Promoting and Tuning Porosity of Flexible Ether-Linked Phthalazinone-Based Covalent Triazine Frameworks Utilizing Substitution Effect for Effective CO2 Capture.

Abstract

Five porous ether-linked phthalazinone-based covalent triazine frameworks (PHCTFs) were successfully constructed via ionothermal polymerizations from flexible dicyano monomers containing asymmetric, twisted, and N-heterocyclic phthalazinone structure. All the building blocks could be easily prepared by simple and low-cost aromatic nucleophilic substitution reactions, showing the large-scale application potential of thermal stable phthalazinone structure in constructing porous materials. Generally, the flexible building blocks are avoided to prevent the networks from collapsing in constructing high surface area porous materials. Our experimental results revealed that the introduction of the substituents can effectively decrease the probability of the network interpenetration from the longer struts and the intermolecular/intramolecular intercalation from the increased degree of conformation freedom in the flexible ether-linkage, the BET surface areas of PHCTFs increasing from 676 to 1270 m2 g-1. Meanwhile, the effects of introducing different sizes (methyl or phenyl group) and amounts (one or two) of substituents on the porosities of the target polymer networks were also investigated in detail. The high CO2 adsorption capacity of 10.3 wt % (273 K, 1 bar) can be ascribed to the strong affinity of the electron-rich N,O-containing networks with CO2. Excitingly, PHCTF-5 demonstrates the high CO2/N2 selectivity up to 138 (273 K, 1 bar), according to the ideal adsorbed solution theory (IAST) for the higher proportion of Vmicro accompanied the electron-rich heteroatoms characteristic. Such high CO2 adsorption capacity and good separation properties are superior to those of many other microporous organic polymers. These properties along with easily up-scalable synthesis make porous PHCTFs promising candidates applied in gas sorption and separation field.