Design And Catalytic Application Of Functional Hollow Metal-organic Frameworks (MOFs) Microspheres

In recent years,hollow metal organic frameworks（HMOFs）materials have been widely studied and applied because of their hollow structure and inherent characteristics of MOFs.In particular,hollow MOFs,as an excellent carrier matrix candidate,not only possess abundant active sites and large specific surface area,but also their hollow structure provides a prerequisite for accelerated mass transfer in the field of catalytic applications.This paper starts from the functional design of hollow MOFs cavity,the functional design of hollow MOFs shell and the construction of hollow MOFs,aiming to solve the following three problems:（I）Large-sized molecular homogeneous catalysts are difficult to be immobilized or the degree of freedom is reduced after immobilization by MOFs;（Ⅱ）Au/MOFs catalyze the synthesis of imines with low TOF value;（Ⅲ）Some shortcomings of hard template technology in the construction of hollow MOFs,etc.The details are as follows:（1）Chiral metal-organic frameworks（CMOFs）have been widely developed and applied in heterogeneous asymmetric catalysis.However,the ways to introduce large-sized and efficient homogeneous asymmetric catalysts into MOFs as well as retain their degrees of freedom remain a great challenge.We successfully confine/encapsulate the large-scale,efficient,and classical homogeneous asymmetric catalyst Salen（Mn（III））into the hollow cavity of hollow ZIF-8 by template method,denoted as yolk-shell chiral salen（Mn（III））@ZIF-8.The catalyst,featuring large-cavity,low density and amphiphilic characteristics,could act as a nano-reactor to accelerate mass transfer and possess phase transfer capability in asymmetric catalysis.As a proof of concept,it was applied to the oxidation kinetic resolution asymmetric reaction that featured an organic-aqueous two-phase system.It exhibited an enhanced catalytic performance with 88%conversion and 90%ee value,which were comparable to that of homogeneous chiral Salen（Mn（III））catalyst.In addition,it still maintains good catalytic activity after being recycled for 4 times.This strategy for the internal functionalization and design of hollow MOFs cavities provides a new feasible scheme for the immobilization of large-scale molecular homogeneous catalysts.（2）The development of efficient heterogeneous catalysts for one-pot tandem/cascade synthesis of imines remains meaningful and challenging.Therefore,as the shell functional design of hollow MOFs,we successfully constructed an Au/MOFs catalyst featured hollow properties and double ZIF-8 shell structure using polystyrene templates（named as Void|（Au）ZIF-8|ZIF-8）.Owing to its structural merits and acid-basic nature,the as-synthesized Void|（Au）ZIF-8|ZIF-8 catalyst exhibited an enhanced synergistically catalytic performance for tandem catalytic synthesis of imines from benzyl alcohol and aniline under air atmosphere and solvent-free condition.Its 170.16 h^-1 of turnover frequency（TOF）was 2.5 times higher than that of the reported catalyst with the highest TOF value.Undoubtedly,this strategy of constructing delicately structured catalysts by functionalizing the shell of hollow MOFs provides a new route for the synthesis of multifunctional catalysts.（3）Hollow MOFs are renowned and important to the material field as a peculiar structural material.After a comprehensive analysis of the first three chapters,we found that the application of template method to construct hollow MOFs under mild conditions is rational,but difficult to construct hollow MOFs in harsh environments.Thus,a novel strategy is developed to produce hollow Cr-MOFs.It relies on the regulation of hydrothermal driven polymer templates to produce phase state transition（viscous-flow state）and escape,thus avoiding the extra template extraction process and the use of toxic organic swelling agents.Hollow MIL-101（Cr）（denoted as Void@MIL-101）with well-defined morphology and exquisite structure can be obtained by polymer templates in this strategy.The Void@MIL-101/Pd prepared from Void@MIL-101 is implemented for catalytic one-pot tandem reductive amination to synthesize secondary aromatic amines,exhibiting the accelerated mass transfer effect of hollow structure and even unambiguous catalytic selectivity.Besides,the technology also enables us to create hollow mesoporous Si O₂,and hollow CPM-243（Cr）.We anticipate that this phase state transition and escape strategy might provide an avenue for the development of hollow materials.In summary,this thesis focuses on the design and synthesis of functionalized hollow MOFs,and deeply explores the effect of functionalized hollow MOFs catalysts on the catalytic performance.The research mentality of this thesis and the proposed construction strategy will provide an effective feasibility scheme for the development of novel catalyst materials.