Preparation And Characterization Of Microwave Irradiation Synthesized Lead Tungstate And Carbon Nanofibers Coated By Ni Nanoparticles

Since the first reports of microwave-assisted synthesis in 1986, microwave heating has been accepted as a promising method for rapid volumetric heating, which results in higher reaction rates and selectivities, reduction in reaction times often by orders of magnitude, and increasing yields of products compared to conventional heating methods. As a result, this has provided the possibility of realizing new reactions in a very short time.In this paper, lead tungstate (PbWO4) microcrystals and carbon nanofibers coated by Ni nanoparticles were synthesized using a microwave-assisted method. The paper focuses on two areas:1. Fast synthesis and morphological control of PbWO4 microcrystals in a water or EG system with surfactant using microwave-assisted method.PbWO₄ microcrystals with special structures were successfully synthesized via a simple and fast microwave-assisted route. The synthesized products were characterized by the techniques of powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The solvent material, pH value, microwave output power and concentration of the cetyltrimethylammonium bromine (CTAB), play an significant role in the morphological control of PbWO₄ microcrystals. The possible formation mechanisms of PbWO₄ samples of various morphologies were discussed. It is demonstrated that the cooperative effect of CTAB and pH value is responsible for the morphological control of PbWO₄ microcrystals. The luminescence properties of the final products were investigated and the as-prepared PbWO₄ microcrystals showed extraordinarily strong room-temperature photoluminescence intensity and were blue-shifted about 10³0 nm compared to the solid structure counterparts.2. The carbon nanofibers are coated by magnetic Ni nanoparticles via a microwave irradiation heating method.The carbon nanofibers were prepared by pyrolysis of acetylene with nanocopper as catalysts. After soaked in an oxidation treatment in the nitric acid for the surface chemistry modification and dispersive property, the carbon nanofibers undergo a two-step pretreatment, sensitization and activation. The final products, Magnetic Ni-coated carbon nanofibers composites were finally fabricated by employing such simple microwave-assisted procedures. The phase structures and morphologies of the composites were characterized by FE-SEM, TEM and XRD. The results showed that a dense and uniform layer of Ni nanoparticles coated on the carbon fibers with an average particle size of 30 nm. In the process of attaching Ni nanoparticles to the surfaces of carbon nanofibers, not only functionally pretreating but also sensitization and activation are indispensable. The size of magnetic Ni nanoparticles on the carbon fibers is adjustable by the amount of added N₂H₄·H₂O. The as-prepared magnetic carbon nanofibers can be aligned as a long-chain structure by an external magnetic field. Magnetic characterization of the prepared fibers on a vibrating sample magnetometer reveals that the prepared composites are ferromagnetic. The magnetic property of the carbon nanofibers coated by Ni nanoparticles was also compared to that of Ni nanoparticles. The saturation magnetization (Ms) of magnetic composites and nickle nanoparciles are 26.5 emu/g and 6.0 emu/g, respectively, considerably smaller than that of bulk nickle.