Design And Constrution Of Functionalized Covalent Organic Frameworks And Investigation Of Photocatalytic And Proton Conduction Properties

Covalent Organic Frameworks(COFs)are a class of crystalline porous organic polymers.Due to their diversity of organic modules,various COF structures have been constructed and wide applications have been investigated.Recently,developing COFs with novel structures and specific functions have become one of great significance research field in chemistry and materials science.In this thesis,firstly,the background and research progress,the building units and topologies as well as bonding types,and the functionalization and application studies of COFs are overviewed.And then,new COFs with different structures and functional groups were synthesized or post-functionalized for photocatalytic generation of 1O2,photocatalytic CO2 reduction and proton conduction,respectively.The specific research contents and conclusions are as follows:(1)Reactive oxygen radicals are widely used in photocatalysis,pollutant degradation and photodynamic therapy.An imidazole-linked porphyrin-based COF(referred to as PyPor-COF)was synthesized.Experimental studies have demonstrated that PyPor-COF not only has high crystallinity,permanent porosity,and extremely high stability,but also shows photoreactive activity with semiconductor characteristics.Electron paramagnetic resonance(EPR)experiments have shown that PyPor-COF can efficiently initiate 1O2 production.In vitro anti-cancer experiments demonstrated that this COF can even trigger 1O2 production and kill cancer cells effectively under physiological environment.This study shows that the imidazole-linked porphyrinbased PyPor-COF is a promising photosensitizer for applications such as photodynamic therapy.(2)The conversion of CO2 into high value-added chemicals is a promising way for carbon fication but challenging.By introduce the metal ions of Co2+,Ni2+,Cu2+ and Zn2+,into the photosensitive PyPor-COF,four metallized PyPor-COFs(named MPyPor-COFs)were constructed.Optical characterizations showed that the photochemical properties of all four M-PyPor-COFs were significantly enhanced compared to the pristine PyPor-COF.The photocatalytic CO2 reduction results showed that the photocatalytic efficiency of Co-PyPor-COF reached a high CO generation rate of 9645 μmol g-1 h-1 with a selectivity of 96.7%.And the Ni-PyPor-COF even can tandemly catalyze the generated CO into CH4.Experimental results and theoretical analysis showed that the significant performance enhancement of M-PyPor-COFs for photocatalytic CO2 reduction should be attributed to the introduction of metal centers into M-PyPor-COFs,which promote the adsorption and activation of CO2 and the desorption of the generated CO,and the introduced Co and Ni ions even reduces the reaction energy barrier of the intermediates.This work shows that effective photocatalysts for CO2 conversion can be constructed by metallization of photoactive COFs.(3)Developing effective proton exchange membrane is important for fuel cells a covalent organic framework based on pyrazine group,PyHATP-1,were constructed,which is a COFs packed from two-dimensional lamellar frameworks with high crystallinity,high stability.Proton conduction investigations revealed that physical doping of phosphoric acid and chemical post-sulfonation treatment can both effectively improve its proton conduction.When combined two methods togeter,the proton conductivity of synthesized H3PO4@PyHATP-1-SO3H even can increase up to 8.8 ×10-2 S cm-1 from 7.2 × 10-6 S cm-1 of PyHATP-1 itself under 353 K and 98%relative humidity(RH).In addition,H3PO4@PyHATP-1-SO3H also exhibited high long-time reusability.This work showed that the acid-modified COFs have a great potential for the application in proton-conduction application.(4)Polyimidazoles are also widely used for proton conduction,and thus imidazole-based COFs are potential proton-conducting materials.An imidazole-based COF,PyTFB-1,was constructed.Characterizations revealed that it displays high crystallinity and high stability.Proton conductivity investigations revealed that PyTFB1 itself exhibited certain intrinsic proton conduction properties,and when strong acids were incorporated into its backbone by chemical post-sulfonation and physical doping of phosphoric acid,the resultant H3PO4@PyTFB-1-SO3H exhibits a ultra-high proton conductivity of 1.15 × 10-1 S cm-1 at 353 K and 98%RH and a long-time reusability.This work provides a new stratergy for fabricating proimising proton conduction materials.