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Surfactant system in functional inorganic nanomaterials synthesis of nanomaterials surface properties of

Author: LiuXiaoXia
Tutor: DingYuanHua；GuoRong
School: Yangzhou University
Course: Physical and chemical
Keywords: Gold nanoparticles Nanostructures Reverse Micelles Metal cations Microemulsion Dendritic Nanorods Cyclohexane Aging time Surfactant system
CLC: TB383.1
Type: Master's thesis
Year: 2007
Downloads: 283
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Abstract

1. Crystallization of 1D Cu₂S/CuS Nanostructures in Triton X-100/ Cyclohexane /Water Reverse MicellesThe shape evolution of Cu₂S/CuS nanostructures, which were produced in Triton X-100/cyclohexane/water reverse micelles, was investigated by the transmission electron microscopy technique as a function of aging time, and the effect of the molar ratio of water to surfactant on the size and shape of Cu₂S/CuS nanostructures was also discussed. The results suggest that at the initial stage the nucleation process was dominant and the shape of Cu₂S nanostructures was preferably confined by the reverse micelle droplets and took spherical forms. With the extension of the aging time, the growth gradually governed the process and the shape of Cu₂S nanostructures evolved first to nanorods, and then to nanowires gradually. The formation of one-dimensional Cu₂S nanostructures is attributed to a directed aggregation growth process mediated by reverse micelle droplets, which was confirmed by high-resolution transmission electron microscopy. Furthermore, the size and shape of Cu₂S nanostructures can be controlled by changing the molar ratio of water to surfactant.In Triton X-100/cyclohexane/water reverse micelles, 1D CuS nanocrystals were also obtained by using H2S as the sulphur source. Similar to the synthesis of 1D Cu₂S, the shape of CuS nanostructures evolves from spherical particles to 1D nanorods, but no nanowires are formed. The formation mechanism of 1D CuS validates that of 1D Cu₂S nanostructures. The above results may reinforce the understanding of the formation mechanism of nanomaterials prepared in surfactant-contained systems, and may provide guidance for synthesizing other nanomaterials with a controllable shape and size.2. Fabrication of PbS Microstructures with Different Shapes in Pluronic F127/ Cyclohexane/H₂O MicroemulsionsHollow PbS nanospheres and branch-like PbS microstructures have been successfully synthesized by the reaction of Pb（Ac）₂ with the S^2- ions released slowly from thioacetamide （TAA） in Pluronic F127/cyclohexane/H₂O microemulsions at room temperature. The obtained hollow PbS nanospheres have a wall thickness of about 40 nm, and the branch-like PbS microstructures have an average size of 0.7-2.2μm. Both the wall of the hollow PbS nanospheres and the branch-like structures consist of cubic PbS nanocrystallites. It has been found that a minimum F127 concentration is required for the formation of hollow and branch-like PbS structures. With increasing F127 concentration, the diameter of the obtained hollow spheres increases gradually, whereas the size of the branch-like structures decreases. The addition of cyclohexane makes the diameter of hollow spheres decrease, but has little effect on the branch-like structures. Increasing the temperature of the microemulsions can significantly decrease the sizes of the hollow and branch-like structures. The complex microemulsion droplets formed by Pb（Ac）₂ and F127 microemulsion droplets act as soft templates for the formation of hollow PbS nanospheres, and the complex monomeric F127 aggregates formed by Pb（Ac）₂ and monomeric F127 chains play a structure-directing role in the formation of branch-like PbS microstructures.3. Adsorption Behavior of Metal Cations on Gold Nanoparticle Surfaces Studied by Isothermal Titration MicrocalorimetryThe adsorption behavior of metal cations on gold nanoparticles was investigated by isothermal titration microcalorimetry （ITC）, and verified by transmission electron microscopy （TEM）, dynamic light scattering （DLS）, and UV-vis absorption spectroscopy. When transition metal cations were titrated into the gold nanoparticle solution, a binding isotherm with a sigmoidal response was obtained; and when alkaline earth cations were titrated into the same system, the binding isotherm changed from the overall exothermic to endothermic nature. The binding enthalpy of transition metal cations and Mg²⁺, Ca²⁺ ions on gold nanoparticles is between -99 and -174 cal/per mole of metal ions, whereas no binding enthalpy is detected for Sr²⁺, Ba²⁺ ions due to their weak binding to gold nanoparticles. Furthermore, the binding enthalpy of metal ions on gold nanopartilces depends on the nature and concentration of added cations, and the strength of exothermic interaction decreases in the order of Cu²⁺>Co²⁺>Zn²⁺ >Cd²⁺ >Mg²⁺ >Ca²⁺>Sr²⁺ >Ba²⁺. The interactions of metal ions with the surface gold atoms and the COO- group of citrate salt weakly bound on gold nanoparticles are the driving force for the binding; and the binding process is enthalpically driven. TEM images and DLS measurements indicate that addition of metal ions result in the growth and aggregation of gold nanoparticles, and the effect of transition metal cations is more significant. After the metal cations were added to the gold nanoparticle solutions, the intensity of the surface plasmon resonance adsorption band at 523 nm of gold nanoparticles decreased, and a new absorption at around 610 nm appeared. This is attributed to surface binding of metal cations on gold nanoparticles, and the resulting aggregation, and thus confirms the ITC results.

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