Synthesis Of Triptycene-and Calixarene-based Porous Organic Polymers And Study Of Their Adsorption Of Water Soluble Pollutants

With the rapid development of the modern industry,a large amount of industrial wastewater has been released to the rivers and lakes,leading to irreversible environmental pollution and also severely threatening the health and safety of human beings.Therefore,the rapid and effective removal of the pollutants has been the major issue to be addressed,also one of the hot research topics,which attracts global attention.The frequently-used decontamination methods at present includes adsorption,catalytical degradation,advanced oxidation,microbe treatment,etc.Among them,the adsorption has been the most promising method owing to the low cost,easy operation and high removal efficiency.Nowadays,the common and traditional adsorbents contain activated carbons,zeolites,resins,etc.Although with very low cost,most of these adsorbents possess slow adsorption rates,low adsorption capacities and no selectivity,which significantly restricts their further developments.Porous organic polymers,abbreviated as POPs,possess the characteristics including diverse structures,high stability,easy functionality,hierarchical pores and abundant active sites,have been regarded as the more effective adsorption materials than the above traditional adsorbents and with more promising practical applications.The cationic dyes and phenolic compounds are important industrial raw materials and the paraquat is one of the most effective and commonly-used herbicides.All of them significantly contribute to the prosperity and development of the modern industry,and also provide changes and convenience for our daily lives.However,the unstoppable release of the above compounds to the environment will result in huge damage to humans owing to the structural stability and biotoxicity.Hence,developing novel porous adsorbents to selectively adsorb and remove these pollutants is an urgent task.The researchers have synthesized diverse POPs for the effective adsorption of dyes,paraquat and phenolic compounds,but still with some shortcomings such as complex synthetic process and relatively poor adsorption performances,thus designing and synthesizing POPs-based adsorbents with novel structures,which can achieve breakthroughs in the adsorption performances including adsorption rates,adsorption capacities and selectivity are of great significance.In this paper,we chose triptycene and calixarene derivatives as the building block and then synthesized a series of POPs with excellent adsorption performances via suitable crosslinked polymerization reactions.Additionally,we also introduced some active groups with stronger interactions with target pollutants into the skeletons of the POPs via the post-modification synthesis strategy to further improve the adsorption performances.The detailed contents of this paper are as follows:(1)We used triptycene and pentiptycene derivatives as the building blocks,and tetrafluoroterephthalonitrile as the crosslinker to fabricate crosslinked porous architectures with hierarchical structures namely P1 and P2 via the nucleophilic substitution reaction.Both P1 and P2 exhibit good thermal stability,and good adsorption performance for dyes and phenolic organic pollutants including MB,MO,Pol and BPA.The removal efficiency of P2 is>99.0%within 10 min for BPA and an adsorption equilibrium for Pol can be reached within 5 min.The maximum adsorption capacity of P1 and P2 for BPA can reach 212.06 mg g-1 and 330.02 mg g-1,respectively and they also show highly selective adsorption abilities towards phenolic organic pollutants.This work provides a new strategy for the design and synthesis of hydrophobic POPs purely composed of aromatic rings.(2)We used resorcinol calixarene as the building block,and octafluoronaphthalene and decafluorobiphenyl as the crosslinkers to two POPs namely P1 and P2 via the nucleophilic substitution reaction.Combining the advantages of porous structures,abundant adsorption sites and electronegative natures,both POP-8F and POP-10F exhibit extraordinary adsorption capacities and rates towards cationic dyes including RhB,MB and CV.Especially for RhB,the removal efficiency can reach nearly 99.0%within 4 min and the pseudo-second-order rate constant of POP-8F is 0.04386 g mg-1 min-1.Notably,the maximum adsorption capacity of POP-8F towards RhB is 2433 mg g-1,surpassing all the previously reported porous adsorbents including covalent organic frameworks,metal-organic frameworks,POPs,biomass adsorbents,activated carbons,etc.In addition,both POP-8F and POP-10F can selectively adsorb cationic dyes among the mixtures of cationic dyes and anionic dyes.More importantly,the calixarene-based POPs can efficiently remove cationic dyes through a simple column filtration and exhibit excellent reusability properties.This work provides a new synthetic method for the improvement of POPs-based adsorbents.(3)We used resorcinol calixarene with four bromine atoms as the building block,and 1,3,6,8-tetraacetylene pyrene as the crosslinker to synthesize POP-Py via Sonogashira coupling reaction,then the alkynyl groups of POP-Py were taken as the reaction sites to react with sodium 3-mercaptopropanesulphonate to synthesize POP-Py-SO3Na.The introduction of sodium sulfonate group further decreases the zeta potential of the POPs and POP-Py-SO3Na possesses more negative charges under neutral conditions,thus significantly improving the adsorption performances towards cationic dyes.Compared to POP-Py,the adsorption rates of POP-Py-SO3Na towards RhB and MB increases a lot,and the adsorption capacity of RhB increases 7 times,up to 1428 mg g-1.Especially for MB,the removal efficiency(η)of POP-Py-SO3Na can be up to 97.5%within 15 s,and reaches the adsorption equilibrium after 45 s,and the η is 99.0%,nearly completely adsorption.Moreover,the k2 of POP-Py-SO3Na towards MB is as high as 4.236 g mg-1 min-1,which is 156-fold of POP-8F in the second work in this paper,and surpasses most of the previously reported porous adsorbents.(4)We continued to use resorcinol calixarene with four bromine atoms as the building block,but tetraphenyl ethylene with boric acid ester moiety as the crosslinker to synthesize POP-TPE via Suzuki-Miyaura coupling reaction,then the phenolic groups of POP-TPE were taken as the reaction sites to react with sodium chlorosulfonic acid to synthesize POP-Py-SO3H.The introduction of sulfonic acid group prominently enhances the electrostatic interaction of POP-Py-SO3H with the anionic pollutants,especially paraquat.The maximum adsorption capacity of POP-Py-SO3H towards paraquat reaches 289.85 mg g-1,this value surpasses most of the previously reported porous adsorbents.The two works provide a new synthesis strategy,that is,post-modification for the improvement of adsorption performances.