Morphology-controlled Synthesis Of MoS₂ Micro/Nanomaterials And Their Performance

Two-dimensional transition metal sulfides have attracted widespread attention owing to their unique layered structure and physical/chemical properties.As a member of the transition metal sulfides,MoS₂ shows many unique properties in many fields.The compositions and morphologies of MoS₂ have a significant impact on the catalytic performance,so it is a great challenge to synthesize MoS₂micro/nanostructures using facile methods.In this dissertation,morphology-controlled MoS₂ catalytic materials were synthesized by the facile hydrothermal methods and their catalytic performances were studied.Then,the MoS₂/r GO composites were synthesized to improve the catalytic performance of MoS₂.The main results are as follows:（1）MoS₂ nanoflowers with the size of 210-430 nm in diameter,which is constructed with nanosheets,were hydrothermally synthesized using sodium molybdate dihydrate（Na2Mo O4·2H2O）as the molybdenum source and potassium thiocyanate（KSCN）as the sulfur source.The influence of precursor ratio,reaction temperature and p H values on the compositions and morphologies of MoS₂ were investigated.Then,the electrocatalytic hydrogen evolution reaction performance was tested,MoS₂ nanoflowers showed enhanced electrocatalytic activity compared with commercial MoS₂.The onset potential was 117 m V,the current density was 10 m A/cm2 at 255 m V,and the Tafel slope was 78 m V/decade.The MoS₂ nanoflowers exposed more amounts of unsaturated S atoms on the edge sites of the MoS₂ nanosheets,resulting in the excellent electrocatalytic activities.In addition,the photocatalytic hydrogen evolution performance of MoS₂ nanoflowers was studied and hydrogen evolution rate was 320 μmol/（g·h）.（2）MoS₂ nanoflower catalysts were synthesized by the hydrothermal method using molybdenum trioxide（Mo O3）as molybdenum source and potassium thiocyanate（KSCN）as sulfur source.The influence of Mo O3 types,precursor ratio,and reaction temperature on compositions and morphologies of MoS₂ was investigated.Then,the electrocatalytic hydrogen evolution reaction performance was investigated.The results indicated that the current density was 10 m A/cm2 when the overpotential was 240 m V and Tafel slope was 72 m V/decade,which was superior to that of the commercial MoS₂ under the same conditions.（3）In order to overcome the deficiency of bare MoS₂,the MoS₂/r GO composites have been successfully synthesized via the hydrothermal method.First,the graphene oxide was synthesized with Hummers method.Then,graphene oxide（GO）was added into hydrothermal system as carriers.Finally,MoS₂/GO were reduced into MoS₂/r GO in the presence of hydrazine hydrate（N2H4·H2O）.The electrocatalytic hydrogen evolution reaction performance of MoS₂/r GO composites were investigated.The results showed that the current density was 10 m A/cm2 at the overpotential of 220 m V and Tafel slope was 68 m V/decade,implying that the catalytic activity was significantly enhanced.（4）MoS₂ microflowers with 3.9-5.8 μm in diameter were successfully fabricated through hydrothermal reduction of Na2 Mo O4·2H2O with diethyldithiocarbamate trihydrate（C5H12NNa S2·3H2O）.The influence of precursor ratio and reaction temperature on the compositions and morphologies of MoS₂ was investigated.The results indicated that the higher temperature was essential for the formation of MoS₂ microflowers.The catalytic performance towards nitrobenzene hydrogenation was investigated.The results indicated that the conversion rate of nitrobenzene was 100 % and the selectivity of aniline was also 100 % at 100 °C for 6 h under the atmosphere of 3 MPa H2.MoS₂ microflowers exposed the higher amounts of coordinatively unsaturated Mo species,so it exhibited a higher activity than commercial MoS₂ toward catalytic hydrogenation of nitrobenzene.