Controllable Synthesis Of Chalcogen Selenium, Tellurium, Lead Selenide And The Study Of Their Property

In this dissertation, liquid phase routes have been successfully developed to synthesize nanostructure materials, such as, selenium, tellurium and selenide semi-conducting materials. One-dimensional (1D) Se nanostructures have been synthesized by a simple reduction process, phase transfer, crystallization and shape evolution on liquid-liquid interface at room temperature. Two-dimensional (2D) bamboo raft-like nanostructures have been synthesized. In addition, the solvothermal technique is introduced to the preparation of the Te nanotubes and PbSe microspheres with interesting morphology. As-prepared inorganic nanomaterials were characterized and the growth mechanisms were investigated. The main results can be summarized as following:1. Synthesis of 1D selenium nanorods.The uniform trigonal Se (t-Se) nanorods have been synthesized on liquid-liquid interface with special property by the crystallization from amorphous selenium (a-Se) at room temperature. Firstly, the reduction of selenious acid solution with hydrazine hydrate in the presence of poly(vinylpyrrolidone) (PVP) can produce a stable dispersion of uniform and amorphous selenium particles with a size of 100 nm. Secondly, further addition of a solvent with low polarity such as n-butyl alcohol into this aqueous solution and mild stirring result in the transportation of a-Se particles onto a liquid-liquid interface between water and n-butyl alcohol. Subsequent crystallization and shape evolution on this interface occurred and finally resulted in the formation of singe crystalline selenium nanorods. This process has been traced by scanning electron microscopy (SEM), ultra-violet-visible (UV-Vis), and X-ray diffraction (XRD). The interface formation and the rearrangement of amphiphilic molecules play very important roles in the formation of the uniform Se nanorods.2. Synthesis of 2D bamboo raft-like single-crystalline Se superstructures. High-yield synthesis of bamboo raft-like single-crystalline selenium superstructures has been realized for the first time via a facile solvothermal approach by reducing SeO₂ with ethylene alcohol in the presence of cellulose acetate (CA). Their lengths and widths of the rafts both reach several tens micrometers, even the widths are longer than the length for parts of them. The thicknesses of these rafts are about tens of nanometers. The lateral direction of the raft is smooth, while longitudinal direction, sawtooth-like. The tip of a single rod comprises many crystal whiskers with the diameter less than 20 nanometers. The formation of raft-like Se has gone through several processes, such as reduction, self-assembly, crystallization. Firstly, the CA will swell and dissolve at 160℃in ethylene alcohol (EG); These fibers from CA will stretch with the temperature rising and provide a frame for the aggregation of Se atoms. Secondly, selenium atoms reduced from SeO₂ will be adsorbed at the surfaces of these fibers with the functional sites. Owing to its intrinsic anisotropic structure, the crystallization of Se proceeds along the c-axis to form one dimensional structure, which leads to the formation of nanorods. The fibers with flexibility and flexual character will become straight due to the rigidity of Se atoms anisotropic crystal growth along the c-axis. The balance and/or their synergistic effects of both intermolecular hydrogen bonds and Van der Waals forces together could make the nanorods hold together and connect each other from their laterals and thus form bamboo rafts. At the same time, the crystallization process is finished for a-Se from amorphous state to trigonal crystal due to stability. It is very possible that there is large difference in properties for the special structure nanomaterial.3. Synthesis of Te nanotubes and PbSe microspheres.Single crystalline nanotubes of t-Te have been synthesized on a large scale by a simple solvothermal reduction route, employing tellurium dioxide (TeO₂) as tellurium source and ethylene alcohol (EG) as both reductant and solvent in the surfactant presence of cetyltrimethyl ammonium bromide (CTAB). The shape of cross-section for samples shows wedge-like in the upper reaction condition. Although, t-Te nanotubes could also been prepared while CA is used as surfactant under other identical experimental conditions, the shape of cross-section of the nanotube is regular hexagon.PbSe microspheres with novel structures been solvothermally prepared by using Se powder as Se source and lead acetate as lead source in EG without any surfactants. These microspheres are composed of ultrathin fold films. In contrast, PbSe polyhedrons have been synthesized under other identical experimental conditions if SeO₂ is used as Se source instead of Se powder.