Study On Liquid Phase Synthesis And Reaction Mechanism Of Zinc Sulfide Nanomaterials

Nanomaterial is the basis and core of nanotechnology, which is the center of information age of the 21 st century. Nanomaterial has unique properties because the wave behaviors of electrons and the interactions between atoms are impacted in nanometer scale. Nanomaterial has aroused wide concern and further study now.Nanostructure ZnS is one kind of excellent semiconductors with a direct broadband gap. It has two types of crystal structures, sphalerite structure under low temperature and wurtzite structure under high temperature. The band gap of cubic structure ZnS is 3.72 eV, while the hexagonal structure is 3.77 eV. ZnS has excellent electro-optical property with yellow and green base shades. It will be widely used in photoelectric regulator,optical transmission,optical sensors,photocatalysis and other optical devices, and it will be the hot spot in materials research. In our work, simple raw materials and methods were used to synthesize epigranular ZnS nanomaterials with regular topography.(1) ZnS microspheres were synthesized by low-temperature hydrothermal method with zinc acetate and sodium thiosulfate as raw materials, CTAB as surfactant. The product is cubic solid sphere with good distribution and uniform particle size. The results showed that the synthesis process of ZnS microspheres is more sensitive of temperature than reaction time. The particle size and crystallinity are not changed while prolonging reaction time after 12h. The surfactant can improve the sphericity and the dispersion of particles. There are Zn-S bond absorption peaks in the infrared region. The principle of this method is clear and simple with high quality product, so it has high practical applicability.(2) ZnS hollow spheres were synthesized in ethylenediamine-ethanol homogeneous system with zinc acetate and CS2 as raw materials and CTAB as surfactant. The hollow sphere is 100nm in diameter with a shell of 30nm. The XRD analysis shows that the product is cubic structure with a high purity but a lower degree of crystallinity. The particle size distribution of ZnS hollow spheres is narrow, but the dispersivity is poor. It is due to the high surface energy of small particles. There are two characteristic absorption peaks of Zn-S at 1132cm-1 and 655cm-1 and without other absorption peaks in infrared spectrogram, which can prove the high qurity of ZnS hollow spheres. A strong absorption peak appears at 226nm in UV-vis spectra with a blue shift of 118nm. The intermediate product of H2S provides not only sulfur source, but also the soft template. The hollow spheres are formed by ZnS particles accumulating around the soft template. Besides, reaction time,reaction temperature and stirring rate have effects on the hollow spheres.50℃for 2h and low speed form the better synthesis conditions.(3) Cubic ZnS with uniform particle size distribution and high crystallinity and sphericity were synthesized by a simple hydrothermal method with zinc acetate and thiourea as raw materials.The doped ZnS microspheres were both synthesized by silver nitrate as doping agent under the same conditions. Doping can refine grains, so doped ZnS microspheres have a larger particle size than undoped ZnS microspheres. Ag doped ZnS microspheres appear absorption peaks at 613cm-1 in the infrared spectrogram, but has no absorb in UV-visible range because its diameter is larger than 1000nm. Doped and undoped ZnS microspheres appear a wide light emission peak at 473nm, which can be attributed to recombination luminescence between honor of sulfur vacancies and silver holes and acceptor of silver-related and luminescence due to the defect energy level caused by sulfur vacancies.