Preparation Of Hydrophobic Gold Nanoparticles And Its Application In Reducation Of 4-Nitrophenol

In recent decades, preparation and application of gold nano-materials have been a hot research issue in nano-materials field. Gold nanoparticles with some characters such as small size effect, surface effect, quantum size effect and macroscopic quantum tunneling effect are widely used in the fields of biomedical engineering, non-linear optics, electronics and industrial catalysis.This thesis introduces a novel surfactant Alkoxybenzylamine (SAOBA), which can be mixed with n-butanol, n-heptane and HAuCl4·4H2O to form W/O microemulsion. Using this reverse microemulsion as template and microwave radiation as heating means, hydrophobic gold nanoparticles with different sizes and morphologies have been prepared by changing the experimental parameters such as the type of the surfactant, the type of the reducing agent, as well as the microemulsion's composition. When the prepared hydrophobic gold nanoparticles are surpported onγ-Al₂O₃, the Au/γ-Al₂O₃ catalyst plays a good catalytic activity in reduction of p-nitrophenol. All the products have been investigated by FT-IR, 1H NMR, MS, UV-vis, TEM, XRD, CA and so on.The main work completed in this thesis are summarized as follows:1. Alkoxybenzylamines (SAOBA) are carried out by zinc dust reduction of alkoyxybenzaloxime, which was obtained from alkoxybenzaldehyde (obtained from p-hydroxybenzaldehyde, vanillin or 3,4-dihydroxybenzaldehyde by O-alkylation) by reacting with hydroxylamine hydrochloride.2. Gold nanoparticles stablized by C8OBA, C₁₂OBA and C16OBA are obtained by n-butanol reduction in situ under microwave irradiation by using the CnOBA(n=8, 12, 16)/n-butanol/n-heptane/HAuCl4/NaOH(aq.) W/O microemulsion as a microreactor. We focus on C₁₂OBA in order to determine the influence of the microemulsion's composition during the progress of formation the size and morphology of gold nanoparticles. The results show that CnOBA can be used not only as a surfactant which helps to form a stable microemulsion system, but also as a good protecting agent for gold nanoparticles. Gold nanoparticles with spherical morphology and small size can be easily obtained with the increasing of C₁₂OBA/ HAuCl4 molar ratio or the increasing of n-heptane/n-butanol volume ratio. The prepared hydrophobic gold nanoparticles with high monodispersity can spontaneously form large areas of the short-range ordered monolayer membrane at the air/water interface.3. Under the promotion of microwave irradiation, by the reduction of propionaldehyde, C8OBA, C₁₂OBA and C16OBA modified hydrophobic gold nanoparticles are prepared in CnOBA(n=8, 12, 16)/n-butanol/n-heptane/propion- aldehyde/HAuCl4 (aq) W/O microemulsion. The expermental results show that the size of the gold nanoparticles gradually decrease and the morphologies of gold nanoparticles gradually change from polygonal to spherical with the increasing length of the alkoxy chain of the CnOBA under the same reaction condition. We still focus on C₁₂OBA to study the morphology of C₁₂OBA-capped Au nanoparticles obtained by propionaldehyde as reductant. The results show that gold nanoparticles with polygonal morphology are obtained by decreasing the C₁₂OBA/HAuCl4 molar ratio or n-heptane/n-butanol volume ratio or increasing the amount of the reductant propionaldehyde. 4. C₁₂OBA-coated gold nanoparticles are synthesized under microwave irradiation in C₁₂OBA/n-butanol/n-heptane/formic acid/HAuCl4(aq.) reverse microemulsion system with formic acid as a reductant. The results illustrate that the size of the gold nanoparticles gradually decreasing with the molar ratio of aime/gold increasing, and the monodispersity of the gold nanoparticles increasing, the morphologies of the paricles gradually change from polygonal to spherical. C8OBA, C16OBA, MDOBA and DDOBA modified naoparticles are also sythesized by the same system. we find that increasing alkoxy chain length and alkoxy chain number are conducive to generate small particle size and good monodispersity gold nanoparticles.5. Au/γ-Al₂O₃ catalyst is prepared by loading the obtained gold sol onto the surface ofγ-Al₂O₃. Then, the catalytic activity in the reduction reaction of p-nitrophenol are tested. Meanwhile, we study the influence of the size of the gold, the amount of the supports and the temperature to the reaction. The optimum reaction conditions are described as follows: the size of the gold naoparticles should be smaller then 10nm, the load ratio of gold nanoparticles is 0.1ωt% and the reaction temperature is 50℃. This Au/γ-Al₂O₃ catalyst can be recycled .