Phase- And Shape-controlled Synthesis Of ZnS Nano- And Microstructures Via Solvothermal Method

Being an important wide-band gap semiconductor, ZnS has received great attention due to its unique properties and been widely used in optical coatings, solid-state solar cell windows, electrooptic modulators, photoconductors, field effect transistors, sensors, transductors, and light-emitting applications. ZnS has cubic and hexagonal crystal phases with different properties. Control of the crystal phase of ZnS by altering the reaction temperature or particle size has been reported, and the thermodynamically metastable phase, hexagonal ZnS nanocrystals were successfully produced at a relative low temperature. Both morphology and phase control of ZnS nanostructure are quite important in preparative chemistry and materials science.Employing Zn(NCS)₂(C₅H₅N)₂ as precursor via a one-step solvothermal process, we synthesize phase- and shape-controlled ZnS structures in different solvents. Using ethylene glycol as solvent, highly monodispersed and uniform nanospheres of hexagonal ZnS were obtained, the diameters could be controlled by changing reaction temperature. Nanospheres with diameters of 200, 350, 450 and 80nm were obtained in 160,180, 200, 220℃, respectively. The formation of ZnS spheres can be attributed to the oriented aggregation of the initially formed ZnS nanocrystals.Using ethylenediamine as solvent, lamella complex ZnS 0.5ENdecompose to hexagonal ZnS gradually under 200℃. Under 220℃, flower-like microstructure assembled with nanorods was obtained in pure ethylenediamine for the first time. Using ethylenediamine mixed with small amount of aqueous HNO₃ as medium, cleavage phenomenon of microflower was observed, and the reason of cleavage was discussed. It was found that the cleavage phenomenon had a great relationship with the growth of ZnS nanocrystals, and one hypothesize was raised to explain its reason.Besides, well-dispersed sphere-like microstructures assembled with cubic nanocrystals of ZnS were obtained in hexyl alcohol, most of spheres are solid and some of them are hollow structure. And the reason of formation of hollow spheres was discussed. In distilled water, flower-like microstructures assembled with cubic nanocrystals of ZnS were obtained, and it was observed that concentration of precursor had obvious influences on final shape of ZnS structures.Phase evolution of ZnS in alkanols was discussed, and it was found that only cubic ZnS could be obtained in mono-hydroxyl alkanols. Hexagonal ZnS was formed in polyol with neighboring hydroxy groups. The effect of precursor and optical properties of products were also studied primarily.