| Size of gold nanoparticles has a significant impact on its application properties,especially for the nanoparticles with diameter less than 3 nm.The geometry and electron structure of the gold nanoparticles will have a great change when the nanoparticles are smaller than 3 nm,hence leading to the chhanging of its application properties.Normally,size controlled synthesis of gold nanoparticles is relying on the use of ligand for the stabilization of gold nanoparticles.Among the gold nanoparticles synthesis methods,size focusing in organic solvent is one of the methods which can precisely control the size of gold nanoparticles through the interaction between gold nanoparticles and mercapto ligands.While,the ligand used for particle stabilization will affect the electronic structure and hence the catalytic properties of gold nanoparticles.As an inert support,silica could stabilize the gold nanoparticles without affecting the intrinsic properties of gold nanoparticles.In this thesis,a new size-controlled method based on both reverse microemultion and size focusing was proposed for the preparation of the gold nanoparticles stabilized in silica and then the properties of this nanocomposite was investigated.In reverse microemultion system,the gold nanoparticles with diameter bigger than 5 nm and broad size distribution(initial gold nanoparticles)were firstly obtained from the reduction of Au(?)-hydroxyethylenediamine complexes by NaBH4.Then,with the addition of water-soluble merapto alcohol,size-focusing process occurred through the interaction between mercapto alcohol and gold nanoparticles,which could form uniform smaller gold nanoparticles.Finally,the smaller gold nanoparticles were stabilized in silica through the sol-gel process.During size-focusing process,the gold nanoparticles with three sizes(<1.0 nm,1.2±0.3 nm,2.6±0.3 nm)were successfully synthesized by modulating the concentration of gold ions(initial gold nanoparticles size),and the molar ratio of gold ions and the selection of different mercapto alcohol.The foregoing three kinds of gold nanopaarticles were stabilized in silica supporrt and named as Au(<1.0nm)-SiO2,Au(1.2nm)-SiO2,Au(2.6nm)-SiO2,respectively.The synthesized Au-SiO2 can catalyze the reduction of aromatic nitro compounds into aromatic amine under room temperature by NaBH4.The smaller gold nanoparticles show a higher catalytic activity and the turnover frequency value was 4.17 min-1 when Au(<1.0nm)-SiO2 was used in the reduction of 4-nitrophenol.The kinetic analysis and Hammett plot revealed the reaction followed the aromatic nitro compounds-hydroxyl amine-aniline derivaitive route,which was consistent with in situ IR spectra analyses.Au(<1.0nm)-SiO2 performed best among the synthesized Au-SiO2 for catalyzing the coupling of Me2PhSiH and ethanol,whose TOF value reached 4.12min-1 at room temperature,and the activation energy was 45.5 kJ/mol.A zero order kinetics had been confirmed,indicating that the reaction was not related to the concentration of the substrates,which could be attributed to the collected reactants on the surface of silica,which provided a saturated reactant around gold nanoparticles and a constant reaction rate independ on concentration.The reaction performed as a zero order reaction.Gold nanoparticles with a size of 2.6 nm performed a surface energy transfer with rhodamine B,and the fluorescence quenching constant was 4.3×103 L/mol.Rhodamine B-Au(2.6 nm)-SiO2 could be used to detect mercapto compounds based on the interaction between gold nanoparticles and mercapto compounds.It was found that the fluorescence increased linearly with the concentration of mercaptoethanol ranging from 45?268 mmol/L,and the detection limit was 7.5 mmol/L.Due to the stabilization of silica,Au(2.6 nm)-SiO2 could be used five times with a constant linear plot. |
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