Preparation Of One-Dimensional Magnetic Nanocatalysts And Its Organic Dyes Degradation Properites

As normal chemical additives, organic dyes are used in a wide rang of industries, such as leather, textile, paint and printing, which are released to the enviroment with wastewater. Most of the organic dyes are direct-acting or indirect-acting carcinogen, if not promptly and effectively remove those toxic contaminants, they can bring about serious environmental threats and serious hazards to ecosystem and human health, respectively. Therefore, it is urgent to effectively deal with the wastewater containing organic dyes. In this thesis, a series of novel one-dimensional magnetic nanocatalysts were synthesized and their catalysis performances toward organic dyes degradation were investigated. The details are as follows:（1） α-Fe2O₃ nanorod were selected as the template-materials to produce homogeneous coated core-shell α-Fe2O₃@SiO2 nanocomposites by using Stober method, then Fe₃O₄@SiO₂ and Fe@SiO2 magnetic core-shell nanocomposites with rod-like morphology were successfully obtained by altering experiment conditions in hydrogen reduction process.（2） The Fe₃O₄@SiO₂@Ag magnetic nanocomposites were synthesized at room temperature by using ascorbic acid as reductant. AgNO₃ as Ag source and Fe₃O₄@SiO₂ magnetic nanocomposite as support. Releationship between the addation amount of AgNO₃ and the size of Ag nanoparticles was systematically investigated. It was found that the size of Ag nanoparticles increased with the increasement of AgNO₃,When the addation amount of AgNO₃ were 0.03,0.05 and 0.1 mmol, the size of Ag nanoaparticles were 7.63 nm,13.5 nm, and 41.2 nm, respectively. It was also found that, compared with bare Ag nanoparticles, the introduction of magnetic support could remarkablely improve the dispersion and crystalline of Ag nanoparticles which decorated on the surfcace of Fe₃O₄@SiO₂ nanocomposties. These as-prepared Ag-MNRs show superior catalytic ability for the degradation of organic dyes Moreover, the Ag-MNRs catalysts displayed typical ferromagnetic behavior and superior magnetic response ability which could be magnetically separated easily and reused. It found that the catalysts still maintained 80% catalytic efficiency after at least five cycles.（3） The Fe3O4@SiO@Ag@Ni trepang-like nanocomposites were synthesized at room temperature by using NH3BH3 as reductant, AgNO₃ as Ag source, Ni（NO₃）₂ as Ni source, and Fe₃O₄@SiO₂ magnetic nanocomposite as support. A series measurements were employed to characterize the phase, composition and strcture of the products. The results reveals that monodispersed Ag nanoparticles have been successfully coated around the Fe₃O₄@SiO₂ nanorods with Ni nanoplatelets covered, which formed the unique trepang-like structure. The Fe₃O₄@SiO₂@Ag@Ni trepang-like nanocomposites exhibit remarkably higher catalytic efficiency than monometallic Fe₃O₄@SiO₂@Ag nanocomposites toward the degradation of rhodamine B （RhB） at room temperature, which can attributed to the unique structure of Fe₃O₄@SiO₂@Ag@Ni nanocomposites. The trepang-like structure provide large specific surface areas, which are favorable for adsorbing the reducing agents and dye molecules and facilitating the catalytic degradation. The electronic structure （d band） of the Ag@Ni core-shell nanoparticles coated on the Fe₃O₄@SiO₂ nanorods could be modified by the interaction between Ag and Ni species through the so-called ligand and strain effects,which may facilitate the eletron transformation. In addition, these samples could be easily separated from the catalytic system by an external magnet and reused, and still maintained 81.5% catalytic efficiency after at sixcycles.（4） The Fe@SiO2@Cu magnetic nanocomposites were synthesized at 80℃ by using ascorbic acid as reductant, Cu（NO₃）₂ as Cu source and Fe@SiO2 magnetic nanocomposite as support. A series measurements were employed to characterize the phase, composition and strcture of the products. The results show that well-dispersed, high-crystalline Cu nanoparticles are successfully decorated on Fe@SiO2 nanorods via a facile solvothermal synthesis strategy. It found that when the addation amount of Cu（NO₃）₂ were 0.01 and 0.03 mmol, the size of Cu nanoaparticles were 10 nm and 33 nm, respectively. The two catalysts all show superior catalytic activity toward the degradation of reactive red,and the rate constant for Fe@SiO2@Cu-0.01 and Fe@SiO2@Cu-0.03 nanocomposites were 0.316 m-1 and 0.20 m-1 respectively. The magnetic measurements show that both of the Fe@SiO2@Cu-0.01 and Fe@SiO2@Cu-0.03 nanocomposites displayed superior magnetic response ability. The the Ms are 107 emu/g and 89 emu/g, respectively, which are relatively high than other reported magnetic caralysts. Both of the Fe@SiO2@Cu nanocomposites show excellent catalytic efficiency even after 5 cycles without any significant loss of activity, indicating that the catalysts exhibit good reusability.