Designed Synthesis And Properties Of Photoelectric Functional Zirconium-Based Metal-Organic Framework Materials

Metal–organic frameworks（MOFs）are an emerging class of highly ordered crystalline porous materials composed of metal nodes and organic ligands connected by coordination bonds.MOFs are widely used in heterogeneous catalysis,gas adsorption and separation,chemical sensing and biomedicine because of their large specific surface area,high porosity,rich composition,and diverse structural types.With the depletion of traditional energy sources and the prospect of carbon neutrality,new energy fields such as solar cells,photocatalysis,and electrochemical energy storage have been rapidly developed.In terms of the structural characteristics of MOFs,the construction of photoelectric functional MOFs and their application in the field of new energy has become a research hotspot.As an important branch of the MOFs family,zirconium-based metal–organic frameworks（Zr-MOFs）with excellent hydrothermal and structural stability provide an ideal platform for the synthesis and performance studies of photoelectric functional MOFs.By rationally modifying and arranging inorganic nodes or organic ligands in Zr-MOFs,the optical,electrical,and magnetic functions of Zr-MOFs can be precisely regulated,and the application scope of MOFs in the field of new energy can be broadened.In this dissertation,a series of stable Zr-MOFs with photoelectic functions were prepared by using mixed ligands or post-synthesis modification strategies,and their performances were investigated for perovskite solar cells,photocatalytic CO₂ reduction,and supercapacitors.The main innovative achievements of the thesis are as follows:1.A series of multicomponent MOFs,namely PCN-139（Zn）-n（n=1–8）,were synthesized through the one-pot method,whose structures consist of 2D layers formed by Zr₆ clusters and TCA ligands and Zn-TCPP ligands as pillars（H₃TCA=tris（4-carboxyphenyl）amineandZn-TCPP=[5,10,15,20-tetrakis（4-carboxyphenyl）porphyrinato]-Zn（II））.In the PCN-139（Zn）-n series,the defect number and pore sizes can be controlled by adjusting the ratios of the electron acceptor Zn-TCPP to the electron donor TCA ligand,thus tuning the charge transport in the motif.Density functional theory（DFT）calculations confirmed the integration of organic donor–acceptor fragments into the stable Zr-MOF system.Furthermore,PCN-139（Zn）-n series were used as an additive to the precursor solution of perovskite to fabricate Zr-MOF-encapsulated perovskite solar cells（PSCs）.Notably,the dopant based on a suitable ratio of Zn-TCPP to TCA in PCN-139（Zn）-5 boosted the interfacial charge extraction and transport,thus significantly improving the cell performance.Additionally,the introduced Zr-MOFs can prevent the intrusion of water molecules into the perovskite films thereby greatly enhancing the long-term thermal and light stabilities of modified PSCs.2.DTDA（1,2-diamino-3,6-bis（4-carboxyphenyl）benzene）ligand and Co metal site were introduced into the skeleton of a flexible Zr-MOF（PCN-700）through the post-synthesis modification strategy to obtain the photocatalyst PCN-700-DTDA（Co）with high catalytic activity.The successful introduction of DTDA ligand and Co metal sites was confirmed by a series of characterizations,and the as-synthesized PCN-700-DTDA（Co）exhibited good stability and wide light absorption range.Furthermore,it was confirmed by X-ray single crystal diffraction and X-ray photoelectron spectroscopy（XPS）that the amino groups in the DTDA ligand could anchor the Co metal sites.In the presence of sacrificial agents and photosensitizers,PCN-700-DTDA（Co）can rapidly convert CO₂ to CO after irradiation with a monochromatic LED lamp（λ=420 nm）with a conversion rate of 7.62 mmol g^-1 for 2 h,which was 69 and59 times that of PCN-700 and PCN-700-DTDA,respectively.3.By post-synthesis modification of pbz-MOF-1,a stable Zr-MOF containingπ-conjugated nanographene moiety,namely PCN-136,was prepared.PCN-136 consists of a Zr₆ cluster and a hexacarboxylate ligand HCHC（hexakis（4-carboxyphenyl）hexabenzocoronene）centered on aπ-conjugated hexabenzocoronene unit.Benefiting from the presence of sp²-bonded carbon atoms in the ligands,the conductivity of PCN-136 was greatly improved compared to pbz-MOF-1.Furthermore,PCN-136 was used as an electrode material for supercapacitor to explore its electrochemical energy storage properties.In 6 M KOH aqueous solution,PCN-136exhibited a specific capacitance of 694 F g^-1 at a current density of 0.5 A g^-1,which was2.5 times that of pbz-MOF-1.