In-situ Polymerization Of Triple Bond In Metal Organic Frameworks For CO₂ Adsorption And Separation

Fossil fuel combustion from stationary sources makes up the majority of the total anthropogenic CO₂ contributions,raising huge environmental challenges facing our planet.Although aqueous alkanolamine solutions are the state-of-the-art capture absorbents that have been broadly implemented in power plants for CO2 capture,their regeneration from carbamates inevitably leads to a huge energy penalty.At present,Physical adsorption methods based on porours materials have many advantages,such as ecomomy,environmental friendly,high efficiency as well as excellent application prospect.Metal-organic frameworks?MOFs?,constructed from organic linkers or clusters,having the advantages of both inorganic and organic materials.Because of their high porosities,structural diversity,tunable pore environments and atomically well-defined skeletons,MOFs have been extensively explored in various applications,such as gas storage and separation,catalysis and chemosensing.Nevertheless,aside from 75%N₂ and 15%CO₂,a typical postcombustion flue gas also contains 5%-7%water,which must be thoroughly taken into consideration for real applications.During the separation process,water molecules,which have higher polarity and binding energy,will strongly compete against CO₂,and therefore,the active adsorption sites in MOFs are easily poisoned by only small amount of water.Consequently,the capacity and selectivity are dramatically dampened under real humid flue gas conditions.Needless to say,many MOF structures are vulnerable under moist conditions,and the collapse of the framework by slow hydrolysis can significantly lower the separation performance and impede their practical application.Based on the above problems,We designed a new method to improve the water stability and the CO₂ selectivity of the metal organic frameworks.This approach has the advantages of simple operation,high processing speed and low raw material cost.The main contents of each chapter are summarized as follows:In the second chapter,we developed an effective strategy by partitioning the channels of MOF-5 into confined,hydrophobic compartments by in situ polymerization of aromatic acetylenes.The study found that after the polymerization the adsorption capacity of the material to CO₂ and the selectivity of CO₂/N₂ were greatly increased.Interestingly,with increasing PN loading,the pores with widths of 1.2 nm?MOF-5 pores?gradually diminish,whereas pore with widths of 0.6 nm?partitioned pores?emerge and are boosted significantly.Compared with pristine MOF-5,the resultant material?PN@MOF-5?exhibits a doubled CO₂ capacity?78 vs 38 cm³/g at 273 K and 1 bar?,23 times higher CO₂/N₂selectivity?212 vs 9?.Within 40 h in a humid environment?RH=40%?,the crystallinity of PN@MOF-5 are preserved after moisture treatment for 40 h.In contrast to the hydrophilic nature of MOF-5 with a water contact angle close to 0°,PN@MOF-5 is hydrophobic and exhibits a water contact angle of 135°.We consider that the performance improvement is caused by the following two aspects:one is that the PN polymers are distributed inside the crystal channels and serve as partitions;another is that the ultra-micropores and large number of exposed of aromatic edges and surfaces in PN@MOF-5 allow it to capture CO₂efficiently.In the third chapter,we implemented the polymerization of triple bond in the pore of UMCM-8 and IRMOF-74-III.The improved stability toward moisture and increased adsorption capacity of PN_6.5@UMCM-8 demonstrate the applicability of the present strategy.In contrast to the hydrophilic nature of IRMOF-74 with a water contact angle close to 0°,PN@MOF-74 is hydrophobic and exhibits a water contact angle of 146°.