Study On Structure And Morphology Control Of CnS And CdS Nanoparticles Prepared By Hydrochemical Method And Their Assembling Effects

The properties of nanoparticles are essentially regulated with their structure and morphologies. Therefore, it is extremely important to know how to control their structure and morphology, mainly including crystal structure, the particle size, shape and its crystallinity. ZnS and CdS semiconductor nanoparticles have special properties in some fields such as photoelectricity, magnetism, catalyse and energetics and so on, which is closely related to their different structures and morphologies. So it is very necessary for the industrialization to prepare ZnS and CdS semiconductor nanoparticles with controllable particle size, shape and crystallinity and their assemble products.First, according to the theoretical analysis and experimental study, the mechanism for structure and morphology control of ZnS and CdS nanoparticles prepared by homogeneous precipitation was revealed, and then the growth unit model and growth mechanism model were established:(1) Based on the design of monodispersed system, microwave heating, spraying materials and homogeneous precipitation technology were adopted to assure the uniformity of the temperature and concentration in the solution. It was found that every nucleation was accompanied with the abrupt change of solution conductivity, thereby the technology of nucleation at high temperature (below 80C)-growth at low temperature (60C) was put forward. Adopting this method, the particle sizes of monodispersed ZnS and CdS nanoparticles were controlled from 4nm to 100nm to utilize the time domino effect of particle growth.(2) Both zinc blend and wurtzite types of ZnS and CdS crystal take [Zn(Cd)-S4]6- and [Zn(Cd)-S4]6+ as their coordination structure, but they have the opposite crystal positions. For zinc blend-type crystal, the growth rate of every crystal face is V<111><001> V<111> so the growth habit of the crystal appears the characteristic of tetrahedron and the crystal is often in the shape of tetrakisoctahedron. For wurtzite-type crystal, [Zn(Cd)-S4]6- and [Zn(Cd)-S4]6+ with different crystal positions distribute in the form of layers along c axis, where the two layers of tetrahedrons whirl 60 around c axis, so the crystal is mainly like hexagonal cone. Under the experimental conditions, NO3- SO42-and Cl- had no effect on the structure and morphology of ZnS. However, blend-type CdS was obtained in NO3- and SO42- system, and wurtzite-type CdS was obtained in Cl- system. This was due to the coordination of Cl- and Cd2+, which changed the supersatration in the solution and the connection patterns of growth units. Cl' anions partly took place of S2- anion, and absorb Cd2+ to move toward it because ofits negative polar higher than S2- anion. Then the produced moment made the 2k layer of anion coordination tetrahedron whirls 60 along c axis from the 2k+l layer one. That is why wurtzite-type CdS was obtained in Cl- system.(3) In the solution, colloidal core and anion coordination tetrahedron were co-existing. When the supersaturation was higher, the growth of particleswas mainly subject to colloidal core and poor crystallinity products were obtained. On the contrary, anion coordination tetrahedron played a more important role and powders with rule shape and better crystallinity were obtained. These growth units were absorbed and join the crystal lattice on the growth interface through collision and aggregation.(4) The powders with better crystallinity and double cone or tetrahedron shape were obtained after amorphous ZnS and CdS were treated by solventthermal method, where blend-type CdS appeared the tetrahedron, but wurtzite-type CdS was in the shape of cone. This technology had such advantages as moving water and impurities, protecting CdS from oxidation and easy recycling organic reagent and so on.Then, ZnS(CdS)/Al2O3 and CdS/Al assembly products were prepared by the bifunctional thiols of CH3CSNH2. In the mixing technology, ZnS(CdS) nanoparticles were attached to the surface of AI2O3 particles, which was very simple. In the originally composed techn...