Controlled-Synthesis Of Aluminum Nanocrystals With Polymer Ligands

Compared with macroscopic materials,nanomaterials have unique and excellent physicochemical properties due to their surface effects and size effects,and have gained important applications in the fields of optoelectronics,catalysis,sensing,and biomedical applications,thereby receiving widespread attention.Among them,metal nanomaterials have played an important role in many aspects and have become one of the most studied fields in nanoscience.Among the many properties of metal nanomaterials,the characteristic optical properties,namely surface plasmon resonance(SPR),are the most concerned and studied.Compared with the traditional noble metal SPR material(gold and silver),aluminum has a wider resonance band,especially in the short-wavelength ultraviolet region,in which aluminum has excellent resonance properties not possessed by gold and silver.In general,chemical synthesis of metallic nanocrystals has developed into a mature chemistry over the past two decades,where impressive progress has been made towards the precise control of nanocrystal size,shape and composition.However,since aluminum has a low oxidation/reduction potential(ORP),it is difficult to obtain aluminum nanomaterials with regular reaction.Therefore,the self-decomposition of aluminum hydride is a common way to chemically synthesize aluminum nanocrystals(Al NCs).In nanosyntheses,organic molecular ligands have been essential for size and shape control,typically through facet-specific organic-inorganic interface absorption.Inspired by the fact that a functional group at the end of a polymer chain is much less reactive with H3 Al than that of a small molecule,we have investigated the use of end-functionalized polymer ligands for the synthesis of Al NCs.Compared with molecular ligands,polymer ligands are more promising in controlled synthesis of Al NCs.Further studies have shown that Al NCs synthesized with dithioester-terminated polystyrene have narrower size distribution and controllable size and morphology.In this thesis,the chemical mechanism of controlled synthesis of Al NCs by dithioester functional groups was revealed in both experimental characterization and theoretical calculations.Based on the controllable synthesis of Al NCs,we also studied the effects of different sizes and different morphologies on the characteristics of surface plasmon resonance.Inspired by the controllable synthesis of Al NCs with dithioester-terminated polystyrene,the effects of other sulfur-containing functional group teminated polymer ligands on the synthesis of Al NCs were investigated.The content of this thesis is summarized as follows:1.In Chapter One,a variety of polymer ligands with different functional groups were designed and synthesized.It was found that compared with small molecule ligands,polymer ligands have greater advantages in the synthesis of Al NCs: more individual Al NCs,less aggregates and narrower size distribution.Among the many polymer ligands tested,dithioester-terminated polystyrene showed the best control.2.In Chapter Two,on the basis of using the polymer ligand dithioester-terminated polystyrene as a ligand,the size,size distribution and morphology of the Al NCs were controlled by adjusting the experimental conditions,and the structure of Al NCs was characterized.By adjusting the concentration of the added catalyst,monodisperse Al NCs with different sizes were obtained.By controlling the concentration of the polymer ligand,the morphology control was achieved,and aluminum nanostructures with different area ratios of Al{111} and Al{100} crystal facets were obtained.At the same time,the interaction of ligands and Al NCs was studied through experimental characterization and theoretical calculations.In addition,since the added ligand affects the supersaturation of the aluminum atoms in the solution,thereby affecting the surface energy of the Al NCs,and leads to the formation of nanostructures with different surface energy.Besides,the effects of the molecular weight of dithioester-terminated polystyrene on the growth of Al NCs are investigated.If the molecular weight is too low,monodisperse Al NCs cannot be obtained.Only high-molecular-weight polymer ligands can achieve the controlled syntheses and the mechanism has also been studied.3.Due to the size-dependent and morphology-dependent properties of plasmonic materials,nanocrystals of different sizes and morphologies exhibit different resonance frequencies,which are directly reflected in the fact that the aluminum nanocrystal solution and powder exhibit different colors.We studied the surface plasmon resonance properties of aluminum nanocrystal solutions and single nanocrystals by UV-Visible spectroscopy and single particle dark-field scattering spectroscopy combing with time-domain finite difference(FDTD)method.The results of these characterization methods are consistent with each other,which proves the size effect of the surface plasmon resonance frequency of Al NCs: as the size of Al NCs increases,the scattering peaks are red-shifted and have different surface plasmon vibration modes.Meawhile,it is also proved that the difference in morphology also has a certain influence on the Al NCs: the increase of the truncation of cube makes the scattering peaks continuously blue-shift.4.When polymer ligands are used to synthesize metal nanocrystals,their molecular weight and concentration have a great influence on the size,morphology and structure of metal nanocrystals.In this thesis,different kinds of polystyrenes with different sulfer-contaning functional ending goups were designed and synthesized.The effects of various experimental parameters on the synthesis of Al NCs were studied by adjusting a series of experimental conditions.The research on the synthesis of Al NCs with dithioester-terminated polymer ligands has been expanded.