Design,synthesis And Properties Of Covalent Triazine-based Frameworks

Carbon capture and storage(CCS)has been identified as one effective approach to reduce the anthropogenic emissions of CO2 which remains the most urgent challenge facing energy sectors.Economically valuable gas sorbents like Covalent Triazine-based Frameworks(CTFs).High surface areas,good physicochemical stability,low skeletal density and multitudinous available structural modification methods enable CTFs to be one of the most promising candidates for a practical CCS process.Pore surface property,which dominates the inherent interaction between the host materials and guest gas molecules,is one of the key factors that determine gas uptake capacity and selectivity.As the cost-effective CCS procedures required,the host-guest interaction should be suitable for gas capture and the same time for reversible release.Pore surface engineering in covalent triazine-based frameworks(CTFs)targeted for their different applications namely as adsorbents,catalysts or sensors remains a critical challenge.For the first time,we compare here two commonly used modification strategies,i.e.pre-designable strategy and post-synthesis modification which have separately been utilized to allow the functionalization of pore walls with pendant organic groups like ethyl ester,acetic acid,acetohydrazides or their mixtures for effective CO2 capture.As for the former strategy,the pre-functionalized building blocks like acetic acid-appended or acetohydrazides-appended dicyanocarbazoles permit the construction of triazine-bridged polycarbazoles(CTF-CSU36@pre,CTF-CSU37@pre)with walls to which a quantitative content of functional units are anchored.While in the later case,the functionalization is made possible by the use of triazine-bridged polycarbazoles with pendant ethyl ester(CTF-CSU20),and then the pendant group undergoes hydrolysis or hydrazide reaction to produce pore surfaces with desired acetic acid(CTF-CSU36@post)or acetohydrazides groups(CTF-CSU37@post)and preferred pore surface polarities.The highest BET specific surface area(625 m2 g-1)was recorded by NOP-36@post utilizing post-synthetic chemistry.However,the highest CO2 capacity(15.9 wt% at 273 K and 1 bar)as well as good IAST selectivity(78.8)was exhibited for CTF-CSU37@post,because of its nitrogen-rich characteristics and uniform ultramicropores through pore surface engineering.It is shown that turning the binding affinity of CO2 and their selective uptake is feasible,and the post-synthetic method enables effective incorporation of functionality onto pore walls,enhancing the CO2 capture performance far beyond those imposed by the pre-designable modification.Secondly,the cyanobenzene has been selected as the basic unit.By modification with the cyanobenzene,the functional groups similar to the foaming agent are introduced as substituents(carboxyl group,sodium carboxylate group,double carboxylate groups and double sodium carboxylate groups).We obtained a series of derivatives of 1,4-dicyanobenzene,and the series of CTFs of the topological structure were obtained by the polymerization of trimerization of carbonitriles(CTF-CSU38,CTF-CSU39,CTF-CSU40 and CTF-CSU41).The highest BET specific surface area(491 m2 g-1),CO2 adsorption(7.9 wt% CO2 at 273 K/0.15 bar,9.9 wt% CO2 at 273 K/1 bar)as well as good IAST selectivity(CO2/N2=72.0)were recorded by CTF-CSU38.The CTF-CSU38 shows the highest SO2 capacity(42.88wt% at 298 K).May due to its nitrogen-rich characteristics and introduced by sodium carboxylate groups.