Catalytic Reduction Of Nitro Aromatic Compounds With Silver Nanoparticle, Synthesis And Application Of Functionalized Particles

Metal nanoparticles have extensive applied in sensor, catalysis, nano-machine,optical switch and so on, because of their special properties such as surface effect,volume effect, quantum size effect, macroscopic quantum tunnel effect etc.. It has beenfound that nanocatalyst can be applied in synthesis of ammonia, environmental protection,water disposal, optical fiber, nanomechanics. Because of surface configuration, geometrycharacter and electron speciality of nanoparticles, nano-sized noble metal particle catalysthas high activity. The catalytic activity and the product selectivity of nanocatalyststrongly depend on the size, shape, surface configuration, electron property and surfaceconfiguration. A metal cluster shows efficient catalytic activity in a redox reactionbecause the cluster can act as the electron relay centre, behaving alternatively as anacceptor and as a donor of electrons. Highly effective transfers of electrons are possibleto be achieved when the redox potential of the cluster is intermediate between theelectron donor and electron acceptor system. When the potential difference between themetal particles and the nitrocompound is increased, the reaction rate increases.Nanocomposites that contain two or more different nanoscale functionalities are also attractive candidates for advanced nanomaterials. Dimer or oligomers heterostructures composed of individual components with different nanoscale properties may give rise to combination of unique properties. Magnetic nanoparticles are being tested in many biomedical applications, such as magnetic resonance contrast enhancement, cell and DNA separation, drug delivery, and gene cloning. Magnetic nanoparticles have also been developed in catalysis field, especially in electrocatalysis and bioelectrocatalysis. Therefore, we can invent more significative functional particles by utilizing synthetically the surface properties of silver/gold nanoparticles and the magnetic properties of magnetic nanoparticles.Based on the above background, the research purpose of this thesis is to synthesize different size, homogeneous distribution silver nanoparticles; use silver nanoparticles for the catalytic reduction of nitrocompound by either adding reducing agent or applying electrochemical potential on the silver assembly, and synthesize the core-shell Fe₃O₄@Au and Fe₃O₄@Ag as the catalysts for the reduction of nitrocompounds. The work includes three aspects:1. Synthesis of silver nanoparticles: Silver nanoparticles with different size, stable, narrow size distribution, homogeneous dispersion were synthesize by controlling reaction time of chemical reduction, and characterized with UV-vis spectroscopy and TEM image.2. Catalytic reduction of silver nanoparticles: The reaction systems involve NaBH₄ as reducing agent, m-nitrobenzenesulfonic acid sodium, p-nitroaniline, p-nitrophenol,2,4,6-trinitrophenol as oxidizing agent, silver nanoparticles as catalyst. The processes were traced with UV-vis spectroscopy. The reactions of p-nitroaniline and p-nitrophenol are mainly studied, including reaction mechanism, products, and the influence factors of reaction rate (the property of oxidizing agent, the concentration and size of silver nanoparticles).3.Synthesis of core-shell functional Fe₃O₄@Au and Fe₃O₄@Ag particles: Fe₃O₄ particles were synthesized by co-deposition. The gold or silver nanoparticles synthesized by sodium citrate reduction. The Fe₃O₄ and gold/silver nanoparticles were linked with (3-mercapto-propyl)trimethoxysilane duringthe multi-step reduction processes.The research results demonstrate that:(1) The different size silver nanoparticles synthesized are spherical, disperse, homogeneous and stable.(2) Silver nanoparticles can catalyse the reduction of several nitrocompounds. The function of silver nanoparticles is virtually the electron relay. The reaction rate is largely affected by the property of oxidizing agent, the concentration and the size of silver nanoparticles.The catalytic efficiency for PNP is larger than that for PNA. The reaction is more efficient as the density of the silver nanoparticles is higher and/or the size of the particles decreases.(3) Core-shell functional Fe₃O₄@Au and Fe₃O₄@Ag particles synthesized also show good catalytic activity for the reduction of nitrocompounds.