Preparation And Photoelectric Properties Analysis Of Metal Organic Framework Derived Composites

The development of science and technology has brought serious energy crisis and electromagnetic wave pollution problems while improving social productivity.The industrialization of clean energy represented by photovoltaic power generation need the support of efficient energy storage devices.And the research of high-performance electromagnetic wave absorbing materials is of great significance in both civil and military aspects such as human health protection and anti-radar reconnaissance.The construction of high-performance energy storage devices and the preparation of microwave absorbing materials are the current hot research direction in the optoelectronic field.Due to their structural diversity,high specific surface area,and porosity,Metal-organic frameworks（MOFs）become ideal templates for the preparation of high-performance energy storage materials and microwave absorbing materials.In this thesis,a series of composites of metal hydroxide/oxide and conductive materials were prepared using Fe-Co-Ni-based MOFs as template materials,and their energy storage properties and microwave absorption properties were systematically investigated based on the material properties.The main innovative results obtained are as follows:（1）Using MOFs as template materials,high-performance positive materials were synthesized to construct a hybrid supercapacitor with excellent performance.To solve poor electrical conductivity and chemical instability of MOFs,a method combining in situ composite CNTs and inorganic ions（OH^-）replace organic ligands was proposed to prepare CNTs/Ni Co LDH positive materials with micro-spherical structures,using Ni Co MOF as template materials.The test results showed that the CNTs were interspersed in the MOF,which effectively increased the specific surface area(from 222 m² g^-1 to 303m² g^-1)of the material and thus enhanced its specific capacitance(from 595 F g^-1 to 1218F g^-1 at 1 A g^-1).OH^-replacing the organic ligand could well preserve the micro-spherical structure of MOF while enhancing its electrochemical stability（72.9%Coulomb efficiency for CNTs/Ni Co MOF,and 96.1%for CNTs/Ni Co LDH）.Using CNTs/Ni Co LDH as positive electrodes and AC as negative electrodes,CNTs/Ni Co LDH//AC hybrid supercapacitors were constructed.It had an energy density of 38.89 Wh kg^-1 at 800 W kg^-1 and a specific capacitance retention rate of 99.379%after 10000 cycles,showing excellent cycling stability.（2）Using MOFs as template materials,battery-type negative materials were prepared to construct high energy density asymmetric supercapacitors.To solve the low specific capacitance of carbon materials,Fe₂O₃/RGO negative materials were prepared using Fe-MOF as template materials.Different from AC,the energy storage mechanism of Fe₂O₃/RGO was predominantly diffusion-controlled,with charge storage via redox reactions,which exhibited a high voltage window of-1.2-0 V and specific capacitance of734 F g^-1(1 A g^-1).To verify its application capability,using Fe-Co-Ni-OH as the positive electrode,which were prepared using Fe-MOF as template materials,AC and Fe₂O₃/RGO as the negative electrode,Fe-Co-Ni-OH//AC hybrid supercapacitors and Fe-Co-Ni-OH//Fe₂O₃/RGO asymmetric supercapacitors was constructed,respectively.At 800 W kg^-1,the former had an energy density of 24.44 Wh kg^-1,and the latter had an energy density of 43.11 Wh kg^-1.In addition,the CNTs/Ni Co LDH//Fe₂O₃/RGO asymmetric supercapacitor constructed with CNTs/Ni Co LDH（Chapter 2）as the positive electrode and Fe₂O₃/RGO as the negative electrode achieved an energy density of 57.55 Wh kg^-1 at800 W kg^-1.The above research fully demonstrated that constructing high-performance energy storage devices can be constructed by enhancing the electrochemical performance of the negative electrode materials.（3）Using MOFs as template materials to design composites with good microwave absorption and loss properties.Fe₂O₃ materials prepared with Fe-MOF as the template material not only have excellent energy storage properties,but also are a good magnetic loss type microwave absorption material.By combining with Ti₃C₂T_x to improve the dielectric loss,Fe₂O₃/Ti₃C₂T_x composites with good microwave absorption performance are obtained.Ti₃C₂T_x can provide large conductivity loss due to its own excellent conductivity,and X-ray photoelectron spectroscopy indicates the presence of surface functional groups,which is conducive to polarization relaxation loss.Spindle-like Fe₂O₃is interspersed with Ti₃C₂T_x,which can increase the layer spacing of Ti₃C₂T_x and increase the contact area between microwave and material,and the multireflection effect is enhanced to improve the microwave loss capacity.The electromagnetic parameters and impedance matching were adjusted by changing the ratio of Fe₂O₃ to Ti₃C₂T_x（1:1,1:2,1:3,and 1:4）,and the microwave absorption capacity of materials was further optimized.When the mass ratio was 1:3,its|Z_in/Z₀|was closest to 1,indicating its microwave absorption capacity attained best.Fe₂O₃/Ti₃C₂T_x composite exhibited good microwave absorption performance with a minimum reflection loss of-34 d B and an effective bandwidth of 1.53 GHz at a thickness of 3 mm,and bandwidth of 2.805 GHz at 1.5 mm.