Size Control And Structure Analysis Of Two-dimensional Au(Ⅰ)-MPA Nanoassemblies

Two-dimensional materials exhibit excellent performance in catalysis,sensing,energy storage,electronics and other applications.Compared with static covalent and inorganic nanomaterials,supramolecular two-dimensional nanomaterials are highly dynamic,complex and adjustable due to the combined effects of various weak interaction forces such as host and guest interaction,electrostatic interaction,hydrogen bonding,etc.These characteristics give supramolecular two-dimensional materials new functional characteristics,such as stimulus response,sensing,molecular recognition,etc.However,these properties also pose a challenge to the size control and structure analysis of supramolecular two-dimensional nanomaterials.Among known supramolecular two-dimensional nanomaterials,Au(Ⅰ)-thiolate two-dimensional nanomaterials are one of the hot topics in science and technology.They are widely used in the fields of photopoluminescence,chiral sensing,preparation of gold nanoparticles or clusters of precursor materials,etc.As is known to all,the structure of materials determines the performance,and the performance determines the application.However,due to the small crystal size,poor structurality and extremely sensitive to electron beam,there is currently no effective means to analyze the structure information of two-dimensional Au(Ⅰ)-thiolate nanomaterials except powder X-ray diffraction(PXRD)characterization technology,which greatly limits the application of this kind of materials.At the same time,due to the complexity of supramolecular self-assembly system,the controllable preparation of such materials is also a challenge.In order to expand the method of controllable preparation and structure characterization of two-dimensional Au(Ⅰ)-thiolate nanomaterial,this paper takes the two-dimensional Au(Ⅰ)-mercaptopropionic acid(Au(Ⅰ)-MPA)nanomaterial system as the research object,and aims to characterize the structure of the material by selective electron diffraction(SAED).In order to reduce the thermal radiation damage caused by high-energy electron beam on the material,The preparation of Au(Ⅰ)-MPA two-dimensional layered nanomaterials with high electron beam radiation tolerance was studied in detail,and the SAED information of the materials was obtained by cryo-electron microscopy.Then,the SAED information was combined with the morphology and PXRD data of the corresponding assembly to analyze the structure information.Firstly,we explored the influence of experimental parameters such as p H,reaction concentration and water content on the assembly system of Au(Ⅰ)-MPA system in the mixed solvent of ethylene glycol(EG)and water,and made it clear that the solubility of the solvent to the reaction intermediate can be controlled by controlling the proportion of the binary mixed solvent composed of EG and water.Thus,the reaction rate and the number of nucleation during the assembly process can be controlled,and finally the size,crystallinity and yield of the assembly can be controlled.Therefore,the size of Au(Ⅰ)-MPA rhomboid nanosheet can be controlled from about 0.2 μm to about 10 μm only by controlling the ratio of the binary mixed solvent composed of EG and water,realizing the span of two orders of magnitude of the assembly.At the same time,the larger size and higher crystallity Au(Ⅰ)-MPA diamond shaped nanosheets prepared are expected to slow down the destruction rate of their structures under the electron beam,which provides the possibility to obtain the SAED information "before the destruction of the crystal structure".Subsequently,we combined the large size and high crystallity Au(Ⅰ)-MPA diamond shaped nanosheet with the cryo-electron microscope.Under the protection of liquid nitrogen at-170℃,the thermal radiation damage of the electron beam on the nanosheet was reduced,and the SAED information of the Au(Ⅰ)-thiolate layered structural materials was obtained successfully.Combined with the morphology of the corresponding assemblage,the orientation of the arrangement of Au(Ⅰ)-S chains in the Au(Ⅰ)-MPA lamellae,the direction of dominant growth and the distance of the aurophilicity in the assemblage were determined.Combined with the PXRD data,the possible cell parameters and the direction of the band axis of the nanosheet are given.