Design,Synthesis And Properties Of Porphyrinato Porous Organic Polymers

Porous organic polymers,composed of organic building units linked by covalent bonds,are a class of porous network materials which are widely used in the fields of separation,heterogeneous catalysis,sensing and energy storage due to their high specific surface area,tunable pores,good stability,low density and designable structure and function.Materials with permanent nanoscale pores exhibit specific properties in terms of mass transfer and active site exposure that are not possible with nonporous materials.It was found that establishing the relationship between morphology,structure and properties and using it as a basis to guide the synthesis of porous materials with high catalytic properties is still challenging.In addition,designing multiple building blocks to construct rich topological network structures is also a research difficulty.Porphyrins have emerged as a class of active building blocks for the construction of functionalized porous organic polymers due to their unique 18 π-conjugated macrocyclic electronic structure,excellent coordination ability,and fascinating optoelectronic properties.This paper revolves around the design and synthesis of porphyrin-based porous organic polymer materials(conjugated microporous polymers and covalent organic frameworks),and studies their applications in electrocatalytic oxygen reduction reaction(ORR),heterogeneous catalysis,photocatalytic carbon dioxide reduction,gas adsorption and energy storage applications.(1)Design and Synthesis Mixed Phthalocyanine-Porphyrin-Based Conjugated Microporous Polymers for Electrocatalytic Oxygen Reduction ReactionFour phthalocyanine-porphyrin staggered conjugated microporous polymers(FePcZnPor-CMP,ZnPcFePor-CMP,FePcFePor-CMP and ZnPcZnPor-CMP)were prepared by Sonagashira-Hagihara coupling reaction using tetraiodometallic phthalocyanine and tetraalkynylbenzene metalloporphyrin as building blocks.A series of spectroscopic and electron microscopic techniques confirmed the successful preparation of conjugated microporous polymers with interlaced phthalocyanine and porphyrin moieties.These polymers exhibit good chemical stability,thermal stability,and permanent porosity.In addition,we investigated the electrocatalytic activity of conjugated microporous polymers containing iron phthalocyanines or iron porphyrins for ORR by cyclic voltammetry,rotating disk electrode and rotating ring disk electrode tests.It was shown that both conjugated microporous polymers containing iron phthalocyanine exhibited excellent ORR catalytic activity in alkaline media with half-wave potentials up to 863-866 mV,which was significantly better than that of the catalyst containing iron porphyrin.Based on the experimental results and theoretical calculations,the reason for the significantly higher ORR catalytic performance of the two Fe-containing phthalocyanine conjugated microporous polymers than the Fe-porphyrin-containing conjugated microporous polymers is that the coordination field of the phthalocyanine macrocyclic ligands is significantly stronger than that of the porphyrins,which is more favorable to stabilize the catalytically active divalent iron ions.This work helps to reveal the origin of the highly efficient ORR activity of Fe-N4 active sites,which is beneficial for the rational design and synthesis of new Fe-N4 catalysts with enhanced oxygen reduction performance.(2)Design,Synthesis and Photocatalytic Properties of Two-Dimensional Ultrathin Covalent Organic Framework NanosheetsThe difficulty of preparing ultrathin two-dimensional covalent organic framework nanosheets on a large scale and in high yields remains,which to some extent limits the exploration of the specific functional and application potential.Therefore,we developed a general bottom-up scalable imine exchange synthesis method to easily synthesize large-scale(>100 mg)and high-yield(>55%)ultrathin(<2.1 nm)imine-bonded two-dimensional covalent organic framework nanosheets(COF-366 NSs,COF-367 NSs,COF-367-Co NSs,TAPB-PDA COF NSs,and TAPB-BPDA COF NSs).In addition,we observed the periodic lattice of COF-367 NSs by scanning tunneling microscopy,demonstrating the ordered structure of COF-367 NSs.Subsequently,a comparative study of nanosheets and bulk COFs for photocatalytic applications was carried out.The ultrathin COF-367 NSs exhibited good single-linear oxygen generation rate and non-homogeneous photocatalytic selective oxidation of thioether compounds to sulfoxide,and were much better than the bulk COF-367.In addition,the COF-367-Co NSs showed efficient photocatalytic carbon dioxide reduction activity in aqueous medium,where the reduction product carbon monoxide yielded up to 10162 μmol·g-1·h-1 with a selectivity of about 78%.The COF-367-Co NSs exhibited much higher photocatalytic carbon dioxide reduction activity than the corresponding bulk COF and were comparable to the performance of the state-of-the-art visible light-driven heterogeneous catalysts reported so far.This work not only develops a new method for the simple and efficient synthesis of covalent organic framework nanosheets,but also advances the application of two-dimensional thin film materials in non-homogeneous catalysis.(3)Three-Dimensional High-connected Covalent Organic Frameworks with scu Topology for High-performance Li-S BatteriesThe development of three-dimensional covalent organic frameworks remains a great challenge due to the limited number of nonplanar building blocks used so far and the difficulty of crystallization and structural resolution.In this chapter,we designed and prepared a D2h-symmetric eighth-order ligand 6,13-dimethoxy-2,3,9,10,18,19,24,25-octa(4’-formylphenyl)pentene(DMOPTP)and used it to synthesize two examples of three-dimensional covalent organic frameworks.DMOPTP was combined with two planar tetragonal building units 1,3,6,8-tetra(4-amino pyrene)and 5,10,15,20-tetra(4-aminophenyl)porphyrin,respectively,to obtain two extended[8+4]linked networks 3D-scu-COF-1 and 3D-scu-COF-2,which have a never-reported dual interpenetrating scu topology and permanent porosity.The specific surface areas of 3D-scu-COF-1 and 3D-scu-COF-2 respectively reached 2340 and 1602 m2·g-1.And both 3D-scu-COF-1 and 3D-scu-COF-2 exhibited efficient CO2 adsorption(212 mg· g-1 and 17.5 wt%for 3D-scu-COF-1 and 226 mg·g-1 and 18.4 wt%for 3D-scu-COF-2 at 273 K).In particular,the porphyrin-based 3D-scu-COF-2,as a novel host material for lithium-sulfur batteries,can effectively adsorb sulfur molecules and lithium polysulfide intermediates,enabling it to exhibit high capacity(1155 mA·h·g-1 at 0.2 C),excellent multiplicative performance(757 mA·h·g-1 at 5 C)and excellent cycling stability(87%still at 100 cycles at 0.5 C capacity retention),which outperformed the pyrene-based 3D-scu-COF-1 and exceeded the majority of porous organic polymer host materials reported to date.