Synthesis Of Lanthanide And Zirconium-based MOFs By Using Tetracarboxylate Ligands And Studies Of Their Photocatalytic Properties

Metal-organic frameworks（MOFs）are a class of highly porous organic/inorganic hybrid materials with high surface area,tunable functionality and rich catalytic active sites,which have been widely used as heterogeneous catalysts.MOFs are excellent platforms for the construction of visible photocatalysts due to their ability simultaneous incorporation of photosensitizers and catalytic active sites in the framework.Using the light-harvesting antenna effect,the ligands in the MOFs can absorb light energy promoting transfer electrons to the catalytic active site through a charge/energy transfer process,making its to possess photocatalytic capability.MOFs with the porous,crystalline and high density active sites are able to improve photogenerated carrier efficiency and reduce the complexation of photogenerated electron-hole pairs,thus enhancing its photocatalytic properties.In this thesis,two types of photoactive organic ligands were designed and the corresponding MOFs were synthesized using a backbone side chain grafting functional group strategy:（1）Design and synthesis of tetracarboxylic acid linear organicligandsH₄BTDI{5,5’-（benzo[c][1,2,5]thiadiazole-4,7-diyl）diisophthalic acid}functionalized with benzothiadiazole（BTz）,which were constructed with lanthanide metals(Ln³⁺)to form photoactive Ln-MOFs;（2）Bay-modified perylene-based tetracarboxylic acid organic ligands,H₄TABPery-buto₄[4,4’,4’’,4’’’-（1,6,7,12-tetrabutoxyperylene-2,5,8,11-tetrayl）tetrabenzoic acid],were designed and synthesized to construct visible light responsive Zr-MOFs with zirconium(Zr⁴⁺).The properties of the above Ln-MOFs and Zr-MOFs for visible light-mediated catalytic oxidation of thioethers was systematically investigated.（1）Synthesis and visible light-mediated catalytic oxidation of thioethers by nano coordination polymers Ln-BTDIA series of nano coordination polymers Ln-BTDI were synthesized using a microwave-assisted synthesis method with benzoic acid as modulator（10 equivalents of benzoic acid,with respect to the ligand）and H₄BTDI as the organic ligand with lanthanide metals(Ln³⁺=La,Ce,Eu,Gd,Tb,Er,Yb).Taking Gd-BTDI as an instance,the synthesized nanospheres have a diameter of 100～150 nm,the BET specific surface area of 36.04 m²/g and bandgap of 2.58 e V.Gd-BTDI can serve as heterogeneous photocatalysts for selective aerobic oxidation of a broad range of thioanisole to their corresponding sulfoxides under visible light irradiation（blue LED,3 W）at room temperature at oxygen atmosphere with high efficiency and excellent selectivity,and be reused for 6 times without significantly decrease in catalytic activity.The mechanism of Gd-BTDI photocatalytic oxidation of anisole reaction was proposed by combining electron paramagnetic resonance spectroscopy（EPR）and free radical active species capture experiments.（2）Synthesis and visible light-mediated catalytic oxidation of thioether by Gd-MOF and Tb-MOFGd-MOF single crystals and Tb-MOF single crystals/microcrystals were synthesized by H₄BTDI and Gd³⁺or Tb³⁺in a reactor at 160℃for72 h using inorganic strong acids（H₂SO₄,HNO₃,HCl）as modulator and water and N,N-dimethylformamide（DMF）as mixed solvents.In contrast to the Gd-BTDI and Tb-BTDI nano coordination polymers,although both Gd-MOF and Tb-MOF are constructed from BTDI,their photocatalytic oxidation of thioethers property is inferior to that of their corresponding nano-ligand polymers under the same photocatalytic conditions.The possible reason is that the smaller size of the Gd-BTDI and Tb-BTDI nano coordination polymers is more conducive to photogenerated electron-hole pair separation compared to single crystals or microcrystals,promoting superior photocatalytic properties.（3）Synthesis of perylene-based Zr-MOFs and properties of visible light-mediated catalytic oxidation of thioethersPerylene-based Zr-Perybuto was synthesized by microwave synthesis and solvothermal synthesis using perylene-based H₄TABPery-buto₄ as the organic ligand and ZrOCl₂·8H₂O as the metal source,with benzoic acid（BA）/trifluoroacetic acid（CF₃COOH）or o-fluorobenzoic acid（o-FBA）/trifluoroacetic acid（CF₃COOH）as co-modulator,respectively.The perylene-based Zr-Perybuto _MWsynthesized using microwave synthesis with o-FBA and CF₃COOH as co-modulator has a regular octahedral morphology with sizes between 2～3μm,the BET specific surface area of 395.40 m²/g and bandgap of 2.44 e V.Zr-Perybuto _MW can serve as heterogeneous photocatalysts for selective aerobic oxidation of a broad range of thioanisole to their corresponding sulfoxides under visible light irradiation（blue LED,3 W）at room temperature at oxygen atmosphere with high efficiency and excellent selectivity,and be reused for 6 times without significantly decrease in catalytic activity.The mechanism of Zr-Perybuto _MW photocatalytic anisole reaction was proposed by combining electron paramagnetic resonance spectroscopy（EPR）and free radical active species capture experiments.In addition,the properties of the bay-site unmodified perylene-based Zr-MOF（UMCM-313）,photocatalytic anisole was also investigated.Comparative experiments revealed that Zr-Perybuto _MW and UMCM-313 have similar photocatalytic properties under the same reaction conditions.It is worth pointing out that the synthesis of the H₄TABPery ligand used in the synthesis of UMCM-313 requires expensive iridium complexes,which are costly and have low yields.In contrast,H₄TABPery-buto₄ uses an inexpensive oxidant and has a high yield,providing a new idea for the construction of perylene-based MOFs.The perylene-based Zr-Perybuto-1 was synthesized using a solvothermal synthesis method with BA and CF₃COOH as co-modulator as irregularly shaped and unevenly distributed octahedra with sizes ranging from 2～10μm,the BET specific surface area of 377.24 m²/g and bandgap of 2.39 e V.The synthesized perylene-based Zr-Perybuto-1efficiently and selectively oxidizes the mustard simulant 2-chloroethyl ethyl sulfide（CEES）to a low toxicity sulfoxide product（CEESO）under room temperature,oxygen atmosphere and visible light irradiation（blue LED,3 W）,and the catalyst retains high catalytic activity after 10 cycles.A reaction mechanism for the visible photocatalytic degradation of CEES by Zr-Perybuto-1 were proposed combining with electron paramagnetic resonance spectroscopy（EPR）.