Preparation Of Heteroatom Functionalized Porous Organic Polymers And Their Adsorption Performance

The pollution of CO₂ and heavy metal(Hg²⁺)have caught serious environmental problems.Porous organic polymers（POPs）have been widely used for pollutants adsorption,energy storage,and multiphase catalysis due to their high BET specific surface area(S_BET),adjustable pore size,multiple functional stategies.In this way,it has great academic value and practical significance to construct functional POPs with specific chemical structures and pore structures.For this purpose,a series of heteroatom（N,S,and so on）functionalized POPs were constructed.The preparation methods and control strategies of structure were investigated.The relationship between the structure of the POPs and the activities of the CO₂ capture and Hg²⁺removal were also consulted.The polymer precursor TPE-TMC was prepared by using aromatic monomer tetraphenylethylene（TPE）and trimesoyl chloride（TMC）according to the Friedel-Crafts acylation reaction.As a kind of two-dimensional planar material,TPE-TMC exhibits extremely low S_BET.Then the rich ketone carbonyl groups on the TPE-TMC were post-crosslinked with rigid monomer of melamine（MA）by Schiff-based reaction,resulting the great increasing of S_BET and V_total,and a kind of three-dimensional（3D）POPs was constructed with high S_BET and V_total of645 m²/g and 0.84 cm³/g,respectively.The pore structure of the POPs could be adjusted through the addition of MA.The resulting TPE-TMC-2MA showed abundant ultramicropores,micropores,and N content,indicative its high CO₂ capture（153 mg/g,273 K/1.0 bar）and Hg²⁺adsorption capacity（433 mg/g）.TPE-TMC-2MA also showed rapid adsorption kinetics,excellent adsorption selectivity,and good reuseability.However,the other flexible amino crosslinking agents such as p-phenylenediamine,ethylenediamine,and diethylenetriamine could not clearly improve the structure and properties of the polymers.Additionally,the universality of the strategy for the post-crosslinking of MA with the rich ketone-based precursor polymers based on the Schiff-based reaction was consulted.A series of ketone-based precursor polymers were constructed through four kinds of aromatic monomers（TPE,triphenylamine（TPA）,tribenzyl-benzene（TPP）,perylene（Py））and three kinds of acyl chloride crosslinkers（oxalyl chloride（OAC）,p-phthaloyl chloride（TC）,and TMC）.And a series of3D POPs were constructed through the post-crosslinked of MA by Schiff-based reaction.The introducing of MA realized the increasing of the S_BET and V_total,and the performance for CO₂ capture（up to 145.0 mg/g at 273 K and 1.0 bar）and Hg²⁺removal（up to 372 mg/g）also increased clearly.The results confirmed the universality of the strategy for the post-crosslinking of MA,and provided a feasible strategy for the functional-crosslinking of other ketone-based POPs.The anhydride crosslinkers were used to replace the acyl chloride crosslinkers,and the feasibility of the reaction of the Friedel-Crafts acylation reaction and the further Schiff-based reaction between the anhydride crosslinkers and aromatic monomers were consulted.The precursor polymers were prepared by the aromatic monomers（TPE,TPA,TPP,Py）and the anhydride crosslinkers（pyromellitic dianhydride and perylenetetracarboxylic dianhydride）according to the Friedel-Crafts acylation reaction,and the 3D POPs were constructed with the further cross-linked by MA based on the Schiff-based reaction.The results indicated that the anhydride crosslinkers have the same performance with acyl chloride.The ragid MA moleculars were further inserted into the 2D planer which have low S_BET,and the porous 3D materials were constructed.The high S_BET and V_total,abundant micropores,ultramicropores,and N content make the MA-based polymers performed well in CO₂ capture（up to 192.9 mg/g,273 K,1.0 bar）and Hg²⁺removal（up to 425 mg/g）.Furthermore,the hierarchical triazine structure of the MA-based polymers make them performed well in the catalytic of the epoxide cycloaddition reaction.Assisted by tetrabutylammonium bromide,the conversion rate can reach 99%（0.1 MPa CO₂,70^oC,8 h）.This work broadens the application of MA-functionalized polymer and provides a feasible method for the design and preparation of POPs with special functionalizations.Three different thioether-functionalized porphyrin polymers were constructed according to two different bottom-up and top-down strategies.TPP1,which was prepared by one-step polycondensation of thioether functionated monomer according to the bottom-up strategy had the highest S_BET（554 m²/g）,V_total（0.32 cm³/g）,and S（16.8%）,indicative of its highest Hg²⁺adsorption capacity（913 mg/g）and high removal rate（>99%）.The adsorption mechanism clarified that the strong coordination between the S species and Hg²⁺.In comparison,TPP2 and TPP3 were fabricated by the thioether functionalization of the porphyrin-based polymers according to the―top-down‖strategy.They showed much lower S_BET,V_total,and S content for the reason that the post-functionalization process greatly blocked the pores and the functional sites were hardly fully post-functionalized,resulting in much lower Hg²⁺adsorption（555mg/g and 609 mg/g,respectively）.This work reveals the advantage of the bottom-up strategy for the construction of the thioether-functionalized polymers and it offers the guidance for the construction of some other thioether-functionalized porphrin polymers.According to the porphyrin cyclization reaction,the thiophene-based structure was introduced to the backbone structure of the polymers,and two kinds of thiophene-based porphyrin polymers（PSF and PS₂F）with different S content and high stability structure were constructed.PS₂F showed high S content of 13.4%,indicative of its high Hg²⁺adsorption capacity（1181 mg/g）and outstanding removal efficiency（>99.9%）.The polymers also showed outstanding adsorption selectivity and good recyclability.The adsorption mechanism indicated that S in thiophene and N in porphyrin all have strong interaction with Hg²⁺.This work reveals the advantages of porphyrin and thiophene structures in the adsorption of Hg²⁺,and provides guidance for the design and preparation of novel Hg²⁺adsorbents.Two kind of thiophene-based covalent organic frameworks（COF-S1and COF-S2）with good crystal structure were constructed by Schiff-based reaction between tetrakis（4-aminophenyl）-ethane and two aldehydemonomers（2,5-Thiophenedicarboxaldehydeand Thieno[3;2-b]thiophene-2,5-dicarboxaldehyde）.The S_BET of the COFs was up to 1499 m²/g.The crystal structure of the thiophene-based COFs were charactered through PXRD and theoretical calculation.The thiophene-based COFs showed high S content,indicave of their good Hg²⁺adsorption performance.Especially for COF-S2,which have the S content of 12.3%,resulting in the capture capacity of 1027 mg/g and the removal efficiency of more than 99%.The COFs also showed outstanding adsorption selectivity and good recyclability,and provides guidance for the design and preparation of novel Hg²⁺adsorbents.Mentionable,the close packing of the COFs given them strong fluorescence,and the fluorescence intensity decreasing with the increasing of Hg²⁺concentration,indicative their application prospect for Hg²⁺detection.