Study On The Synthesis And Capability Of Zn-based And Bi-basednano-composite Oxides

Zn-based and Bi-based composite oxides are widely applied in catalysis. Water pollution is the issue of environmental hot spots, while photocatalytic degradation is one of the effective means of treating dye wastewater. It has important significance to prepare novel Zn-based and Bi-based composite oxide and apply to photocatalytic degradation dye wastewater.(1) The compound ZnCr2O4was prepared by solution combustion method. The effect of fuel, fuel-to-oxidant ratio and salt-assisted on the phase composition, morphology of the as-synthesized products was systematically studied. A good crystalline phase product can be prepared by appropriate fuel and fuel-to-oxidant ratio, accompanied with changes in morphology. In the salt-assisted synthesis, as increasing the amount of salt, the characteristic diffraction peaks gradually become weaken and widen. Compared to non salt-assisted synthesis, dispersibility was improved significantly.(2) The compound ZnAl2O4was prepared by solution combustion method. The effect of fuel, fuel-to-oxidant ratio, precursor pH and inert salt(NaCK KC1) salt-assisted on the phase composition, morphology and performance of the as-synthesized products was systematically studied. Among all the selected fuels, ethanolamine is the suitable fuel for the ZnAl2O4synthesis. The fuel-oxidant ratio also has an influence on the crystalline phase and morphology of the product as well as the pH of precursor. The sample which was prepared in the stoichiometric ratio condiation has a good crystalline phase and the highest photocatalytic activity. Compared to non salt-assisted,with the increasing the amount of salt, the characteristic diffraction peaks gradually weakened and widened, dispersibility and specific area were improved significantly, resulting in good photocatalytic activity (NaCl/M=1/3or KCl/M=2/3).(3) Using bismuth nitrate and calcium nitrate as the basic raw materials, the CaBi2O4can be prepared by hydrothermal synthesis after adjusting pH by ammonia. Ca4Bi6O13can be prepared by sol-gel method by using ammonia, EDTA and citric acid as mixed complexing agents. The morphology of CaBi2O4exhibited irregular particles,while the Ca4Bi6O13presented a cross-shaped, along some direction with multiple fine branch structure. The pH of dye system has a significant influence on the photocatalytic performance. With the pH of the dye solution increasing, the photocatalytic activity of CaBi2O4and Ca4Bi6O13has a significant enhancement, reaching about97%and67%respectively.(4) Bismuth nitrate and ammonia are the basic raw materials for synthesizing hydrated bismuth oxide. Various morphologies, such as flake-like, flower-like, wire-like and bone-like typical structure were successfully synthesized via tuning the experimental parameters. The effect of hydrothermal temperature, hydrothermal time, pH of precursors, solvent, template (SDS, P123, PEG, PVP) on crystal phase, morphology and photocatalytic performance of the as-synthesized products was systematically studied. The results demonstrate that the pH of precursors plays a critical role in the BHO controllable synthesis, only pH>7can synthesize effectively. The photocatalytic activity is associated with many factors, such as crystalline size, morphology, the surface area and so on. In the SDS-assisted synthesis system, as the surface area increaseing, photocatalytic activity was improved remarkably. It may photocatalytic activity was dominated by the surface area in the photocatalytic process. However, in the P123-assisted synthesis system, as the amount of P123increasing, the specific surface area decreased while the photocatalytic performance has a significant enhancement. Three-dimensional flower-like structure prepared by P123-assisted can separate electrons and holes more effectively, thus improving the photocatalytic activity.