Advanced Functional Materials Based On Organic/Inorganic Layered Materials Fabricated By Supercritical Carbon Dioxide

With the development of society,the problems of energy depletion and excessive carbon emission are becoming more and more serious.The establishment of an energy-saving and environment-friendly society has become a common and beautiful expectation of human beings.Among them,the use of supercritical CO₂ to assist in the preparation of advanced functional materials with excellent optical,electrical and magnetic properties is considered to be effective in improving energy utilization rate while achieving the recycling of CO₂.With the advantages of low viscosity,high permeability,and small size（3.3（?））,supercritical CO₂ can not only achieve the exfoliation of layered materials through interlayer intercalation,but also induce the self-assembly of two-dimensional（2D）materials into heterogeneous structures.Based on the above research background,this thesis selects layered metal-organic framework materials（MOFs）and inorganic transition metal oxide materials（Mo O₃）,which are typical layered materials with suitable layer spacing,for free shuttling of CO₂molecules between layers.The nanoscale behavior of supercritical CO₂ in the process of stripping and constructing heterojunctions was investigated experimentally.In addition,the applications of the prepared materials in the field of photoelectromagnetism including photocatalytic CO₂ reduction,electrocatalytic oxygen precipitation（OER）reaction and photomagnetic properties were further investigated,mainly as follows.（1）Preparation of 2D Ni-BDC MOF nanosheets by exfoliation of supercritical CO₂ in pure water system and photocatalytic investigationIn this work,single-layer Ni-BDC（BDC=terephthalic acid）MOF nanosheets were successfully prepared by exfoliating supercritical CO₂ in pure water system,and CO₂ molecules were inserted between the layers to break the interlayer hydrogen bonding force.In addition,the chemisorption behavior of CO₂ on the Ni-BDC MOF surface during the exfoliation process was investigated by synchrotron radiation and in situ infrared characterization.This chemisorption has a"pre-activation"effect on the material for photocatalytic CO₂ reduction applications.The prepared monolayer Ni-MOF nanosheets exhibited high CO yield(16.6 mmol·g^-1·h^-1)and Faraday efficiency（96.0%）.（2）Preparation of 2D Ni-BDC MOF nanosheets by supercritical CO₂ in ethanol/water solvent system and investigation of photovoltaic propertiesIn this work,the two-phase structure of CO₂-ethanol and MOF-water was constructed by taking advantage of the compatibility of supercritical CO₂ with ethanol,and the exfoliation of layered MOF materials was achieved by using the high-speed shear force between phases.The resulting Ni-BDC MOF nanosheets were prepared by TEM,AFM and other characterization means with large lateral size（2μm）and thin nano-thickness（1.1 nm）.The effects of reaction pressure and solvent ratio on the exfoliation effect were also investigated,and the optimal reaction pressure（16 MPa）and solvent ratio（ethanol/water=3/7）were determined.The Ni-BDC MOF nanosheets prepared by exfoliation exhibited excellent electrocatalytic oxygen precipitation（OER）and photocatalytic CO₂ reduction performance.（3）Supercritical CO₂ in ethanol/water solvent system-assisted construction of Mo O₃/Zr Mo₂O₈heterostructure and its photomagnetic propertiesIn this work,based on the previous work,the self-assembly behavior of 2D materials induced by supercritical CO₂ in ethanol/water system was further investigated,and Mo O₃/Zr Mo₂O₈ heterostructured materials with regular rhombic structure were successfully synthesized.The formation process of Mo O₃/Zr Mo₂O₈ heterostructures was also investigated by time-dependent XRD and FT-IR mapping.The material exhibits surface plasmon resonance（SPR）optical effects,as well as large ferromagnetism(0.132 emu·g^-1)at room temperature.