Synthesis And Catalytic Properties Of Gold And Its Alloy Nanocomposites

Gold-bearing nanomaterials have wide application prospects such as optics, electronics, sensors, biomedicine, catalysis field, etc. Gold-bearing nano-materials in catalysis arouse much more attention. In the past 20 years, various gold nano-catalysts with different shapes, structures, and size distributions have been prepared. They have large specific surface areas and excellent interface effects, which could increase the active sites of catalysts, thus increase the contact areas between substrates and catalysts to improve the reaction efficiency. Therefore, the development of new gold-bearing catalytic materials is quite necessary. In this thesis, we prepared gold and gold-palladium alloy nano-catalysts with tunable morphology and size by simple methods, and they were applied to the Ullman homocoupling reaction of aryl halides and the reduction reaction of 4-nitrophenol.1. DMF-protected Au nanoparticles(NPs) with three different particle sizes were synthesized by controlling the reaction temperatures and times. In this catalytic coupling reaction, DMF served as a stabilizer and reductant. In the absence of any additional ligands, these Au NPs showed high catalytic activity in the Ullmann homocoupling of aryl iodides. The effects of Au particle size on the coupling reaction were investigated by the use of three Au catalysts with mean particle sizes of ca. 1.0 nm, 2.5 nm and 5.5 nm, respectively. The catalytic activity of the Au NPs was found to be in the order of Au(2.5 nm) > Au(<1.0 nm) > Au(5.5 nm), indicating that surface Au atoms do not have the same catalytic activity toward such a homocoupling reaction.2. We reported the first synthesis of unique Au-Pd bimetallic alloy nanoparticles(NPs) supported on the hollow Cu2O-Cu O core-shell structure via the galvanic replacement reaction between Au3+, Pd2+ and Cu2 O, forming a unique heterostructure. The size of Au-Pd bimetallic NPs deposited onto the Cu2O@Cu O nanocubes is ca. 15 nm. The morphological evolution can be controlled by the reaction time. Such bimetallic NPs showed high catalytic activity towards the reduction of 4-nitrophenol(4-NP) to 4-aminophenol(4-AP) in water at room temperature. Significantly, the strong synergistic effect between Au and Pd, and the high specific surface area of Cu2O@Cu O enhance the catalytic efficiency. The catalytic system can be reused for five cycles without any obvious decay of catalytic efficiency.