Preparation Of Nitrogen-containing Porous Organic Polymers And Their Adsorption And Catalytic Properties

Porous Organic Polymers(POPs),composed of organic building blocks with different geometric topologies and linked by covalent bonds,are a species of three-dimensional network materials with the advantages of low skeleton density,high specific surface area,abundant pore structure,and flexible functional designability.In recent years,due to their outstanding performance in many fields such as gas adsorption and separation,catalysis,sensing,and energy storage and conversion,the research on POPs have become a new direction in the development of porous materials.Based on the polarization and electron-rich properties of nitrogen atoms,nitrogen-containing POPs demonstrate unique functionality in applications of gas adsorption and separation,photocatalysis,and heterogeneous catalysis.Currently,research on nitrogen-containing POPs still needs further development to overcome problems such as the optimization of synthesis method,regulation of nitrogen content and application expansion of gas adsorption,and chemical catalysis/photocatalysis.Therefore,based on different nitrogen-containing building blocks,this thesis focuses on the design and synthesis of POPs with different nitrogen contents and nitrogen atom bonding types.The effects of the POPs composition,structure and metal loading on the performance of gas adsorption,photocatalytic hydrogen production and heterogeneous catalysis were further explored.The major research contents and outcomes are summarized as following:(1)Based on the Yamamoto coupling reaction,a copolymerization coupling modification method of polybromocarbazole was proposed.By introducing pyridine/bipyridine functional groups with adjustable chemical structures and copolymerization ratios,a series of conjugated microporous polycarbazole networks(PCZNs)with different nitrogen contents were synthesized.The as-prepared PCZNs exhibited tunable specific surface areas between 379 to 1126 m~2g^-1.The introduction of basic nitrogen-containing groups led to the remarkable improved CO₂selective adsorption capacity of PCZNs.Among them,PCZN-8 exhibited a CO₂adsorption as high as 14 wt%at 1 bar and 273 K,and PCZN-10 displayed a high CO₂/N₂(15/85)selectivity of 164,which is 129%and 88%higher than that of pure carbazole-based conjugated microporous polymer,respectively.Benefit from the rigid cross-linked network structure,PCZNs showed an excellent chemical stability in harsh environments such as 6 mol L^-1HCl or 600?ensuring good initial adsorption performance.Furthermore,the PCZN-1 had a gravimetric H₂uptake capacity of 1.35wt%at 1 bar and 77 K.In addition,after the modification of bipyridyl groups,PCZNs formed a unique electron donor-acceptor(D-A)structure,resulting in a good photocatalytic water splitting performance for hydrogen production.The modified PCZNs exhibited a photocatalytic H₂evolution rate as high as 2469?mol g^-1h^-1under visible light(?>420 nm).(2)Based on Chichibabin amination reaction,a novel approach for the synthesis of pyridyl-conjugated microporous polymers(PCMPs)was developed via aminative cyclization reaction using aldehyde and ketone monomers as building blocks.The synthesis could be completed efficiently in 5 min without using any metal catalysts.This method was applicable to most aldehyde and ketone building blocks.The changes of configuration,number of functional groups,and volume of the building blocks of PCMPs could further tune the pore structure,band gap,and photocatalytic water splitting performance.The PCMPs showed the specific surface areas as high as450 m~2g^-1.The PCMPs exhibited high photocatalytic water splitting capacity to produce hydrogen and oxygen,which the hydrogen and oxygen production rates are?100?mol g^-1h^-1and?45?mol g^-1h^-1under visible light(?>420 nm),respectively.The PCMPs showed apparent efficiencies of hydrogen and oxygen production of2.3%and 0.48%(at 420 nm),respectively.(3)Based on Buchwald-Hartwig cross-coupling reaction and chemical oxidative polymerization,a two-step reaction route was proposed for preparing a series of polyaniline-like nitrogen-containing conjugated microporous polymers(NCMPs).The rigid network structures of NCMPs with tertiary amines were confirmed by chemical structure characterization and theoretical calculations.The NCMPs showed the specific surface areas of 58-485 m~2g^-1and the high nitrogen contents of 7.39-11.84%.The NCMPs exhibited excellent CO₂selective adsorption capacity with an uptake capacity of 11 wt%(1 bar,273 K)and selectivity of 360(CO₂/N₂=25/75).Meanwhile,NCMPs also achieved the high H₂adsorption capacity(1.02 wt%@1 bar,77 K)and iodine vapor adsorption capacity(215 wt%@1 bar,358 K).In addition,based on the abundant nano-channels and high nitrogen content,the NCMPs showed excellent performance as heterogeneous catalysts.When 11.8 wt%Pd Cl₂loaded into NCMPs,Pd(II)was reduced to Pd(0)metal particles,showing excellent catalytic performance on Suzuki coupling reaction.The reaction substrate of bromobenzene and phenylboronic acid could be converted into biphenyl within 1 hour.The catalytic activity remained unchanged after 5 times repeated using.(4)Taking advantage of the excellent metal coordinating capacity of the carbene site of triazole groups(TZ),a novel method for the preparation of multi-component(binary,ternary,quaternary,penta-and hexa-)metal alloy polymers(PTZ-M)was proposed via formation of nanocolloids by coordination of polytriazoles(PTZ)with metal(Au,Re,Ir,Os,Pt)salts at room temperature.The transmission electron microscope(TEM)observations indicated that different metals coexisted in the polymeric nanocolloids as the alloys showing a uniform element distribution and lattice structure.Especially,the penta-metal alloy polymer(PTZ-[Au,Re,Ir,Os,Pt])showed the uniform interplanar spacing which is totally different from that of five pure metals.The results confirmed Au,Re,Ir,Os,and Pt have formed as high-entropy alloy with the compositions of 28.6%,22.4%,34.7%,8.2%,and 6.1%,respectively.In addition,the PTZ-[Au,Re,Ir,Os,Pt]exhibited outstanding catalytic hydrogenation reaction activity for nitro compounds,which converting more than 95%of nitro groups to amino groups within 2 min and completing hydrogenation within 6 min.Moreover,a triazole-based porous organic polymer(PTZ-DVB)with a specific surface area of up to 840 m~2g^-1was prepared by the copolymerization of p-styrene and TZ.With the excellent nano-pore confinement and metal coordination ability,the PTZ-DVB could load metal atom Au to form a heterogeneous catalyst(PTZ-DVB-Au),which the specific surface area slightly decreased 771 m~2g^-1compared to the pristine PTZ-DVB.As a heterogeneous catalyst,the catalytic hydrogenation activity of PTZ-DVB-Au for nitro groups was comparable to that of the PTZ-[Au,Re,Ir,Os,Pt]catalyst,which converting more than 97%of nitro groups to amino groups within 4 min and completing hydrogenation within 6 min.