Interfacial Assembly And Characterization Of Metal-Organic Layered Nanostructures

In recent years,two-dimensional(2D)supramolecular assemblies have received extensive attention due to their potential applications in the fields of chemistry,biomedicine,and materials.With the deepening of research,many feasible assembly methods have been developed.Among these,the molecular self-assembly method is the most widely used strategy.The main driving force of molecular self-assembly is intermolecular interactions,including coordination bonds,hydrogen bonds,?-? stacking,hydrophobic effect,electrostatic interactions and host-guest interactions.In general,self-assembly methods mainly include two strategies,i.e.solution self-assembly and interfacial self-assembly,in which the gas/liquid interfacial and liquid/liquid interfacial methods have been widely used in the preparation of nanomaterials.In our laboratory,we have extended the traditional Langmuir monolayer technique,and obtained Janus lamellar nanosheets other than monolayer.In this thesis,we continued to use and further extend the assembly method,and prepared a series of Janus nanosheets of fatty acids with different alkyl chains.Subsequently,researchers have gradually developed a novel liquid/liquid interfacial reaction/assembly method,i.e.the liquid/liquid interface between a solution of one kind of precursor and a pure solvent was constructed firstly;and then another kind of precursor was added dropwise into the pure solvent.Thus,the added precursor diffused to the interface gradually,the adsorption/assembly process carried out gently,and regular structure could be formed.The method was also used in this thesis,and large area of layered ultrathin films composed of ligands and metal ions were fabricated.The main research results are as follows.1.Assembly of Janus lamellar nanosheetsHerein we reported a facile method to fabricate Janus nanosheets with lamellar structure at the air/liquid interface by spreading a water-miscible organic solution of fatty acids onto the surface of an aqueous solution of metal ions.It is different from the traditional Langmuir monolayer technique.Fatty acids and metal ions self-assembled into layered nanosheets with the aid of hydrophobic interaction of alkyl chains and coordination between carboxylic groups and metal ions during the process of spreading of the organic solution at the interface and mutual diffusion of the organic solution and the aqueous solution.The sides facing to air and the subphase are composed of alkyl chains and carboxylates,respectively,indicating that the nanosheets are Janus ones.Various organic solvents,metal ions and fatty acid molecules have been tried to fabricate such layered Janus nanosheets.2.Assembly of large area metal-organic layered ultrathin filmsThe planar liquid/liquid interface between the chloroform solution of the ligands and pure water was constructed firstly,and then the aqueous solution of EuCl3 was added dropwise into the water phase.A film appeared at the liquid/liquid interface after 24 hours.TEM,HRTEM and XRD results indicated that large area layered ultrathin films formed at the liquid/liquid interface;EDS confirmed the existence of Eu(?)element.The monitoring results showed that the formation of the ultrathin films was a result of continuous epitaxial growth of a monolayer film.Synergistic effects of hydrophobic effects,coordination bonds and?-? interactions between the ligands,and the restriction of the interface on the vertical growth are responsible for the formation of the films.The influences of ligands with different molecular structures and metal ions were investigated.This work opens a novel way to fabricate large area ultrathin layered metal-organic films by using common amphiphilic ligands.3.Assembly of large area metal-diacid layered ultrathin filmsWe further extended this method to the bola-type amphiphilic molecule.In the absence or presence of metal ions,large area layered ultrathin films containing perfluorodecanedioic acid were successfully prepared at the liquid/liquid interface.It was found that the ultrathin thin film of PFDDA/Zn(?)has a hexagonal closed packed crystal structure with the crystal parameters of a=0.302 and c=1.9 nm.The formation of the film was attributed to the weaker intermolecular interactions,the restriction of the interfacial phase,and the epitaxial growth.However,dodecanedioic acid and docosanedioic acid formed nanosheets instead of large area films through this approach,reflecting different self-assembly behavior of the perfluorocarbon chains and the hydrocarbon chains.This work will enrich the study on the self-assembly behavior of bolaamphiphilic molecules,and may open a way to prepare large area of layered ultrathin films of functional amphiphilic molecules.