Study On Preparation And Catalytic Properties Of Layered Molybdenum Disulfide And Their Composites

In recent years,energy crisis and environmental pollution solutions based on electrocatalytic and photocatalytic technologies have attracted much attention due to their multiple advantages such as green,efficient and significant economic benefits.The design and development of efficiency,low-cost and stable non-noble metal catalysts is the key to improving the efficiency of photocatalytic and electrocatalytic reactions and promoting the efficient completion of energy conversion.As a typical representative of two-dimensional transition metal dichalcogenides（TMDs）materials based on earth-rich elements,layered molybdenum disulfide（MoS₂）,has excellent optical and electrical properties and is a potential non-precious metal energy conversion catalyst.It is well known that two-dimensional MoS₂ has three main phases 2H,1T and 1T’.However,the most stable 2H-MoS₂ has a poor catalytic effect,and only the asymmetric edge of the layered structure exposes few active sites as the catalytic reaction center.At present,there are few regulation strategies for the edge active sites of MoS₂,and the stability of the regulated samples is generally poor.In view of this,this study focuses on how to obtain the stable active edge of MoS₂ catalysts and break the contradiction between activity and stability.Porous MoS₂ nano islands and their composites with high catalytic activity were designed,and the synergistic enhancement mechanism of catalytic activity and stability was revealed.The main research contents and results are as follows:（1）A facile and controllable one-step hydrothermal driven in-situ porousizing of MoS₂ into self-supporting nano islands,which maximizes the exposure of the edges of MoS₂ grains,so as to effectively utilize the stable active sites at the edges of MoS₂ as efficient hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）bifunctional electrocatalysts.The results of electrocatalytic studies showed that highly active and non-aggregated nano islands greatly enhances the bifunctional electrocatalytic activity of MoS₂ for HER/OER.At low overpotentials of 248 and 300 m V,the porous MoS₂ nano islands could generate a current density of 10 m A·cm^-2 in HER and OER,and have low Tafel slopes of 84 m V·dec^-1 and 220 m V·dec^-1,respectively.Compared with the MoS₂ nanosheets,the overpotential of nano islands morphology is reduced by nearly 200m V in the electrocatalytic reaction.In addition,porous MoS₂ nano islands have excellent OER activity in alkaline electrolyte,and even exhibit better performance than the current commercial Ru O₂ catalyst.This discovery will be another effective strategy to promote robust 2H-phase,instead of 1T/1T’-phase,MoS₂ to achieve efficient endurable HER/OER bifunctional electrocatalysts,which is expected to further replace precious metal catalysts in industry.（2）By incorporating Fe₃O₄ nanoparticles as the magnetic substrate,bridging the synthesized porous MoS₂ nano islands（MoS₂ NIs）on it,a highly efficient magnetic photocatalyst system of MoS₂@Fe₃O₄ was constructed.The Physical and chemical characterization results show that the synthesized composite samples have both magnetic properties and strong visible light absorption.Their multiple pore structure are conducive to enriching the catalytic reaction active sites.At the same time,a series of photocatalytic experiments show that MoS₂ NIs@Fe₃O₄ has excellent degradation effect on typical RhB dyes.After 10 min of dark adsorption and 30 min of light-driven catalysis,the removal rate of RhB dye molecules in aqueous solution could achieve more than 95%,and the degradation efficiency still maintained more than 90%after 5 cycles.Compared with anionic dyes,MoS₂ NIs@Fe₃O₄ possessed selective degradation ability for cationic dyes.The strategy of constructing a magnetic photocatalytic system by coating the porous structure on the surface of the magnetic core solved the difficulty of secondary pollution caused by nano catalysts in the field of photocatalysis.Its high photocatalytic activity also makes it have greatly potential application in photocatalytic treatment of water pollution.