Solution Synthesis Of Noble Metal Nano-And Microstructures And Their Applicatios

Noble metal nano- and microstructures have been of great interest for decades because of their potential applications in photonics, electronics, catalysis and other areas. The properties of noble metal structures depend strongly on not only their sizes but also their shapes. Therefore, it is of interest to develop new synthetic methods that are effective in control of sizes and shapes.Herein, we prepared a variety of noble metal micro- and nanomaterials. We also have investigated many reaction parameters in the formation of specific shapes and sizes of crystals. Those reaction parameters include heating method, reaction medium, reaction temperature, precursor concentration, reaction time, reducing agent, and capping agent. Many micro- and nanomaterials with different shapes and sizes such as Ru, Pt, Pd nanoparticles, Ag nanowires and nanoplates, Au nanoplates, octahedra, decahedra, and dendrites were prepared via microwave heating, solvothermal heating, and oil bath heating methods in aqueous solutions of alcohol ionic liquids (AILs), aqueous solutions of ionic liquids polymers, aqueous solutions of PVP and pristine ionic liquids (ILs). The growth mechanism of the nanomaterials was also investigated. Those synthetic procedures are very simple and easy to control. Detailed contents are summarized as following:1. AILs not only have the special physical and chemical properties of ILs, such as low vapour pressure, low interface tension, good thermal stability and large electrochemical window, but also have the reducing abilities like alcohols, therefore AILs could be used as stabilizers and reducing agents in preparing of nanomaterials. Combining the properties of ILs with microwave heating, Au, Pd, Pt nanoparticles were prepared in aqueous solution of [C3OHmim][BF4]. In contrast with microwave heating, we also prepared Ru, Pt, Pd nanoparticles, Au nanoplates, and Ag nanowires using oil bath heating. The morphological diversity of the products result from the heating efficiency variance and reaction temperature.2. ILs are salts which composed of cations and anions, and melt at or below 100°C. Recently, ILs often serve as potential environmentally benign solvents due to their special physical and chemical properties such as low vapour pressure, low interface tension, and good thermal stability. Compared to conventional heating, microwave dielectric heating has some unique advantages in nanomaterials synthesis, such as rapid volumetric heating, leading to a reduction in reaction times and even the formation of novel nanostructures. ILs are excellent microwave-absorbing agents due to their high ionic conductivity and polarizability, thus combining the properties of ILs with microwave heating should provide a fast and potentially environmentally friendly method for the fabrication of nanomaterials. Large size Au nanoplates and octahedral Au nanocrystals were fabricated via microwave heating of HAuCl4 in [C3OHmim]Cl and [C3OHmim][BF4], respectively. In those synthetic procedures, ILs act as reaction media, reducing agents, and templates, and there are no need of other extra additive agents, thus simplify the synthetic procedures.3. In order to investigate the influence of anions and cations of ILs on the morphologies of Au products in detail, we synthesized 10 kinds of ILs, such as [BMIM]Br, [BMIM]Cl, [BMIM][BF4], [BMIM][PF6], [BMIM][Tf2N], [BMIM][Tos], [EMIM]Br, [EMIM][BF4], [BuPy]Br, [BuPy][BF4]. Several kinds of nano- and microstructures such as large size single crystal Au nanoplates, octahedra, decahedra, dendrites, and nanowires were fabricated via microwave heating of HAuCl4·4H2O in those ILs. The results indicate that the anions and cations of ILs, HAuCl4 concentrations, reaction temperatures, and heating methods are important parameters in the formation of Au products. Among these parameters, anions have more influence than cations on the Au products. Microphase segregation of ILs could play important roles in the formation of nucleis and stabilizing of small nanoparticles, and the different adsorption abilities of various anions and cations on different crystal faces determine the morphological diversities of Au products.4. Alcohol reduction has been known for decades as a generic route to the synthesis of nanomaterials. It is also known that the reducing power of an alcohol decreases as its alkyl chain becomes longer. As a result, polymers with hydroxyl (-OH) end groups would be ideal reductants for controlled synthesis of metal nanostructures. We have prepared Ag and Pd nanoplates in aqueous solution of PVP via oil bath heating method, microwave heating method and hydrothermal method. PVP acts as a dual functional reductant and capping agent in the synthetic route, thus there are no need for extra agents in the synthetic route. Furthermore, the hydrothermal method could accelerate the reaction and reduce the reaction time.5. Ionic liquid polymers have properties of polymers as well as ionic liquids. We synthesized an ionic liquid polymer poly (N-ethyl-4-vinylpyridinium bromide), poly(EtViPy+Br-), and use it as a stabilizer in preparing Pd nanoparticles with diameters of 3.6±0.7 nm. The poly(EtViPy+Br-) stabilized Pd nanoparticles were performed as a catalyst in Suzuki coupling reaction in aqueous solutions. The results demonstrate that poly(EtViPy+Br-) stabilized Pd nanoparticles could catalyze Suzuki coupling reactions in mild conditions. The stability of the colloidal Pd nanoparticles arises from both eletrostatic and steric effects of poly(EtViPy+Br-).