Research On The Preparation And Properties Of Metal-organic Framework Films With Regular And Ordered Two-dimensional Structures

Metal-Organic Frameworks(MOF)are porous crystalline materials with a periodic network structure composed of metal ions and organic ligands.Due to its diverse structure and adjustable performance,it stands out from many materials and is widely used in many fields.With the in-depth research on MOF materials,the preparation of MOF into thin films is a key step for their application in devices.In particular,if a macroscopically ordered and anisotropic MOF film is prepared,it will achieve more unique applications in the fields of sensing,bioanalysis,microelectronics and optics.However,during the preparation of MOF films,the discontinuity of crystal growth will cause problems such as large gaps between the polycrystals on the film surface and poor crystal alignment and orientation,resulting in poor mechanical properties and chemical stability of the film,and serious problems.Affect the performance and application of the film.Therefore,this article explores the use of copper hydroxide nanowire arrays as the precursor,and proposes a new idea of preparing continuous,dense and regular and orderly pore structure of MOF film.The main content is:This paper explores the growth mode of MOF film,and deeply studies the growth mechanism of continuous and uniform polycrystalline MOF film and the regulation mechanism of crystal orientation growth during the formation of polycrystalline MOF film.On the basis of summarizing the commonly used MOF film preparation methods and a series of characterization methods for the film,a scheme of preparing Cu-MOF film by secondary growth method using copper hydroxide nanowire array as the sole metal source is proposed.In this scheme,firstly,the concentration of the reactants is adjusted to generate copper hydroxide nanowires with high aspect ratio characteristics,and then an array of copper hydroxide nanowires is formed on an indium tin oxide(ITO)substrate using a fluid-assisted method.On the prepared copper hydroxide nanowire array,this article uses field emission scanning electron microscope(SEM)to observe and verify the order of the nanowire array.In the second step of this scheme,the copper hydroxide nanowire array substrate is immersed in an organic ligand solution at room temperature,and a Cu-MOF film with a thickness of about 0.9 um and a roughness of 84.73 nm is formed through the displacement reaction.For the obtained Cu-MOF thin film,the crystal preferred orientation(CPO)index of the thin film is calculated according to the X-ray diffraction measurement pattern.In particular,the CPO index calculated for the(00l)direction of the film is all greater than 50,indicating that the film has a clear(00l)orientation.In addition,this article analyzes the influence of the flow rate on the uniformity and orientation of the film by changing the flow rate of the fluid-assisted method.First of all,the flow velocity when the substrate tilt angle is 30° is the optimal condition for the formation of a uniform film.At larger angles,the excessively fast flow rate weakens the adhesion of the copper hydroxide nanowires on the ITO substrate.At a smaller angle,the copper hydroxide nanowire suspension will deposit on the lower part of the ITO surface,resulting in a significant difference in the thickness of the upper and lower parts of the substrate.However,the experimental results show that the flow velocity has little effect on the orientation of the film.Furthermore,the polarized luminescence characteristics of the film were characterized by a fluorescence spectrometer.The fluorescence spectrum of the dye molecules encapsulated in the Cu-BPDC film gave a polarization ratio of about 2.83,which indicates that the dye is in the film pores arranged along the a axis.Orientation in the middle,thus confirming the regularity of the film pore structure.The research in this paper brings effective new ideas for the preparation of two-dimensional structured regularly ordered MOF films in areas where anisotropic physical properties are important,the use of hydroxides as precursors for MOF preparation,and the control of film orientation growth at the nanoscale.