Controlled Synthesis And Property Of Cu-based Binary And Ternary Metal Sulfide Materials

As important semiconductor materials, Cu-based sulfide micro/nanomaterialshave attracted considerable attention owing to their potential use in optical devices,photovoltaic solar cells, bio-tagging, lithium-ion battery, electrochemistry andphotocatalysts, etc. However, the unique photoelectrical properties ofmicro/nanomaterials exhibit distinct microstructure (shape, size) and compositiondependence. Thus, for recent years much attention has been paid to rational designand precise control over the structures, morphologies and composition of Cu-basedsulfide micro/nanomaterials. Many synthetic techniques of Cu-based sulfides havebeen reported. However, conventional solid-state and gaseous-state strategies havemany shortcomings, such as they always require complicated steps and drasticconditions, etc. Comparatively, solution-phase synthetic route effectively reduces sideeactions, shortens reaction time, increases yields and improves reproducibility forobtaining desired micro/nanomaterials. Additionally, microwave-assistedsolvothermal method could provide a relatively simple, green and economical way tosynthesize nanostructured Cu-based ternary metal sulfide materials.Accompanied with the development of the hydrothermal/solvothermal method, apromisingly derivative strategy known as “a mixed solvent method” has been rapidlydeveloped. The mixed solvent is often composed of two or more components, thus itsproperties can be tuned by changing the components and volume ratios, achieving some appropriate synthetic conditions to the desired nanostructures. Recent advanceshave shown that the use of mixed solvent in some cases can be rather effective inproducing micro/nanomaterials with unique morphologies or new nanoarchitectures.The mixed solvent method is also found to be rather effective in the synthesis ofCu-based sulfides with unique nanostructures, especially with the presence of smallorganic amines. In many cases, these small organic amine molecules can play the roleof effective structure-directing agents, in assisting the anisotropic crystal growth.In this paper, Cu-based binary and ternary metal sulfide of have beensuccessfully synthesized by a facile solvothermal method. The different morphologies,microstructures and compositions of the products could be controlled by addition ofsurfactants, mixed solvents and inorganic acid radical ions or simple adjustments ofthe reaction parameters (time, temperature and starting materials). The main researchresults are as follows:First of all, the flake-like CuS nanostructures have been successfully synthesizedby a facile solvothermal method. The other CuS structures (concaved cuboctahedrons,multilayer flower-like, wool ball-like and rose-like) could be obtained throughchanging the reaction parameters (reaction times, surfactants and mixed solvents). Inthe same system, a facile route for the synthesis of high quality CuS mesoporousstructures was developed with thiourea as sulfur source. Investigation results showthat CuS nanoparticles show good photocatalytic activity and capacitive propertiebecause of their mesoporous structures. We have demonstrated anin situ synthesismethod for fabricating MWNT-CuS hybrid nanostructures, and studied theirphotoresponse.In addition, three types of copper sulfides including CuS, Cu7S4and Cu9S5weresuccessfully synthesized under different concentrations of ethylenediamine in a liquidphase synthesis process. The whole shape evolution of Cu7S4microstructures could bemanipulated by adjusting the concentration of ethylenediamine. This study indicatesthat the coordination chemistry of ethylenediamine ligands and copper cations exertsvital effects on the formation of dendritic structure. Furthermore, the experimental conditions such as the reaction temperature and time are also observed to impact themorphology of copper sulfides. The structures of Cu7S4with snowflake-likemorphology provided special paths for the ion diffusion. Therefore, apart from theexcellent discharge rate and good stability, Cu7S4exhibits also a high specificcapacitance of1303.01Fg1at a current density of5Ag1.Finally, metastable cubic zincblende and hexagonal wurtzite CuInS2nanocrystalswere successfully synthesized by a facile microwave radiation method. Themorphology, structure and phase composition of the as-prepared products wereexamined, and the results demonstrated that high-purity and uniform CuInS2nanocrystals were obtained. Further investigation revealed a structural evolutionprocess from cubic zincblende to hexagonal wurtzite with increasing volume ratio ofethylenediamine and ethanol from1:30to1:1at160oC. In addition, the opticalabsorption property of samples was also studied. It was found that the as-synthesizedcubic and hexagonal CuInS2nanocrystals had band gaps of1.503and1.470eV,respectively. Thanks to the superior optical absorption properties for visible light,CuInS2nanocrystals may have potential applications in various nanostructuredoptoelectronic devices. The possible formation mechanism of the product, namely“phase transformation”, was systematically studied.