Study On The Design And Preparation Of Functionalized Porous Aromatic Frameworks For The Adsorption Of Pollutants From Water

Water pollution is an increasingly serious environmental problem and the pollutants discharged into aquatic ecosystem are threatening human survival.The development of novel adsorbents to efficiently remove water pollutants is of great significance.Porous Aromatic Frameworks?PAFs?have exhibited huge application potential in the removal of water pollutants due to their ultra-high specific surface area,excellent physicochemical stability and unique pore structure.However,there are still some issues to be addressed:1)most of the PAFs in their powder forms are difficult to recycle in applications;2)the microporous structure of PAFs is not conducive to the removal of large-size contaminants;3)the bare PAFs framework lacks suitable functional groups,affecting its adsorption selectivity.To solve the above problems,this paper aims at the functionalization of PAFs materials.Through reasonable design,functionalized PAFs are prepared to achieve the following targets:1)enhance the handleability of PAFs,2)improve the pore structure of PAFs to enhance its adsorption performance for large-size pollutants,3)improve the adsorption selectivity towards PAFs.In this paper,a series of functionalized PAFs were prepared by Suzuki coupling reaction in combination with the synthesis of functionalized monomers.The adsorption performance of phenols and organic dye pollutants was systematically studied.The specific research contents are as follows:?1?In the first work,in order to overcome the problem that PAFs in powder forms are difficult to recycle,PAF with build-in magnetic nanoparticles?Fe₃O₄-PAF?was successfully synthesized through a one-port Suzuki coupling reaction.The Fe₃O₄-PAF exhibits good handleability and could be recovered easily by magnetic separation.The adsorption properties of Fe₃O₄-PAF was investigated to remove 2,4-dichlorophenol?2,4-DCP?and bisphenol A?BPA?from water.The Fe₃O₄-PAF showed fast adsorption rate,high adsorption efficiency and high adsorption capacities.It adsorbed 2,4-DCP?0.1 mM?and BPA?0.1 mM?with pseudo-second-order rate constant?k₂?of 2.1 g mg^-1 min^-1and 3.54 g mg^-1 min^-1,respectively.According to Langmuir isotherm model,the maximum adsorption capacities of 2,4-DCP and BPA onto Fe₃O₄-PAF were calculated to be 234.74 mg g^-1and 233.65 mg g^-1,respectively.The Fe₃O₄-PAF also featured good tolerance to harsh conditions,facilitating its application in real water environment and it could be regenerated easily and reused ten times without obvious losing its efficiency.In summary,this study provides a general and effective way to improve the handleability of PAFs and expands the practical application of PAF-based materials.?2?In the second work,in order to improve the adsorption selectivity of PAFs,a charged PAF,PAF-CH₂N?CH₃?₃I,which was densely and homogeneously functionalized with cationic groups and featured with hierarchical porosity,has been successfully synthesized.It shows excellent selectivity towards anionic dye.The hierarchical porosity structure and the high density and homogeneous distribution of the cationic moieties endow the PAF-CH₂N?CH₃?₃I with strong affinity,fast adsorption rate,high adsorption efficiency and adsorption capacities towards anionic dye.It adsorbed MO(50mg.L^-1)and a-MB(50mg.L^-1)with pseudo-second-order rate constant?k₂?of 4.28 g mg^-1 min^-1and 1.38 g mg^-1 min^-1,respectively.According to Langmuir isotherm model,the maximum adsorption capacities of MO and a-MB onto Fe₃O₄-PAF were calculated to be 690 mg g^-1and 476 mg g^-1,respectively.Additionally,the hierarchical structure of PAF-CH₂N?CH₃?₃I is also beneficial for its regeneration.The regenerated PAF-CH₂N?CH₃?₃I can retain about 99%of its initial adsorption efficiency even after 10 adsorption-desorption cycles.These excellent features show that PAF-CH₂N?CH₃?₃I is a promising adsorbent for wastewater treatment.?3?In the third work,we combining the precursor-designed method and the Post-modification method.we successfully prepared a PAF densely functionalized with carboxyl groups,PAF-COOH.PAF-COOH contains high density and homogeneous distribution of carboxyl groups and has dominant mesoporous structure.It shows excellent adsorption selectivity for cationic dyes.The adsorption performance of PAF-COOH is pH dependent and the adsorption performance is greatly improved at high pH value.It adsorbed PSA(200 mg L^-1)and b-MB(200 mg L^-1)at pH=10 with pseudo-second-order rate constant?k₂?of 0.10 mg^-1min^-1and0.435g mg^-1 min^-1,respectively.According to Langmuir isotherm model,the maximum adsorption capacities of PSA and b-MB at pH=10 onto Fe₃O₄-PAF were calculated to be 552.49 mg g^-1 and 775.20 mg g^-1,respectively.In addition,PAF-COOH has no obvious loss of adsorption efficiency even after five adsorption-desorption cycles.These excellent properties of PAF-COOH show its huge application potential in the treatment of water pollutants.