Preparation Of Nano-MoS₂by Hydrothermal Method

Having similar layer structure to that of graphite, the hexagonal system molybdenumdisulfide（MoS₂）are easily to be slipped and therefore presents a lower frictionalcoefficient, which can be used as lubricating materials in machinery, electronics andother fields. Nano-sized MoS₂has more superior performance than normal particles dueto size effect, especially as lubricating materials, which appears good adhesion to thesurface of friction materials, high total covering degree, improved anti-wear andantifriction performance, so nano-MoS₂has an obviously broad application prospect aslubricating materials; Moreover, owing to good performance in optics, electricity andcatalyst domain et al., nano-MoS₂has aroused researcher’s great interests in recent years.The synthesis process of nano-MoS₂is the foundation of application. It is vitallysignificant that how to select proper sulfur sources and reducing agents as well as thesynthesis process, and together with the favor of electrostatic effect and steric-hineranceeffect due to the addition of modifier in the preparation, to prevent nano-MoS₂to beagglomerated, which makes it possible to present fully superior performance fornano-MoS₂.In this research, MoS₂were successfully synthesized via hydrothermal route underPH=1⁶and facile temperature conditions at160℃-240℃in different systems usingammonium heptamolybdate (（NH₄）₆Mo₇O₂₄.4H₂O) as Mo-source, thiourea （CS（NH₂）₂）and thioacetamide （CH₃CSNH₂） as S-source and reducing agent respectively. X-raydiffraction （XRD）, scanning electron microscopy （SEM）, Energy dispersivespectrometer （EDS） and X-ray Photoelectron Spectrum （XPS） techniques were used tocharacterize the samples. The effect of different reaction conditions, such as the moleratio of Mo to S, PH value, reaction temperature and holding time on the morphology,crystalline degree and purity of the resultants were investigated. Being addingseparately into the reactants, the effect and mechanism of CTAB, SDBS and PVP were studied as to prevent the reunion of resultants particles and modify the morphology andsize as well.Ball-like pure MoS₂with good crystallization and100-200nm average particle sizewere successfully prepared. It is showed that the optimum synthesized parameter forMoS₂spheres with high crystallization are as follows: for the reaction system usingthiourea as S-source and reducing agent, the mole ratio of Mo to S can be set as1:4,with PH=2, reaction temperature at220℃and reaction time of24h; for the systemusing thioacetamide as S-source and reducing agent, the mole ratio of Mo to S can beset as1:2, with PH=6, reaction temperature of220℃and reaction time of24h. Besides,all of the surfactants played a certain role in dispersion and morphological control andhelped to hinder the formation of MoS₂layer stacking structure to some extent also.CTAB presents better modifying performance than SDBS and PVP in the system usedthiourea as S-source and reducing agent. CTAB and PVP are both strong dispersions instructure confining for thioacetamide system, furthermore, about100nm MoS₂microspheres with high crystallinity and purity were synthesized in the control of PVPowing to stronger steric-hinerance effect than CTAB. The research provides a newmethod to synthesize100nm ball-like nano-MoS₂with high crystallinity and purity byhydrothermal reaction. The confirmed experimental conditions are as follow: using（NH4）6Mo7O24.4H2O as Mo-source, and CH3CSNH2as S-source and reducing agentswith a mole ratio of Mo to S of1:2, PVP is chosen as dispersant and modifier in thereaction solution system with reaction condition as PH=2, reaction temperature of180-220℃and holding time18-24h.