Hydrothermal Synthesis And Characterization Of Metal Sulfides And Ferric, Manganic Oxides Nanostructures

Metal sulfides and oxides are important materials with a wide range of application. Metal sulfides nanomaterials are a group of important semiconductors. For example, ZnS is one of the most important semiconducts with a wide bandgap of 3.72 eV, which was widely used in the fields of semiconductors, pigments, photoluminescence, solar cells, infrared windows, gas sensors. MnS is also a semiconduct with a wide bandgap, which was usually used as the buffer layers of solar cells. When a small quantity of ions, such as Cd²⁺, Zn²⁺, was doped, the doped MnS shows excellent magnetic property. Metal oxides nanomaterials are really a group of functional materials, which not only have excellent properties such as piezoelectricity, chemical sensors, light sensors as well as the corresponding blocks, but also have a wide range of potential application in transparent electronics, piezoelectric transducers, light-emitting devices, etc. for the shape and size effect. At present, the preparation of metal sulfides and oxides has made a great progress, but their shape-controlled synthesis is not solved still. Therefore, large-scale, cost-effective, simple and practical synthesis and assembly of metal sulfides and oxides with different shapes is of importance for the fundamental research and application.We prepared a few kinds of metal sulfides and oxides with different shapes using a simple hydrothermal method assisted by organic molecules or surfactants, including dendritic, spheric, cubic, hollow cubic and flower-like PbS, spheric ZnS, SnS and CdS, spindle-type α-Fe₂O₃, multi-armed γ-MnOOH, ect. The reation time, temperature, reactant concentration and surfactants were investigated in order to learn about how they affect the shape of the products. Finally, we made a primary study of the formation mechanism of the synthesized nanomaterials with different shapes.We synthesized dendritic PbS nanostructure, which was conglutinated by the nanoparticles, via a low temperature (80℃) hydrothermal method assisted by the surfactant, SDS. We used Pb(Ac)2 as the lead source and TAA as the sulphur source. When another surfactant, CTAB, was added as a reactant, the obtained PbS nanostructure was not dendritic nanostructure but spheric PbS, which was also conglutinated by the nanoparticles. Maybe the formed micelles of CTAB in the solution played the role of soft template, which confined the conglutianted nanoparticles to form the spheric structure. When the reaction temperature wasincreased, the shape of the obtained products was changed. The hollow cubic PbS was obtained when the reaction temperature increased to 120℃. When it was increased to 160 ℃, the obtained product was cubic PbS. When the reaction temperature is 120 ℃ and the sulphur source was replaced by (NH₂)₂CS, the obtained product was 1D PbS nanorod. In addition, When the surfactant, SDS, was replaced by CA or CTAB, we can obtain the flower-like PbS nanostracture.According to the synthesized principle of spheric PbS nanostructure metioned above, we prepared other spheric metal sulfides successfully,such as ZnS, SnS, CdS, etc. This further proved that It is the formed micelles of CTAB in the solution play more important roles in forming the spheric nanostructure as a soft template, not the crystalline structure of the obtained products at low synthesized temperature. When the reaction temperature was increased, especially to 160 ℃, We can not obtain the spheric ZnS nanostructure again, but the triangle ZnS nanoparticles. The obtained SnS products were mainly the plate-like structure. Although the CdS products still have the trend to form spheric structures, which was conglutinated by the nanoparticles, the shape is not spheric again. This proved that the crystalline structure of the obtained products plays more important roles in deciding the shape of products at high reaction temperature than the formed micelle of CTAB as a soft template.We prepared a kind of spindle-type α-Fe₂O₃ via a facile hydrothermal method using glycol as the assisted agent and NH₄Cl as the mineralized agent. The ratio of major axis and minor axis of the synthesized spindle-type α-Fe₂O₃ is about 2/1. We found that the starting reaction concentration of Fe³⁺ has great effect on the shape of the products. When it increased, the length of the minor axis of the α-Fe₂O₃ was elongated and the shape of α-Fe₂O₃ nanoparticles was transformed into sphere from spindle-type. The magnetic property of the α-Fe₂O₃ nanoparticles with different ratio of major axis and minor axis were investigated by the vibrating sample magnetometer(VSM). The results show that they have two kinds of magnetic properties, diamagnetism and paramagnetism.We synthesized a kind of multipods γ-MnOOH via a low temperature hydrothermal method based on the reaction of polyglycol, which has a long chain structure and reductive property, and KMnO₄. When the volume of PEG was controlled or an appropriate mount of surfactant, CTAB, was added as the starting reactant, the obtained product will be 1D γ-MnOOH nanorod or nanowire only. It can easily realize the selective growth of γ-MnOOH multipods and 1D nanowire. When the reaction temperature was increased to 160 ℃, thenumber of the arms of the obtained y-MnOOH multipods were more uniform. They are mainly five-armed γ-MnOOH, 60%. Maybe the stronger reductive property of polyglycol led to the multiple growth centers of γ-MnOOH, When the reaction temperature was increased.