Preparation, Characterization And Application Of MoS₂, WS₂ Nanomaterials

WS₂ and MoS₂ hollow spheres, MoS₂ nanorods, sheets and MoSe₂ nanocrystalshave been successfully synthesized via low-temperature solvothermal andextraction-solvothermal methods, respectively. The tribological properties ofas-prepared MoS₂ hollow spheres were tested.(1) (NH₄)₂MoS₄ and (NH₄)₂WS₄ crystals were firstly prepared according toliteratures. Then, (NH₄)₂WS₄ crystals were used directly as precursor, pyridine assolvent and sodium borohydride (NaBH₄) as reducer, and maintained at 190℃for 48 h.The results show that, WS₂ sheets were attained when no modifier was added, whilehollow sphere-like WS₂ was obtained when using trioctylamine (TOA) ormethyltrioctylammonium chloride (Aliquat-336) as modifier.(2) The optimal conditions were first explored for the extraction ofMoS₄^2-and WS₄^2- by amine extractants-trioctylamine and methyltrioctylammoniumchloride; MoO₄^2- by methyltrioctylammonium chloride, respectively. At the same time,the extractive conditions of MoS₄^2- and WS₄^2- by aniline were also explored.(3) All the as-obtained organic phases containing extracted species were put intoTeflon-lined stainless steel autoclaves and reducer such as hydrazine (N₂H₄·H₂O),sodium borohydride or selenium (Se source) was added, and maintained at 190℃for48 h or 24 h. MoS₂ hollow spheres, nanorods and sheets were obtained by adjustingthe amount of hydrazine. Using sodium borohydride as reductant, WS₂ hollow sphereswith sizes of about 100-200 nm were synthesized. MoSe₂ nanocrystals were alsoprepared by using selenium as selenium source at the same time. (3) In aqueous solution, by the reaction of piperazine andtris(2-amino-ethyl)amine with WS₄^2- respectively, two precursors (pipH₂)[WS₄] and(trenH₂)[WS₄]·H₂O (pip=piperazine, tren=tris(2-amino-ethyl)amine) were prepared,direct pyrolysis of the two processors at 850℃for 12 h in an argon atmosphere, WS₂sheets and nanorods were synthesized, respectively.All the above products were characterized by X-ray power diffraction (XRD),X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM),scanning electron microscopy (SEM), high revolution transmission electronmicroscopy (HRTEM) and EDS, respectively, and the formation mechanism weredicussed.(4) The tribological properties of MoS₂ nano-sized hollow spheres (SL-MoS₂)modified by TOA with size of about 15 nm in liquid paraffin (LP) were studied andcompared with those of the commercial colloidal MoS₂ (CC-MoS₂). Results showedthat the as-prepared nanosize hollow sphere-like MoS₂ is a better anti-wear andfriction-reducing additive in LP than CC-MoS₂.