity were preferentially used to prepare special catalytic materials and gas storage materials, which have become the research focus in recent years.Micro/nano-scale MoS2 particles were successfully prepared by surfactant-assisted hydrothermal method, template-interface synthesis method, the preparation of precursors ammonium tetrathiomolybdate and liquid reduction method, wet solid-phase mechanical ball milling method at room temperature and so on, and conditions of synthesis methods were optimized, products were scientifically characterized, formation mechanism of products were firstly discussed.Micro/nano-scale MoS2 particles have been successfully synthesized by CTAB-assisted hydrothermal technique, and the composition and morphology of the resulting products were analyzed by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM); the effects of CTAB on reaction process and resulted products have also been investigated through structure activity relationship theory. Then, the template-interface synthesis route was employed to prepare micro/nano-scale MoS2 whose phase compositions were analyzed by XRD, and the corresponding reaction mechanism has been discussed. Finally, needlelike ammonium tetrathiomolybdate was synthesized via ultrasonic assistance using ammonium dimolybdate and ammonium as reactants. The phase and purity of the obtained products were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and laser Raman spectroscopy (LRS). The thermal decomposition mechanism of ammonium tetrathiomolybdate was detailedly studied through comprehensive thermoanalysis. Meanwhile, MoS2 nanoparticles were prepared by way of liquid phase reduction method and wet solid-phase mechanical ball milling method at room temperature using ammonium tetrathiomolybdate as raw material, and the phase compositions and morphology of the obtained products were characterized by XRD and SEM.The results show that the as-synthesized MoS2 samples obtained from surfactant-assisted hydrothermal synthesis method mainly belongs to spherical hexagonal phase. The higher is the hydrothermal treatment temperature, and the stronger is the crystallization degree of the product, but the resulted agglomeration is also stronger, so the optimal reaction temperature is set at 180℃through systematically contrasting. The desired products can be easily obtained at low hydrothermal temperature needless of high-temperature sintering under inert gas protection.Among several projects of template-interface synthesis method, as-synthesized MoS2 samples had the highest degree of crystallization using carbon disulfide and sulfur as sulfur source. Though comparing with samples after sintering, it was more advantageous to crystal crystallized at high-temperature sintering under inert gas protection.Brownish red ammonium tetrathiomolybdate with high purity and octahedron morphology were synthesized at 60℃for 1h, and the crystals grow well with integrated and regular appearance. According to the results of comprehensive thermal analysis, ammonium tetrathiomolybdate decomposes and releases molybdenum trisulfide in the temperature range of 180-230℃, also gives off two ammonia molecules and a hydrogen sulfide molecule. In the temperature scope of 310-470℃, molybdenum trisulfide not only continue to decompose during the endothermic reaction process but also release a sulfur atom, and the crystal shape of solid molybdenum disulfide changes accompanied by exothermic phenomenon. More importantly, the technique was simple and easy to operate, and the use of toxic hydrogen sulfide gas was avoided. By comparison, MoS2 were prepared by liquid phase reduction method using ammonium tetrathiomolybdate as raw material and different reductant, the effects of using hydroxylamine hydrochloric as reductant were the best, micro/nano-sized MoS2 prepared by wet solid-phase mechanical milling method, hexagonal phase MoS2 with good phase and crystal shape were obtained at room temperature needless high temperature treatment.