Production And Functional Investigation Of Ultrathin Metal-Organic Framework (MOF) Nanosheets

Two-dimensional nanomaterials have become a research hotspot in the field of nanomaterials because of their potential applications in optical,electrochemical,and catalytic science.This paper briefly describes the main methods for preparing two-dimensional nanomaterials,including top-down and bottom-up methods,and based on which a novel and efficient approach to prepare two-dimensional MOF nanosheets was proposed.With this method,two-dimensional single-layer MOF nanosheets can be well prepared and functionalized.At the same time,the applications of the obtained MOF nanosheets were also explored.The main contents of the paper are summarized as follows:?1?A ligand replacement approach was for the first time used for the production of two-dimensional single-layer MOF nanosheets with three-dimensional layer-pillared MOF precursors.After competitive coordination and subsequent ligand replacement processes,the pillared bridged ligands in the three-dimensional layer-pillared MOFs can be replaced by terminal ligands with more strong coordination capacity,thus forming two-dimensional single-layered MOF nanosheets.The resulting nanosheets were systematically characterized by X-ray Powder Diffraction?XRPD?,Scanning Electron Microscopy?SEM?,and Atomic Force Microscopy?AFM?.The formation process of MOF nanosheet was observed by SEM.The XRPD pattern shows regular diffraction,which indicates that MOF nanosheets have been successfully prepared with a perfect layered structure.The results of AFM measurement show that the thickness of the obtained MOF nanosheets is consistent with the thickness simulated from the crystal data,which indicates that the MOF nanosheets have monolayer thickness.Measurement of water contact angles demonstrated that the surface of MOF nanosheets was hydrophobic,further indicating that both sides of the monolayer MOF nanosheets were modified with hydrophobic pyridine groups.Based on this,the adsorption and separation of benzene/cyclohexane and oil-water separation by MOF nanosheets were explored.?2?The ligand replacement approach was further used to prepare two-dimensional single-layer MOF nanosheets with two-dimensional layer coordination polymers as precursor.The resulted Co?II?nanosheets were systematically characterized by XRPD,SEM,and AFM.The results show that the thickness of the MOF nanosheets is in good agreement with the value analyzed from the XRD results and simulated from the crystal data,further demonstrating that two-dimensional single-layer MOF nanosheets were obtained.Co?II?nanosheets were used as catalysts for the photocatalytic reduction of CO₂ to CO.The result shows that in CH₃CN/H₂O system?v/v=4:1?,a TON of 345 and a TOF of 34.5 h^-1 were achieved.The selectivity to CO reaches as high as 98%.Finally,the superiority of ligand replacement approach for the preparation of functionalized monolayer MOF nanosheets was concluded,including highly efficient,environmentally friendly,low-cost and so on.