Design,Synthesis And Catalytic Applications Of Metal-Organc Frameworks-Derived Nanocomposites

Metal-organic frameworks（MOFs）,emerged as a new class of porous crystalline materialsconsist of metal ions or metal-containing clusters in combination with a continuously expanding library of multi-functional organic ligands,heve been developed into a new research field and attracted more and more researchers focused on fabricating.Their fascinating feature of highly ordered porosity as well as large surface areas,functional pore space and modulatory structure made them useful for applications in gas storage and separation,molecular recognition,sensing,drug delivery,catalysis and electrochemical capacitance of energy and environmental field.In recent years,more nand more papers have been reported MOFs as template to synthesize nanostructured porous materials.MOFs have been proved to be ideal sacrificial templates for fabricating their respective derivatives by changing the thermal conditions in the different atmosphere,such as porous carbons,heteroatom-doped porous carbons,and metal/metal oxide modified porous carbons.The porous carbon-based nanomaterials prepared by this novel MOF-templated route possessed many advantages such as large internal surface area,high crystallinity,tailorable porous structure and easy functionalization with other heteroatoms or metal/metal oxides.Catalytic hydrogenation is one of the most important reactions extensively employed in industry,one of them is reduction of 4-nitrophenol.Traditional,hydrogenation reactions are catalyzed by the noble metal catalyst such as Au,Ag,Pt,Pd-based catalyst,but considering the expensive price and difficulty to recycle,the non-noble metal catalyst（Fe,Co,Ni,Cu and their oxide）emerge at this moment.Because of high surface energies and large surface areas,metal nanoparticles are thermodynamically unstable and apt to aggregate during reactions,thus it’s urgent to protect them from agglomerating and enhance their catalytic activities.MOF-derived metal modified porous carbons will solve this problem.In the chapter Ⅱ,we have synthesized nanostructured Ni-MOF through a typical solvent-thermal synthesis condition.ED patterns are collected by using high resolution transmission electron microscopy（HRTEM）and electron diffraction tomography（EDT）methods,when processing the data and analysizing structure using the SHELX97.Before carbonizing,a hot stage is used for in-situ experiments in TEMto directly observe the change of Ni-MOF.We observe that Ni-MOF was gradually broken at 300 ℃,Ni nanoparticles（NPs）appeared and grew up at 350 ℃.But when the temperature reached 700 ℃,some Ni NPs come out of the carbon and aggregated to larger size.The carbonization temperature of 400 ℃,500 ℃,600 ℃,700 ℃ is confirmed.Furthermore,the Ni NPs carbonized at 600 ℃（Ni-NPC-600）are selected to catalyze 4-nitrophenol（4-NP）,and show high catalytic performance and ultra-high conversion（96%）even after 10 cycles.Herein,we have observed the transition from Ni-MOF to Ni-NPC for the first time using TEM combined with an in situ hot stage,which will be a powerful tool for the carbonization of MOFs to obtain derivations of MOFs with different applications.In the chapter Ⅲ,to verify the rational design and synthesis of different organic linker of MOFs will improve the performance of derivatives.Transmission electron microscopy（TEM）combined with in situ hot stage technique is applied to directly observe the transition from MOF to metal NPs.We have synthesized Ni-ntca（ntca=1,4,5,8-Naphthalenetetra carboxylic acid）,the Ni-ntca is pyrolyzed under the temperature of 400,500,or 600 ℃ to synthesize abundant Ni NPs embedded in hierarchically porous carbon composites which applied in the converting of4-nitrophenol.More importantly,Ni@C-600（carbonizing at 600 ℃）,which has nickel contents of 72.8%,the Ni NPs uniformly disperse in the carbon matrix.The as-prepared samples show high catalytic activity and stability for the reduction of4-nitrophenol（4-NP）to 4-aminophenol（4-AP）with NaBH₄ in aqueous conditions,are much bigger than the previously reported Ni-NPC-600 and other Ni-based catalysts.By contrast,the converting Ni-based MOFs with different ligands to Ni-based catalysts,the catalyst from the shorter ligand exhibite better activity.It is believed that these results will further facilitate the exploration of the technique of the TEM combined with in situ hot stage as a powerful tool in the carbonization of MOFs to obtain MOF-derived materials with different applications.In the chapter Ⅳ,coordination complexes,modularly built from transition-metal clusters as nodes and organic ligands as struts to form an infinite array through extended covalent or coordinate interactions.Because of their facile raw materials,simple to synthesis,bulk to prepare,coordination complexes are used as template sources to prepare carbon-based nanomaterials.This approach provided a new pathway in preparing nanomaterials with simple synthetic route,interesting propertieswhich have been gained much attention of many researchers.The Ni（dmg）₂ was selected as the “proof-of-concept” model to prepare carbon-based nanomaterials.Ni（dmg）₂ has been reported to detect of nickel ions and composed by Ni as metal center and N rich-based organic linker.We report the facile and simple method in preparing non-noble metal Ni-based nanomaterials series through direct thermal conversion of a red precipitate Ni（dmg）₂.The sample composed of much single dispersed mental active site,heteroatom N doped and graphited carbon.Preparing Ni-based nanocatalyst through this method is comparatively low-cost,could be performed at the gram scale,and could be proceed without the aid of additional templates and also the resultant nanocatalysts served magnetic property providing an efficient separation event.In the chapter Ⅴ,nickel based N-doped porous carbon catalyst will improve catalytic activity.Inspired by this,we choose 2,5-thiophenedicarboxylic acid and hexamethylenetetramine as linker to synthesize MOFs（JUC-85（Ni））,and nickle coated N,S-codoped carbon catalyst（Ni@NSC-600）is prepared by an MOF-pyrolyzed method with JUC-85（Ni）.The catalyst show high catalytic activity and stability for the reduction of 4-nitrophenol（4-NP）to 4-aminophenol（4-AP）with NaBH₄ in aqueous conditions.It can reach nearly 100% conversion within 6 min,even when the amount of used catalyst was as low as 0.02 mg.The catalytic rate is calculated to be 10.6×10-3s^-1,the rate constant per gram is 531.9s^-1g^-1,which is higher than all of nickle-based catalysts and some noble metal catalysts.The result show us the heteroatom N and S play a important way in catalytic reaction,which accelarate the reaction rate.