Metal-organic Framework Nanosheets Based On Zr/Hf-oxo Clusters For Catalytic Cyclohexane Oxidation

Metal-organic frameworks(MOFs)are a new type of materials that have emerged in the past two decades.They are constructed from metal connecting nodes and multi-topic ligands.By varying different metal nodes and ligands,MOFs can be designed into materials with unique structures and functions.The applications of MOFs include gas separations,catalysis,sensing,nonlinear optics,nanomedicine etc.MOFs have tremendous potentials both as applied materials and in scientific research.Nano-metal-organic frameworks(nMOFs)are MOFs of nano size which are particularly useful in catalysis,sensing and nanomedicine,etc.A series of Zr-nMOFs with linear dicarboxylic acids have been found wide applications in nanomedicine.However,their crystal structures were not solved.In this thesis,we have systematically studied the synthesis of these Zr-MOF series and determined the structure by rotation electron diffraction(RED)method.We found the structures of two nMOFs,Hfi2-BPDC and Zr12-BPYDC,were built from Zr12-oxo or Hfi2-oxo clusters as SBU in the hcp topology.We subsequently confirmed the structure model with powder X-ray diffraction(PXRD)patterns,N2 sorption isotherms,thermogravimetric analysis and electron microscope images.And we have obtained empirical formulas of the nMOFs.With a combination of dynamic light scattering(DLS)measurements and contact angle tests,we further proved that the nMOFs were terminated with SBUs instead of dangling ligands.Furthermore,with a 2,2'-bipyridine-5,5'-dicarboxylate ligand(BPYDC),we have built the Zri2-BPYDC in the series and loaded transition metals on the BPYDC sites to catalyze the oxidation of cyclohexane with hydrogen peroxide as the oxidant.Cu was found to exhibit the best catalytic activity.Cu with different oxidation state and counterions were used to construct the catalysts,and the reaction time was also varied to optimize the yield.Zr6-BPYDC,an isoreticular MOFs of UiO-67,and BPYDC-MOF-253 were also functionalized with Cu to compare with Zr12-BPYDC.We demonstrated that the unique morphology and bimetallic sites in the structure of the Zr12-BPYDC provide unique opportunities in generating free radicals in Fenton-like processes.These results suggest potentials of the M12-nMOFs in heterogeneous catalysis.