Synthesis And Applicaions Of Metal-organic Frameworks Derived Hollow Materials

Metal-organic frameworks(MOFs)with diverse chemical compositions and tunable structures are ideal precursors for preparing a variety of inorganic materials.Introducing hollow structure to catalysts could endow them with characteristics of low density and large specific surface area,which make catalysts not only expose more active sites,but also have a faster mass transfer rate,thus attracts widespread interests.This thesis mainly focuses on the synthesis of MOF-derived hollow materials and their catalytic properties.Several MOF-derived hollow structures,including hollow mesoporous MOF,hollow mesoporous LDH,multi-shelled hollow LDH and hollow mesoporous carbon materials were prepared by using different MOFs as precursors.The structure-performance relationship was investigated through 4-chlorostyrene oxidation,benzyl alcohol oxidation,oxygen evolution reaction and oxygen reduction reaction.The main contents and conclusions are shown as follows:1.Metal-organic frameworks(MOFs)with uniform porous structures show great promise for size/shape-selective catalysis,however,their microsized pores and narrow channels inherently limit the diffusion of catalytic substrates and their catalytic efficiency.To overcome their drawbacks,we designed a hollow mesoporous MOF with hollow macroporous core and mesoporous shell,featuring a hierarchical porous structure that allows fast diffusion of reactants.The hollow core and mesoporous shell of the MOF were achieved by an elaborate design of a bimetallic MOF with stability differences in both metal-ligand bonds and spatial distribution via a boosted nucleation process,followed by selective etching treatment.Impressively,the hollow mesoporous MOF greatly enhanced the mass diffusion,which is demonstrated by the diffusion experiments,the molecular dynamics simulation,and the catalytic reaction by using 4-chlorostyrene as a probe.In addition,the as-prepared hollow mesoporous MOF exhibited superior catalytic performance when utilized as Pd nanoparticles carrier compared with solid Pd/MOF and commercial Pd/C catalysts toward benzyl alcohol oxidation.2.Layered double hydroxide(LDH)is a sort of two-dimensional materials with diverse chemical compositions.We developed a facile strategy to synthesize hollow mesoporous ternary NiCoFe-LDH(HM-LDH)with highly efficient OER performance.Uniform cobalt 2-methylimidazole(ZIF-67)polyhedrons are utilized as the template which is in-situ transformed into HM-LDH by a simple etching and growth process in the ethanol solution of nickel nitrate and iron nitrate.In particular,benefiting from the hollow mesoporous structure with fully exposed active sites and easy electron/ion transport kinetics,the obtained HM-LDH exhibits outstanding OER performance,outperforming solid NiCoFe-LDH sheet powder(SP)and commercial IrO2.3.Hollow layered double hydroxide with sophisticated structure,such as multiple shells,is a sort of promising materials for various applications,which cannot only boost the performances of LDHs but also endow them with innovative properties.We developed an in-situ transformation strategy to fabricate multi-shelled hollow NiZnCoFe LDH(MSH-LDH)using multi-layered MOFs as templates.Particularly,the as-prepared triple-shelled hollow NiZnCoFe LDH(TSH-LDH)outperformed the double-shelled and single-shelled hollow NiZnCoFe LDH(DSH-LDH,SSH-LDH)in oxygen evolution reaction.This work not only provides a novel strategy to construct multi-shelled LDHs,but also elucidates the superiority of multi-shelled hollow nanostructures in oxygen evolution reaction.4.Combining the advantages of hollow structure and mesoporous structure,the synthesis of hollow mesoporous carbon materials can promote the diffusion of electrons,ions and electrolytes,and greatly improve the performance of carbon materials in the field of electrochemistry.Hollow mesoporous carbon materials were prepared by using polyoxometalate(POM)encapsulated ZIFs as precursors.The structure of hollow mesoporous carbon materials was regulated by using different kinds of POMOF as precursor.The results showed that the construction of hollow or mesoporous structure greatly promotes the electrochemical performance of carbon materials in oxygen reduction reaction.