Preparation And Characterization Of Metal Nanostructures At The Interfaces

In recent years, synthesis and assembly of noble metal nanoparticles and investigation of their properties have been attracted much attention due to their unique optical, electronic and catalytic properties different from the bulk and consequent potential applications. Langmuir monolayer technique is a very effective way in preparation and assembly of nanoparticles. In this thesis, varied nanostructures templated by Langmuir monolayer of functional amphiphilic molecules were obtained in one-step processes via interfacial reactions at the solid/water or air/water interfaces and characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffractometry (SAED), UV-vis spectroscopy and surface enhanced Raman scattering (SERS). The formation mechanism of these nanostructures was discussed. The study of this thesis mainly consists of three parts:I Gold hierarchical nanostructures were prepared at the composite carbon-coated copper grid/Langmuir monolayer/HAuCl4 aqueous solution interfaces. Marigold-like nanoflowers, cereus tetragonus-like dendrites and snowflake-like nanoflowers were deposited on the carbon layers via electroless deposition technology when the Langmuir monolayers of cobalt tetrahexadecyl-tetrapyridinoporphyrazinium bromide (THTPyPzCo), dimethyldipalmitylammonium bromide (DMDPB) and 1,1'-dioctadecyl-4,4'-bipyridium dibromide (DObpyDB) were used, respectively. In three nanostructures, the (110), (001) and (110) crystal faces of gold were parallel to the surface of the water, respectively. The formation of these nanostructures should be attributed to the galvanic reduction between AuCl4- and Cu and electrochemical reaction, the conductivity of the carbon layer for electrons, non-equilibrium growth of the nanostructures, and the templating effect of the Langmuir monolayers. Raman scattering show that these nanostructures have good surface enhanced effect to Rhodamine 6G (Rh6G) and etc.ⅡSliver dendritic nanostructures were prepared at the solid/liquid interfaces via electroless deposition under the inducement of the Langmuir monolayers of 5,10,15,20-tetra-4-oxy(2-stearic acid) phenyl porphyrin (TSPP) and arachidic acid (AA) which were formed at the air/AgNO3 aqueous solution interface. These nanostructures were produced when carbon-coated copper grids were covered on the Langmuir monolayers at lower (<20℃) and higher (20-50℃) temperatures, respectively, and the branches are composed of parallel aligned nanobelts with their (110) face parallel to the interface. The formation of the nanostructures should be attributed to the galvanic reduction of Ag+ions by copper, the electronic conductivity of the carbon layer, the templating effect of the Langmuir monolayer, and the non-equilibrium growth and aggregation of silver nanoparticles at the interface.ⅢPreparation and characterization of gold nanoparticles at the air/water interface. The amphiphilic ionic liquid molecules were spread onto the aqueous HAuCl4 surface and formed monolayers, and then gold ions were reduced by formaldehyde gas or UV-light irradiation at different temperatures to form gold nanoparticles at the interface. It was found that triangular, hexagonal, and truncated triangular single-crystal gold nanoplates were formed at low subphase concentration, while flower-like aggregates composed of fine particles were formed at high subphase concentration. The (111) surface of gold nanoplate was parallel to the surface of the water. The UV-visible spectra also confirmed the formation of the nanoplates and nanoparticles. The formation of the different nanoparticles is related with nucleation and growth process. The thin nanoparticulate films have good surface enhanced Raman scattering effect to Rhodamine 6G (Rh6G) and etc.