Skeleton-Reconstruction And Adsorption Property Study Of Conjugated Microporous Polymers

Conjugated effect,also known as delocalization effect,is an electronic effect which changes the distribution of?electrons in the conjugated system due to the interaction between atoms.Conjugated microporous polymers(CMPs)are a kind of porous polymers with large?–conjugated network,which are assembled by building blocks through covalent bonds.CMPs with well-developed nanopores can be precisely designed and synthesized at the molecular level according to the concept of reticular chemistry.Since the first paper on CMPs was published in 2007,which have attracted extensive attention due to their unique?–conjugated skeleton,high surface area,predesigned monomers,good stability,diverse types of polymerization reactions and modifiable skeleton structure.CMPs showed extraordinary application prospects in gas adsorption and separation,pollutant treatment,energy storage,catalysis,biological diagnosis,drug release,photocatalysis and so on.However,following the development of CMPs,it was more and more difficult to synthesize CMPs for higher surface area through conventional monomer design,reaction system optimization and explore of new reaction types.How to effectively improve the surface area of CMPs was an urgent issue and a major challenge in this field.In order to solve this problem,we proposed a new strategy of porous skeleton reconstruction based on the traditional post-synthetic method,which can effectively improve the surface area and related adsorption properties of the pristine CMPs.This kind of skeleton reconstruction method exhibited good universality and easy-to-operation,which provides a new design idea for the synthesis of novel porous materials,and can effectively improve the performance of CMPs in related adsorption applications.The main research results of this paper were as follows:1.A series of methylene knitted microporous polymers with high surface area,named KCMPs,were successfully synthesized using four aromatic CMPs and dimethoxy methane(FDA)and dichloromethane(DCM)as crosslinkers,taking the advantage of the post-knitting strategy and the easily modifiable skeleton structure of CMPs.Four aromatic CMPs were synthesized by Suzuki-Miyaura cross-coupling reaction,and then the target product KCMPs was obtained by using Lewis acid-catalyzed Friedel-Crafts reaction to knitting methylene bonds on the benzene ring on the skeleton of the pristine CMPs.The pore properties of these polymers showed that the surface area and pore volume of KCMPs were as high as 2267 m² g^–1 and 3.27 cm³ g^–1,respectively,which were 2.3 times and 8.8 times higher than those of the corresponding CMPs.At 1 bar and 273 K,the CO₂ adsorption capacity of KCMP-M4 is 3.98 mmol g^–1,which is 122.2%higher than that of the pristine CMP-4.Moreover,we also analyzed in detail the influence of the skeleton structure of CMPs and the type of crosslinkers on the porous skeletons and CO₂ adsorption performance of KCMPs,as well as the influence of N element doping on the CO₂ adsorption performance.2.An improved molecular expansion strategy based on the post-knitting strategy was provided.In this strategy,the crosslinkers that generated methylene in the post-knitting strategy was replaced with a larger and more rigid crosslinking molecule as the expansion molecule,to realize the molecular expansion of CMPs nanopore structure.In this work,we selected the p-dichlorobenzene and biphenyl dichlorobenzene as the expansion molecules,and two CMPs as the parent materials.By adjusting the proportion and type of the expansion molecules and CMPs,we synthesized a series of high surface area hyper-crosslinked conjugated polymer(HCCPs).The pore properties analysis of the samples showed that the surface area of HCCPs was higher than that of methylene knitting KCMPs.The BET surface area of HCCP-6 was up to 3083 m² g^–1,which was 3.1 and 1.4 times of the pristine CMP-2 and KCMP-M2,respectively.It is worth mentioning that HCCPs can be stably stored in room temperature and air for more than half a year,and show strong acid and base stability.The results of gas adsorption tests showed that HCCPs exhibited excellent high pressure methane storage capacity,and the total CH₄ adsorption capacity of HCCP-6 was up to 0.49 g g^–1 at room temperature at 80 bar.Further,a sulfonic acid functionalized HCCP-SO₃H was synthesized by the traditional post-synthetic method using for gas adsorption and separation,and the HCCP-11 was the parent material.The results of gas adsorption separation showed that the modification of sulfonic acid functional group could improve the CO₂ adsorption selectivity of HCCPs.Then,HCCP-SO₃H was ammoniated,and the gas adsorption and separation test results showed that the ammoniation could further improve the CO₂ adsorption selectivity.In addition,we successfully confined an imidazole-based ionic liquid in HCCP-SO₃H nanopore channels by means of ion exchange of acid-base neutralization reaction,and proposed a novel method for the design and synthesis of porous ionic polymers.3.A series of POSS-crosslinked conjugated microporous polymer(Pc CMPs)using caged octavinyl-POSS(OVS)as functional expansion molecules were synthesized under different conditions using the molecular expansion strategy,where the POSS was a caged inorganic core alternately connected by Si and O elements.The pore properties analysis of the samples showed that the surface area and pore volume of CMPs could be greatly improved via POSS cross-linking,and some POSS-based units could be retained intact during the synthetic process.The BET surface area of Pc CMP-2E was up to 2518 m² g^–1,which was 2.7 times that of the pristine CMP-2.In addition,POSS-based units can provide a large number of adsorption sites for organic micropollutants,among which the maximum adsorption capacity of Pc CMP-2E for bisphenol A in water was as high as 628.9 mg g^–1,higher than most of the reported high effective adsorbents.Comparative experiments and thin-layer through adsorption experiments showed that the adsorption capacity of Pc CMPs on bisphenol A was significantly stronger than that of pristine CMPs,commercially available activated carbon and POSS-based contrast materials,and the highest removal capacity of bisphenol A on Pc CMPs thin layer was nearly 100%.In addition,Pc CMPs showed rapid and high-capacity adsorption capacity for a variety of common organic micropollutants.This work provided a new method for the preparation of highly effective organic micropollutant adsorbents,and effectively expands the scope of molecular expansion strategy.