Synthesis Of Several Nanomaterials By Sol-gel Auto-combustion Method

Nanomaterials with characteristic nanoscale structural dimensions (1-100 nm) have been of interest for more than 20 years and continue to attract attention because of their unique properties. Finding a simple and high yields synthesis strategy of nanomaterials shows great importance for the applications in industry. Combustion synthesis or auto-combustion synthesis is a wide used synthesis method for a variety of conventional materials, characterized by simple process, effective, energy saving and the ability of highly exothermic reactions to be self-sustaining with providing a high combustion temperature (1000-6500k). Then a lot of efforts come to applying this method to the synthesis of nannomaterials:the solution-combustion method, combined with solution method; the sol-gel auto-combustion method, combined with sol-gel method. These two methods show great improvement of the combustion synthesis with a lot of advantages in the synthesis of oxide nanomaterials. In our previous works we have expand the sol-gel auto-combustion method for the synthesis of single metals and alloys. In this work we successfully expand the sol-gel auto-combustion method to other kinds of nanomatirials with a further study of this method in detail. This thesis consists of the following three parts:1) Synthesis of immiscible Alloy by the sol-gel auto-combustion method. Immiscible crystalline NiAg alloy was successfully synthesized by the sol-gel autocombustion method. The structure and composition were examined by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). All evidence supports that homogeneous NiAg alloy with FCC structure was synthesized. The differential thermal analysis-thermogravimetry (DTA-TG) measurement and the contrast research of XRD patterns of the products with a long-time interval show that the alloy has a good thermal stability until 315℃. Unusually some extinction planes are observed in the XRD pattern and HRTEM images. The random distribution of atoms and the large difference between Ni and Ag atom form factors should be regarded as the main reasons for the observation of the extinction planes. The quenching like nonequilibrium thermal process in the combustion and the good complexation of the metal ion in the networks of gels are taken as the key factors for the synthesis of immiscible alloy. And the addition of ethylene glycol in the precursors is found to benefit the formation of NiAg alloy. The choosing of complexing agents, the ratio between fuel and oxidant, the addition of alcohols and other important influencing factors are studied in details.2) Synthesis of kinds of sulfides by the sol-gel auto combustion method. Alloyed wurtzite ZnS, CdS and ZnxCd/-xS (0<x<1) nanocrystals were synthesized by the sol-gel auto-combustion method, using thiourea as complexing agent. The structure, composition and morphology of the products were studied by XRD and transmission electron microscopy (TEM). The composition of the alloyed nanocrystals can be accurately adjusted by tuning the composition of starting materials. The composition dependent optical properties of the products were investigated by UV-visible absorption and photoluminescence spectroscopy. The fuel/oxidant ratio, the temperature for ignition and annealing and other important influencing factors are studied in details. With the ability of accurate control of the composition of ZnxCd1-xS nanocrystal, we successfully fit the cell parameter of the ZnxCd1-xS nanocrystal to that of MnS by composition tuning. And alloyed wurtzite Zn49Cd51S nanocrystals with nearly 15 at.% Mn doped are synthesized. The doping level of Mn in nanoscale sulfide semiconductors is substantially higher than early reports, so far as we know. The structure and composition of the products were studied by XRD. No impurities were found in the products until the doping level increase to 15%. The doping related optical properties of the products were investigated by photoluminescence spectroscopy. With doping Mn in the Zn49Cd51S nanocrystals a characteristic Mn 585nm emission appears and the wide spread defect relating emission diminishes. The intensity of Mn 585nm emission continues to decrease with the increase of doping level.3) The sol-gel auto-combustion assisted synthesis of Carbon nanotubes (CNTs). Carbonaceous solid with cobalt nanoparticles were synthesized by the sol-gel auto-combustion method using Ethylene diamine tetraacetic acid (EDTA) as complexing agent. Multiwall carbon nanotubes are formed by annealing the carbonaceous solid in an inert atmosphere at 450 ℃. The characterizations of the products by scanning electron microscopy, TEM, HRTEM and XRD revealing a tip-growth mechanism of the CNTs, in which they grow with the catalytic metal particles capping the tips. The investigation of the annealing by mass spectrometry combined with differential thermal analysis and thermogravimetry indicates a cobalt double catalyst process, in which hydrocarbon gases are generated from the catalytic decomposition of the carbonaceous solid and CNTs are synthesized with the catalytic decomposition of the released hydrocarbon gases. The growth of CNTs is optimized by tuning of the annealing temperature and the composition of precursors.