Study On The Preparation Of Covalent Organic Polymer And Its Dual Function Application Of Detecting And Removing Hg²⁺

As the pace of urbanization and industrialization is accelerating,various pollution problems have come out.The pollution of heavy metal ions is particularly prominent.The mercury ion(Hg2+)is one of the most toxic heavy metal ions in the environment.It not only pollutes the environment,but also threatens the health of animals and humans.Therefore,more and more researchers are working on the detection or removal of Hg2+and currently some researchers have proposed the concept of dual-functional materials of simultaneously detecting and removing Hg2+based on porous materials such as MOFs and COFs.In this thesis,we develop covalent organic polymers(COPs)as platforms and syntheisize thioether-modified COP(COP-108-S)through the Yamamoto coupling reaction between 1,3,5-tris-(4-bromophenyl)benzene and 1,4-dibromo-2,5-bis((ethylthio)methyl)benzene(the non-thioether modified COP-108 is also prepared for comparsion).For the first time,we achieve the dual-functional application of COPs in simultaneous fluorescence detection and adsorption removal of Hg2+in aqueous solutions.On one hand,the fluorescence detecting properties of COPs materials towards 13 kinds of heavy metal ions including Hg2+ and Fe3+are investigated.The COP materials could both selectively detect the Hg2+ and Fe3+which could be further distinguished by using the logic gate principle.It is found that COP-108-S has better specific recognition of Hg2+than COP-108 due to the presence of thioether groups.The fluorescence titration experiments show that the sensitivity(Ksv)of COP-108-S for detecting Hg2+ is four times higher than that of COP-108,and the detection limit of Hg2+for COP-108-S is calculated to be 1.44 mM.Moreover,the anti-interference and recycling experiments of COP-108-S for fluorescence detection of Hg2+ are also conducted.It is found that the detection of Hg2+ by COP-108-S is not interfered by other metal ions,and the detection efficiency after five times of recycling use shows neglectable decrease.On the other hand,the adsorption ability of COP materials towards Hg2+ in aqueous solution are explored.It can be seen from the adsorption isotherm that the adsorption capacity of COP-108-S is one order of magnitude higher than that of COP-108,and the adsorption isotherm conforms to be the Langmuir isotherm.The maximum saturated Hg2+adsorption capacity of COP-108-S is calculated to be 241 mg g-1.The COP-108-S conforms to be the Pseudo-second order kinetic model,indicating that the adsorption is a combination of physical adsorption and chemical adsorption,and chemical adsorption is dominant.COP-108-S has a removal efficiency up to 99%when excess amount of material is added.In order to investigate the potential for practical applications,a rapid filtration and removal experiment and a recycling experiment are conducted.In the rapid filtration and removal experiment,COP-108-S exhibits a removal efficiency of 86%.The material also show good recycling properties and keeps 99%removal efficiency after 5 cycles of resue due to its good chemical stability arising from carbon-carbon bond connection.This work demonstrates the practical application potential of COP-108-S for Hg2+ removal.