Construction And Performance Of MOFs Photocatalysts Based On Binaphthol And Perylene Derivatives

Photocatalysis is a clean and sustainable catalytic process,which is of great significance to alleviate the increasingly serious energy shortage and global warming.The development of photocatalysts is the core for the construction of photocatalytic systems.Among numerous types of photocatalysts,small organic molecules have diverse structures and adjustable properties,and exhibit fine catalytic activities toward various types of reactions,thus attracting extensive interests.However,small organic molecule photocatalysts are also faced with the challenge of low stability and difficulty in separation and recovery.Heterogenization is an effective way to solve this problem,and one of the strategies for heterogenization is to introduce them into metal-organic frameworks(MOFs).The extremely high surface area,structural diversity and tailorability make MOFs have huge development potential in the field of heterogeneous photocatalysis.The catalytic sites in photocatalytic MOFs are either located on the metal clusters,in the pores,or on the organic ligands.For photocatalytic MOFs constructed through introducing small organic molecules into the ligands,the active sites are hard to leach,and the preparation is also less complex.At the same time,heterogeneity could improve the stability of small organic molecules and make them easy to be separated and recycled.Moreover,the properties of photocatalytic MOFs can be regulated through the structural adjustments of organic ligands,thereby expanding their applications.Therefore,in this paper,binaphthol derivatives and perylene derivatives with visible light responses and photocatalytic potentials were employed as ligands to construct new photocatalytic MOFs,which were adopted to catalyze different types of organic reactions through structural adjustment of ligands to regulate the reactive intermediates.Besides,the catalytic performance and mechanism of the materials were also systematically studied,providing a reference for the development of new photocatalytic MOFs.Binaphthol derivatives produce phenoxy radicals through excited state proton transfer under light irradiation,which are expected to activate substrates through single electron transfer,thus exhibiting photocatalytic activities.In this paper,the carboxylic acid ligand based on binaphthol structure was synthesized from binaphthol through an optimized synthetic route,and the ligand was adopted to prepare the visible light responsive Zr-MOF-OH through solvothermal method with Zr4+.Under the optimized reaction conditions,Zr-MOF-OH exhibited excellent selectivity and substrate compatibility for the photocatalytic oxidation of over twenty sulfide substrates,while the material also exhibited good cycle stability.A series of mechanism exploration experiments confirmed the formation of phenoxy radicals and the new catalytic mechanism for activating sulfide substrates.This work was the first to adopt phenoxyl radical intermediates to activate substrates and catalyze reactions,and no reactive oxygen species were produced in the reaction,making Zr-MOF-OH have excellent selectivity,substrate compatibility and cycle stability.Besides,it also provided a thread for the application of binaphthol derivatives in the field of photocatalysis.Ligands in Zr-MOF-OH will convert into phenolate anions under alkaline conditions,and the excited phenolate anions exhibit fine reduction capabilities,which can be used to catalyze reduction reactions.Photoelectric measurements indicated that the reduction potential of the excited ligands in Zr-MOF-OH under alkaline conditions was lower than various aryl halides,making this MOF suitable for the photocatalytic activation of such substrates.After a series of condition optimization experiments,ZrMOF-OH was employed for the photocatalytic activation of more than twenty aryl halides,which could be derivated by biaryl cross-coupling,hydrodehalogenation,borylation,and thioetherification through changing the radical receptors.Utilizing the photocatalytic performance of phenolate anions in Zr-MOF-OH under alkaline conditions provided a new method for the derivatization of aryl halides at normal temperature and pressure,and further expanded the photocatalytic applications of binaphthol derivatives.The acidic sites of binaphthol based phosphoric acid catalysts can activate various types of substrates and they are widely used for thermal catalysis.The large conjugated structure of binaphthyl skeleton and the acidity of phosphoric acid are expected to enable it to also have the property of excited state proton transfer,thereby producing active intermediates and activating substrates.In this paper,the phosphate group was further modified on the binaphthol ligand,which was adopted to prepare Zr-MOF-P through solvothermal method with Zr4+.This MOF had similar structure and photoelectric properties to Zr-MOF-OH,and it also exhibited good selectivity,substrate compatibility and cycle stability toward the photocatalytic oxidation of various sulfides.A series of mechanism investigation experiments confirmed the catalytic mechanism,the ligands in Zr-MOF-P underwent the excited state proton transfer process under light irradiation,producing oxygen radicals,which activated the sulfides to directly react with the ground state oxygen.This work broadened the applicability of excited state proton transfer mechanism in the construction of photocatalysts,and it was also the first time that a phosphoric acid catalyst was used for photocatalysis,expanding the application fields of phosphoric acid catalysts.Improving the visible light response of ligands through structural adjustments is an effective way to improve the visible light utilization efficiency of photocatalytic MOFs,and their catalytic properties also can be regulated.A new perylene derivative carboxylic acid ligand was prepared by using larger conjugated perylene as the ligand skeleton,which was further modified with electron-donating methoxy groups according to a new synthetic route.And Zr-MOF-Per was prepared by solvothermal method using the ligand and Zr4+.The characterizations of photoelectric performance confirmed that Zr-MOF-Per exhibited an absorption in the whole visible light band,the visible light utilization efficiency was significantly improved.Mechanism exploration experiments indicated that the structural adjustment of ligand lead to a significant change in the catalytic mechanism of Zr-MOF-Per,which could activate oxygen into reactive singlet oxygen under visible light irradiation.Therefore,Zr-MOFPer not only exhibited higher catalytic activity for the photocatalytic oxidation of sulfides,but also had fine catalytic performance toward the photocatalytic semisynthesis of artemisinin from dihydroartemisinin,which required the participation of singlet oxygen.The construction of Zr-MOF-Per verified the feasibility of constructing photocatalytic MOFs using perylene based derivatives,and demonstrated that the properties of MOFs could be regulated through structural modification of organic ligands,laying a theoretical and experimental foundation for the application of photocatalytic MOFs in more challenging reactions.