Construction Of Porous Aromatic Frameworks With Exceptional Porosity Via Dimer-type Building Unit

In the face of increasingly serious environmental problems,the widespread use of clean energy has become an inevitable trend.Methane is considered a greener and cheaper fuel because of its abundance reserves and low carbon dioxide emissions.However,its relatively low volumetric storage density hinders its use as a transportation fuel in the automotive industry.Therefore,the storage and transportation of methane is particularly important.At present,great progress has been made research on adsorbents with high efficiency for methane adsorption.Porous materials have attracted consuming attention for gas adsorption due to their high surface area and large pore volume.In the past decade,many porous organic frameworks?POFs?have been efficiently synthesized.However,the surface areas of most POFs are below 2000 m² g^-1,being trapped in the geometric configuration of building units and effectiveness of polymerization reactions.Therefore,the construction of excellent porous organic frameworks?POFs?with high surface areas and stability is always a tremendous challenge in synthetic chemistry.The geometric confguration and reactive group of building unit are crucial factors to influence the structure and porosity of the resulting product.In this paper,we first proposed that using dimer blocks to construct high porosity porous aromatic frameworks?PAFs?.First,two kinds of dimers,1,4-phenylenebis?tris?4-bromophenyl?silane?and 4,4'-bis?tris?4-bromophenyl?silyl?biphenyl,were synthesized.Then,two PAFs,named PAF-100 and PAF-101,were obtained by Ullmann coupling reaction.The second and third chapters of the paper introduce the synthesis,characterizations and high-pressure methane storage performance of PAF-100 and PAF-101,respectively.The successful synthesis of the target product was demonstrated by infrared,X-ray photoelectron spectroscopy and solid nuclear magnetic resonance.PAF-100 and PAF-101 show high thermal stability with decomposition temperature up to500°C,revealed by the thermogravimetric analysis?TGA?.The BET surface areas of PAF-100 and PAF-101 were 5501 and 5114 m² g^-1 by N₂ sorption isotherms measured at 77 K.In order to further promote the understanding of the polymerization process,the coarse granulation model was used to theoretically simulate and calculate the formation process of two PAFs.The simulation results are in good agreement with the experimental results.Together with their high specific surface areas and high stability,PAF-100 and PAF-101 are excellent carriers for methane storage under high pressure.PAF-100 and PAF-101 show high methane uptake with values of 742 and 622 cm³ g-1at 298 K and 70 bar,respectively.To the best of our knowledge,the total methane uptake of PAF-100 is by far the highest among all porous materials reported to date.Therefore,the synthesis of PAFs with excellent porosity is significant for the storage of methane under high pressure.