Controllable Synthesis And Charge Conduction Properties Of Two-Dimensional Hierarchical Porous Metal-Organic Framework Nanosheets

Two-dimensional（2D）porous nanomaterials have rich pore structures and good solution dime-nsional porous nanomaterials have rich pore structures and good solution processability,bringing opportunities for new generation thin film devices such as electrochemical energy storage devices,s-emiconductor devices,and 2D quantum devices.The porous structure is crucial for the application of2D nanomaterials,and the abundant nanochannels shorten the transmission path of electrons/ions,which is beneficial for more electronic applications.2D metal-organic framework materials（2D MOFs）have the advantages of tunable structures,large specific surface area,and high porosity,and widely used in sensing,electrochemical energy storage,catalysis and other fields.However,most 2D MOFs only have microporous structures smaller than 2 nm,showing poor intrinsic conductivity,which is unfavorable for the penetration and transmission of carriers and the adsorption of large molecules,limiting their application in electrode materials and other electronic fields.So far,most of the pore-making methods for MOF crystals have focused on three-dimensional rigid structures.Exploring effective in situ pore-making strategies for 2D MOFs has important significance for their application in electrical conductivity.To solve the above problems,this study makes use of the soft templating effect of surface-active agents to control the sodium dodecyl sulfate（SDS）template and successfully prepares nanosheets of hierarchical porous ZIF-8（HP-ZIF-8）,ZIF-67（HP-ZIF-67）,and bimetallic Zn Co-ZIF（HP-Zn Co-ZIF）with continuous pores consisting of micropores,mesopores,and macropores.Additionally,CeO₂nanoparticles were loaded onto the MOF nanosheets to prepare heterojunction composite materials of HP-ZIF-8@CeO₂ and HP-ZIF-67@CeO₂.Electrochemical tests reveal that the hierarchical porous MOF nanosheets exhibit higher electronic/ion conductivity and excellent electrochemical per-formance when coupled with CeO₂ heterojunction structures.The specific research is as follows:1.2D stratified porous ZIF-8 nanosheets were synthesized in situ using SDS as a soft template agent by precisely controlling the SDS system’s dosage ratio,concentration,and uniformity of dispersion.The product was distributed independently in rectangular shapes with a side length of about 1.2–2μm and a thickness of 30–57 nm.The nanosheets possessed three types of pore structures,namely micropores,mesopores,and macropores,with micropores being the MOF framework pores,while mesopores and macropores exhibited random distributions.The stratified pores were intrinsic through-hole pores.The effects of different SDS dosage ratios and concentrations on pore structure and nanosheet morphology were gradient-controlled,and the mechanism for the formation of the ZIF-8 stratified porous structure was proposed based on this.2.2D hierarchically porous ZIF-67 nanosheets and bimetallic Zn Co-based 2D hierarchically porous nanosheets with different Zn Co ratios were synthesized using SDS as a soft template agent.The resulting HP-ZIF-67 nanosheet product is a rectangular single-layered sheet with an average side-length of 1.8μm,an average aspect ratio of 1.1,and an average thickness of 57 nm.This structure simultaneously exhibits intrinsic mesoporous pores with sizes of 10–30 nm and macroporous pores with sizes of 100–300 nm.The HP-Zn Co-ZIF series nanosheets also possess mesoporous pores with sizes of 10–30 nm and macroporous pores with sizes of 50–200 nm,all of which are intrinsic through pores.Working electrodes were prepared from HP-ZIF-8 and HP-ZIF-67,and EIS fitting calculations in different electrolytes showed that the Rs,Rct,and Wo of the HP-ZIFs nanosheets were lower than those of non-porous ZIFs nanosheets,demonstrating higher electronic/ion conductivity.3.CeO₂ inorganic salt nanoparticles were synthesized by a hydrolysis reaction and loaded onto HP-ZIFs nanosheets,resulting in the formation of HP-ZIF-8@CeO₂ and HP-ZIF-67@CeO₂ heterost-ructure composite materials.The 5–7 nm CeO₂ nanoparticles were uniform Ly attached and grown on the surface of the HP-ZIFs nanosheets.EIS characterization and fitting calculations indicated that the Rs,Rct and Wo of the HP-ZIFs@CeO₂ composite electrodes were lower than those of the pristine HP-ZIFs nanosheets.Further testing revealed that the CV negative voltage window of HP-ZIFs@CeO₂ was-1.0–0V,where 1)the specific capacitance of HP-ZIF-8@CeO₂ electrode was 97.1F g^-1 at 1 A g^-1,about 4 times higher than that of HP-ZIF-8,and the energy density and power density were 13.5 Wh kg^-1 and 500.1 W kg^-1;2)The HP-ZIF-67@CeO₂ electrode exhibits a specific capacitance of 99.4 F g^-1 at 1 A g^-1,approximately three times that of HP-ZIF-67 alone.The energy density and power density of the composite are 13.8 Wh kg^-1 and 499.1 W kg^-1,demonstrating the excellent conductivity and capacitive performance due to the synergistic effects of the heterostructure.