Research On Preparation And Properties Of Sulfide Cobalt Nanocrystallites

Cobalt sulfide （CoS） is a kind of non-toxic and environmentalfriendly material. It has a special octagonal structure that Co²⁺holds sixangles of the octahedron, and S^2-holds the center. CoS has excellentelectronical, optical, magnetic and catalytic performance due to itselectron configuration of the3d orbital. The CoS can be widely used，such as high energy density batteries, supercapacitors, solarphotovoltaic materials catalysts and so on. In recent years,nanostructured cobalt sulfide has become one of the hotspots in thematerial field. In this paper, a detailed study was done that about CoSnanocrystallites preparation by the sonochemical method andmicrowave hydrothermal method respectively.In this paper, system research on the CoS preparation has beendone. The phase compositions, morphologies and the microstructure ofthe CoS nanocrystallites were characterized by X-ray diffraction （XRD）,transmission electron microscopy （TEM） and selected area electrondiffraction （SAED） analysis.Using analytically pure CoCl₂·6H₂O and Na₂S·9H₂O as the rawmaterials, CoS nanocrystallites were prepared by the sonochemicalmethod. In the experiment, systemly study on the sonochemical methodof process factors are done, that including the initial pH value, reactiontemperature, reaction time, ultrasonic power, complexing agents and soon. The results showed that: experiments need to use acetic acid toadjust the pH of the solution to about2.5, and we can get the CoScrystallites, but the morphology of the product is inconsistent, poorcrystallinity. According to the XRD analysis, pH, reaction temperature,ultrasonic power are all important factors on the product that determinethe purity and crystal properties. Reaction time has not very strongeffect on the product. It is useless that using complexing agent for the preparation of CoS pure phase.Preparation CoS nanocrystallites by the microwave hydrothermal.Firstly, hydrothermal synthesis of CoS nanocrystalline is researched.Results show that the hydrothermal method is not conducive to the CoSpure phase. Then it is comfirmed that using the microwavehydrothermal method to get the CoS nanocrystallites. In order tosynthesize CoS crystallites using microwave hydrothermal process,Co（NO₃）₂·6H₂O and TAA were used as source materials. In theexperimental, system study on the process factors are done, thatincluding the pH value of precursor liquid, reaction temperature,reaction time, the molar ratio of S/Co, the concentration of the Co²⁺,complexing agents and so on. The results show that the CoSnanocrystallites suitable process conditions is the precursor solution isalkaline, microwave hydrothermal temperature is180℃, microwavehydrothermal time is greater than or equal to90min and Co²⁺is0.1mol/L, the molar ratio of S/Co is less than or equal to1.0. The differentmicroscopic structure of the CoS can be synthesized by controlling thereaction time. The crystallinity of the CoS nanocrystals graduallychanged for the better with reaction time prolonging. From90min to150min, the structure of the CoS changed into short rod-like fromhexagonal sheet. CoS crystalline becomes weaker while the S/Co molarratio increases. The grain size of CoS is about13nm that usingmethenamine as the complexing agent. Synthesized crystallized CoSthat has hexagonal sheet structure using sodium citrate as a complexingagent. It is not can be obtained CoS using EDTA-2Na and EDTA ascomplexing agents respectively.