Study On Hydrothermal Synthesis Of One-dimensional CdS Nanomaterials And Their Derivatives

In recent years nanoscale materials, especially with one-dimensional (1D) nanostructures such as rods, wires, and tubes, have attracted intensive investigations due to their unique shapes, size-dependent properties and the intriguing prospects for developments in novel electro-optical applications and catalysis. Obtaining new materials via a relatively simple route and developing the morphology-controlled synthesis methodologies are a goal of great interest in materials chemistry.Hydrothermal method, which is known as a solution-based chemical method, might provide an effective and convenient route to generate nanoscale materials of transition metal sulfides with great advantages such as high efficiency, inexpensive equipments, and dispensing with any inert atmosphere protections. It has been developed and widely used in preparing 1D nanostructured materials, zeolites and ceramic materials etc. It is also one of the most promising methods for controlling product morphology, size, and size distribution in nanomaterials fabrication.As one of the most typical and important semiconductors, CdS has critical applications in many fields, such as solar cells, nonlinear optics, photocatalysis and so on. In this work, 1D CdS nanomaterials and their derivatives, including Zn_xCd₁-xS and Cd₁-xMn_xS, and several other binary transition metal sulfide nanocrystallites, MS (M= Zn, Cd, Co, Ni), have been successfully prepared using hydrothermal method. The products were characterized by TEM,SEM,XRD, SAED, EDS, XPS, ICP, Raman, UV-vis, and PL, respectively.Through three different series experiments: (1) Hydrothermal synthesis of CdS nanorods with four different coordination agents (2) Hydrothermal synthesis of different Chalcogenides with four different salts by using ethylenediamine as the coordination agent (3) Hydrothermal synthesis of CdS nanorods with different sulfur sources, an important result which is differ from the previous claim in the literatures is obtained. That is neither the stability of the intermediate complex nor coordination configuration (bidentate or monodenate) is the critical factor for the shape control ofCdS nanocrystals in the hydrothermal process. Therefore, we proposed a new perspective: the origin of the morphology of CdS crystallites may relate to the geometry structure of the intermediate complex. Besides, following effects are also observed: the coordination agent and its concentration are critical in our synthesis progress, and the sulfur source will not affect the shape of CdS but will control the diameter of CdS nanorods. Thus, based on the experimental results including effects of different sulfide sources, different templates and different sulfides, a complex structure-controlling mechanism was proposed in the hydrothermal process.ZnxCdi.xS, whose physical and chemical properties can be tuned by changing the constitute stoichiometries, is a promising ternary semiconductor material. ZnxCdi.xS such as Zno.72Cdo.28S> Zno.48Cdo.52S and Zno.24Cdo.76S nanorods were successfully synthesized by one-step hydrothermal process in this work. The PL peak position of ZnxCdi-xS is progressively red shifted with increasing the concentration of cadmium.As for Cdi.xMnxS nanorods, the UV absorption shoulder and the two luminescence emission peaks have shifted in different way as the mole ratio of manganese in the nanorods varies. From the characterizations of PL, XRD, TEM and SEM, it can be concluded that manganese is doped into the CdS nanorods and does not present as free MnS impurity. When Cd2+ is partially substituted by Mn2+ ions, the absorption band edge of Cdi.xMnxS has a slight blue shift relative to the pure CdS. As the manganese concentration of Cdi_xMnxS nanorods increasing, the strong luminescence emission peaks located in the reagion of 540nm⁵60nm show a small red shift while the weaker emission peak at 469 nm remains unshifted. From all these observations, it is reasonably suggested that the strong peaks are attributed to the large spectra overlapping of the emission from Mn2+ centers and that from surface states, while the peak at 469 nm may be owed to the deep trap states of the semiconductor.