Design,Synthesis Of MOFs Functional Materials And Investigation On Oxygen Reduction Reaction Of Their Derived Carbon Materials

The design and synthesis of metal-organic frameworks have been of much interest due to their defined and ordered connections,controllable structures,designable metal center and organic ligand,and surface area,which offer important opportunities toward exploration of the potential application in catalysis,optical-electrical sensors,chemical separation and hydrogen storage,etc.Recently,MOFs have been widely used as self-sacrifice template to synthesize porous carbon materials for electrochemical energy applications.In this thesis,we have synthesized a series of MOFs functional materials,which are utilized as precursors to prepare porous carbon for oxygen reduction reaction.Also,two novel MOFs are used to study photochromism and photoswitchable conductance properties.The main achievements are listed below:?1?Dopant-free carbon catalysts with enriched mesopores?PCs?are synthesized by pyrolyzing a nano Fe-MOF-5.Raman spectrum reveal that the carbon defects gradually increase at higher pyrolysis temperature.The morphology of PCs inherit their precursors,Fe-MOF-5.The resultant carbon equips with high specific surface area and broad mesopore size distribution.XPS and EDX spectra demonstrate that PC-800 and-900 contain only C and O elements.It is seems that the formation of carbon defects in sp² carbon matrix arises from the removal of O atoms during pyrolysis procedure.The electrochemical results confirm that PC-800 and-900 possess the highest carbon defects,show the best ORR performance,which is better than that of commercial carbon?active carbon and Vulcan XC-72?.The mutually corroborated experimental results reveal the significant contribution of the carbon defects to ORR activity.?2?Nitrogen-doped carbon materials with hierarchically mesoporous structure are synthesized via the pyrolysis of an interpenetrated non-porous metal-organic framework?MOF?,viz.[Zn2?TPT??BDC?2]·H2O?SCUT-11,TPT=tris?4-pyridyl?triazine,BDC=1,4-benzenedicarboxylate?,as the precursor.This triply-interpenetrated MOF features high density of Zn cations in their interwoven packing structure,which act as effective pore-forming agent to generate mesopores in final carbon.Physicochemical characterizations reveal that the resultant carbon has high specific surface area and bimodal mesopore size distribution,which originate from the removal of metal oxide and/or metal zinc.These textual features favor both oxygen mass transfer and accessibility of catalytically active sites.Electrochemical results confirm that the resultant carbon,synthesized by pyrolysis at 900 ^oC,shows a superior oxygen reduction reaction?ORR?activity,which outperforms the commercial Pt/C catalyst.Further investigation suggests that the as-synthesized carbon catalyst exhibits a remarkable insensitivity towards anions,like sulphate and phosphate,compared with the Pt counterpart.The above features make this carbon catalyst promising to be widely used in different fuel cell types.?3?Nitrogen,sulfur-codoped carbon catalysts with enriched mesopores are synthesized by pyrolyzing a novel N,S-containing MOF,viz.[Zn₂?TDC?₂?DABCO?]·4DMF?SCUT-12,TDC=2,5-thiophenedicarboxylic acid,DABCO=1,4-diazabicyclo[2.2.2]octane?.Single crystal X-ray diffraction reveals that the S-containing ligand?TDC?and N-containing ligand?DABCO?are regularly crystallized into the SCUT-12 framework,which act as internal sulfur and nitrogen source.As such,the two dopant atoms can be uniformly introduced into one precursor at the molecular level,and the codoping of two elements can be achieved in one step during the carbonization,simplifying the conventional protocol.Structural characterization reveals that the resultant carbon is mesoporous and has high specific surface area.As a result,the N,S-codoped carbon pyrolyzed at 900 ^oC?NSMC-900?shows a decent activity to the oxygen reduction reaction?ORR?,which is comparable with that of commercial Pt/C catalyst.And NSMC-900 shows a superior long-term stability to Pt/C.Finally,it is found that the dual element-doped carbon outperforms either one of the mono element-doped carbon,demonstrating the favorable synergistic effect of dual element-doping.?4?Two D-A semiconductor MOFs,[Zn₂?TDC?₂?TPT?]·H₂O?1?and[Zn₄?BTC?₃?₃-OH??H₂O?₃][?CH₃NH₂CH₃??PV?_1/2]·5H₂O?2?are successfully constructed?BTC=1,3,5-benzenetricarboxylic acid,PV=N-phenyl-N'-hydrogen-4,4'-bipyridine?.Single crystal X-ray diffraction reveals that 1 is a three-dimensional framework with triply-interpenetrated packing arrangements.1 features unique close packing,which can reduce the distance between adjacent structural units and benefit electron transfer process.2 features typical host-guest structure,in which the mono-phenyl viologen cations are located at the centre of the channel of the host framework constructed by Zn and BTC as guests,and thus,the framework shows more aromatic rings overlap between the D-A units.Upon light irradiation,the two MOFs exhibit photo-induced electron transfer behaviors.XPS analysis reveals that the electron transfer takes place from the donor carboxylate groups and sulfur in thiophene to the acceptor triazine rings in TPT in 1.Additionally,electrical conductivity measurements show that the conductivities of the two compounds drops sharply after irradiation.The above phenomenon of the two MOFs can be used for the development of photochromism and photoswitchable conductance functional materials.