Controlled Synthesis Of CdS Nanostructures And Their Photocatalytic Properties

CdS is a classical II-VI group semiconductor material with a direct band gap of2.4eV at room temperature. Owing to its unique properties, CdS is widely used inmany fields such as photoelectric conversion, light-emitting diodes, biologicallabeling, and photocatalytic materials. Since the optical, electronic and many otherproperties of nanomaterials strongly depend on size, shape, and structure, controllingthe morphology and size of nanomaterials has been a crucial issue in nanoscienceresearch. In our experiments, by simply changing the reactants dosage, the ratio ofreactant concentration, and the bath temperature in experiments, CdS nanostructureswith different morphologies have been prepared. Researches focus on the factorswhich result in various morphologies of the products, the photoluminescence andphotocatalytic properties of the products.(1) Cadmium sulfide nanorings were synthesized through a convenient andeconomical chemical bath deposition (CBD) process without the use of any surfactantand template. The components, morphologies, structures and optical properties of theproducts are characterized and detected by many techniques. XRD results confirm thatthe sample can be well-indexed as hexagonal CdS. SEM and TEM show that thediameters of CdS nanorings are about200-250nm and the nanorings are composed ofsmaller nanoparticles. Analyses of HRTEM and SAED reveal the polycrystallinenature of the CdS nanorings. The fluorescence spectrum of CdS nanorings displays anemission peak at565nm. A self-assembly mechanism was proposed for the formationprocess of these nanorings on the basis of a series of time dependent experiments.(2) By simply changing the reactants dosage, the ratio of reactant concentration,and the bath temperature in experiments, CdS nanostructures with different morpho-logies have been prepared. Researches focus on the factors which affect the morpho-logies of products. Results show that CdS nanoparticles, chian-like structures and CdSnanorings are respectively obtained when the concentration ratio of Cd(NO3)·4H2Oand thiourea are1:1,1:2.5and1:5. With the ratio of1:5, chian-like structures,nanorings and nanorings are obtained by increasing reactants dosage. Flower-likestructures, nanorings and nanoparticles are respectively prepared at30℃,60℃and90℃. According to the study of the reactions in the experiments, we can conclude thatthe concentration of S2-ion in the solution is the key factor which results in various morphologies of the products.(3) The photocatalytic properties of CdS nanoparticles, nanorings and flower-likestructures were evaluated by photodegradation of rhodamine B (RhB) underirradiation of visible light. The results of photocatalytic experiments are as follows:(a)RhB can be decomposed under irradiation of visible light but can’t in the dark.(b)RhB can be decomposed in the presence of catalysts but can’t in the absence ofcatalysts.(c) The results of photocatalytic experiments demonstrate that these CdSnanostructures exhibit enhanced photocatalytic activities compared to commercialCdS. What’s more, CdS nanoparticles possess the fastest photocatalytic degradationrate in a long time, but the photodegradation velocity of flower-like structuressurpasses that of the nanoparticles after180minutes.